powerwall2 behavior when paired with solar

[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]

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.

[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.

[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.

[JSchnee21]

Well that seems completely asinine. One would think that it would charge from Solar preferentially but then be able to charge from the grid (or generator) when it cannot (or hadn't sufficiently) based on a schedule / heuristic for when power is cheap and the priority of the system -- e.g. load shifting vs. outage protection.

I guess if you live somewhere sunny where it's never cloudy, rainy, snowy, that might work,. But on the East coast, one would certainly get a lot more mileage from a nice 1800rpm, liquid cooled natural gas generator for the same price or less.

Realistically, even with 2 or 3 Powerwalls, you're unlikely to be able to run your HVAC for more than a few hours at 13.5kWh per unit. When Sandy hit, folks that were lucky enough to have natural gas generators ran for days/weeks on end. (while the rest of us tried to find gasoline).

[astroboy]

I don't see how that would even be possible, as they both connect to the same circuit. So I don't think this is a will thing, but a technical feasibility one



I am not sure what would be the value of that even if it had been possible. By doing that you would only get SGIP subsidy on the battery instead of both SGIP and 30% tax credit by adding it to Solar and setting it up to be used for TOU arbitrage.

i guess i don't have any idea what the powerwall looks like in the schematic of the power setup at my house. i had assumed everything was all in parallel - powerwall, solar and grid, with cutoff switches to make sure the powerwall does not feed into the grid when it is down. clearly even if you have solar the PW2 has to be able to draw power from the solar inverter and push power to the grid. are you saying that it is designed to be installed in series between the inverter and the grid?

anyway part of my cunning plan was to operate the PW2 in such a standalone manner for a year to do peak vs. off peak arbitrage, and at that point switch to solar charging (one way or another be it hardware or software) and then claim the ITC at that time. i had already given up on the SGIP since tesla themselves are fully subscribed, but over the last day it does seem that there are installers in the area that can still make claims though as i mentioned they seem to be on step 3 already. but clearly this scheme is a non-starter for a bunch of reasons, so as you say the best thing to do is just get all the subsidies and forget about putting the screws to PGE.

As I mentioned, I don't think you need to be concerned about that. Even when set to do TOU arbitrage (battery being used during peak hours), You can still set your battery reserve to a fairly large percentage and have plenty in case of an outage.
Remember that when connected to solar, you only need to have backup to last you one evening/night, as the next day you will be able to recharge the battery with solar. So with a 13.4 kWh battery, even if you only had it set with a 30% reserve, that would be 4kWh for one evening/night, which I think is plenty.

Using my Excel sheet, I checked how much battery is used in TOU arbitrage with various level of reserve (based on my hourly consumption and 8600kWh per year usage)
SGIP requires 52 full capacity cycle, or 697kWh used from the battery in a year.
If I set the battery usable capacity to only 15% (85% reserved for backup). I get a battery usage of 733 kWh for the year (more than required).
So that to me means you can really keep a very large backup capacity even in the TOU arbitrage mode required for SGIP

being a belt and suspenders (and tape and rope) kind of guy i wanted to plan for scenarios where we can back up for a couple days even if it is cloudy or there is wildfire smoke. if we do nothing at all (like while on vacation) the house burns about 10kwh per day, so a single powerwall is only good for ~1 day in the absence of the sun. but i agree that the SGIP requirements are very modest; i'd just like to be able to have 100% when i know i'm going to need it... when we are occupying the house we use closer to 24kwh per day. obviously we'd have to just turn a bunch of stuff off in the interest of keeping the refrigerator running.

anyway if the new fire rules are real i think the whole thing is dead for me. i can't install these things anywhere else but on the side of the garage and i'm not sure just one powerwall gets me where i want to be. we'll see.


edit: i will check out your spreadsheets. i had written a perl program that takes all my PVOutput data and simulates the different TOU rates but that software has no notion of storage. it will probably be easier to try your spreadsheets than hack all of that stuff in at this point.

[scrambler]

well the consensus on the tesla energy forum is that no installer would set up a PW2 as standalone if there was solar already on the premises.

I don't see how that would even be possible, as they both connect to the same circuit. So I don't think this is a will thing, but a technical feasibility one

what i wanted was standalone for a year and then solar past that point .

I am not sure what would be the value of that even if it had been possible. By doing that you would only get SGIP subsidy on the battery instead of both SGIP and 30% tax credit by adding it to Solar and setting it up to be used for TOU arbitrage.

i did hear about the storm mode and supposedly tesla did activate it before the PGE PSPS. what bothers me about that is that i'm relying on tesla to allow me to do this, rather than being able to just decide on my own.

As I mentioned, I don't think you need to be concerned about that. Even when set to do TOU arbitrage (battery being used during peak hours), You can still set your battery reserve to a fairly large percentage and have plenty in case of an outage.
Remember that when connected to solar, you only need to have backup to last you one evening/night, as the next day you will be able to recharge the battery with solar. So with a 13.4 kWh battery, even if you only had it set with a 30% reserve, that would be 4kWh for one evening/night, which I think is plenty.

Using my Excel sheet, I checked how much battery is used in TOU arbitrage with various level of reserve (based on my hourly consumption and 8600kWh per year usage)
SGIP requires 52 full capacity cycle, or 697kWh used from the battery in a year.
If I set the battery usable capacity to only 15% (85% reserved for backup). I get a battery usage of 733 kWh for the year (more than required).
So that to me means you can really keep a very large backup capacity even in the TOU arbitrage mode required for SGIP

[astroboy]

well the consensus on the tesla energy forum is that no installer would set up a PW2 as standalone if there was solar already on the premises. that seems to be the main problem. worse, what i wanted was standalone for a year and then solar past that point which is such a special case that i'm sure i could never get it to happen. heck, even the company that installed my panels on behalf of sunpower won't answer my calls/emails about installing batteries. if you call them when you want to spend money and they don't reply what are the odds they'll call you back when you want a favor?

i did hear about the storm mode and supposedly tesla did activate it before the PGE PSPS. what bothers me about that is that i'm relying on tesla to allow me to do this, rather than being able to just decide on my own.

IMO the easiest path is just to install the powerwalls and use them within the ITC/SGIP rules. however, i just read on the tesla energy forum that california has a new fire code for 2020 which effectively makes it impossible to mount more than one powerwall on your... wall. they want the batteries to be off by themselves on pedestals if > 20KWh of storage. that might kill the whole thing for me since i decided 2 powerwalls is the minimum to get me thru any prospective outages.

[scrambler]

I think you need to separate Powerwall with solar and standalone.

My understanding is that in a Standalone configuration you can get the SGIP subsidy if you set it up for load shifting (charge at Off Peak and use in part and peak). Even in that mode you can still set a reserve so You have enough battery backup during and outage. What PG&E requires is that you use at least 52 x Full battery capacity in that mode. This is easily achieved even with a decent reserve.
Also the power wall has a Storm option that will automatically override the above mode and keep the full capacity for backup.

If interested, I made an Excel sheet that allows to simulate the charge and discharge of the battery in that mode based on your own hourly consumption, and computes the dollar saved based on your TOU rates

https://www.solarpaneltalk.com/forum/solar-panel-talk-information/new-members-please-introduce-yourselves-here/401750-long-time-solar-owner-new-to-forum?p=405749#post405749

When used with solar, you cant charge from the grid if you want the Tax credit and SGIP, but the benefit to you are still the same, as the battery will be charging during solar hours, and be used during the peak hours (4 to 9 or so). So as a result, you end up not using peak hours electricity.
I have a similar version of the other Excel sheet to do NEW simulation that includes simulating the battery usage in that mode

https://www.solarpaneltalk.com/forum/solar/the-pros-and-cons-of-solar-energy/402317-net-metering-pg-e-vs-mce-in-california?p=402393#post402393

[astroboy]

PowerWalls have a mode called Time Based Control which is primarily a load shifting mode. They charge from the sun in the morning. Then they power the critical loads with solar duing the early peak and then use the battery to power the critical loads after the sun goes down. Is that what you would like to do?

With Self Generation Incentive Program incentives the payback in California can be fairly attractive. That would explain why reportedly over 50,000 have been sold. Others are clearly eyeing that market. Even Generac has a battery product to do that. That way they can offer a solution that can leverage existing grid tied solar and offer extended capability during a blackout.

I am also on EV-A and NEM 2. Are you on NEM 2?

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?

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

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.

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.

[Ampster]

........... but i realized that since i'll be on EV-A for another year, load shifting would offset the cost of the powerwalls quite a bit. however, it's sounding like this is impossible if there is solar on the premises.

PowerWalls have a mode called Time Based Control which is primarily a load shifting mode. They charge from the sun in the morning. Then they power the critical loads with solar duing the early peak and then use the battery to power the critical loads after the sun goes down. Is that what you would like to do?

With Self Generation Incentive Program incentives the payback in California can be fairly attractive. That would explain why reportedly over 50,000 have been sold. Others are clearly eyeing that market. Even Generac has a battery product to do that. That way they can offer a solution that can leverage existing grid tied solar and offer extended capability during a blackout.

I am also on EV-A and NEM 2. Are you on NEM 2?

[astroboy]

yeah those shutoffs are why i've been thinking about this again. really, for me, the purpose of powerwalls would be to have backup power, as only during the summer months do i overproduce power. but i realized that since i'll be on EV-A for another year, load shifting would offset the cost of the powerwalls quite a bit. however, it's sounding like this is impossible if there is solar on the premises.

[Ampster]

I remember reading somewhere that it could be changed after installation but you need to call Tesla to do it.

I have spent four years on the Tesla Forum and to date I have not heard of anyone who has been successful in having their PowerWall charge from the grid if they have solar. There is an exception, totally in the control of Tesla called Storm Watch. If they detect a future condition they can do an over the air exception for those areas that are affected and let them charge from the grid. That actually happened in California last week when PG&E and SCE announced they were going to turn of power to certain areas due to high winds that threatened to cause fires. That allowed those people to charge from the grid shortly before the announced power outages so they could enter the blackout with fully charged batteries.

Another more serious limitation to me is that when Powerwall is configured to charge from solar it also can't be charged from a generator.

Are there any circumstances that a Powerwall can be charged from a generator? To date I have not heard of any.

[astroboy]

I remember reading somewhere that it could be changed after installation but you need to call Tesla to do it.

Another more serious limitation to me is that when Powerwall is configured to charge from solar it also can't be charged from a generator.

right - i was looking at SMA's "island" inverters and at least according to their marketing material those inverters can handle a variety of generation types.

[solardreamer]

understood - what i was told is that if an installer is pairing the powerwall with solar they will set this option at install time and the user cannot undo it. that's what i'm trying to suss out.

I remember reading somewhere that it could be changed after installation but you need to call Tesla to do it.

Another more serious limitation to me is that when Powerwall is configured to charge from solar it also can't be charged from a generator.