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Using powerwalls for load shifting only

mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
so how many years payback?

So it seems like there a a horrible economic case for powerwalls! I do have to compute how much peak energy I pay over the last year, because it is fair to look at it as offsetting all the high cost energy, but I don't understand why powerwalls are seemingly so popular in PG&E areas if the economics of them are so terrible.
 

h2ofun

Active Member
Aug 11, 2020
3,001
646
auburn, ca
So it seems like there a a horrible economic case for powerwalls! I do have to compute how much peak energy I pay over the last year, because it is fair to look at it as offsetting all the high cost energy, but I don't understand why powerwalls are seemingly so popular in PG&E areas if the economics of them are so terrible.
IMO, it is because so many use emotion of hating PGE. So many tweaks the numbers to get whatever answer they want. There are reasons I have yet to have a person in the solar business "sell" me on buying PW's, unless one just has money to burn. I was talking to a solar person yesterday who is putting panels on a house a few doors down. He said no way would he tell a customer to get PW's, too much money and they do not last long. His input was put on solar, and then they install 22KW generators. Issue solved for our area, since most of us have propane tanks.
 

mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
IMO, it is because so many use emotion of hating PGE. So many tweaks the numbers to get whatever answer they want. There are reasons I have yet to have a person in the solar business "sell" me on buying PW's, unless one just has money to burn. I was talking to a solar person yesterday who is putting panels on a house a few doors down. He said no way would he tell a customer to get PW's, too much money and they do not last long. His input was put on solar, and then they install 22KW generators. Issue solved for our area, since most of us have propane tanks.

I hate PG&E too - who doesn't? But that doesn't mean I should burn a ton of money just to somehow try and get even with them. They only get away with what they are doing because of the CPUC and state government allowing them to do it. You can't really criticize a company for acting in it's own best interest I suppose.

We have a lot of energy use because its a large house, and I have 24KW of solar array, and actually generate quite a bit of energy during the day. I know I can't sell everything back in the peak hours, but was looking to see what the sort of best case was. I have to look at how much peak energy we use and see if that changes the economics just by avoiding that expense, but it looks pretty doubtful.

I don't think depending on PW's for backup use is nearly as good as a generator. If there is a nasty storm that takes out power, you may not be able to charge. And if you end up with an extended power outage, that is hard to deal with too. Generators really do a better job for backup, and you can get transfer switches of all sizes, so you don't have to break up panels into blocks of backed up and non backed up circuits.

But I confess I was surprised at how bad the economics are just on the load shifting piece. We have lots of people in my community lobbying the city to force everyone off gas appliances, and that solar and batteries will make our city's power use all green. But the economics of storage look like it will be a very long time before any of that actually makes sense.
 
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miimura

Well-Known Member
Aug 21, 2013
6,539
6,347
Los Altos, CA
I hate PG&E too - who doesn't? But that doesn't mean I should burn a ton of money just to somehow try and get even with them. They only get away with what they are doing because of the CPUC and state government allowing them to do it. You can't really criticize a company for acting in it's own best interest I suppose.

We have a lot of energy use because its a large house, and I have 24KW of solar array, and actually generate quite a bit of energy during the day. I know I can't sell everything back in the peak hours, but was looking to see what the sort of best case was. I have to look at how much peak energy we use and see if that changes the economics just by avoiding that expense, but it looks pretty doubtful.

I don't think depending on PW's for backup use is nearly as good as a generator. If there is a nasty storm that takes out power, you may not be able to charge. And if you end up with an extended power outage, that is hard to deal with too. Generators really do a better job for backup, and you can get transfer switches of all sizes, so you don't have to break up panels into blocks of backed up and non backed up circuits.

But I confess I was surprised at how bad the economics are just on the load shifting piece. We have lots of people in my community lobbying the city to force everyone off gas appliances, and that solar and batteries will make our city's power use all green. But the economics of storage look like it will be a very long time before any of that actually makes sense.
There is another thing you have to think about when you have a large solar array. If you don't owe money at true-up before you get Powerwalls, you aren't going to save anything with rate arbitrage because you don't owe anything. The only way you can get any arbitrage benefit is if you're on a CCA that pays for all surplus generation, like SVCE. However, I think Menlo Park is outside the SVCE territory.
 
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h2ofun

Active Member
Aug 11, 2020
3,001
646
auburn, ca
I hate PG&E too - who doesn't? But that doesn't mean I should burn a ton of money just to somehow try and get even with them. They only get away with what they are doing because of the CPUC and state government allowing them to do it. You can't really criticize a company for acting in it's own best interest I suppose.

We have a lot of energy use because its a large house, and I have 24KW of solar array, and actually generate quite a bit of energy during the day. I know I can't sell everything back in the peak hours, but was looking to see what the sort of best case was. I have to look at how much peak energy we use and see if that changes the economics just by avoiding that expense, but it looks pretty doubtful.

I don't think depending on PW's for backup use is nearly as good as a generator. If there is a nasty storm that takes out power, you may not be able to charge. And if you end up with an extended power outage, that is hard to deal with too. Generators really do a better job for backup, and you can get transfer switches of all sizes, so you don't have to break up panels into blocks of backed up and non backed up circuits.

But I confess I was surprised at how bad the economics are just on the load shifting piece. We have lots of people in my community lobbying the city to force everyone off gas appliances, and that solar and batteries will make our city's power use all green. But the economics of storage look like it will be a very long time before any of that actually makes sense.
I agree. And if I look at my solar production during peak hours I am sending back, its a joke how little gets generated.

This topic is mostly emotion. But boy do I get beat up saying batteries are not the end all
 

mikesm

Member
Apr 25, 2021
24
15
menlo park, CA
There is another thing you have to think about when you have a large solar array. If you don't owe money at true-up before you get Powerwalls, you aren't going to save anything with rate arbitrage because you don't owe anything. The only way you can get any arbitrage benefit is if you're on a CCA that pays for all surplus generation, like SVCE. However, I think Menlo Park is outside the SVCE territory.
Actually Menlo Park mandates the use of SVCE, a CCA. So that isn't the issue... See here: Peninsula Clean Energy | City of Menlo Park - Official Website, and I do owe a fair amount at true up time...
 
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