Powerwall for Planned Power Outages

[Owner]

I live in California in an area that PG&E can sometimes decide to turn off the power.
I live on the peninsula on the west side of the San Francisco Bay. We are not very windy and don't have those dreadful winds that other areas of California get. But PG&E can decide what they will. Where I immediately live they did not turn the power off in 2019.

But now with the coronavirus, the former backup plan was to just pack up a few things and find a hotel with the power on. Seems like a less viable solution now. And food in the refrigerator and freezer seems more valuable than in 2020. The former argument was say even a $300 a night hotel for say 3 nights would be only $1000 a year if it is required.

So looking for a powerwall or another brand equivalent. Elon's recent behavior makes me much more open to a non-Tesla alternative. I have briefly looked at a generator option but these do not seem any cheaper and the greenie in me rebels against the thought.

I have a 13 year old solar system that I think is producing 3.8kW - but I for the life of me can't find the documentation. It is a little less than I could use as I pay up a couple hundred dollars a year to PG&E, but it is likely too old to expand.

What I have not been able to find anywhere is succinct information on why I can't keep charging the powerwall during an outage if the solar is active. If this capability were there, I think 1 powerwall would be enough. But the Tesla person said that feature is not available. Technically why not?

I'm perfectly okay with just running the fridge, the internet, and a few small devices such as laptop, microwave, phones etc... during an outage. If this low usage model will work with 13.5kWh, 1 powerwall should be sufficient. No need to run things like dishwasher, laundry, A/C (its not that hot here) or charge the car (go to a supercharger). Am I missing something?

 

[MorrisonHiker]

What I have not been able to find anywhere is succinct information on why I can't keep charging the powerwall during an outage if the solar is active. If this capability were there, I think 1 powerwall would be enough. But the Tesla person said that feature is not available. Technically why not?

You can. Solar will continue to charge the Powerwalls even if the grid is down. Only one Powerwall is needed if you only back up certain outlets. If you back up the entire house or need to backup a 30 amp or larger outlet, two Powerwalls are necessary.

We did an endurance test last year and went 8 days (over 200 hours) off the grid, just using solar and Powerwalls.

 

[Mokuzai]

That doesn't sound right... Only thing I can think is if the size of your solar array is too small to fully power your house (or the backup loads) during the day then there would be no excess to go into the powerwall.

 

[Owner]

You can. Solar will continue to charge the Powerwalls even if the grid is down. Only one Powerwall is needed if you only back up certain outlets. If you back up the entire house or need 240V, two Powerwalls are necessary.

We did an endurance test last year and went 8 days (over 200 hours) off the grid, just using solar and Powerwalls.

Why do you need 2 powerwalls for 240V?

How many Powerwalls did you get for 8 days - that's a long outage.

 

[Owner]

That doesn't sound right... Only thing I can think is if the size of your solar array is too small to fully power your house (or the backup loads) during the day then there would be no excess to go into the powerwall.

I'm assuming you can technically charge the powerwall directly from the grid? Or non-technically charge the powerwall from the solar and use the energy from the grid to power the house?

 

[MorrisonHiker]

Why do you need 2 powerwalls for 240V?

How many Powerwalls did you get for 8 days - that's a long outage.

We had 4 Powerwalls (upgraded from 3). Solar would charge the Powerwalls and house during the day and then the Powerwalls would power the house when the sun was down. It was an intentional outage as we were trying to test how long we could live off the grid. We even had a snowstorm and were able to clear the panels and keep things running.

I'm assuming you can technically charge the powerwall directly from the grid? Or non-technically charge the powerwall from the solar and use the energy from the grid to power the house?

If you have solar, you can only charge the Powerwalls from the grid if Storm Watch is activated due to severe weather conditions or planned outages. Normally if you have solar, the Powerwalls are only charged via solar.

 

[Mokuzai]

I'm assuming you can technically charge the powerwall directly from the grid? Or non-technically charge the powerwall from the solar and use the energy from the grid to power the house?

If you have solar you can only charge from the grid under stormwatch. If the weather service expects an event in your area or if there is a planned outage then the battery will prepare itself by charging from the grid. Otherwise it's expected you get all your battery charging from solar. If you play with the advanced time based controls you can get the battery to charge from solar while you run the house off the grid.

 

[Mokuzai]

Why do you need 2 powerwalls for 240V?

Each powerwall has a certain amount of load it can support. We have two powerwalls and were told that it was not enough to support our AC unit even with a slow start device so the AC is not backed up during an outage. However the AC does run off the batteries while the grid is connected. If we had another couple powerwalls we could power the whole house during an outage.

 

[Mokuzai]

If it's within your budget you may want to consider expanding that solar array. You don't necessarily need to connect it into your existing inverter or whatever you're using. We have two independent arrays working off different technologies (one inverter with load balancers and one with micro-inverters). The federal tax credit is 26% through the rest of the year. If you qualify for the residential equity resiliency rebate through SGIP then two powerwalls are essentially free. It depends on if you live in a qualified fire zone and if you can prove a backup need for your home.

 

[Owner]

residential equity resiliency rebate through SGIP

No, I'm fortunate enough to not be in a Tier 2 or Tier 3 area. They are up in the surrounding hills where the forest is really dense. So no great discounts for me. The power didn't go out, just Comcast did.

I might consider expanding it but it doesn't seem worth it if my true up numbers were around $300 last year. If that were more I would think about it. I will probably consider it if my inverter goes belly up - the first one did but it was still under warranty.

 

[SSonnentag]

I live in California in an area that PG&E can sometimes decide to turn off the power.
I live on the peninsula on the west side of the San Francisco Bay. We are not very windy and don't have those dreadful winds that other areas of California get. But PG&E can decide what they will. Where I immediately live they did not turn the power off in 2019.

But now with the coronavirus, the former backup plan was to just pack up a few things and find a hotel with the power on. Seems like a less viable solution now. And food in the refrigerator and freezer seems more valuable than in 2020. The former argument was say even a $300 a night hotel for say 3 nights would be only $1000 a year if it is required.

So looking for a powerwall or another brand equivalent. Elon's recent behavior makes me much more open to a non-Tesla alternative. I have briefly looked at a generator option but these do not seem any cheaper and the greenie in me rebels against the thought.

I have a 13 year old solar system that I think is producing 3.8kW - but I for the life of me can't find the documentation. It is a little less than I could use as I pay up a couple hundred dollars a year to PG&E, but it is likely too old to expand.

What I have not been able to find anywhere is succinct information on why I can't keep charging the powerwall during an outage if the solar is active. If this capability were there, I think 1 powerwall would be enough. But the Tesla person said that feature is not available. Technically why not?

I'm perfectly okay with just running the fridge, the internet, and a few small devices such as laptop, microwave, phones etc... during an outage. If this low usage model will work with 13.5kWh, 1 powerwall should be sufficient. No need to run things like dishwasher, laundry, A/C (its not that hot here) or charge the car (go to a supercharger). Am I missing something?

Your small PV system is probably only large enough to keep a single Powerwall topped off during an extended outage. My rough calculations say your 3.8 KW system can provide a hair over 13 kWh/day. So if you are sparing with your power usage, it should suffice to keep a single Powerwall running indefinitely, barring any extended rainy days. I don't see any flaws in your plan.

 

[SSonnentag]

I'm assuming you can technically charge the powerwall directly from the grid? Or non-technically charge the powerwall from the solar and use the energy from the grid to power the house?

Generally, you can only charge the Powerwall from solar. There are exceptions as stated, but I wouldn't count on them as they rely on some other system correctly predicting an outage.

 

[gpez]

Each powerwall has a certain amount of load it can support. We have two powerwalls and were told that it was not enough to support our AC unit even with a slow start device so the AC is not backed up during an outage. However the AC does run off the batteries while the grid is connected. If we had another couple powerwalls we could power the whole house during an outage.

Sounds like you're mixing up voltage and watts a bit.

A single Powerwall is capable of 240 volt split phase (so two 120v hots that are 180 degrees out of phase plus a neutral) as per the spec sheet.

Most high wattage appliances, such as dryers, ovens, and air conditioners, use 240 volts as it is more efficient (more volts = less amps). As you noted earlier a single Powerwall cannot provide enough watts to start and maintain those devices so you'll need more than one and perhaps a soft start as well - but a single Powerwall does provide the requisite 240 volts.

tl;dr: additional Powerwalls give you more watts, not more volts.

 

[Mokuzai]

Sounds like you're mixing up voltage and watts a bit.

I was simplifying without getting into technicals. But yes it's the amp draw that determines the need for more powerwalls. Watts = Amps * Volts.

 

[gpez]

I was simplifying without getting into technicals. But yes it's the amp draw that determines the need for more powerwalls. Watts = Amps * Volts.

Gotchya. I'm all for simplicity but saying if you need 240v you need 2 Powerwalls is a bit misleading

 

[Mokuzai]

Gotchya. I'm all for simplicity but saying if you need 240v you need 2 Powerwalls is a bit misleading

Well...I did say load. Though yes I did respond to a question about volts I was more explaining why you may need more powerwalls.

 

[Owner]

Your small PV system is probably only large enough to keep a single Powerwall topped off during an extended outage. My rough calculations say your 3.8 KW system can provide a hair over 13 kWh/day. So if you are sparing with your power usage, it should suffice to keep a single Powerwall running indefinitely, barring any extended rainy days. I don't see any flaws in your plan.

I think your rough calculations are very good. I looked at Saturday May 9 and 10kWh/day was sent to the grid. That was the max. So even on a sunny day (well mostly sunny) in almost summer no car charging and regular usage, I agree with you. I won't be able to generate enough electricity for a second Powerwall.

 

[Owner]

"barring any extended rainy days."

If there were extended rainy days, we would not have any power shut offs as the wildfire planned outage would not be in effect!

 

[Owner]

Okay, another potential roadblock. My wi-fi in that part of the garage and house is pretty lame. I have a lot of stone walls and stainless steel and fancy stuff that interfere. Its pretty far away from either the router or the extender that is wired under the house. Anyone have a clue on this part?

Cellular signals are there but weak also due to topography (hills).

 

[Mokuzai]

My wi-fi in that part of the garage and house is pretty lame.

They hooked up our powerwalls to our router through a powerline adapter.