Unveiling the Mystery Behind Grid Down Solar Regulation by Powerwall | How to Use Maximum Solar Resource During Grid Outages
Grid down Solar regulation by Powerwall is a complex issue that many solar owners face. I recently experienced this with my 3 Powerwall2's supplied by three SMS 5000w inverters, which have a max solar generation of 15kW. During the grid down situation in the morning, the Powerwall was at 30% and began to charge. The house was drawing about 2kW since I shut down the AC units and pool pump. At 67% charge, the solar input reached around 9.5kW, about 7.5kW net, and the system shut down the solar. To try to get it running again, I disconnected two of the three inverters from their DC inputs but did not flip off their AC breakers. However, the Powerwall never began to charge again during the rest of the day when less than 5kW was being generated.
At another house where I have a single Powerwall, it shut down the solar when the battery reached 100%. This makes sense as there is nowhere for the power to go but it never reconnected to the solar even when the battery was down to 70% charge. Once grid power was restored, all returned back to normal operation.
I've thought about this situation and searched online for answers but without much luck. One thing I think I have learned is that each Powerwall can charge at a 5kW rate so my 3 Powerwalls should have been able to accept up to 15kW input. True?
Another example comes from someone who had a grid outage one summer on a sunny afternoon. Their two Powerwalls were full at the time so Solar shut off and their house drew from them. They noticed that Solar production resumed when PWs were about 97%. This continued for several hours and they had full solar production (up to 10 kW) as they kept their house load high to be using all energy produced and kept PWs from filling up.
It seems like there are still some unanswered questions regarding how these systems work in prolonged Grid Down situations and how best to use maximum solar resource available. How are your panels/inverters/PWs wired? Do you have a set of strings going to each inverter and then each inverter going to a PW? Are they facing different directions? Is there a way to see the charge state of each Powerwall? What are the reconnection parameters? And what is the "qualification period required by local requirements" for re-connecting? Hopefully more experienced users can help shed some light on this topic.
How many Powerwalls do I have?
You have 3 Powerwall2's supplied by three SMS 5000w inverters.
What is the maximum solar generation?
The maximum solar generation is 15kW.
What happened during a recent grid down occurring in the morning?
During a recent grid down occurring in the morning, the Powerwall was at 30% and began to charge. The house was drawing about 2kW since I shut down the AC units and pool pump. At about 67% charge, the solar input reached about 9.5kW, about 7.5kW net, and the system shut down the solar.
What did I do to try to get it working again?
I shut off 2 of the 3 inverters by disconnecting the DC in. I did not flip the Inverter AC breakers. But the Powerwall never began to charge again during the rest of the day when less than 5kW was being generated. Once grid power was restored, the system went back to normal operation.
What happened at another house with only one Powerwall?
At another house with only one Powerwall, during grid down the single Powerwall at that location shut down the solar when the battery reached 100% charge. That makes sense of course since there is nowhere for the power to go but it never reconnected to the solar even when the battery was down to 70% charge. Once grid was up, all was back to normal.
Is my understanding of how the system should work consistent with your understanding?
Yes, your understanding of how the system should work is consistent with my understanding and experience.
What is the maximum energy rate to each Powerwall?
The maximum energy rate to each Powerwall is 5 kW from each of 2019 PWs… Newer ones have a higher rate.
Does your system reconnect at 97% charge?
Yes, our system "reconnected" at 97% charge.
What are the reconnection parameters?
Tesla info says "Once Powerwall has the ability to accept power again, your solar inverter will be signaled to produce and will re-start after the qualification period required by your local requirements". It is unclear how often the Powerwall re-checks its ability to "accept power" and what the "qualification period required by your local requirements" is.
How are your panels/inverters/PWs wired?
We have a set of strings going to each inverter and then each inverter going to a PW. They are facing different directions. The inverters are wired in parallel and the PWs are wired in series.
What is the maximum solar input?
The maximum solar input is 15kW, which is the combined total of all three inverters.