Looking at ROI calcs for Powerwalls

[mikesm]

Hi. Given the new tax rules for standalone battery installation and continued PG&E price increases, I figured it would be good to look again at the math on whether or not installing powerwalls makes sense for us. We have a large house in the Menlo park area, and a fairly large solar array that over the last month generated about 73 KWh of energy a day (in august it was generating about 140 KWh a day, and last Jan about 50 KWh a day). But we are still net energy importers (we have a large house and salt water pool)- and at least the last few bills showed most of the usage was during partial and peak hour use under the EV-2a tariff (we have a hybrid Pacifica that only charges off-peak). The house is about 3 yrs old, and we wired it during construction to support a powerwall install in the garage, so install costs should be quite modest.

We also have a 30 KW diesel generator for backup power (I got a great deal on a new Kohler industrial unit and 400A transfer switch), so the backup power function of the powerwalls is pretty useless to me, esp since Tesla doesn't support generators in any kind of intelligent way). So the math is purely based on nulling out partial and peak hour usage with energy stored during the day. To cover the peak and partial peak demand, I would probably need 4 PWs of storage, and the solar generally can fill them pretty easily most days.

Is there a calculator that can feed in actual PG&E usage data for a year and have it grind out the savings for multiple configurations? I can go back and look at net peak and partial peak hour month by month from PGE bills,, but it would be nice if there was a spreadsheet that could do the calcs for me.

Given the policies being followed in CA, I figure electricity prices will only get higher for energy, so the math should get better in the future, I know PW's for non-solar installs are hard to come by, but if the math doesn't work there is no point in seeing about what it would take to get an installation.


thanks!

 

[getakey]

I downloaded my PG&E usage for a year. Then I adjusted all my Peak usage to Partial Peak. I could save ~$900/year. Pretty long ROI. That said, I'm on EV1-A and will soon switch to EV2-A. That will give me much more sun in Off Peak not Partial and the rate differential will be greater.

 

[jjrandorin]

Hi. Given the new tax rules for standalone battery installation and continued PG&E price increases, I figured it would be good to look again at the math on whether or not installing powerwalls makes sense for us. We have a large house in the Menlo park area, and a fairly large solar array that over the last month generated about 73 KWh of energy a day (in august it was generating about 140 KWh a day, and last Jan about 50 KWh a day). But we are still net energy importers (we have a large house and salt water pool)- and at least the last few bills showed most of the usage was during partial and peak hour use under the EV-2a tariff (we have a hybrid Pacifica that only charges off-peak). The house is about 3 yrs old, and we wired it during construction to support a powerwall install in the garage, so install costs should be quite modest.

We also have a 30 KW diesel generator for backup power (I got a great deal on a new Kohler industrial unit and 400A transfer switch), so the backup power function of the powerwalls is pretty useless to me, esp since Tesla doesn't support generators in any kind of intelligent way). So the math is purely based on nulling out partial and peak hour usage with energy stored during the day. To cover the peak and partial peak demand, I would probably need 4 PWs of storage, and the solar generally can fill them pretty easily most days.

Is there a calculator that can feed in actual PG&E usage data for a year and have it grind out the savings for multiple configurations? I can go back and look at net peak and partial peak hour month by month from PGE bills,, but it would be nice if there was a spreadsheet that could do the calcs for me.

Given the policies being followed in CA, I figure electricity prices will only get higher for energy, so the math should get better in the future, I know PW's for non-solar installs are hard to come by, but if the math doesn't work there is no point in seeing about what it would take to get an installation.


thanks!

I dont know if there is such a calculator or not, and I am not the most math minded person here. With that being said, powerwalls from third parties (the only way you would get them in that situation (are going to be probably 11-12k each, irregardless of your previously setup "easy setup".

Since you have a generator, and specify that the backup utility to you from powerwalls is zero, what you are really asking is:

"how much peak / off peak usage do I need to have, for it to equal out to 44-48k of electricity usage".

The solar doesnt factor into the equation since you already have it. I suspect that, even if you took your entire monthly electric bill, ignoring peak / off peak, just "what you pay monthly" and divided that by a round number of 45k for 4 powerwalls, you would have a quick guestimate of whether that works out for you or not. I expect it doesnt (work).

 

[schan1w]

$0.25 saved per kWh of peak/part peak that you shift X 13.5 kWh per PW = $3.375 saved per day per PW X 365 = $1232 saved per year per PW

you won't realize all of that due to losses and differences like winter rates, etc.

 

[mikesm]

$0.25 saved per kWh of peak/part peak that you shift X 13.5 kWh per PW = $3.375 saved per day per PW X 365 = $1232 saved per year per PW

you won't realize all of that due to losses and differences like winter rates, etc.

Thanks. That is an excellent way to get an upper bound on ROI. If it doesn't make sense in the best case, there is no point in looking at the more complicated math. So with 4 PW's it would be almost $5K a year is maximum savings. If you wanted a 5 yr payback, then the cost would need to be less than $25K. Still borderline in even the best case. Battery storage is still too expensive to make this a mass market approach to demand shifting, even with a rapacious utility like PG&E.

 

[Southpasfan]

$0.25 saved per kWh of peak/part peak that you shift X 13.5 kWh per PW = $3.375 saved per day per PW X 365 = $1232 saved per year per PW

you won't realize all of that due to losses and differences like winter rates, etc.

Another, more simple way to look at it is:

1. Without powerwalls your nighttime savings are at the mercy of the NEM policy of your utility. I have heard of some NEMs so poor that even with banked solar credits you still pay $0.25, which mis perhaps what shan1w is saying.

2. If so, you don't have to look at it in ROI measured in years, my three PW's financed cost is about $200 per month. They "save" about $300 per month.

Done.

 

[mikesm]

Another, more simple way to look at it is:

1. Without powerwalls your nighttime savings are at the mercy of the NEM policy of your utility. I have heard of some NEMs so poor that even with banked solar credits you still pay $0.25, which mis perhaps what shan1w is saying.

2. If so, you don't have to look at it in ROI measured in years, my three PW's financed cost is about $200 per month. They "save" about $300 per month.

Done.

I'm not sure I understand the point you are making. I pay (now winter rate) 0.42 a KWh in peak hour. Displacing that usage from peak to off-peak would save $0.43-0.25 or $0.18 a KWh. About 1/3 of my total use is in the peak hour. I am not a net generator of power in the offpeak time except during the summer, though I forget under NEM 2.0 what I am getting paid for that excess generation.

MY PGE bill is pretty high, but it's mostly due gas charges used to heat the 20x50 pool to the 80's, which the girls in the family demand.

 

[JakiChan]

By my math Powerwalls didn't really break even in 10 years. However, they did do other things:

• Maximizes consumption of local solar power. My system is a bit oversized.
• Protection against the occasional outage.
• Protection against the next "flex alert" event. My 2 Powerwalls should be able to keep my AC on from 4-9 (or 3-10 if it comes to that).

 

[h2ofun]

By my math Powerwalls didn't really break even in 10 years. However, they did do other things:

• Maximizes consumption of local solar power. My system is a bit oversized.
• Protection against the occasional outage.
• Protection against the next "flex alert" event. My 2 Powerwalls should be able to keep my AC on from 4-9 (or 3-10 if it comes to that).

and they cost TONS of money

 

[JakiChan]

and they cost TONS of money

Yes, they're probably a bit overpriced. If Span worked with a different battery platform I'd probably have gone that route but they don't as of yet so here we are...

 

[tfan2018]

With grid charging realistically I don't need more than one Powerwall, but two would have been nice so I could comfortably use AC and heating and also participate in the demand response programs which are highly lucrative right now.

 

[mikesm]

With grid charging realistically I don't need more than one Powerwall, but two would have been nice so I could comfortably use AC and heating and also participate in the demand response programs which are highly lucrative right now.

I'm not sure what you mean by highly lucrative. How does this change the basic economics of Powerwalls? Peak hour pricing is already high enough in PG&E land that I can effectively run the house on my diesel generator for less than the cost of PG&E on a $/KWh basis during summer prices.

 

[tfan2018]

I'm not sure what you mean by highly lucrative. How does this change the basic economics of Powerwalls? Peak hour pricing is already high enough in PG&E land that I can effectively run the house on my diesel generator for less than the cost of PG&E on a $/KWh basis during summer prices.

I earned nearly $1200 from Aug thru Oct thanks to Ohmconnect. I wouldn't have earned anything near that without my powerwall. If I had two powerwalls that amount would nearly be $2000. This earning potential won't last long, though. Ohmconnect previously devalued their program and they surely will again since their current rewards structure hasn't factored in the new functionalities we have with Powerwalls this year.

 

[jhn_]

I'm not sure what you mean by highly lucrative. How does this change the basic economics of Powerwalls? Peak hour pricing is already high enough in PG&E land that I can effectively run the house on my diesel generator for less than the cost of PG&E on a $/KWh basis during summer prices.

I participate in Tesla’s VPP demand response program here in New England. Our three Powerwalls earned us just under $2800 in direct payments in 2021 participating in this.
Utility incentives for solar installs with Powerwalls were at the time of our install $0.05 greater per kw of net solar generated. This earned us just under $800 in direct payments in 2021.

Compared to solar alone that had an ROI of just over 8 years, these additional cash flows mean that by spending more on the project to add 3 Powerwalls our ROI changed to just over 6 years. Plus we get all the other non-monetary benefits. Was a no brainer in our case.

 

[mikesm]

Interesting. How does one factor in these additional payments in planning? Sounds like at least Ohmconnect is changing the fee structure (downwards)? Those numbers are pretty material given the basic business case for load shifting.

 

[tfan2018]

With NEM 3.0 and beyond, it's going to be critical in the future to generate and use more of your own energy. It is advisable to get at least one powerwall to future proof, regardless of direct payments from these demand response programs (which only further help the payback).

 

[mikesm]

With NEM 3.0 and beyond, it's going to be critical in the future to generate and use more of your own energy. It is advisable to get at least one powerwall to future proof, regardless of direct payments from these demand response programs (which only further help the payback).

Ah yes, Sacramento is "owned" by PG&E and the rest. However even the most aggressive plan for NEM 3.0 I have seen would grandfather NEM 2.0 users for at least 10 yrs. So for me, who built a new house and have solar etc... already installed, I will likely not be affected by it for a long time.

Maybe in another 5-6 years we'll have a lot cheaper options for energy storage that Tesla is currently providing. Either way, I don't see how NEM 3.0 factors into this decision-making for people who have solar already.

 

[RKCRLR]

Ah yes, Sacramento is "owned" by PG&E and the rest. However even the most aggressive plan for NEM 3.0 I have seen would grandfather NEM 2.0 users for at least 10 yrs. So for me, who built a new house and have solar etc... already installed, I will likely not be affected by it for a long time.

Maybe in another 5-6 years we'll have a lot cheaper options for energy storage that Tesla is currently providing. Either way, I don't see how NEM 3.0 factors into this decision-making for people who have solar already.

Here's the problem with retroactively changing the grandfathering - it goes back to the first NEM install. In my case I initially installed solar in 2009 and then upgraded in 2019. If they retroactively change the NEM grandfathering to only 10 years then my upgrade may not have a positive ROI depending on what else is in NEM3.

 

[MattTGuy]

Hi. Given the new tax rules for standalone battery installation and continued PG&E price increases, I figured it would be good to look again at the math on whether or not installing powerwalls makes sense for us. We have a large house in the Menlo park area, and a fairly large solar array that over the last month generated about 73 KWh of energy a day (in august it was generating about 140 KWh a day, and last Jan about 50 KWh a day). But we are still net energy importers (we have a large house and salt water pool)- and at least the last few bills showed most of the usage was during partial and peak hour use under the EV-2a tariff (we have a hybrid Pacifica that only charges off-peak). The house is about 3 yrs old, and we wired it during construction to support a powerwall install in the garage, so install costs should be quite modest.

We also have a 30 KW diesel generator for backup power (I got a great deal on a new Kohler industrial unit and 400A transfer switch), so the backup power function of the powerwalls is pretty useless to me, esp since Tesla doesn't support generators in any kind of intelligent way). So the math is purely based on nulling out partial and peak hour usage with energy stored during the day. To cover the peak and partial peak demand, I would probably need 4 PWs of storage, and the solar generally can fill them pretty easily most days.

Is there a calculator that can feed in actual PG&E usage data for a year and have it grind out the savings for multiple configurations? I can go back and look at net peak and partial peak hour month by month from PGE bills,, but it would be nice if there was a spreadsheet that could do the calcs for me.

Given the policies being followed in CA, I figure electricity prices will only get higher for energy, so the math should get better in the future, I know PW's for non-solar installs are hard to come by, but if the math doesn't work there is no point in seeing about what it would take to get an installation.


thanks!

Thanks for this. I'm in the process of assessing my potential ROI. How many square feet of solar array do you have to 73Kwh? Is it made up of panels or solar roof tiles?

 

[ptdusn]

We have 2 powerwalls and right now they are charging to 100% by Noon/1 o'clock. SRP is on the winter schedule of 5-9am/pm being peak charging .10/Kw. Off peak is .08/Kw. So we are using ZERO from the grid and putting 4-5Kw BACK once the PWs charge. With their Mandatory Service fee of $32 our Nov bill was $32!! Where normally without the solar, we would have had a $85 bill.