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PW Only Charges from Solar?

Seattle Tom

Member
Mar 31, 2016
503
525
Seattle, WA
Hi, all.

I had a Powerwall and Solar install two weeks ago. It passed inspection last Tuesday (right after Labor Day) - yeah!

The utility hasn’t been out to install the second meter yet, so the solar is off. But we happened to have a large lightning storm in Seattle last weekend and I thought why not turn on the Powerwall so if the power goes out, I at least get some backup function.

So I flipped those breakers, the PW light turned solid green and appeared in my app with 24% charge. But it would not charge from the grid even when I set it to Backup Only at 100%. Over two days it dropped to 21% charge, so I turned it back off.

I called Tesla Energy Support and they said since the PW is designed to work with solar, it won’t turn on and charge from the grid. The rep said they could “force it” on to charge from the grid if it got dangerously low in charge (2% or so), but besides that it won’t.

Needless to say, this doesn’t seem right to me. Aren’t there some customers with ONLY a Powerwall? I’m almost sure I’ve seen pics on the “Power Flow” from others where the solar and grid are charging the PW and powering the house. Any advice on what I might be doing wrong from a setting perspective? Or is the Tesla Energy rep right? Thanks!
 

MorrisonHiker

S 100D 2021.4.12
Mar 8, 2015
9,404
8,548
Colorado
In the US, Powerwalls can normally only charge from solar if you have solar installed as well. If you don't have solar, then they can be charged from the grid.

If there is severe weather in your area and you have Storm Watch enabled, then the Powerwalls can temporarily (and automatically) be charged from the grid. Once the severe weather warning ends, the Powerwalls will go back and only charge from solar again.
 

Seattle Tom

Member
Mar 31, 2016
503
525
Seattle, WA
Thanks for the helpful reply, MorrisonHiker. Support was right and I was wrong, which is strange since I tell my wife I’m never wrong.

I’ll be patient and wait for solar to be activated. Thanks!
 

boaterva

Supporting Member
Apr 2, 2016
7,562
3,736
Northern Virginia, USA
Thanks for the helpful reply, MorrisonHiker. Support was right and I was wrong, which is strange since I tell my wife I’m never wrong.

I’ll be patient and wait for solar to be activated. Thanks!
The other problem is that Stormwatch doesn’t seem to appear immediately for new installations. If it had, and you had a Thunderstorm Warning, you would have charged automatically from the grid as @MorrisonHiker was discussing.

I had a time when my inverter was out of commission (waiting for Tesla to arrive to replace it) and the PWs were drifting down. One morning I woke up and noticed they were mostly charged again. Stormwatch to the rescue as we’d had a Thunderstorm Warning (and no rain) the night before.

The problem for new installs is that some features do not appear for a few days after install. I had Solar first then PWs so don’t know if you need your solar activated completely or not.
 

Ostrichsak

Active Member
Sep 6, 2018
3,254
3,201
Colorado, USA
In the US, Powerwalls can normally only charge from solar if you have solar installed as well. If you don't have solar, then they can be charged from the grid.

If there is severe weather in your area and you have Storm Watch enabled, then the Powerwalls can temporarily (and automatically) be charged from the grid. Once the severe weather warning ends, the Powerwalls will go back and only charge from solar again.

This is kind of crazy to me since they do it for safety. It would seem to me that in a severe enough storm to trigger this exception outages could be likely and emergent outages that require repair could create for a dangerous condition for those working upstream if they think the circuit is disconnected and shouldn't have power present. If Powerwalls are allowed to charge off of the grid this could energize circuits upstream that are thought to be disconnected.

In related news, I saw as part of the proposed new green deal or whatever they're calling it that part of the focus is on electrifying school buses. Part of the proposal would have them acting as stationary Powerwalls during the day able to supply power to the local grid in the event of some sort of an outage some maybe the plan is to address this very topic with some form of granularity rather than the existing hard black/white line. I could see this for maybe the school structure to avoid sending power upstream but the portion I read made it sound like they were proposing it could help with peaker plant production which would require more than just sending it to the immediate structures.
 

cwied

Member
Jan 13, 2015
867
616
San Mateo, CA
This is kind of crazy to me since they do it for safety. It would seem to me that in a severe enough storm to trigger this exception outages could be likely and emergent outages that require repair could create for a dangerous condition for those working upstream if they think the circuit is disconnected and shouldn't have power present. If Powerwalls are allowed to charge off of the grid this could energize circuits upstream that are thought to be disconnected.
I'm not sure I follow this argument. Charging from the grid should have nothing to do with energizing circuits upstream. In case of a power outage, the Powerwall Gateway will disconnect from the grid, preventing any kind of backfeed.
 
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gpez

Member
Apr 25, 2019
625
501
USA
@Seattle Tom hello Seattle neighbor!

I have solar + Powerwall, the latter was turned on back in April. Since PSE does full net metering my Powerwall install is exclusively for backup purposes (no ToU shifting). Interestingly enough my Powerwall did not activate Storm Watch on Saturday when we had those huge thunderstorms - I've got a bug open with Tesla to figure out why. If it didn't activate then I can't imagine when it possibly would due to weather out here!

The Powerwall is quite an incredible piece of tech as it can be set up and configured quite differently depending on laws, regulations, utility considerations, and power needs. By default the Powerwall charges exclusively from solar in the US due to an IRS tax ruling regarding the Solar Investment Tax Credit (ITC) back in 2018. I'm not a tax expert but my understanding comes from the excepted section below and my CPA agrees. This is something I discussed at length with my solar installer, Puget Sound Solar, as they were interested in understanding the nuances of how the system behaves. If you don't want the federal tax credit you can likely get Tesla to reconfigure your Powerwall so that it can charge from the grid.

One thing to know is that in this configuration the Powerwall can charge entirely from the solar while your home draws from the grid. A concern of mine was that if there were multiple small outages in a row that the Powerwall wouldn't be able to recharge properly if the net to the battery was the solar - house draw. Example here is that if your Powerwall needs to be charged while PV is producing 3kw and home is drawing 2kw the Powerwall will charge at 3kw and the utility will provide 2kw. That way the full solar amount is going to charge the Powerwall instead of the difference of 1kw (3kw solar - 2kw home draw).

Additionally what you noticed is that the Powerwall itself consumes about 300wh of it's own battery a day, or about 1.5% of the total capacity, that once your solar comes online you'll find a small draw from the PV to the Powerwall to top itself off. I see it every morning as soon as the sun comes up.

https://www.irs.gov/pub/irs-wd/201809003.pdf

"(…) all energy that is used to charge the Battery can be effectively assured to come from the Solar Energy System is essential for this ruling. Section 25D(d)(1) of the Code includes as a requirement in its definition of “qualified solar water heating property expenditure” that at least half of the energy used by such property for such purpose is derived from the sun. The definition of “qualified solar electric property expenditure” under § 25D(d)(2) omits this language. Thus, the Congress purposefully chose to include a 50 percent usage requirement in the definition of “qualified solar water heating property”, but the Congress did not include such language in the definition of “qualified solar electric property.” This demonstrates that the Congress expects the energy used by a “qualified solar electric property expenditure” to be derived solely from the sun. Accordingly, 100 percent of the energy used by the Battery must be derived from the sun. If this is not the case, the Battery does not meet the definition of “qualified solar electric property” in the Code."
 
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Cirrus MS100D

Supporting Member
Jul 6, 2017
681
2,039
Pennsylvania, USA
To add, I don't believe I've read about anybody in the USA being able to get Tesla to change the settings of the Powerwall to charge from the grid, even if they don't intend to claim the ITC. In other words, if you had a swimming pool full of cash, bought a 30kW system and 10 Powerwalls and told Tesla, "I'm not taking the ITC - let me charge my Powerwall from solar PV or the grid!" they will still say "No, sorry" as far as I know.

I'm curious about what they're going to do after the ITC is scheduled to sunset in 2 more years- will they automatically set all new installations to charge off of either? Will they allow systems installed during the ITC to eventually charge from the grid? Is there anything in the law that says they can "never ever ever" do that if they were once claimed under the ITC?
 
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miimura

Well-Known Member
Aug 21, 2013
6,071
5,650
Los Altos, CA
To add, I don't believe I've read about anybody in the USA being able to get Tesla to change the settings of the Powerwall to charge from the grid, even if they don't intend to claim the ITC. In other words, if you had a swimming pool full of cash, bought a 30kW system and 10 Powerwalls and told Tesla, "I'm not taking the ITC - let me charge my Powerwall from solar PV or the grid!" they will still say "No, sorry" as far as I know.

I'm curious about what they're going to do after the ITC is scheduled to sunset in 2 more years- will they automatically set all new installations to charge off of either? Will they allow systems installed during the ITC to eventually charge from the grid? Is there anything in the law that says they can "never ever ever" do that if they were once claimed under the ITC?
If you don't have solar, you can still buy a Powerwall and use it to offset Peak period usage and use it for backup in case of grid outage. It will charge from the grid because there is no other source.
 

gpez

Member
Apr 25, 2019
625
501
USA
To add, I don't believe I've read about anybody in the USA being able to get Tesla to change the settings of the Powerwall to charge from the grid, even if they don't intend to claim the ITC. In other words, if you had a swimming pool full of cash, bought a 30kW system and 10 Powerwalls and told Tesla, "I'm not taking the ITC - let me charge my Powerwall from solar PV or the grid!" they will still say "No, sorry" as far as I know.

I'm curious about what they're going to do after the ITC is scheduled to sunset in 2 more years- will they automatically set all new installations to charge off of either? Will they allow systems installed during the ITC to eventually charge from the grid? Is there anything in the law that says they can "never ever ever" do that if they were once claimed under the ITC?

Swimming pool full of cash would be great ($2.2b if it was $1 bills according to WolframAlpha)!

I haven't heard if Tesla actually allows US customers to charge from the grid, know it's doable in terms of Powerwall capabilities and potential configuration (as experienced with Storm Watch).

Your follow up question is a great one - no idea what the lookback period is (if there is one?). Will likely take another clarification letter from the IRS or a congressional act...
 
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Cirrus MS100D

Supporting Member
Jul 6, 2017
681
2,039
Pennsylvania, USA
If you don't have solar, you can still buy a Powerwall and use it to offset Peak period usage and use it for backup in case of grid outage. It will charge from the grid because there is no other source.
Oh absolutely and in some cases it could almost make financial sense, but as @gpez said, there’s not TECHNICAL reason why it can’t charge from the grid when paired with solar, they simply don’t allow it to happen in the USA unless Stormwatch gets enabled, and they control that. It’ll be very interesting to see what happens on 1/1/2022.
 

boaterva

Supporting Member
Apr 2, 2016
7,562
3,736
Northern Virginia, USA
Oh absolutely and in some cases it could almost make financial sense, but as @gpez said, there’s not TECHNICAL reason why it can’t charge from the grid when paired with solar, they simply don’t allow it to happen in the USA unless Stormwatch gets enabled, and they control that. It’ll be very interesting to see what happens on 1/1/2022.
You mean for new customers? All the old ones will have been assumed to have used the ITC and no change.
 

Cirrus MS100D

Supporting Member
Jul 6, 2017
681
2,039
Pennsylvania, USA
Yes, but one would presume at some point (5 years? 10 years? 20 years? 30 years?) one should be able to make an argument to the IRS that < some sufficient period of time > has passed such that the benefits of the original ITC have now sunsetted from a tax perspective and that owners of the system that were originally prevented from charging batteries from the grid should now be permitted to to do so.

Case in point, if you buy a PV + PW system today and claim the 30% ITC but then decide to add another PW to the system in 5 years, can you charge THAT one PW from the grid but not the originals?

This is as more a question for an accountant and the IRS I’m guessing.
 

Cirrus MS100D

Supporting Member
Jul 6, 2017
681
2,039
Pennsylvania, USA
The ITC "vests" over 5 years, so that is the time period during which the batteries much be charged only from solar.

Cheers, Wayne
Super helpful, thank you very much for this info! Is this buried in the law or tax code somewhere? I’ve spent admittedly little time trying to find the source, but I also don’t know where I’d even begin to look.
 

wwhitney

Member
Nov 2, 2017
765
919
Berkeley, CA
Super helpful, thank you very much for this info! Is this buried in the law or tax code somewhere? I’ve spent admittedly little time trying to find the source, but I also don’t know where I’d even begin to look.
IRS Form 3468 is where I believe businesses claim the solar ITC. The instructions to the form talk about recapture and the 5 year vesting period. Homeowners use IRS Form 5695 to claim the solar ITC, and I don't see anything in its instructions about recapture, but I assume the rules would be the same.

Cheers, Wayne
 
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