Just the right balance in presentation and stats. I am a subscriber. One point in a never perfect world. It may also be useful spending just £35 on a DIY swoop over of a fused spur connection to the hot water tank with a progammable controller where you have an off peak supply (Octopus-Go). Not as environmentally friendly granted but with a small PV array and larger battery storage capacity, this could be an initial approach. We are still trying to work out the export to grid issues when the battery is 100%. For us, this happens 1-2 hours during the day when the sun shines. Question for Octopus: Can you have an off peak tariff and still get paid for exporting? That sounds like having your cake and eating it.
Thanks for the kind words, Michael 🙂 Yes, that is the other approach, and to see how that works out in the utility - just do the following: 1. Select "Electricity" instead of "Gas" 2. Set the insufficient days to "365" (which essentially "turns off solar") 3. Make your investment £35 4. Set the cost of electricity to your off-peak rate Your question for Octopus is a good one... it does sound like having your cake and eating it, but off-peak is all about flattening the demand curve (good) and any export you sell is likely being used by your neighbour, which means less load on fossil fuel generators (also good). We just need a transmission/distribution network that can manage all that.
Re the sport whilst on Octopus- Go, having just got my Solar/Battery installed i checked this yes there is an export with GO but its a miserly £0.3p because its exactly like the cake and eat it! I'm going to do it just because I\m not giving it away for free😁
Re-export - Yes Octopus’ rate for a split tariff is just 4p, but you can export with anyone else regardless of supply under the SEG. Nobody pays a “fair” rate but 5-5.5p is available by shopping round. I had to, as Octopus will only accept genuine MCS certificates, not comparable QA schemes such as Flexi-Orb.
I've had a Solar I Boost for 8 years now. I get the FIT so no need to worry about export payment calculations. In that time I've sent over 7000 kwh to my water tank from my 4kw solar PV array. Now I no longer use my oil boiler to heat my hot water but use Octopus GO cheap rate tariff to top up my tank overnight and then let the sun replenish it during the day. That cuts my CO2 by loads which is the most important thing to me!
Hi John, sounds like you’re doing all the right things 👍🏻😀 And having the FiT payments certainly frees you from the temptation of putting export profit above CO2 reduction that many people will have to decide on now as export rates increase… 🤔
I installed my Solar iboost 7 years ago with a 5KW array inverter limited. I did leave space to have thermal solar added for hot water and had a super-insulated thermal solar ready tank installed. The installer said I would never do it as the SolarEdge would give me all the hot water without any hassle. To date he has been right and it provides all hot water from the end of March until end of October and only requires a small top up from the boiler during winter. Again I have FIT payments so this makes it an easier calculation. It was certainly much cheaper than having a battery at the time, although I am now considering a battery on the DC side to reduce clipping and also maybe thermal solar as well to maximise total co2 reduction, but then it might be best still just to increase the PV array. Either way I love the solar I boost.
Thank you Gary, another exceptionally good video that sets the standard for all things renewable here on UA-cam. Thorough, clear and concise, a great help, thank you again.
This is such a helpful video thank you. The calculator helped me put data to my gut feeling that an Eddi hot water diverter for me would never pay back. Cheers.
We have a new water tank as part of a house refurbishment and were using Economy 7 to heat the water as we have no mains gas in the village. Just 2 of us in the house. Had solar fitted this week and have an Eddi fitted. I knew the payback should be good with current price of electricity (Octopus), but £196 (inc lost export when i get the smart meter) vs £477 is £281 annual saving - or a payback of 21 months! Great explanation and calculator!
Hey Gary I am a big fan for diverters as they work well in OZ... 1.Our grid is garbage that can make exporting difficult. 2. Reliability, cost and simplicty is a word better than a heatpump. 3. Our export tariff is miserable. 4. Average array size is constantly rising and export in Australia is regarded as waste. 5. A diverter turns the water heater into a thermal battery. 6. I can use a diverter to help stabilise the local grid by creating a more gentle export and not drive the grid volts through the roof.
Hi Peter, thanks for sharing this insight about the consumer energy market in Australia. I'm hoping that new players like Octopus Energy (they're close by in NZ at the moment) enter your market and shake things up! :-)
Great explanation video Gary, much appreciated. Without knowing these automatic devices existed, I installed a more primitive, but far cheaper addition to our system. A high current smart switch on the immersion heater spur works via the Smart Life app and Alexa. On days with excess solar, when our battery is full, I can easily switch on/off the heating element. It also provides a timer routine for 7.5p Octopus off-peak as an alternative. The smart switch only cost £25 and has already paid for itself!
That's brilliant, Duncan! And just goes to show, you don't have to spend £hundreds or £thousands to get a great return! Thanks for the kind words about the video :-)
Hi Sounds very interesting. Can you tell me the name of the smart switch. I was also wondering if there is a device that not only controls the timings of the immersion heater but also can tell you the current temp of the water in the cylinder. The Tesla smart thermostat looked interesting but I don't think it's compatible with my cylinder. Ideally I need something I can control remotely with an app. Thanks
One other cost to consider is the boiler start up and heating the water in the pipes. Heating the boiler mass and 60 feet of pipes (counting both ways) may be small, but not insignificant. My oil boiler has only been on for one day since May, when we had a cloudy week, the riveter has saved a lot of oil.
Hi Gary, great video! A tiny fly in the ointment is that in running a gas boiler, you are also running a pump (60 to 100 watts depending on size) as well as the boiler fan (30 watts) and associated controls. The pump runs continuously in the on timed periods. I have done some of my own calculations on power use for this, but in winter months, when the heating is on at the same time, these costs would be incurred anyway heating the house.
Hi John, thanks for kind words on the video And good point - modelling any real world system accurately is hard, but I’ve tried to include enough that people can make informed conclusions. The electric cost of running a gas system required could be calculated as a small percentage on top of the gas cost (maybe < 5%?)
Hi Gary, greetings from Oxford. Thanks for this great channel! We don’t have solar (yet), but do have an EV and Octopus Go tariff. For us, gas is currently 15p per kWh, and cheap rate electricity is 7.5p per kWh. So we turned off water heating by the gas boiler, and added a timer to the immersion heater to heat our water with off-peak electricity. This saves us money, and reduces our emissions. In the summer months we now use no gas at all, as we swapped our old gas hob for an electric induction one.
You're just down the road from me then :-) Thanks for the kind words. And it sounds like you're doing really well on the "green" front even without solar! Are you able to get solar where you are, and is it something you're considering?
@@GaryDoesSolar Hi Gary, thanks for engaging. We are Cumnor side of Oxford, I saw you use an example address of Wytham in a video, so you might be just a few miles away, if so, give my regards to The White Heart and the Post Office/Tea Shop - great scones! We are indeed looking at solar, but our roof is not ideal as the main slopes are East/West, we are definitely keen on the GivEnergy AIO battery, 9 or perhaps 13.5kWh with the aim of energy arbitrage, and will need some element of solar PV at the same time, as a battery alone will attract VAT. I’m quite practical, so am considering constructing a frame on the south facing gable end to place panels there at circa 40 degrees, otherwise I think we would see very little PV generation through the winter months with roof panels.
@@simonreeves2017 Hi Simon, ah yeah - that was just an example location - I'm actually Southwest of Oxford - maybe only 30 minutes to Cumnor 🙂 Now, you might an East/West array is almost as good as a South array in fact. Two of my friends have East/West arrays and they publish their stats: Tim: ua-cam.com/channels/xT6jy59i_38H3Zy04VXzbg.html Dan: www.youtube.com/@DanEVSolar7
Excellent presentation, when doing the investigation on my Eddie system I found that our water tank was losing 71w per hour. This did make a big difference with only a couple in the house and low export payback. System well worth using.
This is a great video and I like the utility. My only two comments are: 1) People should check back every month or so, with the gas prices changing so fast at the moment. 2) There is an argument in favour of being able to use solar to heat water to protect yourself from gas supply problems, or if you would just rather not be burning gas to keep warm on environmental grounds.
@@GaryDoesSolar . It took my installer four months to sort out all the glitches with software on our new fronius battery inverter system. God knows how much more hassle it would have been tweaking a diverter. I've learned the hard way that the more you trust in automation, the lazier you get. I call manual switching voluntary rationing. Power is to expensive now to not be self disciplined.
Whether diverters are worth it depends on your situation. For us on a FIT contract that assumes we export half of what we generate whether we do or not. We have been using a solar Iboost for many years and have saved over 9Mwh. So our excess solar power really is free. In practice we get free hot water for about 9 months a year and contributes for the other 3. When the sun doesn't heat the tank we use the built in timer to heat using cheap rate electricity which is very similar to gas.
HiTerry, being on a FiT contract certainly helps a lot with regard to payback on a solar diverter. 9MWh is a lot of energy - well done! It might take me a few years to get to that point :-)
Great explanation. Another consideration is maintenance costs. When the excess solar output is less the power rating of the HWS element, most solar diverter units momentarily store & build up the energy until there is sufficient available to power the element for several seconds or so. This on-off cycling of the element can substantially shorten the element’s operating life. Hence the increased maintenance costs of more frequent element replacement. Also, when in this pulsing mode it is not very efficient because the very first part of every energy pulse is wasted in bringing the element back up to a temp which can then heat the water.
@@GaryDoesSolar Don’t know if you’ve already covered it, but may I suggest another way to minimise exported power is to use the load switching functions available in some solar inverters. Eg Fronius to mention 1 brand name. When the optional smart meter & data comms card are installed, these inverters can be programmed to switch a contactor/relay when certain solar production, consumption & export conditions are met. I have mine controlling a pool pump but the operating principle would be the same for hot water. The inverter only turns on the pump when more than 1,100 watts is being exported. The pump is rated at 1,000 watts so the 100 w buffer makes sure turning the pump on won’t then draw some off the grid. To avoid cycling off/on due to a passing cloud the pump is programmed to keep operating for 10 mins if the solar output drops & grid draw occurs. If after this time the solar still isn’t producing enough to run the pump without grid draw then pump remains off until there is again. This could be from full sun returning or other loads within the house reducing. The only thing the inverter looks for is more than 1,100 watts being exported. Should it be an overcast/rainy day with insufficient output to trigger the start of the pump, the inverter is programmed to run it for 3 hours from 1am on cheaper overnight rates. So a hot water system could be turned on the same way to ensure hot water for that morning shower. If the water reaches temp before the set hours are up the thermostat turns it off. So, before going off and buying an independent device, I urge your followers to investigate if they already have the technology required in extant equipment to achieve a similar outcome. This of course would substantially reduce the capital cost & so dramatically reduce the payback period.
I have the Solar IBoost, I had it installed around May this year at a total cost of £430, as the thermostat had failed that controlled the emersion heater. I checked yesterday & you can do this at anytime how much it has saved for the day, the last 24hrs, the last week & since it was installed. So far it's saved me over 600Kwh that would have been gas heated. Since it was installed, I have only had the boiler on twice to help heat up the water for a bath. I get no payback from my panels as they were installed for free, the company get the payback. Well worth it for me as it's also environmentally better too.
@@Bondy1986 I don't have a battery, the sender unit goes direct to the feed in at the meter so it can see when I'm sending power to the grid. The IBoost sits where the switch was for the emersion heater & tells it how much it can put in the element from around 10 watts up to around 3kw. I didn't get the IBoost buddy as they are in short supply but I'm coping without it. I wish I done it 7yrs ago when I had the solar panels put up.
There are many benefits of a DC battery over an AC one, so it’s worth making a total assessment. For example, DC batteries are more efficient on the AC/DC conversions, and if you have an oversized array, your inverter can store the generation above its rated limit into the battery.
Nice clear explanation of the pro’s and con’s of solar diverters and their payback. Your model can’t of course cater for everyone’s situation, such as having an air source heat pump like I do. I have considered a solar diverter but it just wasn’t something I got round to. In the non-winter months where the ASHP is only on to heat the hot water its using about 2-2.5kW a day which I’ve figured is probably low enough not to make it worthwhile changing
Thanks Geoffrey :-) Not sure if you saw my follow up video to this one here too: ua-cam.com/video/6zc1g1bz0eA/v-deo.html Yeah, ASHP is just a wonderful technology, especially when used in conjunction with solar and battery. I feel the days of solar inverters in the general market are numbered (so long as export rates remain above 12p/kWh ...
@@GaryDoesSolar Yes I did see that thanks and agree with your conclusion about the financial case not stacking up any more if you’re getting paid to export - and with rates at ~15p/kW it makes absolute sense to do so.
Gary - Just want to mention - Sunsynk Solar systems can also do this what the EDDI does somewhat. You set the menu to export power via the AUX port to drive the immersion heater. Surplus energy from the solar panels are used to charge the batteries while power is sent to the immersion heater. The export kick in percentage can easily be adjusted based on battery SOC, to send power to the immersion heater. Cost for this was a RCB Contatcor, some twin and earth cable, a MCB - let's say a couple of pounds. The solar diverters are just more variable. But many of us do not have our water heaters [geysers] on Solar - it is on grid and just nees top up during the day and the solar supply feeding it, then saves money as this topup power in the daytime comes from solar not grid.
Dear friend, let's say I have a 3kw water heater. In case my PV generates 2kw, for example, and the battery is 100% charged, would the AUX port use the 2kw available from the PV to power the heater and the last 1 kw from the battery or from the grid? The thing is that export is not allowed in my country so I am looking for a way to fully utilize the PV generation. This prevents me from using a power diverter, from what I understand. However, I am not sure whether it is a good idea to use the battery for heating the water (it seems wasteful, I do not know why :D). In other words, can the AUX port work like a diverter meaning it would ONLY use the excess solar, or it would supplement the 2kw PV power with battery/grid? Thanks!
All these calculations are based on a lot of if’s! However in my view a solar diverter is always worth having, for the simple reason that one’s reducing the amount of gas, a fossil fuel one using. My solar diverter both heats the water and it’s second circuit heats our towel rails. As we installed solar when FIT payments were available using all our solar doesn’t effect our FIT payment, It’s a win win. We use a myenergi Eddi diverter.
I'm afraid that's the name of the game with real word modelling - hence why there are so many fields that can be adjusted to suit everyone's particular circumstance. It can never be perfect - it only has to be good enough for people to get a reasonable idea on the value of a diverter to them. Great news that your diverter is working out for you, and yes, win, win because of the FiT payments! :-) Eddi does seem to be the best in the market, by far.
This diverter idea looks perfect for my plug-in Ioniq plus my new water heater. Having to fart about plugging in and out when the sun shines/doesn't is a bit of a bind. Not too sunny in Denmark. Thankyou Sir - I am now a subscriber.
Really interesting video Gary. I’m just starting my renewables journey with an ESS system hopefully being installed in the coming weeks followed by solar PV as soon as I can get hold of some decent panels. After watching your video, I’m in no hurry to install a solar diverter! Thanks.
Hi Craig, are you able to say a little more about your ESS system? Sounds intriguing. Is it a flywheel or compressed gas or something? 😳 And whatever it is, is it not quite expensive…? Sorry, this is not an area I’ve looked at.
@@GaryDoesSolar Hi Gary, it's just a lithium (LiFePo4) battery system, nothing more elaborate than that. The system I'm looking at is from Victron Energy who make the Multiplus-II inverter/charger, and Pylontech who make the battery modules. Victron have a range of inverters but the one I'm looking at can deliver 5000VA (about 4.4kW) and can also operate in the event of a grid power outage. It's basically the same system as in the UA-cam channel "The EV Puzzle" Hope this helps and sorry if this answer is a bit more boring than you were hoping for. 😂
Hi Craig, I'm very familiar with Nigel's setup on The EV Puzzle - I watch all his videos 🙂Ok, if your setup is similar to that, then you can't really go wrong! I was seriously considering Pylontech batteries but in the end I've gone for a GivEnergy system as it should be able to link to Octopus Energy smart tariffs. We'll see how it all goes when I eventually get my install (planned for Dec/Jan).
Very interesting video which has convinced me that, in my circumstances, a diverter is not a sensible option. One point with the calculator though. It assumes that the water is being heated from scratch every day. With my very well insulated tank the water is still hot the next day, even after I have used some for a shower, so does not have to be heated from the average temp. In larger households where all the water is being used then it would work out ok..
Hi David, glad you liked the video, Now, actually, my assumption in the utility is that any unused water in the tank stays hot! The utility purely concerns itself with the flow of water through the tank and the energy required to support that flow. Hope that explains...
Gary, that is of course one if the concerns. We spend all the money to build a system of one type or another with a payback period of perhaps less than 10 years. However, after that policies and/or prices change and the consumer is often disadvantaged. It feels like the solar contracting/gov't policy in this area is still the 'wild west' and gives me pause due to the volatility.
Yeah, it's not easy to figure out the payback for any system investment in a sea of constant changes (energy prices and policies etc.) Prices are falling over time, so waiting for a little less volatility is no bad thing...
Great video and explanation including the graphics. My issue is that the current export of 15p means payback is difficult. Additionally the tank losses are ~25% per day when full, therefore heating up during the day with solar would still need to boost with gas to have an early morning shower. So for me these are great during the FiT when export was use it or lose it, but now would be better to get paid to export from a pure financial perspective. N.B. not burning gas has a plethora of other benefits.
Hi Alistair, it might be worth you looking at a new tank - I changed mine recently and now only have losses of circa 2-3% a day. I think you'll be interested in this follow-up video I made then, which covers the increasing export rates in more detail: ua-cam.com/video/6zc1g1bz0eA/v-deo.html
I've noticed that unlike solar panel manufacturers, that typically provide 20 plus years of warranty and inverter manufacturers who provide 5 - 10 years, these diverter manufacturers typically offer just 1-2 years of warranty. I've also read many reviews that suggest that this reflects how long many of them last. So even if payback is 2 years, there is often no benefit it would seem and there is the carbon cost of manufacturing and disposing of the unit.
I have purchased a second hand unvented cylinder which will have a DC element wired directly to some pv panels this will be a pre heat source to the main cylinder inlet, therefore reducing any waste of pv power.
@@GaryDoesSolar they are more common to the American market as they are used in off grid situations, Amazon is the best place to source. DC elements are more difficult to use when it comes to switching them on and off via a thermostat as the current is not alternating (AC) but using a relay could be the answer (I'm still researching) we require hot water every day so to pre heat via pv panels with an immersion heater and perhaps a solar water heater/parabolic solar heater/wood burner using the indirect loop of the cylinder would help.
I have modified my boiler to reduce it’s power and I turn it on from 11am to 4pm with a clock driving the contractor in my electrical panel. It cost way less than a diverted and get a close enough result.
Yes, i have done a similar thing, but still looking for some tweaks to activate the Hot Water system when there is good sun & a timer for minimal inputs when it is cloudy.
great channel Gary, discovered via google on a search for PV / combi / HW tank results My question to you / anyone reading I don't have PV yet but assuming some major renovation works go ahead, i would dispose of my aging traditional boiler, and an accompanying solar thermal solution / oversized pressurised tank, and go PV fully across my south facing roof (approx 60sqm) I like the idea of a combi boiler and going tank-less (a bit more space, but also a simpler and lower install cost solution). Except that, now you have enlightened me on solar diverters, they seem a great idea to mop up excess (outside of home / EV car use). What i can't reach a conclusion on, is whether it would be 'better' to do without the additional cost complexity of a pressurised tank and diverter, and instead it an electric heated shower in one of bathrooms. I.e. if the sun is out and a shower is needed - then 'free' hot water. If no sun, then fairly efficient hot water from the combi. I am not considering use of batteries in the above. Your thoughts? My question is not about which is better for the planet, more, which is better for my pocket..
Thanks for taking the time to watch my videos and also to comment :-) Now, unfortunately, l'm not really in a position to provide individual advice, (not least because of potential liability issues - even if that advice is given free, such is the world today). You're best to speak to an installer about that, or post a comment onto a solar forum (e.g. this one in the UK: facebook.com/groups/2197329430289466) Good luck with whatever you decide!
I have an eddi, highly recommended. my gas boiler no longer used for hot water ever.. octopus go used to charge battery and heat hw, 00.30 to 04.30. solar does the rest of the hw heating during daytime via eddi. occasionally use battery to heat hw in evening. with current gas prices... absolute life saver.
Like your analyses most informative. I have a recently installed Air Source Heat Pump, using a kilowatt-hour can generate 2-3.5 kilowatt-hours worth of hot water with any spare solar. There's also the Octopus "Cosy" tariff for ASHP combined with battery I am able to use solar and off peak power to cover most of my energy usage. Charge 10 kilowatt-hours 4-7 am sunrise produces a mix until next off peak 1.00-4.00pm.which takes my batteries to full this is then used through to the evening. Leaving only a few hours at night at standard rates. This seems to me the most carbon neutral and cheapest way of using your energy production. Don't yet know how my ROI will stack up. With current UK govt grants it's a no brainer. A Cosy tariff spread sheet would be a useful tool.
Hi Andy, thanks for the great feedback! :-) Yeah - the cosy tariff looks interesting. Worth you checking out Tim & Kat's channel here, which covers the cosy tariff in detail: ua-cam.com/video/7d7fE8vRl4s/v-deo.html
Exactly. Saving money is not the only reason to go green. I am installing 6kw of amorphous silicone and also 1kw of mono crystalline plus 4 vacuum tube water preheating panels. Practically everything bought at auction or used. Next step is to get huge batteries so i can avoid the subscription, taxes and maintenance fees in France.I would rather spend €20 a month on fuel than be connected at those rates. Shame they don't really want to buy it back as i will have excess at times. I also have a small gas water heater a pellet stove and a small wood stove in-case it hits -20. Pellet stove and wood stove were free, paid £420 for the vacuum tube system with pump expansion tubes and heat exchanger immersion tank plus controller. Bought my grid tie inverters used, the panels were made in Switzerland but the company went bust and the mono / polly panels i have are all used also.
I'm quite impressed with how you've built up your setup in a highly cost-efficient way! :-) Agreed, individually, we can and should and all make an effort to reduce our carbon footprint, however small. Even taking steps to further insulate properties has a direct effect. I wish you all the best in your continued journey.
I've got a diverter and from my experience if your smart with encouraging baths during the day then you can save significant sums of money. Our cost was £400 and installed and it's paid back £40 at current KW prices in just 5 months.
You shouldn't have to change your washing behaviour. You can use batteries to store the energy or just feed power into other appliances or the whole house. It doesn't actually matter what uses the energy: by using the energy from solar, you are reducing how much energy you are taking from the grid. The issue is that you can wire up immersion heaters to cheap rate economy 7 during the night, and good insulation on the water tank will keep that water warm throughout the day, so what you need to do is look at the unit cost (the pence per kilowatt hour) of heating up the water from night time Economy 7 rate electricity and compare that to the equivalent unit cost of the power generated from solar and decide which is the cheapest way to heat the water in the immersion tank. And you should be considering the financial benefit of the feed-in tariff, as mentioned by another poster here and deciding whether it more cost effective to consume that excess solar generated electricity or feed it into the national grid. You can't make assumptions on this, you have to calculate it and use that as the basis of your decisions.
Another cracking video Gary. The costing didn't seem to capture the price of having an emersion tank brought and fitted, unless that was part of the £100 installation? I think for those on FIT payments, it's a hard sell break even wise. A friend gets around 1k pa, and gets not on the most lucrative FIT scheme. For us SEG peasants, I'll be lucky to make £100+ pa with a 6k system lol. Food for thought certainly
Thanks very much, Stuart :-) Yeah, I took the view that most homes (in the UK anyway) that have water tanks, already have immersion heaters fitted. Maybe that's not the case? But yes, if a tank has to be purchased, then that cost should be added to the diverter cost. True, those on FiT payments, seemed to have won the lottery :-)
A better cheaper but harder way to do it is detecting export power with Home Assistant and controlling appliances with HA automations, especially when having a heat pump witch dedicated diverters can't power.
Similar to what I'm doing with a home automation controller and Home Assistant. I detect excess power and then use an AC diversion load to use up that excess: ua-cam.com/video/H0LWO1GWN1w/v-deo.html I have a tankless gas water heater so no tank to dump that excess energy into, so it goes to heating the house on cool days.
Thank you that is very interesting. I have never really thought about it in terms of what the gas would cost if I were to burn it and sell the generated electricity. The fact that I would get more cash, albeit pennies, was not something that had occurred to me. I am still going to charge with solar as it gets us one step closer to net zero. I hope to ditch the gas completely in a couple of years.
Gary another back of the net presentation. For me the worth of a diverter was something I never considered. I thought it was an essential in any system as it was storing excess energy. Having run the utility using multiple options, for me, I realise It would never pay for itself. I now see that in my case, where im contemplating an ASHP, its far more effective in the higher solar producing months to heat the tank using solar / ASHP and then take any dregs that Scottish power deem give me for export. Then put the cost of a diverter down as a deposit on a bigger battery
Thanks for the kind words, Jim - you are most welcome! :-) Your proposed strategy looks sound. And in general, I think everyone is finally waking up to ASHP (great). I might look at a video on this at some point. It's a shame that diverters don't really deliver the payback that they appear to provide. If the costs were say half, the story would perhaps be different...
Very interesting. As a single person when getting quotes it seemed intuitive to me that the payback period would be very long just because of the small amount of hot water i use especially given much of it is in the winter when obviously solar input is minimal.
Might be a stupid question but @7:50 timestamp, isn't the energy required to heat that one litre just a kW value? Wouldn't you need a timeframe for it to become kWhr value?
I can understand your question, and it's purely down to the difference between power and energy. When you switch the immersion heater on it will start heating the water. That means the immersion heater is instantly consuming power... but in the first few seconds, the water temperature doesn't change. It's only after a finite time at that level of power that the water starts to heat up. And when it has risen by 1 degree, you multiply the power by the time taken to get the energy requirement (which is in kWh).
A diverter was one of my first 'projects' on my PV - using the EmonTX from Open Energy Monitor and some open source code from a very smart contributor (total cost
We have one and they're great - free hot water for 9 months of the year, and reduced costs for the other 3 months since with a large tank (300L plus), we can wait a couple of days for a good solar day to dump a load of energy in it. You don't always need a fancy brand one with an app and all the cost of supporting the marketing department. They can be very cheap and wire directly into the fuze box. Ours is a RM1B23D50 solid state relay. Saved us hundreds since we got solar panels.
@@brianrussell6988 No idea, the electronics all comes in the relay. The electrician just wired it in while I was there, it's a quick job. It has its own circuit from the fuse box directly to the immersion tank.
@@GaryDoesSolar Yes! The unit kicks in automatically when there is any excess solar. The data sheet says "The zero switching relay switches ON when the sinusoidal curve crosses zero and switches OFF when the current crosses zero." There are sensors on the solar and mains inputs.
Didnt know Octopus had raised export prices to 15p. Nice one 👍 Only bummer "Currently, you can't be on both outgoingOctopus and OctopusGo, our EV tariff, at the same time"
Yeah, it's only for certain tariffs (I've now added a note to the video description, in case of confusion). But see my pinned comment, where I comment on why higher export rates should eventually appear on all tariffs...
Hi Gary, great video! A tiny fly in the ointment is that in running a gas boiler, you are also running a pump (60 to 100 watts depending on size) as well as the boiler fan (30 watts) and associated controls. The pump runs continuously in the on timed periods. I have done some of my own calculations on power use for this, but in winter months, when the heating is on at the same time, these costs would be incurred anyway heating the house.
@@GaryDoesSolar The cynic in me things they'll only go to Octupus's previous of 7.5p max, but love to be proved wrong. I think you can use anybody for SEG, so I'll stick to the Go tariff until March, then I'll have seen my 1st worse case generation period. Maybe then which to the better export rate for 6-8 month then back on Go. You still waiting for DNO sign off?
I am using a Sonoff switch with Home Assistant (HA) to turn on the immersion heater. HA can estimate solar and turn on during peak times. When I am not generating enough via solar, the battery makes up the shortfall and switches off. If I start drawing from the grid, it switches off.
Gary, new viewer, happy discovery via the YT Algo. We have had a 12kw solar system for about 5 years, and as a retired GC I tried to do a lot of my own homework before our system purchase and installation (SunPower). We are in Southern California so solar here is a no-brainer, but could you do something on how people in the UK (or other often cloudy areas) can figure out their ROI for solar. BTW: Since retirement I have done a couple small, RV based "off-grid" systems, and I can say, I have already leared a fair amount from your videos. Thanks so much.
Thanks Paul - great to hear you’re enjoying my videos 😀 Regarding ROI, did you see my video on that very topic? Here is the link: m.ua-cam.com/video/FvjuJQZRrvA/v-deo.html
The only thing I am 'missing' in this video is the fact that there is actually no real "diverting power". These "diverters" are nothing but smart automated switches. They have some means of measuring the consumption and production (either through CT clamps, or by connecting directly to the inverter through protocols like modbus, ...) and switch devices on/off/or power them at an according rate. I am currently building this myself, because these "diverters" are not as complicated, as I initially thought (and they are quite expensive for what they actually do in my opinion). I bought a cheaper 3 phase power controller that I had installed with my solar and hooked it up to a nodemcu board to be able to controll the power through wifi. I read the power readings from the inverter over modbus and I have a little logic setting the percentage of power on the power controller accordingly (the logic being pretty much identical to what you explained in this video).
I would argue that "diverting" is indeed taking place, because if there was no diverter in the system, excess solar would automatically be exported. Having such a unit causes that excess to be used by (and therefore diverted to) the immersion heater in the water tank. Now, great to hear you're building a diverter yourself - not everyone has the skills to take on such a challenge! :-) I'd be interested to hear how you manage the power reduction as this is what sets apart the premium models (like MyEnergi Eddi) from the rest of the market. The Eddi unit can throttle the power without chopping/corrupting the sine wave too much.
@@GaryDoesSolar I am aware, that my "criticism" is mainly based on how I interprete the word "diversion" and I understand your response completely. I just think the word and the name of these "diverters" imply they do actually control the flow of electricity somehow, which they only do passively by simply closing or opening cicuits. It makes them sound more complicated than what they actually are, automatic switches. The thing is. If one did this task manually, by manually switching on the dishwasher, water heating element, or whatever with a simple flip of a switch when enough power comes from the solar panels, one would probably never call this task "I divert power to the heating element" (unless they were doing a bit from Star Trek :D). Instead they would simply say: "I switched it on!". The "diverters" don't do anything different. Except maybe from having a power controller (voltage regulator) included in them, which allows power going to certain electrical appliances to be "limited". In most cases these are Phase-fired controllers. You can find devices from TriHero like the SCR3 for 3-Phase voltage regulation and they cost a fraction of what an eddi costs, which can only regulate 1 phase power, as far as I know? The eddi works the same way, and it cuts the phases exactly the same way as the heating elements don't care at all about this (motors and other things do care though!!) I have a variant of this TriHero 3-Phase regulator that is being sold where I live. These are perfect for "dumb" things like heating elements, but ofc for things like more complicated devices (washing machines, dish washers, car chargers, ...) they are useless. By simply controlling these with an esp, or raspberry pi, you get the same smart switch for much cheaper, but you don't get a vendor lock-in as you do with an eddi (in which case you need to buy a powerwall and all other switches from that myenergy vendor). Simply because different protocols and standards (or even proprietary ones like with the eddi) are used in the diverters, and the different vendors of appliances. So it might be that you have a diverter installed that can ragulate a "dumb" heating element in the water cylinder, but it might not be able to talk to a powerwall that you have, or it might not be able to start/stop tumblers/washing machines that you have around. So maybe my criticism is not as much about the actual word "diverter' but about the limited capabilities of these expensive devices when it comes to compatibility with all home appliances (beyond water heaters). Building it yourself does not guarantee compatibility, but the chances are higher you get many different devices connected. If you only use it to heat water, these devices seem too overengineered and overpriced for what they do. Compare 2 numbers, and set a voltage regulator ... I guess all I should've said is: diverters are very simple. If you are interested and somewhat know electronics (it really not complicated) and maybe even have a raspberry pi or esp lying around, you can try and build this yourself (note: the voltage regulators need to be put in place by professional electricians ofc!! (but so do the diverters, so there is no difference)). If you get to the inverter data in many cases you don't even need ct clamps as the inverter has the data already (and provides it on modbus, webinterfaces, possibly other open protocols). A single phase ssr relay, or voltage regulator can be bought for 1/10th of the price of one of these diverters ... and don't underestimate what one can learn and the fun one can have in the process :D!
Thanks the kind words. I guess the problem is that the diverter is managing the use of excess solar, and of course, central heating is generally required outside of those times. That said, use of a battery and heat pump would head in the right direction 👍🏻
Great video, a lot for my brain to take in. I have a SunSynk Hybrid inverter which has auxiliary connections that can be set to heat an immersion, not totally sure how it works but I think the only difference between the auxiliary and essential supply is that auxiliary only pulls from battery or solar, not grid and I do think, it works irrespective of the house and battery being satisfied, it is all the time except 00.30 and 04.30 (when no solar and battery charging from off peak). I do not think it has the facility to supply less than 3kw so it seems a very broad brush approach, all or nothing. After some thought I controlled the cable feeding the immersion via a Timeguard Wi-Fi controlled fused spur model FSTWIFITU which allows me to time control the immersion and works very well as I can remotely switch on and off. Before my solar/battery installation I never used the immersion, so not surprisingly I did not factor in the 4/5 kWh a day to heat the water, which is fine off of the solar and battery during the summer but I figure I might have to revert to my boiler during the low solar months to avoid draining 25% of my battery on water heating. I am not too upset as the auxiliary is part of the package and the Timeguard cost less than £50 I would be delighted if someone would confirm my observations of exactly how the SunSynk auxiliary works and you are the man to do it
Hi Mike, thanks - I also made a follow up to that video here, in case you did not already see: ua-cam.com/video/6zc1g1bz0eA/v-deo.html Thanks for taking the time to describe your solar setup and situation. I don't have any expertise on Sunsynk products, but hopefully, someone reading this can help answer your questions. Failing that, I'd suggest you join this Facebook group and ask there: facebook.com/groups/2197329430289466 Good luck!
Hi Gary, How smart are these diverters? By this I mean, can they be programmed to take into account different situations. For example, the max export on a G98 is 3.86 kW, so can the diverter be set up to only kick in if there is solar excess (house draw + 3.86kW export)? If so, can they be configured to not kick in during high tariff export periods? I’m also assuming that you would only need to use the immersion heater for short periods to get the water up to the desired temp, so will the diverter only kick in when that temp drops and for only as long as required to get back up to temp? If the aim is to be as green as possible and therefore paying back the initial outlay for the diverter is not considered part of the equation, but you want a mechanism to heat water in an environmentally friendly way, can the hot water system be configured to only use the diverter through the solar/battery and never draw from the grid? Thanks
The EDDI unit I was considering at the time was quite intelligent, and could also perhaps be controlled by Home Assistant. However, in this follow-up video I made, I concluded that none of that mattered when you looked at the bigger picture against a backdrop of relatively high export rates: ua-cam.com/video/6zc1g1bz0eA/v-deo.htmlsi=Jkvu5VWD1b9sQ_l- As export rates fall in line with increased grid-scale renewables however, the situation will change again, and solar diverters (with intelligent control like you suggest) could well be back on the table...
I had the solaredge iboost but within 2 years it broke down three times. I switched to the Solic 200 and it works very well and I have hot water solar powered all the time.
Same here. The Iboost seems pretty feeble and doesn't cope with a bigger tank or higher water temperatures. Just about to replace mine with immersun or eddi. Why did you go for Solic200?
If you ignore cost of the water heater: We simply end up comparing the ratio of the cost of gas to the revenue you can get for your solar. On todays gas prices of 7p per kWh: If I can sell my excess electric at 9p or more then it's cheaper to use gas and sell the excess electric. Given Octopus paying me 15p to 20p for my excess solar... I certainly regret purchasing the Eddi, in fact I have it always off now. (Unless I misunderstood something important!)
Yeah, EDDIs (and other solar diverter products) are currently not useful to most people. If export prices come down again, that could change of course.
Excellent video, subscribed. Your analysis agrees with my back-of-envelope calculation that predicted a very long (or even no) payback for a single occupant. I was originally intending to install solar hot water panels and a thermal store cylinder but even DIY the cost is ridiculous. Now I'm in the process of installing a twin immersion cylinder and Eddie controller to use some solar PV excess. It will still have a long payback but is a fun project and provides a source of hot water if the gas stops flowing.
Hi Matt - glad you enjoyed the video - and thanks for subscribing! 😀 Yeah, the rate at which holes are appearing in nordstream2, the gas might indeed stop flowing!! 🤣
Thanks for sharing - very informative and certainly clarified the topic. With my home set up I have need to have my inverter in my garage remote from the house where my hot water immersion heater is located. Do you know how far away the sensors can be away from the actual solar diverter unit? Thx
Some products, like Eddi allow the sensors to be far away by using a radio link (MyEnergi Hub) - worth a look. And the latest units just connect straight into your WiFi...
Great video always temper your expectations with a 50 % fail rate as Murphy's law is prominent, for instance I live in Ontario Canada 6 years ago I installed solar with a 7 year pay back calculated but to my surprise in the 3rd year the government decided to rewrite the Ontario credit for electricity which is great I love getting a credit but it changed my pay back period to 10 years. But do not worry 3 years after they increased the prices so I am now back on track to a 7 year pay back which is next year. Also I find some sun year hours are much better than others which may be the rain/snow events seem to be longer. Oh I have a 100% electric home so I use 17,000 kwh a year so when I reach my pay back I will be up grading Solar is the future of my energy.
Thanks :-) Yeah, and this is the problem with any long-term investment. Nobody can predict the future (at least, I've not met anyone yet who can). And in today's world it seems that anything is possible - things that reduce your payback period, and things that lengthen it! I totally agree, residential solar will be the future for most people's home energy :-)
My Immersun diverter tells me how much electricity that has been sent to the immersion heater every day. I use this to calculate the returns at the price per kWhr of gas. I don't use average water consumption per household to work out the return, surely somewhat vague. The Immersun has been installed near enough to 10 years now and has supplied 21,800kWh to my 160 litre hot water tank. I calculated it needed some three years before payback when gas was cheap. Now.....!
Note that the best value Octopus tariff is the Tesla Power tariff for those with a Tesla battery (you may want to do a video on this). However you cannot use this tariff if you have a hot water diverted.
Interesting video, and all of the videos for that matter, thank you Gary, We are on a FIT (with Scottish Power) at 19p/6p rate but have our electricity with Octopus. We have a 4K array but no battery or EV's. It's a large house, old, reasonable insulation, but is oil fired via a boiler driving hydronic under floor heating and hot water through a 300L thermal store (boiler runs on demand 24hrs via a tank stat). No gas locally and electric cooking. The oil has cost us a lot in the past 12 months and I started reconsidering solar diverters again. We average about 12KwH of electric usage per day. Yes, batteries are a great way forward but a costly investment, if you can find them and an installer. I get the idea of an Octopus variable tariff but wonder if dumping the FIT would prove costly for us, even with generous rates on offer from Octopus. I just wonder if a solar diverter is a decent "part way house" for us for now? Trouble is, with a thermal store holding half the tank above 55 degrees, would the incremental temperature increase offered by an immersion heater with a maxed out temperature setting offer a decent pay back period for a solar diverter? Any thoughts or handy calculators or formulae would be most welcome! Thanks
Hi Ian, thanks for the kind feedback on this and other my videos. You may have seen my follow-up solar diverter video where I feel the financial case for one is no longer there in light of the higher export rates we're seeing at the moment: ua-cam.com/video/6zc1g1bz0eA/v-deo.html The fact you're on on FiT though means that it's still worth it for you - I would certainly hold onto that tariff for as long as you can! :-) I've not seen any calculators unfortunately. If I do, I'll certainly let you know!
@@GaryDoesSolar Thank you for the reply Gary. Indeed my FIT rate does seem a lot more attractive than the rates on offer recently and this is what made me wonder if there is any logic in moving to one of the new Octopus schemes. In addition, we're on a simple PV generation meter so are not paid for what we export, simply what we generate plus a notional amount for perceived export. It seems like, if we stay where we are, we could do worse than buy a PV dump system and also add a battery at a more suitable time, all the while keeping the FIT rate that we currently enjoy. Sadly though, at our old house things were even better as our FIT rate was 44.1p! - one of the few downsides of escaping from the city and moving to the countryside is loosing the early adoption FIT rate that we had.
We have moved into a house with a solar diverter and pressure tank in the loft but it does not seem to work. I might consider getting someone to look at it, thanks for video.
Hi Gary - this video is exactly what i am thinking about at the moment and whether installing a diverter and immersion water heater/cylinder would be cost effective. I have a 13 year old solar system with the original solar tariff so I get paid for export no matter what is actually exported. So this means it doesn't matter how much i export as i will always be paid the same amount (50% of my generation). I have also got battery storage fitted and would like to use the spare energy i make and heat water. As a rough estimate, do you think it would be cost effective any pay back if i install an immersion heater/cylinder and diverter? Many thanks in advance
Hi Anthony, yes - you're in a. very good situation being on the UK's Feed-in-tariff mechanism, and that can make operating a solar diverter more attractive. I'd try different scenarios using the calculator mentioned in the video, to see if it works out well.
Thanks very much, indeed, another fantastic presentation. A brilliant balance that makes a potentially complex topic understandable. Purely for interest, we live in Dorset with two sizable roofs south and east facing @ 18° pitch. I'm not sure exactly what I'm going to do yet. Because we live out in the bush and use electricity, oil, and log burner, I was thinking of dumping surplus into the electric underfloor heating and water.
Good video & content Gary. I'm just about to start on my Solar journey & I have a survey booked for next week & I'm considering a solar diverter. The problem I have is that our gas boiler fed HW cylinder is 38 years old & I bet the internals are covered in limescale. It is a factory foamed cylinder with an addition jacket around it & has a short reach top mounted emersion heater which only heats up approx 30% of the water in the top of the tank. The fact that it is 38 years old I'm wondering if it's worth upgrading it for a better insulated modern tank with a lower side mounted emersion heater? I know this will add substantially to the cost & payback scenario but can't help thinking that the old tank is due for a change & would a be a weak link in my solar system if I keep it.
My advice for what it’s worth! As a retired heating engineer is absolutely change the Cylinder for one of the new stainless steel fully insulated ones. I’d also advise you go for one with two Emerson heater, one near the bottom and the other near the top. Then you can choose wether to heat al or part of the tank. Your old Cylinder has done well to last so long and leaks can be expensive, as my sister recently found out.
@@CMWobby1 Thanks for that. Decision made, I'm going to change it. Just hope I can get one which has similar connection positions to the old 36 x 18 to avoid too many pipework changes.
I'm considering an oversized solar PV system, then using a 2 output diverter to firstly heat hot water cylinder using immersion heater, then heat our home using an electric radiator. Requires calculating, but I'd size so that the system can provide (or supllement) home heating during spring and autumn, just to reduce the demand placed on our gas central heating system.
I've been using an iBoost solar diverter set to heat my hot water for several years. This year I fitted a second one to divert energy to a storage heater. It too worked fine. The iBoost+ lets you select the export power detection level when the diverter kicks in so the battery charges first, then the immersion heater, then the storage heater. The only problem is that during the winter when I would like to charge the storage heater, there is little or no solar available even with my 6.8Kw array
@@iainmackay9269 Nice!, that would be my dream setup. I guess the only way to get that storage heater charged mid winter is for even more solar PV? Or install Solar Thermal to charge your hot water, so the PV is free'd up more for the storage heater? What type of storage heater are you using?
Hi Gary, all your videos are great - many thanks. If you have a battery, is it better to use the excess solar to charge it rather than having a diverter?
Most definitely, John - fill your battery first, because that saves you the retail cost of buying that same electricity. Then, with the excess, you have a choice: 1. Divert it to your water tank 2. Export it (if you can achieve a good rate, like the Octopus 15p/kWh) Win, win! Thanks for your kind words on my videos :-)
Hi Gary, very interesting as I have recently had solar, 3.2 Kw and 2 batteries,6.4 Kw fitted but still exporting on some occasions. My hot water at the moment is now heated with a "Fischer" system using phase change materials and the gas now only supplies heating. Probably be different in the winter. I am considering buying some panels to direct feed an immersion heater in a small water tank. This would not be my main source of hot water but just to supply a shower and small sink, probably be used 3 times a week. Wondering if this would be viable. Actually thinking about it maybe get a battery and run an electric shower.
If you're getting a battery for the electric shower, you may want to ensure it can discharge at the rate your shower needs it. See my video here (2m50s in): ua-cam.com/video/3vwDrfuXyik/v-deo.html
Without majorly modifying my top-heated cylinder, I diverted 483kWh in a year. At 80% efficiency, gas costs 12.86p per kWh and export earns 6.79p per kWh. The annual value of the diverter is £29.31. The payback would be 10 years.
Yeah, the calculator I used in the video shows that for export rates higher than 12p, you’re far better off financially exporting that energy and just using gas. It’s a shame really because I really like the concept of solar diverters. Here’s my follow up video on the topic: ua-cam.com/video/6zc1g1bz0eA/v-deo.html
Really interesting video. I've got a combi boiler and lost my immersion tank when this was installed. I would have to look at getting one installed again , if possible, and adjust the installation cost to cover this. One of the benefits of the combi is getting hot water at near mains pressure, thus the immersion tank would have to be a pressurized one to keep this benefit. I've got a few questions now for my heating engineer!
Thanks Mick - our hot water cylinder is unvented, which means we get near-mains pressure too (fab!) Yeah, your heating engineer will advise better than I can. Good luck in whatever you decide!
@@GaryDoesSolar When you look back in time the Victorians was cleaver. So adopted there ideas some what. And went for Solid Fuel Central Heating in the 80s. Price was almost double of Gas central heating at that time. But over the years we saved loads. And all you need is a Vented Indirect Cylinder which is a few hundred Quid depending on size you need. So I get Hot Water from my log burner during winter time easy. Solar would just help with Hot water in the period when Log burner would melt you. And ultimately with an Air Source Heat Pump for those days when its just chilly run off solar. No Gas since the 80s Sid was not a Happy Bunny. Now Solar would eliminate 80% of Electric if I plan it right. Logs cost me 450 quid and being old fart it reduces to Zero this year with winter fuel allowance. Get the wife a flat iron and a kettle for the log burner winner lmao.
@@GaryDoesSolar Foot note. Tried China for Panels by the way. Not cost effective unless you buy 100 or more then you would save a considerable amount. Batteries are cheaper and costs 250 quid for shipping. If and when I find decent recommended Company will post them here. They do offer a Trial Period on some before you pay full amount and free returns if there are problems.
You can get, and I have it, an electric immersion heater which holds hot water at mains pressure. The shower is the best shower I have ever had. It's very powerful and it's hot. Flow rate is excellent. That same tank feeds the hot water taps in the property.
Thanks for the videos Gary. Most helpful I’ve come across by far. If I didn’t have a diverter, and I switched the immersion on while the PV panels were generating, wouldn’t the PV panels directly power the immersion? Or if I timed the immersion to come on during the day, a well insulated tank would act as a battery?
Hi Jamie - that’s very kind of you to say! 😀 Yes, you’re right about manual or timed immersion heater control - that’s essentially what the diverter does for you automatically. But the advantage the diverter has is that it can vary the power to the immersion (rather than just all or nothing). That’s important because if you have clouds coming over for a few minutes (as is typical in many countries) it will automatically reduce the power in order not to draw from the grid. A timer solution would not know about the clouds, and I doubt you’d want to be watching the sky all day with your finger on the switch 🤣 Hope that helps 👍🏻
The video was very interesting and your calculator is extremely helpful. I heat my water using oil and assuming 70p per ltr this would be 7p/kW (10.35kW per ltr of heating oil) which makes a diverter very unattractive. I wonder if you could extend your calculator to allow inputting of oil as a choice? Many people who want solar are comparing to oil, rather than gas because we live to far from gas mains.
Great to hear the video was useful to you! Now, I understand others have used the utility for oil instead of gas - they just had to calculate the numbers a little...
You missed out the dual immersion scenario common in North America, with 1 at the top of the cylinder, and 1 low down, the top one heats first and only when the top of the cylinder is up to heat does the power get diverted to the lower heater.
We haven't got a hot water cylinder, but considered one instead of using our combi boiler. However I think your installation costs are rather optimistic. With our Fronius system their solar diverter with installation I can see being a £1k If we then bought a Mixergy tank, another £1k After installation, probably £2.5k! We would never pay that back, especially with our highly efficient daalderop combi. If you can do it cheap with an existing hot water cylinder okay, but many of these add on systems and fancy hot water tanks, you just never pay them back in reality.
Hi Michael - yes, the video is specially targeted for people who already have a water tank with an immersion heater - as this is the minimum requirement for a unit like an Eddi. The model does all for extra costs to be added, including tanks, but that will likely destroy any chance of a decent payback.
Interesting calculator. But if you have a heat pump with a COP of say 3, this alters the electricity input on days with insufficient solar dramatically. As an aside, should I be using 3 times more free electricity, or just using my heat pump to do the job, and exporting to the grid?!
Hi Tam, thanks for taking the time to comment. Now, the calculator is really for gas (or fossil fuel) boilers. I haven't looked into heat pumps yet, but maybe someone else here could comment on that?
The payback model used in your calculations is in my view a bit flawed! The usual method of heating a tank of hot water is to switch the boiler on once or twice per day. Ours is once per day in the morning before we shower. Irrespective of how much of that hot water we use the remaining hot water in the tank cools over night to get heated up the next day. The amount of gas used is therefore not directly proportional to the number of house occupants. This is quite easily demonstrated if you heat up your hot water but use none for a day. Your boiler will reheat the same tank full the next day. The means the payback period for 1 and 2 house occupants is rather better than you calculate. PS I do like your videos as they are very clear and demystify the technology very well...thanks.
Hi Chris, thanks for the kind words. In making any utility modelling the real world, the more accurate you want it to be, the more exponential the effort. I therefore choose a mainstream use case of a family of 4 who would use the entire tank at least once a day. Even if your case, where hot water remains in the tank, cooling over the remainder of the day - I’d hope your tank would have a high efficiency rating. My own tank will only lose a couple of degrees in 24 hours.
We are on South Australia and have had a totally separate 315 litre Evacuated Tube solar hot water system for 8 years it has an electric boost that is only used very occasionally during winter, the rest of the year all heating is free from the sun....... 🙂🙃🙂🙃🙂🙃🙂
We’re about to have solar installed and have decided against a solar diverter. The problem we have is that the cylinder is in the 2nd bedroom cupboard and (although well insulated) it obviously leaks some heat into that room (enough that the radiator is only on about 5-10 days of the year). The window is south facing so the last thing we want during summer is to put more heat into the cylinder during the day, and of course in the winter there is unlikely to much excess solar. We currently heat it using gas for 90mins in the morning, have all our showers etc. and it then leaves us with enough hot water through to the afternoon. Late afternoon we then give it a 30min boost which is good for evening use. I’m considering having a timer fitted and keeping the same routine but using the immersion heater. It would take about 50% out of the solar battery in the morning to fully heat and could use solar excess for the afternoon boost.
Hi Stephen, it sounds like you’ve got a great strategy for your hot water management, and it’s working well. Definitely worth looking at cladding your cylinder and pipes if you haven’t done so already 👍🏻
If the immersion heater has a thermostat then just run a timer on it as the simplest form of diversion. You could if handy with computers get a raspberry pi or PC to turn on the switch with a shelly or various IOT power switches depending on the amp rating of the heater (or use the shelly/IOT to activate a larger relay/contactor). Though if you are getting 15pc per KWH switch the whole house off and send it to the grid....
Agreed, this is a simpler and perhaps cheaper method, but the benefit of a fully-fledged diverter comes in when there is occasional cloud cover. When that happens, the diverter will reduce power to the immersion to match the available solar excess, so no draw from the grid. With a simple timer solution, you will be drawing from the grid every time a cloud comes over. Agreed that higher export rates break the payback for solar diverters.
@@GaryDoesSolar How do they work PWM? A simple timer would be a problem for cloudy days - I use this approach at the moment though not efficiently - just turn the timer off when the day is no good for solar or if during the day it gets good or bad. Ideally like to find some machine learning approach as sadly my feed in to the grid is likely to be cut completely so will have potential excess power but wont be able to determine its capability unless its consumed. I think Fronius ohm-pilot or perhaps others can just pull power from the DC side of the panels and use that to power external loads, again these systems are pretty pricey....For those with time of use power you could look at using a grid-tie inverter with batteries (ua-cam.com/video/yv6TTT57y_U/v-deo.html) at least cut loads overnight and/or feed back if the export price is justifiable to do so.
@@rw-xf4cb usually a triac that fires as many mains cycles as needed - a bit like a light dimmer but more sophisticated as it will be switching up to 3kW for the immersion - needs quite a chunky heatsink as each Amp needs to dissipate 1W of power...
Hi Gary, do you know if there are any easy ways to do this with a combi boiler? It obviously doesnt store water but do you know of any methods to store water/retro fit to benefit from over solar generation?
Hi Ryan, so with the combi-boiler, it’s only consuming electricity when the hot water is being drawn, which is usually just a minute or so typically on occasion (and slightly longer if taking a shower or filling a bath). Excess solar has a very different profile, perhaps several hours during the middle part of the day. There’s no way to toes the two, unless there is a bigger - namely a water cylinder. Worth watching my follow-up video here (ua-cam.com/video/6zc1g1bz0eA/v-deo.html) as if you’re looking to make a financial return, given the excellent export rates available on many tariffs at the moment, it actually doesn’t make sense to divert. But if you really want to make use of your excess solar to heat water, then a cylinder is the way to go, assuming your property can house such.
Hi Gary, thanks for the excellent channel. For those of us with no gas supply and using oil for water heating, is it easy to adapt your economic evaluation to represent the situation with an oil alternative to gas?
You're very welcome, Ian - thanks for taking the time to watch. Now, I would say, yes it should be easy to substitute oil instead of gas. You'll need to get some handle on the efficiency of heating water with oil though... Good luck!
I try and divert excess solar into the car. On good solar days I can turn on the immersion heater even if there is only say 1kw being exported and leverage the extra 2kw from the battery. After the water is up to temp the battery will then recharge. A diverter makes no economic sense to me but the biggest concern is it draining my battery.
Great video/research. But you are forgetting one important thing. The "battery" capacity of the water tank. You won't be able to dump *all* your excess power into the tank. There is a limit to how cold you can let the water get (due to Legionella bacteria, min 50 deg all the way to the tap) and you can't go all the way up to 100 C either. In pracsis you are limited to a max of around 60-65 (the temp where the pot starts making noise when you boil something). If you go above this, the calcium in the water separates and glogs the tank. Even if you accept you have to clean it often, you probably don't want 70 or 80 deg C coming out of you taps or shower. Especially if you have smaller kids. You www page already knows the kwh pr deg. So if you allow inputting tank volume and min/max temp, you easily get kwh "battery" capacity of the tank. And then there is the timing. There is a huge difference if the whole family shower in the morning or evening when there is no sun or during a sunny day.
Thanks Jesper - and this is the problem building any model of the real world. The effort required is exponentially proportionate to the resulting real-world accuracy, unfortunately. Therefore, what I’ve hoped to achieve is a model that’s at least adequate enough for people to make a relatively informed decision on 👍🏻 In my model, it’s not about about trying to dump all of the excess into the tank. It’s about dumping sufficient excess to cover daily hot water requirement - the assumption here is that the tank size is large enough for all in the house. You’ve given me food for thought though, on how I might improve on the model (if I get time) - thank you!
Jesper, in Australia tempering valves are fitted to prevent super hot water being sent to showers, baths, etc. They mix the hot water with cold to limit the temp to 55 deg to prevent scalding. Don’t know if available there but well worth fitting for safety if they are.
@@jnygaarddk I don’t have hard water where I am. In Perth, where they do have hard water, temp limiting valves are mandatory as well. So must not be a big problem or slighter quicker replacement cycle. (TLV should be checked annually & replaced every 3-5 years to ensure working correctly.) The other thing peeps know they need to do in hard water areas is manually operate the HWS over pressure temperature valve weekly to avoid it being stuck shut by calcium.
Thanks for the interesting video. Good point about estimating the amount of hot water you can actually consume, not many videos mention that but its the limiting factor in my case. Might be worth pointing out that anyone on a pre 2019 Feed In Tariff (like me) is paid nothing for what they actually export, so all of the generated electricity is free to use. They essentially make up a number and assume that 50% of the generated energy is exported, so you get the same amount whether you export none of it, or all of it. Secondly your gas boiler efficiency seems way too high at a system level. You have to use gas heating up the boiler itself, the pipework in-between (and more importantly the water in those pipes) and most of that heat leaks away after use. Typical figures from my system given similar starting conditions are 2.5 kWh of solar electricity (reported by the diverter), vs 5 kWh of gas (reported by the smart meter). I'd be cautious about directly comparing them, but approx. 50% efficiency would seem to be a more realistic estimate. Just for info, I bought a second PV diverter (second hand so not too expensive) and have connected it to a string of convector heaters totalling 3 KW. When the thermostat on the hot water tank stops it taking in any more energy I switch on the second system and use the heaters to provide some background heat to the house. Works well (4,700 kWh harvested so far) and could be used to divert power in a house without a hot water cylinder (e.g. combi boiler fitted). Obviously, can't be used in summer because the house is warm anyway, but helps most of the year.
Thanks Robert 😀 yeah, I do like to bring everything back to first principles and build from there. And relating everything to personal consumption took me away from tank sizes etc. 👍🏻 Now, I think you’re probably right about just how inefficient water heating via gas is. I chose “80%” only as average of old vs boilers. But, really, even with a new boiler, 80% might be too optimistic :-/ I like the way you’ve self-utilised as much solar are you can!
Thanks Robert 😀 yeah, I do like to bring everything back to first principles and build from there. And relating everything to personal consumption took me away from tank sizes etc. 👍🏻 Now, I think you’re probably right about just how inefficient water heating via gas is. I chose “80%” only as average of old vs boilers. But, really, even with a new boiler, 80% might be too optimistic :-/ I like the way you’ve self-utilised as much solar are you can!
Hi. Thanks for the video. In the calculation, regarding the export value that needs to be considered. It says that the higher the rate the less feasible a diverter is. If we get paid for power generated whether we use it or not, we still get paid the full amount do we need to put zero in this box?
Ah, now you might be on a FiT scheme. This utility wasn’t designed for that unfortunately. I would enter “0” as you say, and see what the utility says.
I don't know why the evacuated tube type of solar arrays are so blooming expensive? People with enough knowledge can make their own for hardly any money, so why are they so expensive when professionally made? And so, we have to go with the diverter option, which isn't the best of the 2 options..... oh well! As ever, a good explanation here!
Cheers - yeah, the problem is that solar thermal panels are single use case (i.e. heating water) whereas solar PV is way better as the output of that can be used for all sorts of purposes. I'd suggest people consider a heat pump for heating water if you want to get away from gas/oil however.
On the sell back vs use locally q.... Paradoxically if you are environmentally minded the best tactic is to keep as much of the energy as you might otherwise sell back, and don't use external fuel unless you have to. This keeps the export production lower which keeps prices higher. That in turn means your neighbour will want to do the same, and will do the same. That has a better ripple effect, and more solar means more people save, while external price isn't dented by new supply... If lots of people just sell back, the incentive degrades unless feed in tariffs become higher in response - but that's very unlikely when export supply increases. So others who haven't gone over yet will see you making a few p for export, and however environmentally minded you are, you've just convinced all your neighbours not to bother.... whereas if you keep the energy, they'll all climb on for both environmental and financial reasons, to make copycat savings. The only beneficiary from a export is the energy company, until they offer the same price (or higher) for feed in as for usage.
Interesting theory, Jonathan. Not sure if I agree with it though - if neighbours see that you are making money from export, they'll still want the same, no? We're a long way from there being sufficient solar export to affect the national supply. At best in the UK it's only 8%...
Interesting calculator, thanks. 7.5p per kWh of electricity seems a bit cheap though given current price cap rates, unless you're able to only do it overnight on time of use tariff?
I have a £20 solution ( Shelley device with a scene referenced to energy monitor ) it’s limited and no data to evidence but I’m sure will be a winner. Essentially only heats when there is more export than the immersion rating. I’ll think of a solution that works around my 1k typical overcast days
You are forgetting that the iBoost+ diverter has a second channel so that when the hot water tank cuts off it sends the surplus to channel 2, My channel 2 divert is to a 3kw storage heater (Ceramic Bricks Inside) in our main living room so that it keeps it comfortable in the day and has enough stored in it for evening use thus saving on our Gas central heating of that room, in the peek of winter when low on solar I switch that circuit over to a time clock to use cheep off peak electric to get it's charge, I consider this device as a TV or Washing Machine and not interested as to it's payback costs over years, If all new buildings were fitted with these then payback does not come into any running calculations
For anyone more technically inclined, a smart switch on the immersion heater and monitoring your batteries / talking to the communications bus on your inverter would sound like it'll do the trick. Inverters seem to have RS485, CAN or Ethernet comms options.
I've not got a solar diverter for my hot water; just 2 of us in the house and we only need hot water for 2 showers and a bit of washing up each day. I have, however, noticed that using my 3kW immersion heater in the morning just before my economy 7 tariff ends for the day is cheaper than using gas. 20 minutes; 1kWh is plenty for us. In the day time, I use a 1kW kettle to heat water for washing up. Sounds a bit of a performance, but I find it's second nature now. I do, however, use a diverter for electric car charging. Myenergi Zappi.
Hi Andrew, yeah, I think more and more people are seeing that with the right tariffs, using electricity is cheaper than gas - not least because of gas inefficiency 👍🏻
Not sure if you're still reading these comments, but one of the considerations when costing a solver diverter is that what is the difference between having a solid averture and just running a simple timer to run the hot water service during the day? I did these numbers and with the cost of the solar diverter at $1,000 in a timer at $150. The difference in how much power I would import was so negligible that it was laughable
Hi Dave, yeah - I guess the only thing to be careful of with the timer is if clouds come over for a period, which means you might be inadvertently pulling from the grid.
@@GaryDoesSolar I have been running this for over a year, The thing with the clouds is you're going to have to do it anyway because you need the hot water so whether it's cloudy or not it's not much difference if it's cloudy you going to have to import off the grid anyway. If it's not cloudy then you're running the solar any difference is negligible at best. Definitely doesn't cover the cost of the diverter, Having said that, I live in Melbourne, Australia so I get a fair bit of sun
Ah yes, living in Melbourne certainly means you won’t suffer clouds very much 😀 What I was trying to say is that units like the Eddi have the ability to curtail the level of heating (say 50%) to avoid pulling from the grid, whereas with a timer it’s binary: all or nothing.
This is what I have. I have a 5 hour boost timer which you can set between 1 and 5 hours. Cost me about £35. I also installed a 1kw immersion heater (about £70 I think) as the likely hood I'll make over 1kw in the day is high but It often drops below 3kw if a cloud comes over for example so a 3kw immersion is more likely to pull from the grid at certain times. So I just leave the 1kw on for longer. With my 4kw system and a 1kw immersion I can also run other things at the same time like my dishwasher ~2kw and a heated towel rail ~500w. I just switch things on and off to balance the electric. Basically a manual version of a solar diverter.
To be fair when I'm making excess solar I just switch on the immersion...after 30 mins or so the thermostat switches off and we've enough hot water to last us...2 adults....no payback period as no outlay!
It's very informative, and covers many of the considerations I entered into my own spreadsheet. However the great trouble with asking whether an energy saving device is worth is the assumption that energy prices and costs remain predictable. When I got my solar panels installed in 2020, I made an assumption of 6% future electricity price inflation. I calculated it was worth it at that rate (14 years payback), vs not worth it at 0% inflation (23 years payback). History since 2020 has taken a different path to assumptions and I've now returned over 20% of my original investment in that time. Not bad! So is it worth it? I think questions of investment should be framed in terms of these things actually being insurance products. By investing in these products you are covering the risk of higher energy prices to come. Conversely if energy prices fall some years in the future, that may well only have happened because enough people invested in Energy Saving products! The low prices are in themselves their own reward!
Thanks for taking the time to comment, Anthony - I really value your opinions 👍🏻 I like your thinking about insurance - trying to predict anything that might happen in the future (even in 2-weeks time!) is fraught with danger 🤣 In any utilities I provide, I simply try to keep them as flexible as possible, so that people can enter their own estimations on future tariffs etc. I wasn’t sure what feedback I’d get, but it seems that the model I put together is reasonably valid. Btw, I can see you’ve just published another video on your battery. Looking forward to watching it later this evening 😀
Just the right balance in presentation and stats. I am a subscriber.
One point in a never perfect world. It may also be useful spending just £35 on a DIY swoop over of a fused spur connection to the hot water tank with a progammable controller where you have an off peak supply (Octopus-Go). Not as environmentally friendly granted but with a small PV array and larger battery storage capacity, this could be an initial approach. We are still trying to work out the export to grid issues when the battery is 100%. For us, this happens 1-2 hours during the day when the sun shines.
Question for Octopus: Can you have an off peak tariff and still get paid for exporting? That sounds like having your cake and eating it.
Thanks for the kind words, Michael 🙂
Yes, that is the other approach, and to see how that works out in the utility - just do the following:
1. Select "Electricity" instead of "Gas"
2. Set the insufficient days to "365" (which essentially "turns off solar")
3. Make your investment £35
4. Set the cost of electricity to your off-peak rate
Your question for Octopus is a good one... it does sound like having your cake and eating it, but off-peak is all about flattening the demand curve (good) and any export you sell is likely being used by your neighbour, which means less load on fossil fuel generators (also good). We just need a transmission/distribution network that can manage all that.
Re the sport whilst on Octopus- Go, having just got my Solar/Battery installed i checked this yes there is an export with GO but its a miserly £0.3p because its exactly like the cake and eat it! I'm going to do it just because I\m not giving it away for free😁
Re-export - Yes Octopus’ rate for a split tariff is just 4p, but you can export with anyone else regardless of supply under the SEG. Nobody pays a “fair” rate but 5-5.5p is available by shopping round. I had to, as Octopus will only accept genuine MCS certificates, not comparable QA schemes such as Flexi-Orb.
@@duncanforrester6126 Problem for me as I export loads but don't have an MCS certificate
I think you can but it is only 4p kWh and the installation has to be carried out by an approved MCS contractor
I've had a Solar I Boost for 8 years now. I get the FIT so no need to worry about export payment calculations. In that time I've sent over 7000 kwh to my water tank from my 4kw solar PV array. Now I no longer use my oil boiler to heat my hot water but use Octopus GO cheap rate tariff to top up my tank overnight and then let the sun replenish it during the day. That cuts my CO2 by loads which is the most important thing to me!
Hi John, sounds like you’re doing all the right things 👍🏻😀
And having the FiT payments certainly frees you from the temptation of putting export profit above CO2 reduction that many people will have to decide on now as export rates increase… 🤔
I installed my Solar iboost 7 years ago with a 5KW array inverter limited. I did leave space to have thermal solar added for hot water and had a super-insulated thermal solar ready tank installed. The installer said I would never do it as the SolarEdge would give me all the hot water without any hassle. To date he has been right and it provides all hot water from the end of March until end of October and only requires a small top up from the boiler during winter. Again I have FIT payments so this makes it an easier calculation. It was certainly much cheaper than having a battery at the time, although I am now considering a battery on the DC side to reduce clipping and also maybe thermal solar as well to maximise total co2 reduction, but then it might be best still just to increase the PV array. Either way I love the solar I boost.
Thank you Gary, another exceptionally good video that sets the standard for all things renewable here on UA-cam. Thorough, clear and concise, a great help, thank you again.
Thanks very much, Steve! :-)
What a brilliant little video.
Excellent, you nailed the topic.
Cheers from Oz
Thanks very much 😀 Really happy to hear that!
Welcome back, Gary. Another great video. Thank you for sharing this great info!
Many thanks! :-)
This is such a helpful video thank you. The calculator helped me put data to my gut feeling that an Eddi hot water diverter for me would never pay back. Cheers.
You're most welcome Trevor. Yeah, I nearly had one fitted myself... until I did the number crunching!
We have a new water tank as part of a house refurbishment and were using Economy 7 to heat the water as we have no mains gas in the village. Just 2 of us in the house. Had solar fitted this week and have an Eddi fitted. I knew the payback should be good with current price of electricity (Octopus), but £196 (inc lost export when i get the smart meter) vs £477 is £281 annual saving - or a payback of 21 months! Great explanation and calculator!
Hi Rowan, thanks for taking the time to comment, and very happy to have helped you here! :-)
Hey Gary
I am a big fan for diverters as they work well in OZ... 1.Our grid is garbage that can make exporting difficult. 2. Reliability, cost and simplicty is a word better than a heatpump. 3. Our export tariff is miserable. 4. Average array size is constantly rising and export in Australia is regarded as waste. 5. A diverter turns the water heater into a thermal battery.
6. I can use a diverter to help stabilise the local grid by creating a more gentle export and not drive the grid volts through the roof.
Hi Peter, thanks for sharing this insight about the consumer energy market in Australia. I'm hoping that new players like Octopus Energy (they're close by in NZ at the moment) enter your market and shake things up! :-)
Thanks!
My pleasure and your Super Thanks is gratefully received :-) All the best!
Great explanation video Gary, much appreciated. Without knowing these automatic devices existed, I installed a more primitive, but far cheaper addition to our system. A high current smart switch on the immersion heater spur works via the Smart Life app and Alexa. On days with excess solar, when our battery is full, I can easily switch on/off the heating element. It also provides a timer routine for 7.5p Octopus off-peak as an alternative.
The smart switch only cost £25 and has already paid for itself!
That's brilliant, Duncan! And just goes to show, you don't have to spend £hundreds or £thousands to get a great return! Thanks for the kind words about the video :-)
Hi Sounds very interesting. Can you tell me the name of the smart switch. I was also wondering if there is a device that not only controls the timings of the immersion heater but also can tell you the current temp of the water in the cylinder. The Tesla smart thermostat looked interesting but I don't think it's compatible with my cylinder. Ideally I need something I can control remotely with an app. Thanks
One other cost to consider is the boiler start up and heating the water in the pipes. Heating the boiler mass and 60 feet of pipes (counting both ways) may be small, but not insignificant. My oil boiler has only been on for one day since May, when we had a cloudy week, the riveter has saved a lot of oil.
And with the price of oil these days, you must be pretty chuffed with that 👍🏻
Hi Gary, great video! A tiny fly in the ointment is that in running a gas boiler, you are also running a pump (60 to 100 watts depending on size) as well as the boiler fan (30 watts) and associated controls. The pump runs continuously in the on timed periods. I have done some of my own calculations on power use for this, but in winter months, when the heating is on at the same time, these costs would be incurred anyway heating the house.
Hi John, thanks for kind words on the video
And good point - modelling any real world system accurately is hard, but I’ve tried to include enough that people can make informed conclusions. The electric cost of running a gas system required could be calculated as a small percentage on top of the gas cost (maybe < 5%?)
Hi Gary, greetings from Oxford. Thanks for this great channel! We don’t have solar (yet), but do have an EV and Octopus Go tariff. For us, gas is currently 15p per kWh, and cheap rate electricity is 7.5p per kWh. So we turned off water heating by the gas boiler, and added a timer to the immersion heater to heat our water with off-peak electricity. This saves us money, and reduces our emissions. In the summer months we now use no gas at all, as we swapped our old gas hob for an electric induction one.
You're just down the road from me then :-) Thanks for the kind words. And it sounds like you're doing really well on the "green" front even without solar! Are you able to get solar where you are, and is it something you're considering?
@@GaryDoesSolar Hi Gary, thanks for engaging. We are Cumnor side of Oxford, I saw you use an example address of Wytham in a video, so you might be just a few miles away, if so, give my regards to The White Heart and the Post Office/Tea Shop - great scones! We are indeed looking at solar, but our roof is not ideal as the main slopes are East/West, we are definitely keen on the GivEnergy AIO battery, 9 or perhaps 13.5kWh with the aim of energy arbitrage, and will need some element of solar PV at the same time, as a battery alone will attract VAT. I’m quite practical, so am considering constructing a frame on the south facing gable end to place panels there at circa 40 degrees, otherwise I think we would see very little PV generation through the winter months with roof panels.
@@simonreeves2017 Hi Simon, ah yeah - that was just an example location - I'm actually Southwest of Oxford - maybe only 30 minutes to Cumnor 🙂 Now, you might an East/West array is almost as good as a South array in fact. Two of my friends have East/West arrays and they publish their stats:
Tim:
ua-cam.com/channels/xT6jy59i_38H3Zy04VXzbg.html
Dan:
www.youtube.com/@DanEVSolar7
Excellent presentation, when doing the investigation on my Eddie system I found that our water tank was losing 71w per hour. This did make a big difference with only a couple in the house and low export payback. System well worth using.
Thanks Angela - glad you enjoyed 😀 and great to hear your diverter is working out 👍🏻
This is a great video and I like the utility. My only two comments are: 1) People should check back every month or so, with the gas prices changing so fast at the moment. 2) There is an argument in favour of being able to use solar to heat water to protect yourself from gas supply problems, or if you would just rather not be burning gas to keep warm on environmental grounds.
Hi Richard. Thanks for the kind words 😀 Yeah, I totally agree with you on both points 👍🏻
I have a very simple diverter. It's called the on off switch. Utterly reliable.
Definitely something to be said for simplicity 😀 but wouldn’t work for me. I’d forget all the time 🤣
@@GaryDoesSolar .
It took my installer four months to sort out all the glitches with software on our new fronius battery inverter system. God knows how much more hassle it would have been tweaking a diverter. I've learned the hard way that the more you trust in automation, the lazier you get.
I call manual switching voluntary rationing. Power is to expensive now to not be self disciplined.
Whether diverters are worth it depends on your situation. For us on a FIT contract that assumes we export half of what we generate whether we do or not. We have been using a solar Iboost for many years and have saved over 9Mwh. So our excess solar power really is free. In practice we get free hot water for about 9 months a year and contributes for the other 3. When the sun doesn't heat the tank we use the built in timer to heat using cheap rate electricity which is very similar to gas.
HiTerry, being on a FiT contract certainly helps a lot with regard to payback on a solar diverter. 9MWh is a lot of energy - well done! It might take me a few years to get to that point :-)
Great explanation. Another consideration is maintenance costs. When the excess solar output is less the power rating of the HWS element, most solar diverter units momentarily store & build up the energy until there is sufficient available to power the element for several seconds or so. This on-off cycling of the element can substantially shorten the element’s operating life. Hence the increased maintenance costs of more frequent element replacement.
Also, when in this pulsing mode it is not very efficient because the very first part of every energy pulse is wasted in bringing the element back up to a temp which can then heat the water.
Hi Mark, thanks for pointing out. I didn’t know that. I guess immersions were never designed for such erratic behaviour…
@@GaryDoesSolar Don’t know if you’ve already covered it, but may I suggest another way to minimise exported power is to use the load switching functions available in some solar inverters. Eg Fronius to mention 1 brand name.
When the optional smart meter & data comms card are installed, these inverters can be programmed to switch a contactor/relay when certain solar production, consumption & export conditions are met.
I have mine controlling a pool pump but the operating principle would be the same for hot water. The inverter only turns on the pump when more than 1,100 watts is being exported. The pump is rated at 1,000 watts so the 100 w buffer makes sure turning the pump on won’t then draw some off the grid. To avoid cycling off/on due to a passing cloud the pump is programmed to keep operating for 10 mins if the solar output drops & grid draw occurs. If after this time the solar still isn’t producing enough to run the pump without grid draw then pump remains off until there is again. This could be from full sun returning or other loads within the house reducing. The only thing the inverter looks for is more than 1,100 watts being exported.
Should it be an overcast/rainy day with insufficient output to trigger the start of the pump, the inverter is programmed to run it for 3 hours from 1am on cheaper overnight rates. So a hot water system could be turned on the same way to ensure hot water for that morning shower. If the water reaches temp before the set hours are up the thermostat turns it off.
So, before going off and buying an independent device, I urge your followers to investigate if they already have the technology required in extant equipment to achieve a similar outcome. This of course would substantially reduce the capital cost & so dramatically reduce the payback period.
I have the Solar IBoost, I had it installed around May this year at a total cost of £430, as the thermostat had failed that controlled the emersion heater. I checked yesterday & you can do this at anytime how much it has saved for the day, the last 24hrs, the last week & since it was installed. So far it's saved me over 600Kwh that would have been gas heated. Since it was installed, I have only had the boiler on twice to help heat up the water for a bath. I get no payback from my panels as they were installed for free, the company get the payback. Well worth it for me as it's also environmentally better too.
That's just brilliant, Paul :-)
@@Bondy1986 I don't have a battery, the sender unit goes direct to the feed in at the meter so it can see when I'm sending power to the grid. The IBoost sits where the switch was for the emersion heater & tells it how much it can put in the element from around 10 watts up to around 3kw. I didn't get the IBoost buddy as they are in short supply but I'm coping without it. I wish I done it 7yrs ago when I had the solar panels put up.
There are many benefits of a DC battery over an AC one, so it’s worth making a total assessment. For example, DC batteries are more efficient on the AC/DC conversions, and if you have an oversized array, your inverter can store the generation above its rated limit into the battery.
Nice clear explanation of the pro’s and con’s of solar diverters and their payback. Your model can’t of course cater for everyone’s situation, such as having an air source heat pump like I do.
I have considered a solar diverter but it just wasn’t something I got round to. In the non-winter months where the ASHP is only on to heat the hot water its using about 2-2.5kW a day which I’ve figured is probably low enough not to make it worthwhile changing
Thanks Geoffrey :-)
Not sure if you saw my follow up video to this one here too: ua-cam.com/video/6zc1g1bz0eA/v-deo.html
Yeah, ASHP is just a wonderful technology, especially when used in conjunction with solar and battery. I feel the days of solar inverters in the general market are numbered (so long as export rates remain above 12p/kWh ...
@@GaryDoesSolar Yes I did see that thanks and agree with your conclusion about the financial case not stacking up any more if you’re getting paid to export - and with rates at ~15p/kW it makes absolute sense to do so.
Gary - Just want to mention - Sunsynk Solar systems can also do this what the EDDI does somewhat. You set the menu to export power via the AUX port to drive the immersion heater. Surplus energy from the solar panels are used to charge the batteries while power is sent to the immersion heater. The export kick in percentage can easily be adjusted based on battery SOC, to send power to the immersion heater. Cost for this was a RCB Contatcor, some twin and earth cable, a MCB - let's say a couple of pounds. The solar diverters are just more variable. But many of us do not have our water heaters [geysers] on Solar - it is on grid and just nees top up during the day and the solar supply feeding it, then saves money as this topup power in the daytime comes from solar not grid.
Thanks for sharing this info - and the more I hear about Sunsynk, the more I'm liking their products! :-)
Dear friend, let's say I have a 3kw water heater. In case my PV generates 2kw, for example, and the battery is 100% charged, would the AUX port use the 2kw available from the PV to power the heater and the last 1 kw from the battery or from the grid? The thing is that export is not allowed in my country so I am looking for a way to fully utilize the PV generation. This prevents me from using a power diverter, from what I understand. However, I am not sure whether it is a good idea to use the battery for heating the water (it seems wasteful, I do not know why :D). In other words, can the AUX port work like a diverter meaning it would ONLY use the excess solar, or it would supplement the 2kw PV power with battery/grid? Thanks!
All these calculations are based on a lot of if’s! However in my view a solar diverter is always worth having, for the simple reason that one’s reducing the amount of gas, a fossil fuel one using. My solar diverter both heats the water and it’s second circuit heats our towel rails. As we installed solar when FIT payments were available using all our solar doesn’t effect our FIT payment, It’s a win win. We use a myenergi Eddi diverter.
I'm afraid that's the name of the game with real word modelling - hence why there are so many fields that can be adjusted to suit everyone's particular circumstance. It can never be perfect - it only has to be good enough for people to get a reasonable idea on the value of a diverter to them.
Great news that your diverter is working out for you, and yes, win, win because of the FiT payments! :-) Eddi does seem to be the best in the market, by far.
This diverter idea looks perfect for my plug-in Ioniq plus my new water heater. Having to fart about plugging in and out when the sun shines/doesn't is a bit of a bind. Not too sunny in Denmark. Thankyou Sir - I am now a subscriber.
Thanks for subscribing, William 😀 Great to see my videos getting further reach. Hopefully Denmark will get more sun soon! 👍🏻
Really interesting video Gary. I’m just starting my renewables journey with an ESS system hopefully being installed in the coming weeks followed by solar PV as soon as I can get hold of some decent panels. After watching your video, I’m in no hurry to install a solar diverter! Thanks.
Hi Craig, are you able to say a little more about your ESS system? Sounds intriguing. Is it a flywheel or compressed gas or something? 😳 And whatever it is, is it not quite expensive…? Sorry, this is not an area I’ve looked at.
@@GaryDoesSolar Hi Gary, it's just a lithium (LiFePo4) battery system, nothing more elaborate than that. The system I'm looking at is from Victron Energy who make the Multiplus-II inverter/charger, and Pylontech who make the battery modules. Victron have a range of inverters but the one I'm looking at can deliver 5000VA (about 4.4kW) and can also operate in the event of a grid power outage. It's basically the same system as in the UA-cam channel "The EV Puzzle"
Hope this helps and sorry if this answer is a bit more boring than you were hoping for. 😂
Hi Craig, I'm very familiar with Nigel's setup on The EV Puzzle - I watch all his videos 🙂Ok, if your setup is similar to that, then you can't really go wrong! I was seriously considering Pylontech batteries but in the end I've gone for a GivEnergy system as it should be able to link to Octopus Energy smart tariffs. We'll see how it all goes when I eventually get my install (planned for Dec/Jan).
Very interesting video which has convinced me that, in my circumstances, a diverter is not a sensible option. One point with the calculator though. It assumes that the water is being heated from scratch every day. With my very well insulated tank the water is still hot the next day, even after I have used some for a shower, so does not have to be heated from the average temp. In larger households where all the water is being used then it would work out ok..
Hi David, glad you liked the video, Now, actually, my assumption in the utility is that any unused water in the tank stays hot! The utility purely concerns itself with the flow of water through the tank and the energy required to support that flow. Hope that explains...
Gary, that is of course one if the concerns. We spend all the money to build a system of one type or another with a payback period of perhaps less than 10 years. However, after that policies and/or prices change and the consumer is often disadvantaged. It feels like the solar contracting/gov't policy in this area is still the 'wild west' and gives me pause due to the volatility.
Yeah, it's not easy to figure out the payback for any system investment in a sea of constant changes (energy prices and policies etc.) Prices are falling over time, so waiting for a little less volatility is no bad thing...
Great video and explanation including the graphics. My issue is that the current export of 15p means payback is difficult. Additionally the tank losses are ~25% per day when full, therefore heating up during the day with solar would still need to boost with gas to have an early morning shower. So for me these are great during the FiT when export was use it or lose it, but now would be better to get paid to export from a pure financial perspective. N.B. not burning gas has a plethora of other benefits.
Hi Alistair, it might be worth you looking at a new tank - I changed mine recently and now only have losses of circa 2-3% a day.
I think you'll be interested in this follow-up video I made then, which covers the increasing export rates in more detail: ua-cam.com/video/6zc1g1bz0eA/v-deo.html
Wauw, this is wonderful (and new) information for me. Nicely done.
Thank you, Adrian! Hope it’s useful to you 👍🏻😀
I've noticed that unlike solar panel manufacturers, that typically provide 20 plus years of warranty and inverter manufacturers who provide 5 - 10 years, these diverter manufacturers typically offer just 1-2 years of warranty. I've also read many reviews that suggest that this reflects how long many of them last. So even if payback is 2 years, there is often no benefit it would seem and there is the carbon cost of manufacturing and disposing of the unit.
Hi Chris, I agree - and it seems that the electronics required to manipulate AC waveforms just don't last forever...
I have purchased a second hand unvented cylinder which will have a DC element wired directly to some pv panels this will be a pre heat source to the main cylinder inlet, therefore reducing any waste of pv power.
Hi Robbie, I didn’t realise there were DC-powered cylinder heaters available. Sounds like a great solution! 😀
@@GaryDoesSolar they are more common to the American market as they are used in off grid situations, Amazon is the best place to source. DC elements are more difficult to use when it comes to switching them on and off via a thermostat as the current is not alternating (AC) but using a relay could be the answer (I'm still researching) we require hot water every day so to pre heat via pv panels with an immersion heater and perhaps a solar water heater/parabolic solar heater/wood burner using the indirect loop of the cylinder would help.
I have modified my boiler to reduce it’s power and I turn it on from 11am to 4pm with a clock driving the contractor in my electrical panel. It cost way less than a diverted and get a close enough result.
Nice one! 👍🏻
Yes, i have done a similar thing, but still looking for some tweaks to activate the Hot Water system when there is good sun & a timer for minimal inputs when it is cloudy.
Thanks for the video Gary .
You’re most welcome, Peter 👍🏻
great channel Gary, discovered via google on a search for PV / combi / HW tank results
My question to you / anyone reading
I don't have PV yet but assuming some major renovation works go ahead, i would dispose of my aging traditional boiler, and an accompanying solar thermal solution / oversized pressurised tank, and go PV fully across my south facing roof (approx 60sqm)
I like the idea of a combi boiler and going tank-less (a bit more space, but also a simpler and lower install cost solution).
Except that, now you have enlightened me on solar diverters, they seem a great idea to mop up excess (outside of home / EV car use).
What i can't reach a conclusion on, is whether it would be 'better' to do without the additional cost complexity of a pressurised tank and diverter, and instead it an electric heated shower in one of bathrooms. I.e. if the sun is out and a shower is needed - then 'free' hot water. If no sun, then fairly efficient hot water from the combi.
I am not considering use of batteries in the above.
Your thoughts? My question is not about which is better for the planet, more, which is better for my pocket..
Thanks for taking the time to watch my videos and also to comment :-)
Now, unfortunately, l'm not really in a position to provide individual advice, (not least because of potential liability issues - even if that advice is given free, such is the world today). You're best to speak to an installer about that, or post a comment onto a solar forum (e.g. this one in the UK: facebook.com/groups/2197329430289466) Good luck with whatever you decide!
I have an eddi, highly recommended. my gas boiler no longer used for hot water ever.. octopus go used to charge battery and heat hw, 00.30 to 04.30. solar does the rest of the hw heating during daytime via eddi. occasionally use battery to heat hw in evening. with current gas prices... absolute life saver.
Great to see you've managed to cut down your gas usage, Nick :-)
Like your analyses most informative.
I have a recently installed Air Source Heat Pump, using a kilowatt-hour can generate 2-3.5 kilowatt-hours worth of hot water with any spare solar.
There's also the Octopus "Cosy" tariff for ASHP combined with battery I am able to use solar and off peak power to cover most of my energy usage.
Charge 10 kilowatt-hours 4-7 am sunrise produces a mix until next off peak 1.00-4.00pm.which takes my batteries to full this is then used through to the evening. Leaving only a few hours at night at standard rates.
This seems to me the most carbon neutral and cheapest way of using your energy production. Don't yet know how my ROI will stack up. With current UK govt grants it's a no brainer.
A Cosy tariff spread sheet would be a useful tool.
Hi Andy, thanks for the great feedback! :-)
Yeah - the cosy tariff looks interesting. Worth you checking out Tim & Kat's channel here, which covers the cosy tariff in detail: ua-cam.com/video/7d7fE8vRl4s/v-deo.html
Exactly. Saving money is not the only reason to go green. I am installing 6kw of amorphous silicone and also 1kw of mono crystalline plus 4 vacuum tube water preheating panels. Practically everything bought at auction or used. Next step is to get huge batteries so i can avoid the subscription, taxes and maintenance fees in France.I would rather spend €20 a month on fuel than be connected at those rates. Shame they don't really want to buy it back as i will have excess at times. I also have a small gas water heater a pellet stove and a small wood stove in-case it hits -20. Pellet stove and wood stove were free, paid £420 for the vacuum tube system with pump expansion tubes and heat exchanger immersion tank plus controller. Bought my grid tie inverters used, the panels were made in Switzerland but the company went bust and the mono / polly panels i have are all used also.
I'm quite impressed with how you've built up your setup in a highly cost-efficient way! :-) Agreed, individually, we can and should and all make an effort to reduce our carbon footprint, however small. Even taking steps to further insulate properties has a direct effect. I wish you all the best in your continued journey.
I've got a diverter and from my experience if your smart with encouraging baths during the day then you can save significant sums of money. Our cost was £400 and installed and it's paid back £40 at current KW prices in just 5 months.
Electric export prices are more than import gas prices. So it makes no sense to divert PV to HW.
Great to hear! It’s worth considering what Swwils said though, if you can achieve a relatively high export price
You shouldn't have to change your washing behaviour.
You can use batteries to store the energy or just feed power into other appliances or the whole house. It doesn't actually matter what uses the energy: by using the energy from solar, you are reducing how much energy you are taking from the grid.
The issue is that you can wire up immersion heaters to cheap rate economy 7 during the night, and good insulation on the water tank will keep that water warm throughout the day, so what you need to do is look at the unit cost (the pence per kilowatt hour) of heating up the water from night time Economy 7 rate electricity and compare that to the equivalent unit cost of the power generated from solar and decide which is the cheapest way to heat the water in the immersion tank.
And you should be considering the financial benefit of the feed-in tariff, as mentioned by another poster here and deciding whether it more cost effective to consume that excess solar generated electricity or feed it into the national grid.
You can't make assumptions on this, you have to calculate it and use that as the basis of your decisions.
Another cracking video Gary. The costing didn't seem to capture the price of having an emersion tank brought and fitted, unless that was part of the £100 installation?
I think for those on FIT payments, it's a hard sell break even wise. A friend gets around 1k pa, and gets not on the most lucrative FIT scheme. For us SEG peasants, I'll be lucky to make £100+ pa with a 6k system lol.
Food for thought certainly
Thanks very much, Stuart :-) Yeah, I took the view that most homes (in the UK anyway) that have water tanks, already have immersion heaters fitted. Maybe that's not the case? But yes, if a tank has to be purchased, then that cost should be added to the diverter cost.
True, those on FiT payments, seemed to have won the lottery :-)
A better cheaper but harder way to do it is detecting export power with Home Assistant and controlling appliances with HA automations, especially when having a heat pump witch dedicated diverters can't power.
True, but most people are not familiar with setting up those kind of technologies. Perhaps a future video… 👍🏻
Similar to what I'm doing with a home automation controller and Home Assistant. I detect excess power and then use an AC diversion load to use up that excess:
ua-cam.com/video/H0LWO1GWN1w/v-deo.html
I have a tankless gas water heater so no tank to dump that excess energy into, so it goes to heating the house on cool days.
Thank you that is very interesting. I have never really thought about it in terms of what the gas would cost if I were to burn it and sell the generated electricity. The fact that I would get more cash, albeit pennies, was not something that had occurred to me. I am still going to charge with solar as it gets us one step closer to net zero. I hope to ditch the gas completely in a couple of years.
You’re welcome! And yes, I think we can all do our bit to reduce our dependency on fossil fuels 👍🏻 Good luck with your solar journey!
Gary another back of the net presentation.
For me the worth of a diverter was something I never considered. I thought it was an essential in any system as it was storing excess energy.
Having run the utility using multiple options, for me, I realise It would never pay for itself.
I now see that in my case, where im contemplating an ASHP, its far more effective in the higher solar producing months to heat the tank using solar / ASHP and then take any dregs that Scottish power deem give me for export. Then put the cost of a diverter down as a deposit on a bigger battery
Thanks for the kind words, Jim - you are most welcome! :-) Your proposed strategy looks sound. And in general, I think everyone is finally waking up to ASHP (great). I might look at a video on this at some point. It's a shame that diverters don't really deliver the payback that they appear to provide. If the costs were say half, the story would perhaps be different...
Very interesting. As a single person when getting quotes it seemed intuitive to me that the payback period would be very long just because of the small amount of hot water i use especially given much of it is in the winter when obviously solar input is minimal.
Especially true if your HW is on demand from a modern efficient boiler
Hi joe - thanks got watching! Yeah, the more I look at it, the more I see that the situations where a diverter is worth it financially are few.
Might be a stupid question but @7:50 timestamp, isn't the energy required to heat that one litre just a kW value? Wouldn't you need a timeframe for it to become kWhr value?
I can understand your question, and it's purely down to the difference between power and energy. When you switch the immersion heater on it will start heating the water. That means the immersion heater is instantly consuming power... but in the first few seconds, the water temperature doesn't change. It's only after a finite time at that level of power that the water starts to heat up. And when it has risen by 1 degree, you multiply the power by the time taken to get the energy requirement (which is in kWh).
A diverter was one of my first 'projects' on my PV - using the EmonTX from Open Energy Monitor and some open source code from a very smart contributor (total cost
Sounds like you have a great setup there 👍🏻
We have one and they're great - free hot water for 9 months of the year, and reduced costs for the other 3 months since with a large tank (300L plus), we can wait a couple of days for a good solar day to dump a load of energy in it. You don't always need a fancy brand one with an app and all the cost of supporting the marketing department. They can be very cheap and wire directly into the fuze box. Ours is a RM1B23D50 solid state relay. Saved us hundreds since we got solar panels.
What are you using to activate the relay when you have excess solar?
@@brianrussell6988 No idea, the electronics all comes in the relay. The electrician just wired it in while I was there, it's a quick job. It has its own circuit from the fuse box directly to the immersion tank.
Hi Simon, great that you’ve found a solution that works well 😀
I echo Brian’s question though - would be good to understand when it kicks in 👍🏻
@@GaryDoesSolar Yes! The unit kicks in automatically when there is any excess solar. The data sheet says "The zero switching relay switches ON when the sinusoidal curve crosses zero and switches OFF when the current crosses zero." There are sensors on the solar and mains inputs.
Sounds great - and clearly works! 🙂
Didnt know Octopus had raised export prices to 15p.
Nice one 👍
Only bummer "Currently, you can't be on both outgoingOctopus and OctopusGo, our EV tariff, at the same time"
Yeah, it's only for certain tariffs (I've now added a note to the video description, in case of confusion). But see my pinned comment, where I comment on why higher export rates should eventually appear on all tariffs...
Hi Gary, great video! A tiny fly in the ointment is that in running a gas boiler, you are also running a pump (60 to 100 watts depending on size) as well as the boiler fan (30 watts) and associated controls. The pump runs continuously in the on timed periods. I have done some of my own calculations on power use for this, but in winter months, when the heating is on at the same time, these costs would be incurred anyway heating the house.
@@GaryDoesSolar The cynic in me things they'll only go to Octupus's previous of 7.5p max, but love to be proved wrong.
I think you can use anybody for SEG, so I'll stick to the Go tariff until March, then I'll have seen my 1st worse case generation period.
Maybe then which to the better export rate for 6-8 month then back on Go.
You still waiting for DNO sign off?
Yeah, I'm with SSEN and I'm told that it's 4-5 months these days for G99 sign off! Madness! Let's see what happens...
I am using a Sonoff switch with Home Assistant (HA) to turn on the immersion heater. HA can estimate solar and turn on during peak times. When I am not generating enough via solar, the battery makes up the shortfall and switches off. If I start drawing from the grid, it switches off.
That sounds like an elegant solution - love it! :-)
Gary, new viewer, happy discovery via the YT Algo. We have had a 12kw solar system for about 5 years, and as a retired GC I tried to do a lot of my own homework before our system purchase and installation (SunPower). We are in Southern California so solar here is a no-brainer, but could you do something on how people in the UK (or other often cloudy areas) can figure out their ROI for solar. BTW: Since retirement I have done a couple small, RV based "off-grid" systems, and I can say, I have already leared a fair amount from your videos. Thanks so much.
Thanks Paul - great to hear you’re enjoying my videos 😀 Regarding ROI, did you see my video on that very topic? Here is the link: m.ua-cam.com/video/FvjuJQZRrvA/v-deo.html
@@GaryDoesSolar no, I think I have some mining to do. Thanks for the link...
The only thing I am 'missing' in this video is the fact that there is actually no real "diverting power". These "diverters" are nothing but smart automated switches. They have some means of measuring the consumption and production (either through CT clamps, or by connecting directly to the inverter through protocols like modbus, ...) and switch devices on/off/or power them at an according rate. I am currently building this myself, because these "diverters" are not as complicated, as I initially thought (and they are quite expensive for what they actually do in my opinion).
I bought a cheaper 3 phase power controller that I had installed with my solar and hooked it up to a nodemcu board to be able to controll the power through wifi. I read the power readings from the inverter over modbus and I have a little logic setting the percentage of power on the power controller accordingly (the logic being pretty much identical to what you explained in this video).
I would argue that "diverting" is indeed taking place, because if there was no diverter in the system, excess solar would automatically be exported. Having such a unit causes that excess to be used by (and therefore diverted to) the immersion heater in the water tank.
Now, great to hear you're building a diverter yourself - not everyone has the skills to take on such a challenge! :-) I'd be interested to hear how you manage the power reduction as this is what sets apart the premium models (like MyEnergi Eddi) from the rest of the market. The Eddi unit can throttle the power without chopping/corrupting the sine wave too much.
@@GaryDoesSolar I am aware, that my "criticism" is mainly based on how I interprete the word "diversion" and I understand your response completely. I just think the word and the name of these "diverters" imply they do actually control the flow of electricity somehow, which they only do passively by simply closing or opening cicuits. It makes them sound more complicated than what they actually are, automatic switches. The thing is. If one did this task manually, by manually switching on the dishwasher, water heating element, or whatever with a simple flip of a switch when enough power comes from the solar panels, one would probably never call this task "I divert power to the heating element" (unless they were doing a bit from Star Trek :D). Instead they would simply say: "I switched it on!". The "diverters" don't do anything different. Except maybe from having a power controller (voltage regulator) included in them, which allows power going to certain electrical appliances to be "limited". In most cases these are Phase-fired controllers. You can find devices from TriHero like the SCR3 for 3-Phase voltage regulation and they cost a fraction of what an eddi costs, which can only regulate 1 phase power, as far as I know? The eddi works the same way, and it cuts the phases exactly the same way as the heating elements don't care at all about this (motors and other things do care though!!) I have a variant of this TriHero 3-Phase regulator that is being sold where I live. These are perfect for "dumb" things like heating elements, but ofc for things like more complicated devices (washing machines, dish washers, car chargers, ...) they are useless. By simply controlling these with an esp, or raspberry pi, you get the same smart switch for much cheaper, but you don't get a vendor lock-in as you do with an eddi (in which case you need to buy a powerwall and all other switches from that myenergy vendor). Simply because different protocols and standards (or even proprietary ones like with the eddi) are used in the diverters, and the different vendors of appliances. So it might be that you have a diverter installed that can ragulate a "dumb" heating element in the water cylinder, but it might not be able to talk to a powerwall that you have, or it might not be able to start/stop tumblers/washing machines that you have around. So maybe my criticism is not as much about the actual word "diverter' but about the limited capabilities of these expensive devices when it comes to compatibility with all home appliances (beyond water heaters). Building it yourself does not guarantee compatibility, but the chances are higher you get many different devices connected. If you only use it to heat water, these devices seem too overengineered and overpriced for what they do. Compare 2 numbers, and set a voltage regulator ... I guess all I should've said is: diverters are very simple. If you are interested and somewhat know electronics (it really not complicated) and maybe even have a raspberry pi or esp lying around, you can try and build this yourself (note: the voltage regulators need to be put in place by professional electricians ofc!! (but so do the diverters, so there is no difference)). If you get to the inverter data in many cases you don't even need ct clamps as the inverter has the data already (and provides it on modbus, webinterfaces, possibly other open protocols).
A single phase ssr relay, or voltage regulator can be bought for 1/10th of the price of one of these diverters ... and don't underestimate what one can learn and the fun one can have in the process :D!
You have 3 phase power at home from the grid? Which country are you in?
excellent analysis and explanation. Just wondering if the solar diverter can contribute to central heating?
Thanks the kind words. I guess the problem is that the diverter is managing the use of excess solar, and of course, central heating is generally required outside of those times. That said, use of a battery and heat pump would head in the right direction 👍🏻
Great video, a lot for my brain to take in. I have a SunSynk Hybrid inverter which has auxiliary connections that can be set to heat an immersion, not totally sure how it works but I think the only difference between the auxiliary and essential supply is that auxiliary only pulls from battery or solar, not grid and I do think, it works irrespective of the house and battery being satisfied, it is all the time except 00.30 and 04.30 (when no solar and battery charging from off peak). I do not think it has the facility to supply less than 3kw so it seems a very broad brush approach, all or nothing. After some thought I controlled the cable feeding the immersion via a Timeguard Wi-Fi controlled fused spur model FSTWIFITU which allows me to time control the immersion and works very well as I can remotely switch on and off. Before my solar/battery installation I never used the immersion, so not surprisingly I did not factor in the 4/5 kWh a day to heat the water, which is fine off of the solar and battery during the summer but I figure I might have to revert to my boiler during the low solar months to avoid draining 25% of my battery on water heating. I am not too upset as the auxiliary is part of the package and the Timeguard cost less than £50
I would be delighted if someone would confirm my observations of exactly how the SunSynk auxiliary works and you are the man to do it
Hi Mike, thanks - I also made a follow up to that video here, in case you did not already see: ua-cam.com/video/6zc1g1bz0eA/v-deo.html
Thanks for taking the time to describe your solar setup and situation. I don't have any expertise on Sunsynk products, but hopefully, someone reading this can help answer your questions. Failing that, I'd suggest you join this Facebook group and ask there: facebook.com/groups/2197329430289466 Good luck!
Hi Gary,
How smart are these diverters? By this I mean, can they be programmed to take into account different situations. For example, the max export on a G98 is 3.86 kW, so can the diverter be set up to only kick in if there is solar excess (house draw + 3.86kW export)? If so, can they be configured to not kick in during high tariff export periods? I’m also assuming that you would only need to use the immersion heater for short periods to get the water up to the desired temp, so will the diverter only kick in when that temp drops and for only as long as required to get back up to temp?
If the aim is to be as green as possible and therefore paying back the initial outlay for the diverter is not considered part of the equation, but you want a mechanism to heat water in an environmentally friendly way, can the hot water system be configured to only use the diverter through the solar/battery and never draw from the grid?
Thanks
The EDDI unit I was considering at the time was quite intelligent, and could also perhaps be controlled by Home Assistant. However, in this follow-up video I made, I concluded that none of that mattered when you looked at the bigger picture against a backdrop of relatively high export rates: ua-cam.com/video/6zc1g1bz0eA/v-deo.htmlsi=Jkvu5VWD1b9sQ_l-
As export rates fall in line with increased grid-scale renewables however, the situation will change again, and solar diverters (with intelligent control like you suggest) could well be back on the table...
I had the solaredge iboost but within 2 years it broke down three times. I switched to the Solic 200 and it works very well and I have hot water solar powered all the time.
Same here. The Iboost seems pretty feeble and doesn't cope with a bigger tank or higher water temperatures. Just about to replace mine with immersun or eddi. Why did you go for Solic200?
I'll look into the Solic 200 - sounds like it's working well for you!
If you ignore cost of the water heater: We simply end up comparing the ratio of the cost of gas to the revenue you can get for your solar. On todays gas prices of 7p per kWh: If I can sell my excess electric at 9p or more then it's cheaper to use gas and sell the excess electric. Given Octopus paying me 15p to 20p for my excess solar... I certainly regret purchasing the Eddi, in fact I have it always off now. (Unless I misunderstood something important!)
Yeah, EDDIs (and other solar diverter products) are currently not useful to most people. If export prices come down again, that could change of course.
Excellent video, subscribed. Your analysis agrees with my back-of-envelope calculation that predicted a very long (or even no) payback for a single occupant.
I was originally intending to install solar hot water panels and a thermal store cylinder but even DIY the cost is ridiculous. Now I'm in the process of installing a twin immersion cylinder and Eddie controller to use some solar PV excess. It will still have a long payback but is a fun project and provides a source of hot water if the gas stops flowing.
Hi Matt - glad you enjoyed the video - and thanks for subscribing! 😀 Yeah, the rate at which holes are appearing in nordstream2, the gas might indeed stop flowing!! 🤣
Thanks for sharing - very informative and certainly clarified the topic. With my home set up I have need to have my inverter in my garage remote from the house where my hot water immersion heater is located. Do you know how far away the sensors can be away from the actual solar diverter unit? Thx
Some products, like Eddi allow the sensors to be far away by using a radio link (MyEnergi Hub) - worth a look. And the latest units just connect straight into your WiFi...
Great video always temper your expectations with a 50 % fail rate as Murphy's law is prominent, for instance I live in Ontario Canada 6 years ago I installed solar with a 7 year pay back calculated but to my surprise in the 3rd year the government decided to rewrite the Ontario credit for electricity which is great I love getting a credit but it changed my pay back period to 10 years. But do not worry 3 years after they increased the prices so I am now back on track to a 7 year pay back which is next year. Also I find some sun year hours are much better than others which may be the rain/snow events seem to be longer. Oh I have a 100% electric home so I use 17,000 kwh a year so when I reach my pay back I will be up grading Solar is the future of my energy.
Thanks :-)
Yeah, and this is the problem with any long-term investment. Nobody can predict the future (at least, I've not met anyone yet who can). And in today's world it seems that anything is possible - things that reduce your payback period, and things that lengthen it!
I totally agree, residential solar will be the future for most people's home energy :-)
My Immersun diverter tells me how much electricity that has been sent to the immersion heater every day. I use this to calculate the returns at the price per kWhr of gas. I don't use average water consumption per household to work out the return, surely somewhat vague. The Immersun has been installed near enough to 10 years now and has supplied 21,800kWh to my 160 litre hot water tank. I calculated it needed some three years before payback when gas was cheap. Now.....!
Wow - nearly 22 MW 😳 well done! 👍🏻
Note that the best value Octopus tariff is the Tesla Power tariff for those with a Tesla battery (you may want to do a video on this). However you cannot use this tariff if you have a hot water diverted.
Thanks David for this insight! 😀
Thank you for the calculator
My pleasure - hope it’s useful to you 👍🏻
Thanks Gary. What a guy!
Thank you, Dan - love it!! 😀😀
Interesting video, and all of the videos for that matter, thank you Gary,
We are on a FIT (with Scottish Power) at 19p/6p rate but have our electricity with Octopus. We have a 4K array but no battery or EV's. It's a large house, old, reasonable insulation, but is oil fired via a boiler driving hydronic under floor heating and hot water through a 300L thermal store (boiler runs on demand 24hrs via a tank stat). No gas locally and electric cooking.
The oil has cost us a lot in the past 12 months and I started reconsidering solar diverters again. We average about 12KwH of electric usage per day.
Yes, batteries are a great way forward but a costly investment, if you can find them and an installer. I get the idea of an Octopus variable tariff but wonder if dumping the FIT would prove costly for us, even with generous rates on offer from Octopus. I just wonder if a solar diverter is a decent "part way house" for us for now? Trouble is, with a thermal store holding half the tank above 55 degrees, would the incremental temperature increase offered by an immersion heater with a maxed out temperature setting offer a decent pay back period for a solar diverter?
Any thoughts or handy calculators or formulae would be most welcome!
Thanks
Hi Ian, thanks for the kind feedback on this and other my videos. You may have seen my follow-up solar diverter video where I feel the financial case for one is no longer there in light of the higher export rates we're seeing at the moment: ua-cam.com/video/6zc1g1bz0eA/v-deo.html
The fact you're on on FiT though means that it's still worth it for you - I would certainly hold onto that tariff for as long as you can! :-)
I've not seen any calculators unfortunately. If I do, I'll certainly let you know!
@@GaryDoesSolar Thank you for the reply Gary. Indeed my FIT rate does seem a lot more attractive than the rates on offer recently and this is what made me wonder if there is any logic in moving to one of the new Octopus schemes. In addition, we're on a simple PV generation meter so are not paid for what we export, simply what we generate plus a notional amount for perceived export. It seems like, if we stay where we are, we could do worse than buy a PV dump system and also add a battery at a more suitable time, all the while keeping the FIT rate that we currently enjoy. Sadly though, at our old house things were even better as our FIT rate was 44.1p! - one of the few downsides of escaping from the city and moving to the countryside is loosing the early adoption FIT rate that we had.
@@ianbeck5897 Well, I'd certainly welcome the countryside over the city having worked in the latter for many years 🙂
We have moved into a house with a solar diverter and pressure tank in the loft but it does not seem to work. I might consider getting someone to look at it, thanks for video.
You're most welcome Patrick - and I hope you're able to get things sorted without too much trouble...
Hi Gary - this video is exactly what i am thinking about at the moment and whether installing a diverter and immersion water heater/cylinder would be cost effective. I have a 13 year old solar system with the original solar tariff so I get paid for export no matter what is actually exported. So this means it doesn't matter how much i export as i will always be paid the same amount (50% of my generation). I have also got battery storage fitted and would like to use the spare energy i make and heat water. As a rough estimate, do you think it would be cost effective any pay back if i install an immersion heater/cylinder and diverter? Many thanks in advance
Hi Anthony, yes - you're in a. very good situation being on the UK's Feed-in-tariff mechanism, and that can make operating a solar diverter more attractive. I'd try different scenarios using the calculator mentioned in the video, to see if it works out well.
Thanks very much, indeed, another fantastic presentation. A brilliant balance that makes a potentially complex topic understandable. Purely for interest, we live in Dorset with two sizable roofs south and east facing @ 18° pitch. I'm not sure exactly what I'm going to do yet. Because we live out in the bush and use electricity, oil, and log burner, I was thinking of dumping surplus into the electric underfloor heating and water.
Thanks for your kind words, Nic! 😀
Your planned strategy sounds like it could work 👍🏻
Good video & content Gary. I'm just about to start on my Solar journey & I have a survey booked for next week & I'm considering a solar diverter. The problem I have is that our gas boiler fed HW cylinder is 38 years old & I bet the internals are covered in limescale. It is a factory foamed cylinder with an addition jacket around it & has a short reach top mounted emersion heater which only heats up approx 30% of the water in the top of the tank. The fact that it is 38 years old I'm wondering if it's worth upgrading it for a better insulated modern tank with a lower side mounted emersion heater? I know this will add substantially to the cost & payback scenario but can't help thinking that the old tank is due for a change & would a be a weak link in my solar system if I keep it.
My advice for what it’s worth! As a retired heating engineer is absolutely change the Cylinder for one of the new stainless steel fully insulated ones. I’d also advise you go for one with two Emerson heater, one near the bottom and the other near the top. Then you can choose wether to heat al or part of the tank.
Your old Cylinder has done well to last so long and leaks can be expensive, as my sister recently found out.
Thanks for the kind words, Colin :-)
And thanks also to C M, who has hopefully helped you decide on what to do.
@@CMWobby1 Thanks for that. Decision made, I'm going to change it. Just hope I can get one which has similar connection positions to the old 36 x 18 to avoid too many pipework changes.
I'm considering an oversized solar PV system, then using a 2 output diverter to firstly heat hot water cylinder using immersion heater, then heat our home using an electric radiator. Requires calculating, but I'd size so that the system can provide (or supllement) home heating during spring and autumn, just to reduce the demand placed on our gas central heating system.
That sounds like a very good plan! Hope it goes well 👍🏻
I've been using an iBoost solar diverter set to heat my hot water for several years. This year I fitted a second one to divert energy to a storage heater. It too worked fine. The iBoost+ lets you select the export power detection level when the diverter kicks in so the battery charges first, then the immersion heater, then the storage heater. The only problem is that during the winter when I would like to charge the storage heater, there is little or no solar available even with my 6.8Kw array
@@iainmackay9269 Nice!, that would be my dream setup. I guess the only way to get that storage heater charged mid winter is for even more solar PV? Or install Solar Thermal to charge your hot water, so the PV is free'd up more for the storage heater? What type of storage heater are you using?
Hi Gary, all your videos are great - many thanks.
If you have a battery, is it better to use the excess solar to charge it rather than having a diverter?
Most definitely, John - fill your battery first, because that saves you the retail cost of buying that same electricity. Then, with the excess, you have a choice:
1. Divert it to your water tank
2. Export it (if you can achieve a good rate, like the Octopus 15p/kWh)
Win, win!
Thanks for your kind words on my videos :-)
Hi Gary, very interesting as I have recently had solar, 3.2 Kw and 2 batteries,6.4 Kw fitted but still exporting on some occasions. My hot water at the moment is now heated with a "Fischer" system using phase change materials and the gas now only supplies heating. Probably be different in the winter. I am considering buying some panels to direct feed an immersion heater in a small water tank. This would not be my main source of hot water but just to supply a shower and small sink, probably be used 3 times a week. Wondering if this would be viable. Actually thinking about it maybe get a battery and run an electric shower.
If you're getting a battery for the electric shower, you may want to ensure it can discharge at the rate your shower needs it. See my video here (2m50s in): ua-cam.com/video/3vwDrfuXyik/v-deo.html
Without majorly modifying my top-heated cylinder, I diverted 483kWh in a year. At 80% efficiency, gas costs 12.86p per kWh and export earns 6.79p per kWh. The annual value of the diverter is £29.31. The payback would be 10 years.
Yeah, the calculator I used in the video shows that for export rates higher than 12p, you’re far better off financially exporting that energy and just using gas. It’s a shame really because I really like the concept of solar diverters. Here’s my follow up video on the topic: ua-cam.com/video/6zc1g1bz0eA/v-deo.html
Really interesting video. I've got a combi boiler and lost my immersion tank when this was installed. I would have to look at getting one installed again , if possible, and adjust the installation cost to cover this. One of the benefits of the combi is getting hot water at near mains pressure, thus the immersion tank would have to be a pressurized one to keep this benefit. I've got a few questions now for my heating engineer!
Thanks Mick - our hot water cylinder is unvented, which means we get near-mains pressure too (fab!) Yeah, your heating engineer will advise better than I can. Good luck in whatever you decide!
@@GaryDoesSolar When you look back in time the Victorians was cleaver. So adopted there ideas some what. And went for Solid Fuel Central Heating in the 80s. Price was almost double of Gas central heating at that time. But over the years we saved loads. And all you need is a Vented Indirect Cylinder which is a few hundred Quid depending on size you need. So I get Hot Water from my log burner during winter time easy. Solar would just help with Hot water in the period when Log burner would melt you. And ultimately with an Air Source Heat Pump for those days when its just chilly run off solar. No Gas since the 80s Sid was not a Happy Bunny. Now Solar would eliminate 80% of Electric if I plan it right. Logs cost me 450 quid and being old fart it reduces to Zero this year with winter fuel allowance. Get the wife a flat iron and a kettle for the log burner winner lmao.
@@GaryDoesSolar Foot note. Tried China for Panels by the way. Not cost effective unless you buy 100 or more then you would save a considerable amount. Batteries are cheaper and costs 250 quid for shipping. If and when I find decent recommended Company will post them here. They do offer a Trial Period on some before you pay full amount and free returns if there are problems.
Love it, John! And I'm old enough to remember Sid as well 🙂
You can get, and I have it, an electric immersion heater which holds hot water at mains pressure.
The shower is the best shower I have ever had. It's very powerful and it's hot. Flow rate is excellent. That same tank feeds the hot water taps in the property.
Thanks for the videos Gary. Most helpful I’ve come across by far. If I didn’t have a diverter, and I switched the immersion on while the PV panels were generating, wouldn’t the PV panels directly power the immersion? Or if I timed the immersion to come on during the day, a well insulated tank would act as a battery?
Hi Jamie - that’s very kind of you to say! 😀 Yes, you’re right about manual or timed immersion heater control - that’s essentially what the diverter does for you automatically.
But the advantage the diverter has is that it can vary the power to the immersion (rather than just all or nothing). That’s important because if you have clouds coming over for a few minutes (as is typical in many countries) it will automatically reduce the power in order not to draw from the grid. A timer solution would not know about the clouds, and I doubt you’d want to be watching the sky all day with your finger on the switch 🤣
Hope that helps 👍🏻
The video was very interesting and your calculator is extremely helpful. I heat my water using oil and assuming 70p per ltr this would be 7p/kW (10.35kW per ltr of heating oil) which makes a diverter very unattractive. I wonder if you could extend your calculator to allow inputting of oil as a choice? Many people who want solar are comparing to oil, rather than gas because we live to far from gas mains.
Great to hear the video was useful to you! Now, I understand others have used the utility for oil instead of gas - they just had to calculate the numbers a little...
You missed out the dual immersion scenario common in North America, with 1 at the top of the cylinder, and 1 low down, the top one heats first and only when the top of the cylinder is up to heat does the power get diverted to the lower heater.
Thanks Andrew - I was aware but didn’t want the video to be too detailed. Many solar diverters allow for dual immersion operation, certainly 👍🏻
We haven't got a hot water cylinder, but considered one instead of using our combi boiler.
However I think your installation costs are rather optimistic.
With our Fronius system their solar diverter with installation I can see being a £1k
If we then bought a Mixergy tank, another £1k
After installation, probably £2.5k!
We would never pay that back, especially with our highly efficient daalderop combi.
If you can do it cheap with an existing hot water cylinder okay, but many of these add on systems and fancy hot water tanks, you just never pay them back in reality.
Hi Michael - yes, the video is specially targeted for people who already have a water tank with an immersion heater - as this is the minimum requirement for a unit like an Eddi.
The model does all for extra costs to be added, including tanks, but that will likely destroy any chance of a decent payback.
Interesting calculator. But if you have a heat pump with a COP of say 3, this alters the electricity input on days with insufficient solar dramatically. As an aside, should I be using 3 times more free electricity, or just using my heat pump to do the job, and exporting to the grid?!
Hi Tam, thanks for taking the time to comment. Now, the calculator is really for gas (or fossil fuel) boilers. I haven't looked into heat pumps yet, but maybe someone else here could comment on that?
The payback model used in your calculations is in my view a bit flawed! The usual method of heating a tank of hot water is to switch the boiler on once or twice per day. Ours is once per day in the morning before we shower. Irrespective of how much of that hot water we use the remaining hot water in the tank cools over night to get heated up the next day. The amount of gas used is therefore not directly proportional to the number of house occupants. This is quite easily demonstrated if you heat up your hot water but use none for a day. Your boiler will reheat the same tank full the next day. The means the payback period for 1 and 2 house occupants is rather better than you calculate.
PS I do like your videos as they are very clear and demystify the technology very well...thanks.
Hi Chris, thanks for the kind words.
In making any utility modelling the real world, the more accurate you want it to be, the more exponential the effort. I therefore choose a mainstream use case of a family of 4 who would use the entire tank at least once a day.
Even if your case, where hot water remains in the tank, cooling over the remainder of the day - I’d hope your tank would have a high efficiency rating. My own tank will only lose a couple of degrees in 24 hours.
We are on South Australia and have had a totally separate 315 litre Evacuated Tube solar hot water system for 8 years it has an electric boost that is only used very occasionally during winter, the rest of the year all heating is free from the sun....... 🙂🙃🙂🙃🙂🙃🙂
Love it ❤️😀👍🏻
We’re about to have solar installed and have decided against a solar diverter. The problem we have is that the cylinder is in the 2nd bedroom cupboard and (although well insulated) it obviously leaks some heat into that room (enough that the radiator is only on about 5-10 days of the year). The window is south facing so the last thing we want during summer is to put more heat into the cylinder during the day, and of course in the winter there is unlikely to much excess solar.
We currently heat it using gas for 90mins in the morning, have all our showers etc. and it then leaves us with enough hot water through to the afternoon. Late afternoon we then give it a 30min boost which is good for evening use. I’m considering having a timer fitted and keeping the same routine but using the immersion heater. It would take about 50% out of the solar battery in the morning to fully heat and could use solar excess for the afternoon boost.
Hi Stephen, it sounds like you’ve got a great strategy for your hot water management, and it’s working well. Definitely worth looking at cladding your cylinder and pipes if you haven’t done so already 👍🏻
@@GaryDoesSolar Thanks, and yes it’s all well insulated.
If the immersion heater has a thermostat then just run a timer on it as the simplest form of diversion. You could if handy with computers get a raspberry pi or PC to turn on the switch with a shelly or various IOT power switches depending on the amp rating of the heater (or use the shelly/IOT to activate a larger relay/contactor). Though if you are getting 15pc per KWH switch the whole house off and send it to the grid....
Agreed, this is a simpler and perhaps cheaper method, but the benefit of a fully-fledged diverter comes in when there is occasional cloud cover. When that happens, the diverter will reduce power to the immersion to match the available solar excess, so no draw from the grid. With a simple timer solution, you will be drawing from the grid every time a cloud comes over.
Agreed that higher export rates break the payback for solar diverters.
@@GaryDoesSolar How do they work PWM? A simple timer would be a problem for cloudy days - I use this approach at the moment though not efficiently - just turn the timer off when the day is no good for solar or if during the day it gets good or bad. Ideally like to find some machine learning approach as sadly my feed in to the grid is likely to be cut completely so will have potential excess power but wont be able to determine its capability unless its consumed. I think Fronius ohm-pilot or perhaps others can just pull power from the DC side of the panels and use that to power external loads, again these systems are pretty pricey....For those with time of use power you could look at using a grid-tie inverter with batteries (ua-cam.com/video/yv6TTT57y_U/v-deo.html) at least cut loads overnight and/or feed back if the export price is justifiable to do so.
@@rw-xf4cb usually a triac that fires as many mains cycles as needed - a bit like a light dimmer but more sophisticated as it will be switching up to 3kW for the immersion - needs quite a chunky heatsink as each Amp needs to dissipate 1W of power...
Hi Gary, do you know if there are any easy ways to do this with a combi boiler? It obviously doesnt store water but do you know of any methods to store water/retro fit to benefit from over solar generation?
Hi Ryan, so with the combi-boiler, it’s only consuming electricity when the hot water is being drawn, which is usually just a minute or so typically on occasion (and slightly longer if taking a shower or filling a bath). Excess solar has a very different profile, perhaps several hours during the middle part of the day. There’s no way to toes the two, unless there is a bigger - namely a water cylinder. Worth watching my follow-up video here (ua-cam.com/video/6zc1g1bz0eA/v-deo.html) as if you’re looking to make a financial return, given the excellent export rates available on many tariffs at the moment, it actually doesn’t make sense to divert. But if you really want to make use of your excess solar to heat water, then a cylinder is the way to go, assuming your property can house such.
Hi Gary, thanks for the excellent channel.
For those of us with no gas supply and using oil for water heating, is it easy to adapt your economic evaluation to represent the situation with an oil alternative to gas?
You're very welcome, Ian - thanks for taking the time to watch. Now, I would say, yes it should be easy to substitute oil instead of gas. You'll need to get some handle on the efficiency of heating water with oil though... Good luck!
I try and divert excess solar into the car.
On good solar days I can turn on the immersion heater even if there is only say 1kw being exported and leverage the extra 2kw from the battery. After the water is up to temp the battery will then recharge.
A diverter makes no economic sense to me but the biggest concern is it draining my battery.
Yeah, if you have an EV, that seems a much better way to utilise your solar generation :-)
Great video/research. But you are forgetting one important thing. The "battery" capacity of the water tank. You won't be able to dump *all* your excess power into the tank.
There is a limit to how cold you can let the water get (due to Legionella bacteria, min 50 deg all the way to the tap) and you can't go all the way up to 100 C either. In pracsis you are limited to a max of around 60-65 (the temp where the pot starts making noise when you boil something). If you go above this, the calcium in the water separates and glogs the tank. Even if you accept you have to clean it often, you probably don't want 70 or 80 deg C coming out of you taps or shower. Especially if you have smaller kids.
You www page already knows the kwh pr deg. So if you allow inputting tank volume and min/max temp, you easily get kwh "battery" capacity of the tank.
And then there is the timing. There is a huge difference if the whole family shower in the morning or evening when there is no sun or during a sunny day.
Thanks Jesper - and this is the problem building any model of the real world. The effort required is exponentially proportionate to the resulting real-world accuracy, unfortunately.
Therefore, what I’ve hoped to achieve is a model that’s at least adequate enough for people to make a relatively informed decision on 👍🏻
In my model, it’s not about about trying to dump all of the excess into the tank. It’s about dumping sufficient excess to cover daily hot water requirement - the assumption here is that the tank size is large enough for all in the house.
You’ve given me food for thought though, on how I might improve on the model (if I get time) - thank you!
Jesper, in Australia tempering valves are fitted to prevent super hot water being sent to showers, baths, etc. They mix the hot water with cold to limit the temp to 55 deg to prevent scalding. Don’t know if available there but well worth fitting for safety if they are.
@@markboscawen8330 OK, but how do you/they tackle the calcium issue then?
@@jnygaarddk I don’t have hard water where I am. In Perth, where they do have hard water, temp limiting valves are mandatory as well. So must not be a big problem or slighter quicker replacement cycle. (TLV should be checked annually & replaced every 3-5 years to ensure working correctly.) The other thing peeps know they need to do in hard water areas is manually operate the HWS over pressure temperature valve weekly to avoid it being stuck shut by calcium.
Exporting PV surplus @.15p KWHR
And using my gas boiler @.4p kwhr is my current method.
Sounds good!
Thanks for the interesting video. Good point about estimating the amount of hot water you can actually consume, not many videos mention that but its the limiting factor in my case.
Might be worth pointing out that anyone on a pre 2019 Feed In Tariff (like me) is paid nothing for what they actually export, so all of the generated electricity is free to use. They essentially make up a number and assume that 50% of the generated energy is exported, so you get the same amount whether you export none of it, or all of it.
Secondly your gas boiler efficiency seems way too high at a system level. You have to use gas heating up the boiler itself, the pipework in-between (and more importantly the water in those pipes) and most of that heat leaks away after use. Typical figures from my system given similar starting conditions are 2.5 kWh of solar electricity (reported by the diverter), vs 5 kWh of gas (reported by the smart meter). I'd be cautious about directly comparing them, but approx. 50% efficiency would seem to be a more realistic estimate.
Just for info, I bought a second PV diverter (second hand so not too expensive) and have connected it to a string of convector heaters totalling 3 KW. When the thermostat on the hot water tank stops it taking in any more energy I switch on the second system and use the heaters to provide some background heat to the house. Works well (4,700 kWh harvested so far) and could be used to divert power in a house without a hot water cylinder (e.g. combi boiler fitted). Obviously, can't be used in summer because the house is warm anyway, but helps most of the year.
Thanks Robert 😀 yeah, I do like to bring everything back to first principles and build from there. And relating everything to personal consumption took me away from tank sizes etc. 👍🏻 Now, I think you’re probably right about just how inefficient water heating via gas is. I chose “80%” only as average of old vs boilers. But, really, even with a new boiler, 80% might be too optimistic :-/ I like the way you’ve self-utilised as much solar are you can!
Thanks Robert 😀 yeah, I do like to bring everything back to first principles and build from there. And relating everything to personal consumption took me away from tank sizes etc. 👍🏻 Now, I think you’re probably right about just how inefficient water heating via gas is. I chose “80%” only as average of old vs boilers. But, really, even with a new boiler, 80% might be too optimistic :-/ I like the way you’ve self-utilised as much solar are you can!
Hi. Thanks for the video. In the calculation, regarding the export value that needs to be considered. It says that the higher the rate the less feasible a diverter is. If we get paid for power generated whether we use it or not, we still get paid the full amount do we need to put zero in this box?
Ah, now you might be on a FiT scheme. This utility wasn’t designed for that unfortunately. I would enter “0” as you say, and see what the utility says.
I don't know why the evacuated tube type of solar arrays are so blooming expensive?
People with enough knowledge can make their own for hardly any money, so why are they so expensive when professionally made? And so, we have to go with the diverter option, which isn't the best of the 2 options..... oh well!
As ever, a good explanation here!
Cheers - yeah, the problem is that solar thermal panels are single use case (i.e. heating water) whereas solar PV is way better as the output of that can be used for all sorts of purposes. I'd suggest people consider a heat pump for heating water if you want to get away from gas/oil however.
On the sell back vs use locally q....
Paradoxically if you are environmentally minded the best tactic is to keep as much of the energy as you might otherwise sell back, and don't use external fuel unless you have to. This keeps the export production lower which keeps prices higher. That in turn means your neighbour will want to do the same, and will do the same. That has a better ripple effect, and more solar means more people save, while external price isn't dented by new supply...
If lots of people just sell back, the incentive degrades unless feed in tariffs become higher in response - but that's very unlikely when export supply increases.
So others who haven't gone over yet will see you making a few p for export, and however environmentally minded you are, you've just convinced all your neighbours not to bother....
whereas if you keep the energy, they'll all climb on for both environmental and financial reasons, to make copycat savings.
The only beneficiary from a export is the energy company, until they offer the same price (or higher) for feed in as for usage.
Interesting theory, Jonathan. Not sure if I agree with it though - if neighbours see that you are making money from export, they'll still want the same, no? We're a long way from there being sufficient solar export to affect the national supply. At best in the UK it's only 8%...
Interesting calculator, thanks. 7.5p per kWh of electricity seems a bit cheap though given current price cap rates, unless you're able to only do it overnight on time of use tariff?
Hi Alan, yes it is just an example off peak rate (UK Octopus Go - 00:30 till 04:30) 👍🏻
I have a £20 solution ( Shelley device with a scene referenced to energy monitor ) it’s limited and no data to evidence but I’m sure will be a winner. Essentially only heats when there is more export than the immersion rating. I’ll think of a solution that works around my 1k typical overcast days
Cool :-)
Love mine hot water april to September
Great stuff! 😀👍🏻
You are forgetting that the iBoost+ diverter has a second channel so that when the hot water tank cuts off it sends the surplus to channel 2, My channel 2 divert is to a 3kw storage heater (Ceramic Bricks Inside) in our main living room so that it keeps it comfortable in the day and has enough stored in it for evening use thus saving on our Gas central heating of that room, in the peek of winter when low on solar I switch that circuit over to a time clock to use cheep off peak electric to get it's charge, I consider this device as a TV or Washing Machine and not interested as to it's payback costs over years, If all new buildings were fitted with these then payback does not come into any running calculations
For many though, payback for any solar diverter solution that heats water is most definitely a concern...
Why not just use a 48v DC heating element and bypass the conversion to AC? That is how I see most people doing it here in the states...
I didn't know that - sounds like a great solution!
For anyone more technically inclined, a smart switch on the immersion heater and monitoring your batteries / talking to the communications bus on your inverter would sound like it'll do the trick. Inverters seem to have RS485, CAN or Ethernet comms options.
Nice solution! Thanks for sharing, Aftab :-)
I've not got a solar diverter for my hot water; just 2 of us in the house and we only need hot water for 2 showers and a bit of washing up each day. I have, however, noticed that using my 3kW immersion heater in the morning just before my economy 7 tariff ends for the day is cheaper than using gas. 20 minutes; 1kWh is plenty for us. In the day time, I use a 1kW kettle to heat water for washing up. Sounds a bit of a performance, but I find it's second nature now. I do, however, use a diverter for electric car charging. Myenergi Zappi.
Hi Andrew, yeah, I think more and more people are seeing that with the right tariffs, using electricity is cheaper than gas - not least because of gas inefficiency 👍🏻
Not sure if you're still reading these comments, but one of the considerations when costing a solver diverter is that what is the difference between having a solid averture and just running a simple timer to run the hot water service during the day? I did these numbers and with the cost of the solar diverter at $1,000 in a timer at $150. The difference in how much power I would import was so negligible that it was laughable
Hi Dave, yeah - I guess the only thing to be careful of with the timer is if clouds come over for a period, which means you might be inadvertently pulling from the grid.
@@GaryDoesSolar I have been running this for over a year, The thing with the clouds is you're going to have to do it anyway because you need the hot water so whether it's cloudy or not it's not much difference if it's cloudy you going to have to import off the grid anyway. If it's not cloudy then you're running the solar any difference is negligible at best. Definitely doesn't cover the cost of the diverter, Having said that, I live in Melbourne, Australia so I get a fair bit of sun
Ah yes, living in Melbourne certainly means you won’t suffer clouds very much 😀
What I was trying to say is that units like the Eddi have the ability to curtail the level of heating (say 50%) to avoid pulling from the grid, whereas with a timer it’s binary: all or nothing.
This is what I have. I have a 5 hour boost timer which you can set between 1 and 5 hours. Cost me about £35. I also installed a 1kw immersion heater (about £70 I think) as the likely hood I'll make over 1kw in the day is high but It often drops below 3kw if a cloud comes over for example so a 3kw immersion is more likely to pull from the grid at certain times. So I just leave the 1kw on for longer. With my 4kw system and a 1kw immersion I can also run other things at the same time like my dishwasher ~2kw and a heated towel rail ~500w. I just switch things on and off to balance the electric. Basically a manual version of a solar diverter.
nice interior,
Green screen 😀
To be fair when I'm making excess solar I just switch on the immersion...after 30 mins or so the thermostat switches off and we've enough hot water to last us...2 adults....no payback period as no outlay!
Hi Jeff, this sounds like a very pragmatic solution!
It's very informative, and covers many of the considerations I entered into my own spreadsheet.
However the great trouble with asking whether an energy saving device is worth is the assumption that energy prices and costs remain predictable. When I got my solar panels installed in 2020, I made an assumption of 6% future electricity price inflation. I calculated it was worth it at that rate (14 years payback), vs not worth it at 0% inflation (23 years payback).
History since 2020 has taken a different path to assumptions and I've now returned over 20% of my original investment in that time. Not bad!
So is it worth it? I think questions of investment should be framed in terms of these things actually being insurance products. By investing in these products you are covering the risk of higher energy prices to come. Conversely if energy prices fall some years in the future, that may well only have happened because enough people invested in Energy Saving products! The low prices are in themselves their own reward!
Thanks for taking the time to comment, Anthony - I really value your opinions 👍🏻 I like your thinking about insurance - trying to predict anything that might happen in the future (even in 2-weeks time!) is fraught with danger 🤣
In any utilities I provide, I simply try to keep them as flexible as possible, so that people can enter their own estimations on future tariffs etc. I wasn’t sure what feedback I’d get, but it seems that the model I put together is reasonably valid.
Btw, I can see you’ve just published another video on your battery. Looking forward to watching it later this evening 😀