Is 1 PowerWall better than No PowerWall?

[KHYE]

I've been going back and forth on whether to get PW or not. I'm in SoCal, with SCE and plan to get 8.16 kW solar panel.

The prob is 2 PWs' ROI will take too long to recoup the cost. My goal of getting PW is to offset peak hour usage, not for blackout. From what I have read in last few months, SCE doesn't provide 1:1 NEM. During peak hours, i have to pay more and only get wholesale price for the over generating power.

Can I just go with one? Is 1 PW enough to offset the peak hour usage? How can I figure this out? My daily power usage is about 17.55 kwh.

Thanks.

 

[SolarBob]

It takes Solar Energy to charge the PW. So rather you are using Solar Energy from your panels, or from the PW it is a wash. So if you do not need any backup I do not see the need for any power wall. If you have a lot of excess Solar Energy during the day that provides your needs for power, and can charge the PW's then it might make sense.

That way after dark you can use the excess energy to run your house. However, it is a net zero situation, meter forward, meter backward.

I have two PW's because we live in a PGE high blackout area. I keep them always charged at 40%.

My input, thanks!

 

[jjrandorin]

I've been going back and forth on whether to get PW or not. I'm in SoCal, with SCE and plan to get 8.16 kW solar panel.

The prob is 2 PWs' ROI will take too long to recoup the cost. My goal of getting PW is to offset peak hour usage, not for blackout. From what I have read in last few months, SCE doesn't provide 1:1 NEM. During peak hours, i have to pay more and only get wholesale price for the over generating power.

Can I just go with one? Is 1 PW enough to offset the peak hour usage? How can I figure this out? My daily power usage is about 17.55 kwh.

Thanks.

If you dont want backup, its better to just buy more solar to offset the lack of 1:1 net metering. "Getting paid the wholesale price" is something that happens at true up (after your 12 month cycle). There tends to be a lot of confusion about that. You get credit for your solar at the rate that is in place at the time you feed it into the grid.

The "wholesale price" thing is ONLY if you are a net producer at the true up period. The peak usage times of 4-9pm cost more to use electricity than off peak, so you need to have more PV to cover that time, but you can simply use the utility as a battery if there is no concern about power outages.

 

[MorrisonHiker]

If you only use 17 kWh per day, then 1 Powerwall should be enough to cover your usage during your peak period.

Also, remember that without a Powerwall or similar battery system, your solar will not work at all if there is a grid outage. While you might not expect to have any outages, they are always possible and we've had many multi-day grid outages since our solar and Powerwalls were installed. If we didn't have Powerwalls, our solar would be disabled and wouldn't be able to power anything during an outage. There are various threads about people in Texas who didn't see the need for Powerwalls since they have free electricity at night but then they went days without power during the recent storm because their solar systems were offline. If they'd had a Powerwall, many of them never would've lost power.

If you have at least one Powerwall, you can power lights, the refrigerator and many small appliances. You wouldn't be able to power an electric range or electric dryer or other appliances that are 240V.

 

[gpez]

If you only use 17 kWh per day, then 1 Powerwall should be enough to cover your usage during your peak period.

Also, remember that without a Powerwall or similar battery system, your solar will not work at all if there is a grid outage. While you might not expect to have any outages, they are always possible and we've had many multi-day grid outages since our solar and Powerwalls were installed. If we didn't have Powerwalls, our solar would be disabled and wouldn't be able to power anything during an outage. There are various threads about people in Texas who didn't see the need for Powerwalls since they have free electricity at night but then they went days without power during the recent storm because their solar systems were offline. If they'd had a Powerwall, many of them never would've lost power.

If you have at least one Powerwall, you can power lights, the refrigerator and many small appliances. You wouldn't be able to power an electric range or electric dryer or other appliances that are 240V.

Just because I actually don't know this answer - if you had a non-backed up sub panel with the high wattage appliances wouldn't those just pull from the grid if it exceeds the 1 PW capabilities? Not 100% ideal but would still offset a substantial amount.

 

[holeydonut]

If you dont want backup, its better to just buy more solar to offset the lack of 1:1 net metering. "Getting paid the wholesale price" is something that happens at true up (after your 12 month cycle). There tends to be a lot of confusion about that. You get credit for your solar at the rate that is in place at the time you feed it into the grid.

The "wholesale price" thing is ONLY if you are a net producer at the true up period. The peak usage times of 4-9pm cost more to use electricity than off peak, so you need to have more PV to cover that time, but you can simply use the utility as a battery if there is no concern about power outages.

This approach only works if your utility allows you to over-size your solar array, and you have the space on your roof to over-size your array.

Since PG&E can enforce a "110% of previous annual consumption" rule, it can be very difficult to offset the crazy differential between peak-time and off-peak time if you are on the EV2A TOU Plan. E-TOU-C is probably manageable, but keep in mind the CPUC has granted PG&E the ability to change TOU C rates and hours at will; so there's no guarantee the rates will remain manageable 5 years from now.

While a single battery's ROI will still be tough to quantify from a pure financial perspective, I believe adding at least one battery will help shield you a bit from having to worry about the PoCo's BS. This comfort is worth something... even if it's not purely monetary.

 

[SolarBob]

If you an outage I thought that during the day your solar will charge your power walls, providing you have solar sun during the day.

Power Walls need to get you through the night or when there is no sun producing solar power.

Am I mistaken here?

 

[MorrisonHiker]

If you an outage I thought that during the day your solar will charge your power walls, providing you have solar sun during the day.

Power Walls need to get you through the night or when there is no sun producing solar power.

Am I mistaken here?

You can use Powerwalls to power the house at night, during peak (expensive) periods or whenever you like. They can also continue powering the house and keep the solar system running during a grid outage.

 

[KHYE]

Thanks everyone for your feedback/input.

For dealing with blackouts, i already have a dual fuel generator I can use to get by. The goal to get PW is mainly for offsetting the peak hour rates.

 

[MorrisonHiker]

Just because I actually don't know this answer - if you had a non-backed up sub panel with the high wattage appliances wouldn't those just pull from the grid if it exceeds the 1 PW capabilities? Not 100% ideal but would still offset a substantial amount.

We have whole-house backup so I'm not certain how a non-backed up sub panel would work. I would assume they would pull from the grid as necessary if the grid was up.

Ah. I get where you are going now. It would offset other household usage during peak, etc. but I would think A/C and other 240V appliances could be the majority of the load during peak. Our household load is about 1 kW throughout the day (no A/C) so 1 Powerwall could easily offset all of our usage during peak. If we had A/C, then one Powerwall would only be able to offset a small percentage during peak period as I imagine A/C would be much higher than 1 or 2 kW.

 

[SolarBob]

You can use Powerwalls to power the house at night, during peak (expensive) periods or whenever you like. They can also continue powering the house and keep the solar system running during a grid outage.

Do the PW's charge during the day using Solar Energy during an PGE outage. That is what I was told.

 

[MorrisonHiker]

Thanks everyone for your feedback/input.

For dealing with blackouts, i already have a dual fuel generator I can use to get by. The goal to get PW is mainly for offsetting the peak hour rates.

If you want to offset or back up 240V appliances then one Powerwall isn't sufficient. For example, if you have 240V A/C, one Powerwall wouldn't be able to handle it. It could offset usage of other 120V electronics.

 

[MorrisonHiker]

Do the PW's charge during the day using Solar Energy during an PGE outage. That is what I was told.

Yes. Whenever the power goes out, our Powerwalls keep our solar system running. Solar can then be used to power the house and recharge the Powerwalls.

 

[holeydonut]

If you want to offset or back up 240V appliances then one Powerwall isn't sufficient. For example, if you have 240V A/C, one Powerwall wouldn't be able to handle it. It could offset usage of other 120V electronics.

Ah. I get where you are going now. It would offset other household usage during peak, etc. but I would think A/C and other 240V appliances could be the majority of the load during peak. Our household load is about 1 kW throughout the day (no A/C) so 1 Powerwall could easily offset all of our usage during peak. If we had A/C, then one Powerwall would only be able to offset a small percentage during peak period as I imagine A/C would be much higher than 1 or 2 kW.

If the utility was operational, I think one PW could offset some 240V appliances for the TOU-shifting benefit. However, if the utility goes offline, I agree one PW isn't enough to reliably operate a single 240V appliance.

For example, my oven is electric, and draws about 5 kW when it's heating up (about 20 amps). So it's basically right at the max that one single PW could put out. But, when the utility is operational, this oven would maybe take 4 kW from the battery and 1 kW from the utility. Then when it's at operating temperature, it would be on battery power. Of course 1 battery may be exhausted rather quickly with a ton of 240v going at the same time... so there's that problem as well.

Anyway, my point is there's still a benefit to a single Powerwall even if it's not a full-resiliency-off-grid benefit.

IMO, with 3 batteries, I think I've consumed like 10 kWh from PG&E since the middle of February. Having PG&E be the backup and extra-battery is a nice feeling since it means my day to day usage and behavior cannot be impacted by PG&E. But if I get 3 straight days of cloud-cover, PG&E can step in with their outrageously expensive energy.

 

[h2ofun]

Thanks everyone for your feedback/input.

For dealing with blackouts, i already have a dual fuel generator I can use to get by. The goal to get PW is mainly for offsetting the peak hour rates.

then imo a pw for you has no roi. but if you have ectra money

 

[hayhayday]

What utility do you use?

 

[KHYE]

If you want to offset or back up 240V appliances then one Powerwall isn't sufficient. For example, if you have 240V A/C, one Powerwall wouldn't be able to handle it. It could offset usage of other 120V electronics.

Yea, my expectation has to be realistic, with one PW, I don't expect to run A/C.

What utility do you use?

SCE.

 

[brian.c]

I am in a similar situation, would like PW, but just too hard to justify the costs. I thought about doing just a single, like you suggested, but decided at this point it was much easier to adjust my usage during peak hours. We have had maybe 6-8 power outages in over 10 years, most of those were resolved within a couple hours, so not much of a need for backup power. I have an older solar array that is just over 10 years old, so plan to revisit the PW in a few years. At that point It might be worth while to replace my old system and add the PWs.

 

[hayhayday]

Looks like the average price delta is about 27c. If a third of your usage is during peak times that would be about 6kw a day which should almost always be more than generation from a 8kw system
27c x 6 = $1.62 * 360 days a year = $583
At a 8k after tax credit installed cost your breakeven is almost 14 years while the powerwall is only warrantied for 10. Doesnt seem like it would be worthwhile if there is not value to backup.

 

[KHYE]

Looks like the average price delta is about 27c. If a third of your usage is during peak times that would be about 6kw a day which should almost always be more than generation from a 8kw system
27c x 6 = $1.62 * 360 days a year = $583
At a 8k after tax credit installed cost your breakeven is almost 14 years while the powerwall is only warrantied for 10. Doesnt seem like it would be worthwhile if there is not value to backup.

Thanks for the calculation