powerwall2 behavior when paired with solar

[astroboy]

well i suspect that tesla is configuring PW2 in this way in the presence of solar so that people don't run afoul of the rules for the ITC and SGIP. but who knows, maybe it is a hard limitation as scrambler suggests.

the weather situation for me is pretty reasonable. there are maybe 14 days out of the year that i need to run the AC. if the outage happened during those times i'd just suck it up. realistically these PGE outages will probably take place in the fall or the spring, and most likely in the fall. during that time there's generally no morning fog and although the sun is a bit lower, my system can generate around 75% of what it generates in the middle of the summer... so i can probably get by with 2 powerwalls.

[solardreamer]

...

since i'm interested in the PW2 primarily for backup power, and the incentives are targeted at self-generation and grid supplanting, my goals and the state's are kind of at odds. but it doesn't matter since tesla essentially forces you to operate the powerwalls in a mode that's aligned with what the state wants. so i might as well try to get the credits, although it does seem like the SGIP is getting harder and harder to claim. based on the SGIP spreadsheets it seems like the installers in my area might already be on step 3.

My understanding is that SGIP was specifically designed to discourage people getting batteries mainly for backup power usage. I think there is a requirement to cycle batteries regularly (almost daily?) and Tesla forces that on PW2 which probably shortens battery life. In general, PW2 seems too restrictive to me, it's kind of like having a condo vs a house. You can own a condo but only have limited control of it.

[Ampster]

well i suspect that tesla is configuring PW2 in this way in the presence of solar so that people don't run afoul of the rules for the ITC and SGIP. but who knows, maybe it is a hard limitation as scrambler suggests.

Tesla controls the configuration and as I mentioned earlier there is talk they may aggregate Powerwalls into some arrangement. They are already doing that in Vermont or somewhere on the east coast in conjunction with a utility.

the weather situation for me is pretty reasonable. there are maybe 14 days out of the year that i need to run the AC. if the outage happened during those times i'd just suck it up. realistically these PGE outages will probably take place in the fall or the spring, and most likely in the fall. during that time there's generally no morning fog and although the sun is a bit lower, my system can generate around 75% of what it generates in the middle of the summer... so i can probably get by with 2 powerwalls.

I did have two Powerwalls on order but eventually cancelled them in order to buy a hybrid inverter. My logic was that I wanted greater flexibility to scale up more economically. The Powerwalls are limited to 30 Amps and my hybrid can handle 60 Amps. However my normal loads to my critical loads panel are normally not more than 25 Amps. More importantly if I wanted to add more kWhr capacity with a Powerwall I would have to buy another Powerwall but at least you save on the gateway. With a hybrid inverter you can just add batteries for more capacity. I like to DIY and I did not need a turnkey solution.

[Ampster]

For some reason an earlier draft of this response was flagged as potential spam so I am reposting it since I could not tell what the spam flag was based on.

i am on NEM-1 - PTO in november 2015. which is why it looks like i only have until november 2020 to stay on EV-A. EV2-A, at least according to my scripts, will take my yearly bill from +/- $200 to +$1200 per year. E-TOU-B would bring me to like $800 per year and E-TOU-A like $900 per year. as far as i can tell NEM-2 is pretty much the same as NEM-1 except that they get to charge you a one-time $150 interconnection fee... does that sound right to you?

Yes, the only thing I would add is that NEM 2 also includes Non Bypassable charges. That tips the scales a little more in favor of a Powerwall because you can save on those by not using grid power as much. The NBCs only amount to $0.03 per kWhr but depending on your timing of consumption it could shorten the payback slightly.

also from reading around it sounds like installing powerwalls would let them force me onto NEM-2.

I think that is true if you get SGIP money. You do not have to get PG & E permission to install a load shifting inverter as long as it does not sell back to the grid. To be clear, you need a building permit but when I talked to the County building department about my hybrid inverter they were more concerned about me putting a NEMA enclosure around my Nissan Leaf batteries. I looked and could not find anything on PG & E's website or in my PTO that suggested that I needed their permission to install generating capacity behind the meter. I am using the term generating capacity literally, to be consistent with how PG&E describes the use of inverters to deliver power.

my idea was actually more radical than just the peak/partial-peak load shifting. because i didn't do enough reading at the tesla forum, i thought that i would be able to do off-peak to peak load shifting with the powerwall, at least for this last year while there's a 30 cent spread between the two on EV-A. however, 1) PGE explicitly forbids this and only lets you export as much energy as your solar plant would make, 2) tesla won't let you charge the PW2 from the grid, and 3) you can't claim the federal ITC (and certainly not the SGIP rebate) if you are charging from the grid. with some creative accounting i thought maybe i could claim the 26% ITC in 2020 but that might have been a stretch.

but it turns out what you describe here is the only option - to load shift between peak and partial peak. i guess i'd have to model how this would really work money-wise. i suppose as long as the powerwall lets you keep exporting energy at peak it could still pay off (especially if you are running your house from the partial-peak power stored in the battery and exporting all the solar during peak) but the deltas would seem to be pretty incremental. even if the PW2 cost is reduced by the state and federal incentives it will still take a very long time to pay for itself thru load-shifting.

Yes, as far as the powerwall is concerned there is only that option. However, if you don't need the ITC, you could buy a hybrid inverter, charge it off peak at $0.15 and offset your loads during peak. That differential is attractive in the summer when there is a $0.35 differential between off peak and on peak. Less so in the winter or during mid peak. You also have to account for inverter and charging losses and long term cost of batteries. If you buy a bimodal/hybrid inverter that is capable of AC coupling then you can leverage your existing grid tie solar. In many cases you don't need to buy solar panels to run many hybrid inverters.

since i'm interested in the PW2 primarily for backup power, and the incentives are targeted at self-generation and grid supplanting, my goals and the state's are kind of at odds. but it doesn't matter since tesla essentially forces you to operate the powerwalls in a mode that's aligned with what the state wants. so i might as well try to get the credits, although it does seem like the SGIP is getting harder and harder to claim. based on the SGIP spreadsheets it seems like the installers in my area might already be on step 3

The State's goals have resulted in so much solar that the Independent System Operator is actually curtailing some large renewable energy generation during the morning when solar ramps up. If this eventually results in some pricing mechanism that encourages people to put load on the grid when renewables are being curtailed then it might be a different ballgame. There is some talk of Tesla selling aggregate load (Powerwalls charging from the grid) in some scheme to reduce curtailment of renewables. That would be consistent with the State's goals. This is all pie in the sky talk but to me the key is to build a system that is flexible.

[Ampster]

i am on NEM-1 - PTO in november 2015. which is why it looks like i only have until november 2020 to stay on EV-A. EV2-A, at least according to my scripts, will take my yearly bill from +/- $200 to +$1200 per year. E-TOU-B would bring me to like $800 per year and E-TOU-A like $900 per year. as far as i can tell NEM-2 is pretty much the same as NEM-1 except that they get to charge you a one-time $150 interconnection fee... does that sound right to you?

Yes, the only thing I would add is that NEM 2 also includes Non Bypassable charges. That tips the scales a little more in favor of a Powerwall because you can save on those by not using grid power as much. The NBCs only amount to $0.03 per kWhr but depending on your timing of consumption it could shorten the payback slightly.

also from reading around it sounds like installing powerwalls would let them force me onto NEM-2.

I don't think that is true because a person I have known seven years is still on NEM 1 and he got a Powerwall with SGIP money. He has a very restrictive generating limit in his SGIP agreement.

my idea was actually more radical than just the peak/partial-peak load shifting. because i didn't do enough reading at the tesla forum, i thought that i would be able to do off-peak to peak load shifting with the powerwall, at least for this last year while there's a 30 cent spread between the two on EV-A. however, 1) PGE explicitly forbids this and only lets you export as much energy as your solar plant would make, 2) tesla won't let you charge the PW2 from the grid, and 3) you can't claim the federal ITC (and certainly not the SGIP rebate) if you are charging from the grid. with some creative accounting i thought maybe i could claim the 26% ITC in 2020 but that might have been a stretch.

but it turns out what you describe here is the only option - to load shift between peak and partial peak. i guess i'd have to model how this would really work money-wise. i suppose as long as the powerwall lets you keep exporting energy at peak it could still pay off (especially if you are running your house from the partial-peak power stored in the battery and exporting all the solar during peak) but the deltas would seem to be pretty incremental. even if the PW2 cost is reduced by the state and federal incentives it will still take a very long time to pay for itself thru load-shifting.

Yes, as far as the powerwall is concerned there is only that option. However, if you don't need the ITC, you could buy a hybrid inverter, charge it off peak at $0.15 and offset your loads during peak. That differential is attractive in the summer when there is a $0.35 differential between off peak and on peak. Less so in the winter or during mid peak. You also have to account for inverter and charging losses and long term cost of batteries. If you buy a bimodal/hybrid inverter that is capable of AC coupling then you can leverage your existing grid tie solar. In many cases you don't need to buy solar panels to run many hybrid inverters.

since i'm interested in the PW2 primarily for backup power, and the incentives are targeted at self-generation and grid supplanting, my goals and the state's are kind of at odds. but it doesn't matter since tesla essentially forces you to operate the powerwalls in a mode that's aligned with what the state wants. so i might as well try to get the credits, although it does seem like the SGIP is getting harder and harder to claim. based on the SGIP spreadsheets it seems like the installers in my area might already be on step 3

The State's goals have resulted in so much solar that the Independent System Operator is actually curtailing some large renewable energy generation during the morning when solar ramps up. If this eventually results in some pricing mechanism that encourages people to put load on the grid when renewables are being curtailed then it might be a different ballgame. There is some talk of Tesla selling aggregate load (Powerwalls charging from the grid) in some scheme to reduce curtailment of renewables. That would be consistent with the State's goals. This is all pie in the sky talk but to me the key is to build a system that is flexible.

[astroboy]

My understanding is that SGIP was specifically designed to discourage people getting batteries mainly for backup power usage. I think there is a requirement to cycle batteries regularly (almost daily?) and Tesla forces that on PW2 which probably shortens battery life. In general, PW2 seems too restrictive to me, it's kind of like having a condo vs a house. You can own a condo but only have limited control of it.

it's not so terrible though - i think they want you to push your full battery capacity back to the grid 52 times per year... so that's the equivalent of one full cycle per week.

it's true that you have limited control; i don't like that but on the other hand it's a fully turnkey solution.

[ButchDeal]

i think they want you to push your full battery capacity back to the grid 52 times per year...

The battery power should NEVER be pushed to the grid. What the incentives and rules are designed to do is get owners to cycle the battery for the homes use, thus avoiding grid use.

[Ampster]

it's not so terrible though - i think they want you to push your full battery capacity back to the grid 52 times per year... so that's the equivalent of one full cycle per week.
..........

Butch is correct, I think the regulation says that the battery from must be charged 75% of the time from solar.

[astroboy]

ok i misunderstood but regardless they are only saying you need to discharge the equivalent of a full battery approx once per week. my point being that the rest of the time if you want to keep the energy as backup, you can do that.

however at least on some TOU plans it does make sense to charge the battery during partial peak times and then self-consume during peak times so that you can export 100% of your solar to the grid. i don't know if in my case that would be more or less than the requirement for SGIP, i have not run the numbers for my own system.

a bigger problem for me seems to be that i can't find anyone to install one of these. one of the bigger companies in the bay area just shined me on and the company that installed my solar has not gotten back to me. probably nobody needs any new business. and if these new fire code rules are real, i won't be able to install more than 1 powerwall in 2020.

[scrambler]

Remember the Powerwall has two modes dedicated to be as smart as possible in maximizing this.

Advanced Time based Control Balanced, and Advanced Time Based Control Cost saving

https://www.tesla.com/en_AU/support/energy/powerwall/mobile-app/modes-of-operationwithsolar

I think you can trust them to manage the system for your lower cost of operation while meeting SGIP requirement

[scrambler]

a bigger problem for me seems to be that i can't find anyone to install one of these. one of the bigger companies in the bay area just shined me on and the company that installed my solar has not gotten back to me. probably nobody needs any new business. and if these new fire code rules are real, i won't be able to install more than 1 powerwall in 2020.

I think the last batch of Programmed outages from PG&E is not helping with that.
Solar installers in the Bay Area have a history of skimming the market, and this is not going to help...

[astroboy]

admittedly i am one of these people - i have been thinking about this for a long time but the PSPS made me revisit the idea. at least back in 2015 i had at least 3-4 companies that were interested in installing panels on my house but 4 years ago is a lifetime around here.

[astroboy]

well, i pulled the trigger. decided not to gamble on SGIP and just go tesla direct. fully anticipating them telling me i can only have 1 powerwall since the install will almost certainly take place in 2020.

[Ampster]

well, i pulled the trigger. decided not to gamble on SGIP and just go tesla direct. fully anticipating them telling me i can only have 1 powerwall since the install will almost certainly take place in 2020.

Do you think that is an inventory restriction on Tesla's part? From what I understand of the pricing is the first one includes the gateway which is not needed for a second PowerWall. Is that your understanding?

[astroboy]

yes i believe one gateway can serve multiple powerwalls, so that is OK. from what i've read at the tesla forums, the state of california has new fire codes for 2020 which state that you may not hang more than 20kwh of battery on your house - instead the batteries need to be on pedestals some distance from the house. there's at least one person in san francisco for whom the city has decided to enforce this early, and they won't sign off on the final inspection even though the install (2 powerwalls) is complete and it's still 2019.

tesla are asking around $18k for two powerwalls, while 3rd parties are in the $21-23k range. they're just marking up the price by the anticipated SGIP rebate, even though everyone is on the waitlist right now until sometime mid-2020 when the state is expected to replenish the funding. regardless, tesla has already reached their 'developer cap' so they can not apply for SGIP funds even if the money was available.