AC-Coupled vs DC-Coupled (Solar Batteries)
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- Опубліковано 23 кві 2024
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Solar Surge will teach you all about being energy independent and how to set up your home to run off-the-grid during an emergency. We empower families to take control of their energy generation and storage so that they will never be left in the dark without electricity.
In this video, Joe discusses AC vs DC- Coupled Battery Systems and which are the best when it comes to a solar and battery storage system for your home.
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The 2nd very significant advantage of a DC coupled battery has to do with over-sized system (which happens on most roofs with proper design) - When you have a given Inverter (say, 7.6KW) but have on the roof PV panels that sum up to much more power than that (say, 11KW). During peak production hours (around noon) the extra power (beyond the 7.6KW) doesn't need to be clipped and wasted, but can be directed and used to charge the DC battery.
You mean Ac?
Excellent video and timely. Researching now for home retrofit to add battery storage.
Great video, simple explanation.
Great video Joe! I'm surprised you didn't put a shout-out to hybrid inverters like EPCube, etc., that can do both DC and AC coupling.
SolarEdge sponsored this video so the main point was to teach how DC coupling provides higher efficiency.
Great video, thank you. I run an entire solar edge system, so I’m very interested in adding the solar edge battery’s.
Joe, thanks for this! Other advantages to DC coupling are that the voltages are higher. Since volts x amps is power, that means thinner wires and less expensive installation. Fewer conversions means fewer disconnect switches, transformers, etc. As you get into commercial contexts, you start to avoid 3 phase power and let the battery float voltage for your whole DC microgrid. You can oversize your array quite a bit relative to your inverter size which also makes things cheaper. You can also interconnect very large arrays because interconnection is an AC limit, not DC. You can bring power to a new building much faster than new AC service from the utility. The only other major advantage to AC coupling is the redundancy that allows half your system to work if one inverter breaks. With DC coupling you are completely down if the hybrid inverter breaks.
I am finding for retrofits with a preexisting solar edge grid tied system that it’s easier to swap in a home hub inverter and DC couple instead of AC coupling.
Good feedback. If you want to stay within the SolarEdge ecosystem, this approach makes sense. And Solar Edge is offering discounted upgrades for existing system owners want to upgrade to the new inverter.
I have DC coupleed Solarege batteries with backup. There is 3-5 second delay from when the power goes out and battery auto transfer kicks in my DC coupled system. I am using uninterruptible power supply (UPS) on my sensitive units such as my computers and electronics, but with an AC coupled system, there is no delay when what power goes out and the back up kicks in. That should be a big factor that no one talks about.
I don't see here any info on how much is lost converting rhe DC coming of the roof to the correct DC current going to charge the car and the same to make it compatable to charge the😮 batteries. What are the losses there?
I have 18 Q-Cell QTron425's with the Enphase IQ8M micro-inverters. I have a 1:1 ratio under NEM2 in NH.
The IQ8Ms have a max output of 325VA I am getting clipping at 5.9kW (18x325w) from about 10-2 on sunny days. That is about a 1.3/1 ratio, and I thought 1.4/1 and below was good, but I feel like there is a lot of energy that I'm not capturing. (Would the IQ8A have been better at 349VA and 1.2/1?)
I'm not unhappy with this, but I was wondering if there is a way to capture this the extra DC power with a battery -- potentially lowering the voltage to the inverter to prevent clipping? Is this possible with my setup?
AC is less efficient than DC over long distances. However, AC is more economical to convert back and forth between voltages using transformers. DC systems need to convert to AC, then go through a transformer, and convert back to DC, so extra steps are involved. DC voltage conversions can be also done efficiently using "buck" and "boost" converters, but in either case, there is more conversion overhead, and more cost at conversion. However, DC looses very little power over distance other than resistive losses, which are minimized at higher voltage. AC transmission has inductive and capacitative (reactive) losses in addition to resistive losses.
Is there a microinverter that also lets a battery charge from DC when there is no demand for AC? And then a microinverter attached to the battery to provide AC from battery power when the solar panel isn't providing enough?
I believe you’re talking about Enphase. They do a solution like that, and I believe they only convert twice rather than 3 points of conversion.
@@MrDontcareify Thanks for the info :)
Microinverters can't do that. Enphase is an AC coupled architecture and cannot do any DC coupling.
It depends on how you define the terms. The battery is inherently DC and the microinverters inside the battery casing invert the power back to AC.
So if we’re talking about a pure line of dc to dc like the power optimizers, then no.
But even with SolarEdge there is a point of inversion at the solar inverter. Which means that you would need either an additional inverter for their batteries or their proprietary inverter for Energy Hub.
Microinverters like Enphase do maximum power point tracking plus conversion to AC. DC to DC micro converters like Ampt or APSystems or SolarEdge Optimizers do the former but not latter and save the AC conversion for later at the inverter. You can't really have it both ways with those devices except products like Sol-Ark allow you to DC couple and AC couple solar at the same time. That would get at your objective.
What about DC to DC voltage conversion.?
From power optimizers? Any losses from that conversion are quite minimal, unless the buck-boost converters inside the power optimizers are not functioning properly.
All conversions have loss. But DC to DC has far less.
At what distance between the solar panel and the home (where the electric panels and batteries are located) does it become more efficient to convert to AC at the solar panel?
I wouldn’t recommend that. Just use sufficient size wire to bring the high voltage DC back to the house.
@@SolarSurge I was thinking long distance, like 300+ feet.
Assuming your DC voltage is higher than what the AC will be, it's much better to keep it as DC, you'll have lower loses in a given cable size and length. The reason the grid is AC has nothing to do with it being more efficient, really long distance transmission is often done in DC to lower loses, AC has the advantage of using cheaper transformers to step the voltage up or down as required.
@@Pete856 Sometimes it is hard to get that across. A PV array @ 400 volts is better for long distances(within reason) than 240V AC
Run the DC back to the house. Generally speaking, whatever has the higher voltage is what you want to run for long distances.
Reliability, safety, redundancy trump efficiency every time. AC coupled battery and microinverters for me no question. Solar is cheep, if you’re worried about efficiency just add more solar.
Solar Edge is said to be around 99% efficient due to its design and since it doesn't do all the back and forth from DC to AC and AC to DC up to 3 times. Some AC systems are said to lose up to 30% of the energy made by the solar panels in those 3 changes that Joe talked about. That can make for a very important difference in the energy your system creates for you to use or sell back to the electric company if you have a small roof and or you are limited on the number of solar panels you can install.
I think you also need to consider the quality of electricity when considering these battery backup systems. It's a bit more complex and the video did provide a simple explanation of some of the differences. However, when looking at the voltage and current response of the DC coupled battery systems it is severely distorted in comparison to solutions such as Enphase. These distortions could lead to failure of motors and overheating of those components when the battery system is supplying the energy. In my opinion batteries are still not a great solution for backup and really need to be utilized as consumption insurance to avoid high electricity bills.
Interesting video. Thanks
I would like to add a missing consideration. DC Voltage of panels, home batteries and car batteries rarely mach, so you have to apply DC-DC converters to, for example, reach from the solar panels the 800V of a car battery or a high voltage home battery . DC-DC converters have also energy loses, so both ways ar not so far from the energy efficiency point of view.
Great point!
Solark and eg4 are way ahead in their systems. Though the ability to charge an ev off the inverter is cool. Evs themselves arent as reliable as we need them to be yet.
So you have Solaredge as a sponsor that makes DC solar systems. Then you happen to make this video about the advantages of DC leaving out all the disadvantages such as the fire risks of running high voltage cabling through your house. You have increasingly sold your soul to your sponsors as you used to not be biased. You are losing your credibility.
Feel free to share the statistics of residential fires caused by the leaders of DC optimizers. Joe's not wrong in his video. Multiple conversions will result in a loss of energy. DC coupling is much better.
@@A_Guy_Named_Eric It’s the DC cabling on the roof to the string inverter that is high voltage and a fire risk. Don’t take my word for it as there are many house insurers here in Europe that require AC systems due to lower probability of fires. I do agree that DC is more efficient for charging any battery.
By your logic, things are much more dangerous in Europe where they use 240 volt throughout homes rather than the much safer 120 volts we used in homes in the US, right?
It’s not the wires in the homes that is the problem, it’s the DC wires on the roof.
@@MrDontcareify Why? Where is the data or engineering analysis that supports that claim?