If there is a long-term blackout, and the system with Powerwall does not have enough energy to make it through the night, will the system self-start again when the solar panels come on the next day?
Yes, as soon as the solar picks up to cover your home usage needs, the PW2 will begin to charge up. I live in Edmonds, WA and have not used any grid energy since the last week in February, supplying our all electric home, charging both our Tesla's (MS and M3) and are exporting ~70 percent of our solar energy back to grid. We have 1 13.2 kWh solar system and two-PW2 batteries. I love the Powerwall batteries, which are an incredible complement to our solar system. We don't have a lot of brownouts/blackouts here, but the PW2's would work to keep the lights on during a power outage.
"the PW2's would work to keep the lights on during a power outage"
Is there a way to test this ? (e.g. Flip the Gateway switch to simulate power outage?)
There should be a way to interrupt grid power to simulate an outage. We (myself and a Tesla technician) did this when our system was started up to ensure that the switchover was operational under a variety of load conditions.
However, since the grid interconnect for different system is likely different, It would not be wise for me to advise you how to perform this operation. I wouldn't want to be responsible for anything "crashing" due to advice that was not applicable to your system.
I am surprised that this was not tested when your system was not started up. I advise that you contact Tesla for instructions.
Tesla-Dave almost answered my question, but not quite. It makes sense that if it has enough stored juice to make it through the night, it will continue to operate. What I'm wondering is if it can restart on its own from a dead condition (battery exhausted), without needing grid power to power the inverters during initial power on.
@william, our 2 PW2’s drained to zero for 5 days during February, and charged back fully once the snow cleared off of the solar panels. So the answer to your question is yes.
I'm in So. CA, and at the end of my dual PW installation (in early Feb 2019), in order to simulate grid loss, I shut down as many of the house loads as was practically possible, and flipped the main breaker in my main electrical panel. I minimized house loads because switch contacts, like in a circuit breaker, will sometimes arc if they're opened under a large load. Arcing isn't good for the contacts.
Upon opening the main, the PWs took over the house flawlessly, and I let them run everything for a few hours. Upon switching the main back on, the PWs relinquished home power back to the grid, and the PWs began charging again from the solar. PWs won't charge from the grid, except in Power Watch mode.
This was a pretty good simulation of a grid loss, but it wasn't truly representative of what the grid might look like when it goes down. The grid is notoriously noisy in fault conditions. I saw this when there was a scheduled maintenance outage a few weeks later. One of the legs of the 240V had a strange pulsing voltage on it that drove the TEG nuts. While on backup, half of the lights in the house pulsed at about a one hertz rate. As soon as I saw this, I quickly pulled my main breaker, and once I was isolated from the noisy grid, the PWs behaved as expected. I re-enabled the main after I was certain that the grid was back up.
In April, I noted that there was a firmware update for the PWs to 1.36, and one of the notes says "Improved grid stability for backup systems". I trust that this update addresses the weird behavior I saw. I suspect that the programmers widened a control system hysteresis loop a bit. I'm now running 1.37.
I agree with @gregbrew's summary of his simulated power outage. We did three similar checks on our two PW2's to simulate outages, and the PW2's operated flawlessly to take over and keep the lights on and everything working. They work as advertised and we absolutely love how well they operate with our 13.2 kWh solar PV system to minimize our reliance on grid sourced energy.
I"ve got a 4.5 kwh out for solar panels, best that I have gotten is about 3.8 kwh thus far, have put back into the grid regularly have had at least two power outages since installing and powering up the inverter and powerwalls, the powerwall have worked flawlessly thus far with a full load on the system