Powerwall 2 backup power loss

Powerwall 2 backup power loss

We've recently had a solar array and Powerwall 2 installed. After applying through my energy provider to change to a feed in plan, I've been instructed that they need to upgrade my electrical meter. To do this they've asked me to shut down my solar system until the work has been done, presumably so that the meter can be worked on safely in case I'm not home when the work is done.

Instead of losing the advantages of my new solar system and Powerwall for up to 30 days while I wait for that work to be done, before I left the house this morning, I have simply isolated the house from the meter (and grid) by opening the grid supply breaker. This is confirmed in the Powerwall app by the "Grid" icon being crossed out and the Powerwall entering "Backup" mode.

The Powerwall is configured in "self powered" mode.

The following output from the app tells the story:

We woke up at point 1 and had warm showers, the spike is our water heater.

At point 2 the Powerwall hit 15% charge which was my reserve amount, you can see that at this time load shifted to grid supply as expected

At point 3 I configured the Powerwall to zero reserve and then opened the grid supply circuit breaker on my switchboard. Coincidentally we started receiving power from our solar array. I checked the appliances were running fine from the battery before leaving the house. The battery was at around 15% charged and charging from the solar array. You can see we had a nice clear day and were getting good supply from the solar inverter.

At point 4 The battery reached 100% charge and as I would later find out we at least momentarily lost steady supply to the house.

Between point 4 and point 5 my solar inverter output was zero according to the Tesla app and the metrics directly from the inverter itself. During this time there was no reason to assume there was any loss of solar input to the inverter, it was a nice clear and mild day. Obviously with no load the inverter cannot provide power. There was a small standby load at that time, but that seems to have been drawn from the battery.

At point 5 the battery drew some charge from the solar inverter. After recharging, the inverter continued to provide the output to cover the standby load being drawn from the house, up until point 6 when we ran out of daylight.

When I got home at point 7, the house had power being drawn from the Powerwall. I saw my digital clocks flashing a time that indicated they had lost power and powered back on at the same time Powerwall reached 100% charge, however the fact that the clocks were on at all indicates that they had a steady supply from the Powerwall since then. I closed the grid supply circuit breaker at this time and turned on the washing machine and microwaved some dinner (the spike just after point 7).

My question is, would a short power loss be expected when the battery reached 100% charge in this situation? Is the Powerwall only able to fully handle sudden shifts in loads when there is a grid supply?

sonnyh85 | May 21, 2018

I had this same issue before the grid gave me permission to operate. When the battery becomes fully charged, it goes to standby, but then the solar has nowhere to go and shuts down. Most the time this is a seamless transfer, but if you have appliances and such running at the time, you may see a blip in the system. Most clocks will stay on, but there are some sensitive clocks that will catch the blip and they will blink. My oven would blink, but my Bose clock radio would not. My only concern was allowing the solar and inverter to shut off in an overload function several times a day for several days. Luckily for me I only had to wait 14 days for PTO. I learned I could survive off grid for quite a few days, as long as it wasn't raining! Good luck!

sonnyh85 | May 21, 2018

One other thing I noticed is that your high spikes are higher than the PW2 can handle and that will shut down the system. You can see that in peak 2 and 7. 5.5 is max for the PW2.

AaronJH | May 21, 2018

Thanks sonny85. Glad to know my situation is not unusual at least.

In my experience when your load exceeds the powerwall's maximum output, the load will be supplemented by another source if available. You can see in the spike after 7 the blue area indicating house load exceeds the powerwall output (around 5kw) in green, then you can see a spike in white under that where grid supply was used to produce enough power to meet the demand.

I presume if that spike had of occurred when I had the grid supply breaker opened, with no other power source available, I would have experienced a shutdown of the powerwall as you described.

jeff | June 14, 2018

That's some strange looking graphs from your app. Home usage shows little flat-top mesas with zero in between early am. What's turning on and off during that time? Fridge? Do you get a lot of sunlight where you are? You might consider cutting off the grid with a breaker, and use the backup mode in the app. We do it like that and we get enough sunlight to carry us through the night into the next day. Our AC usage is air conditioner, electric water heaters or stoves. The only time we turn on the grid is if we've been running the clothes dryer several times and there's little late afternoon sun. Then the grid goes on for 2-3 hours, it runs the house and charges the battery up, at which point we shut if off with the breaker. This might happen 3-4 times in a month. Tesla says this is an approved way to use the system. Ours, however seems to have a mind of its shuts down completely, and at random...heavy load / no load, sun / no sun, grid / no grid. Doesn't matter. Totally at random, and then usually it resets itself within seconds, sometimes minutes, and sometimes not at all...requires a complete shutdown restart, but usually it does reset. No one from our installer or Tesla has found the cause of this.