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Tesla Solar Design Feedback

sojglenn

New Member
Mar 8, 2021
2
0
San Francisco Bay Area
I live in the south bay area of CA and have been working with Tesla on a proposal for Solar + 2 Powerwalls. Tesla originally spec'd an 8.16 kW + 2 PW system based on my electrical usage. After the home assessment, based on the details of my roof, they can only install a 6.12 kW system + 2 PW's and they now don't project that I will break even over a 20 year period. There are also significant limitations on the placement of the powerwalls and they have determined that the only viable location is on the back of our house (adjacent to our very small back yard) which isn't the greatest. The panels would certainly be a hedge against rising electric rates and the PW's would give me protection against power outages, but the thing no longer seems like a slam dunk.

I know this is a judgement call, but looking for opinions from others who have gone through a similar thought process.
 

h2ofun

Active Member
Aug 11, 2020
1,551
249
auburn, ca
I live in the south bay area of CA and have been working with Tesla on a proposal for Solar + 2 Powerwalls. Tesla originally spec'd an 8.16 kW + 2 PW system based on my electrical usage. After the home assessment, based on the details of my roof, they can only install a 6.12 kW system + 2 PW's and they now don't project that I will break even over a 20 year period. There are also significant limitations on the placement of the powerwalls and they have determined that the only viable location is on the back of our house (adjacent to our very small back yard) which isn't the greatest. The panels would certainly be a hedge against rising electric rates and the PW's would give me protection against power outages, but the thing no longer seems like a slam dunk.

I know this is a judgement call, but looking for opinions from others who have gone through a similar thought process.
how many other investments do you make that will not break even over 20 plus years. I did not get my PV and PW's based on ROI. I did from emotion and I cannot take the money with me.
 

getakey

Active Member
Jan 28, 2020
1,038
329
95762
IMO, you should separate the Solar from PWs for ROI. Solar alone should have a decent ROI depending on your rate plan. For me, I wasn't looking for ROI from the PWs. The main function I want them for is backup. If there is some ROI from rate arbitrage, that is icing on the cake.
 

arnolddeleon

Supporting Member
Jul 21, 2012
683
767
SF Bay Area
Know what your goals (and it likely is plural) are. Save money? Cool tech? Backup power? Green energy/save the planet? "stick it to the man?" Make yourself happy?

Solar is dramatically cheaper on day one than any off peak rate that a consumer can get in PG&E land.

4 kW solar + 1 Powerwall is cheaper the off peak rates as well. This assigns no value to time shifting or moving/consuming the solar production to offset a higher rate.

Do you "need" that second Powerwall?

Assumption: You can get decent financing.
 
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holeydonut

Supporting Member
Jun 27, 2020
979
587
East Bay NorCal
I'll chime in here with the same message I've posted in other threads about ROI in NorCal...

With PG&E's gaming of TOU rates and obvious initiatives to push people to behavior modify, PV+ESS pay for themselves in a way that is not monetary.

Here's a flier about how you can do your part as a California resident to help make sure you don't use energy during peak time under a time of use rate plan. Yes, they actually advise you to start treating your family to meals that do not require your stove.

It looks like everyone in California will be steered to a TOU rate plan soon even if they don't have solar. And the rate differential between peak and off-peak will continue to climb (especially for people who are paying normal rates instead of the CARE/FERA rate).

If you get PV + ESS you can ignore propaganda and manipulation from PG&E. Maybe you'll still want to charge your car with off-peak energy; but other than that you can just do whatever you want when you want. As others have said, life's too short. Buy back a good quality of life and stick it to your neighborhood power company with some solar & batteries.
 

bevo

Member
Mar 10, 2021
35
14
Irvine
In my case, ROI for powerwall simply doesn't exist. Currently, my solar makes more energy than I can use so TOU additional charges doesn't apply as my $ balance will still be negative after 12 months. Secondly, saving on NBC doesn't exist with powerwall as there's a ~$10 monthly fee anyways. So there's little to no savings to be had by installing powerwall for me.
So powerwall would then only be used as insurance against power outage. However, I've only had 1 instance of no power over the last 1-2 years and that's when my power was turned off to install solar, ironically. And I can't recall a time in which a power outage was long enough to be more than a minor inconvenience. Of course having said that, we'll be hit by an earthquake and not have power for a week.
May still get a powerwall in the future, but it won't be because of any ROI calculation.
 
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tfan2018

Member
Apr 14, 2018
71
20
USA
I think if you oversized your solar panels, powerwall ROI isn't really possible. It's when solar is undersized slightly then you can arbitrage the TOU rates with PW. Do I have it right?
 
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holeydonut

Supporting Member
Jun 27, 2020
979
587
East Bay NorCal
I think if you oversized your solar panels, powerwall ROI isn't really possible. It's when solar is undersized slightly then you can arbitrage the TOU rates with PW. Do I have it right?


Technically, if you are on any TOU rate plan, you're still exposed to the TOU rate differential.

When you use your own solar energy, that's all fine and good. But when you bank energy to the grid, you're probably doing so at off-peak and shoulder rates. Peak rates kick in when solar production is waning to non-existent, so you'll be taking energy from the grid at this time.

Even if you perfectly sized your solar system to your annual usage, if you use a skewed amount during peak time then you'll have a net deficit. That energy you take from PG&E during peak (no sunlight) costs more than what you earned when banking earlier in the day.

There's a reason people want 1:1 net metering (what you bank is what you use). But instead we keep seeing the CPUC allow the solar-benefit to be eroded through the applciation of TOU.

Absolute worst case is if you perfectly sized your solar system, then added an EV. Now it'll be a struggle to get PG&E to let you add more solar, and you'll probably be on EV2A which has very aggressively skewed TOU rates.
 

tfan2018

Member
Apr 14, 2018
71
20
USA
Technically, if you are on any TOU rate plan, you're still exposed to the TOU rate differential.

When you use your own solar energy, that's all fine and good. But when you bank energy to the grid, you're probably doing so at off-peak and shoulder rates. Peak rates kick in when solar production is waning to non-existent, so you'll be taking energy from the grid at this time.

Even if you perfectly sized your solar system to your annual usage, if you use a skewed amount during peak time then you'll have a net deficit. That energy you take from PG&E during peak (no sunlight) costs more than what you earned when banking earlier in the day.

There's a reason people want 1:1 net metering (what you bank is what you use). But instead we keep seeing the CPUC allow the solar-benefit to be eroded through the applciation of TOU.

Absolute worst case is if you perfectly sized your solar system, then added an EV. Now it'll be a struggle to get PG&E to let you add more solar, and you'll probably be on EV2A which has very aggressively skewed TOU rates.

Would EV2A be the preferred rate plan rather than TOU-C if powerwall fully covers peak usage, since off peak is lower with EV2A and there is bigger arbitrage due to higher off-peak vs on-peak price difference? It seems I would either have to choose TOU-C or EV2A unless I choose to install a second meter for EVB
 

h2ofun

Active Member
Aug 11, 2020
1,551
249
auburn, ca
Technically, if you are on any TOU rate plan, you're still exposed to the TOU rate differential.

When you use your own solar energy, that's all fine and good. But when you bank energy to the grid, you're probably doing so at off-peak and shoulder rates. Peak rates kick in when solar production is waning to non-existent, so you'll be taking energy from the grid at this time.

Even if you perfectly sized your solar system to your annual usage, if you use a skewed amount during peak time then you'll have a net deficit. That energy you take from PG&E during peak (no sunlight) costs more than what you earned when banking earlier in the day.

There's a reason people want 1:1 net metering (what you bank is what you use). But instead we keep seeing the CPUC allow the solar-benefit to be eroded through the applciation of TOU.

Absolute worst case is if you perfectly sized your solar system, then added an EV. Now it'll be a struggle to get PG&E to let you add more solar, and you'll probably be on EV2A which has very aggressively skewed TOU rates.
I would have been better to have just have PV, no EV, and no PW. Then I would be allowed to stay on TOU-c. I would make more solar than could use, and the peak vs non peak is trivial. So, you are not forced on ev2-a with PV only
 
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h2ofun

Active Member
Aug 11, 2020
1,551
249
auburn, ca
Would EV2A be the preferred rate plan rather than TOU-C if powerwall fully covers peak usage, since off peak is lower with EV2A and there is bigger arbitrage due to higher off-peak vs on-peak price difference? It seems I would either have to choose TOU-C or EV2A unless I choose to install a second meter for EVB
Unless you are forced to ev2-a I would stay on tou-c
 

tfan2018

Member
Apr 14, 2018
71
20
USA
I would have been better to have just have PV, no EV, and no PW. Then I would be allowed to stay on TOU-c. I would make more solar than could use, and the peak vs non peak is trivial. So, you are not forced on ev2-a with PV only

Does PG&E force customers onto EV-2A depending on certain criteria? I was under the assumption that if you have an EV, then it would be an option to go to EV-2A, but not mandatory. Does having powerwall also cause PG&E to force you on a specific TOU plan?
 

h2ofun

Active Member
Aug 11, 2020
1,551
249
auburn, ca
In case scenario would PG&E force a customer to got o EV2-A? Also, are you suggesting TOU-C is better due to minimal price difference between on and off peak for that rate plan?
EV I believe for ev2-a. I know some PW's will, may only by if SGIP was involved. But why hassle the peak vs non peak 3 time difference of EV2-a. Now, if one has gas heat, not as big of a deal. But I have electric heat, and with very little winter PV production, the batteries will not be worth much. So unless I bank TONS of solar in the summer, I maybe killed with costs in winter I cannot get back. Now if you want to try and play the game, which some do, great, but it is a hassle for little return IMO if you can stay on TOU-c
 

holeydonut

Supporting Member
Jun 27, 2020
979
587
East Bay NorCal
Yeah, EV2A only makes sense if you have an EV that you drive a ton... or battery to charge using off-peak power.

Like if you get Powerwalls without solar they put you on EV2-A if you get SGIP money. Actually I wonder if H2ofun will be allowed to stay on TOU-C...

I think PG&E's 110% of prior year consumption rule is bogus. It basically requires you to spend money with them to prove you have demand, then you can build some solar. But you can't start building an oversized array in anticipation of future use.
 

holeydonut

Supporting Member
Jun 27, 2020
979
587
East Bay NorCal
I just saw this link about an initiative in Australia to penalize homeowners who get solar without batteries because they want to make solar-only (no batteries) customers face a penalty for exporting solar to the grid. While I don't see this coming to California; the PoCos have repeatedly said they want solar customers to "pay" for the burden on the grid due to rooftop resi solar. So expect some sneaky shenanigans to persist even beyond what NEM 3.0 rules allow.

For Australia, It sounds like the excess solar has required Australia's PoCos to enhance their infrastructure to deal with the inrush of solar energy at certain times of the day. And they picked a rather obvious/overt tactic to make the solar customers pay instead of having the 80% non-solar folks pay.


While I still think the ROI on a monetary basis for batteries would be a tough sell... but think of the lower stress and general apathy you'll have toward your corrupt CPUC and corrupt PoCos in the long run is worth some $.

Can you imagine solar customers having to flip their big blade disconnect to the off position during a sunny day to avoid fines? hehe disconnects.
 
Last edited:

charlesj

Active Member
Oct 22, 2019
1,052
218
Monterey, CA
I live in the south bay area of CA and have been working with Tesla on a proposal for Solar + 2 Powerwalls. Tesla originally spec'd an 8.16 kW + 2 PW system based on my electrical usage. After the home assessment, based on the details of my roof, they can only install a 6.12 kW system + 2 PW's and they now don't project that I will break even over a 20 year period. There are also significant limitations on the placement of the powerwalls and they have determined that the only viable location is on the back of our house (adjacent to our very small back yard) which isn't the greatest. The panels would certainly be a hedge against rising electric rates and the PW's would give me protection against power outages, but the thing no longer seems like a slam dunk.

I know this is a judgement call, but looking for opinions from others who have gone through a similar thought process.
If you do decide to go with that smaller inverter, ask Tesla to give you a 1.5 ratio of Dc to AC ratio. You will generate max power over a mush longer timespan.
 

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