Powerwall-Solar newbie -- long time Tesla car owner

[WSE51]

I'm very glad to discover this forum as there seems to be no User Manual for Powerwall systems.

My installation was just completed this week: 4 Powerwalls with 14.2 kW rooftop solar, in Los Angeles.

Only about 35% of my average home needs will be generated with solar: Our house is not well oriented for solar, has rooftop gables limiting the number of solar panels, plus our family of five has 5 Teslas, so our usage is high.

An important function for the PW is backup as my neighborhood suffers about 4 outages per year, generally 2-8 hours long. Of course, being in earthquake country there is risk of very extended blackouts following a major quake.

LA DWP does not allow me to charge the PW from the grid, only from solar.

If anyone has written a FAQ on how to best adjust the app settings to individual needs, I'd love to see it. I've been reading the posts and between all the app's options, changes in weather (thankfully LA gets a lot of sun), and changes in Tesla algorithms, it seems like a complex task.

 

[abasile]

We also use significantly more energy than our solar panels generate. Day to day, the main function of the Powerwalls is to reduce or zero out our usage of the grid during expensive peak hours. For this, I've had them in the "Advanced" time based control "balanced" mode, with our peak/off-peak hours set to correspond with our electric rate plan (TOU-D-A with SCE). Normally, we leave our backup reserve set in the range of 50-70%, but if we need to charge an EV during peak hours, then I'll first lower the reserve to 10-20% so that the energy can come from the Powerwalls.

Regarding outages, the Powerwalls are great for occasions when the power is down for a day or less. We and others have had problems with our Powerwalls not charging from solar during grid outages. I was told by a Tesla technician who came to our house that the Powerwall firmware has unresolved issues. This is a serious concern to us because of the possibility of extended outages caused by earthquakes or other natural disasters. My expectation is that Tesla will address this, as charging from solar during outages is and was a key Powerwall selling point.

 

[commasign]

I have a similar setup. 4 powerwalls and a 20kW solar PV system. I leave powerwall on 100% backup in the winter months. Rest of year I set it to self consumption mode with 25% reserved for backup.

 

[WSE51]

We and others have had problems with our Powerwalls not charging from solar during grid outages. I was told by a Tesla technician who came to our house that the Powerwall firmware has unresolved issues. This is a serious concern to us because of the possibility of extended outages caused by earthquakes or other natural disasters. My expectation is that Tesla will address this, as charging from solar during outages is and was a key Powerwall selling point.

abasile, do you know whether the system acts differently in a simulated blackout (i.e. manually cutting off the grid) vs. an actual blackout? My installer created a simulated blackout and the Powerwalls still charged.

 

[miimura]

abasile, do you know whether the system acts differently in a simulated blackout (i.e. manually cutting off the grid) vs. an actual blackout? My installer created a simulated blackout and the Powerwalls still charged.

I don't see how the Powerwall system could tell the difference. I had the problem with the solar going down while the Powerwall was in backup mode (ie. grid down) but during a test this week, the Powerwalls held the frequency at 60.0Hz and the solar continued generating normally.

How you configure the Powerwalls depends mostly on your rate plan. If you elect a plan that has low off-peak rate and high peak rates, then you will want to use one of the Time Based Control choices. I suggest you start with Balanced. If you are in SCE territory, I suggest you try to get on the TOU-D-Prime plan. It is new. I don't know anything about the LADWP rate plans.

 

[WSE51]

Thanks miimura. I am on LA DWP and they only seem to have one TOU plan. DWP told me to opt-into it after my final inspection and meter installation, which is in a few days.

 

[miimura]

I just looked at the LADWP web site. Strange rate plan.

During the winter months there is almost no differential in rates. Only the months of June-Sept have a significant differential and it's only 1.5x to 1.6x. The PG&E EV-A rate is 3.89x ($0.1256 vs. $0.489/kWh) Summer and 2.6x Winter.

It also looks like there was a non-seasonal significant rate hike in October 2018.

The good thing is that you can make a significant amount of solar during the Peak period of 1-5pm. PG&E EV Peak is 2-9pm, so many people without batteries use up a lot of their peak generation in the evenings after the sun goes down.