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arbitrage with power wall

Olle

Member
Jul 17, 2013
783
402
Orlando, FL
I'm sure this question has been answered many times but I can't find it; for those of you with Power Walls and time of use rate like in this picture, can you buy at the super off peak and sell at peak? Sounds too good to be true is there a catch?
upload_2019-6-14_8-5-1.png
upload_2019-6-14_8-5-1.png
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
If you have Powerwalls without solar, that could be possible. If you have solar and Powerwalls in the US, you can't charge them from the grid unless Stormwatch has been activated.
 

cwied

Member
Jan 13, 2015
867
616
San Mateo, CA
To give additional background: the reason for this restriction is that the Federal tax credit requires storage systems to be charged only from solar. There is a five year vesting period on the tax credit, so my speculation is that this restriction will be lifted when that period passes.
 
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gpez

Member
Apr 25, 2019
632
507
USA
As someone who has solar and is taking the credit on my Powerwall I have not tried but I believe you can ask Tesla to change your setting. Of course doing so would make you ineligible for the credit.

All of that said can you actually sell stored energy? As in does the Powerwall support that scenario?
 

cwied

Member
Jan 13, 2015
867
616
San Mateo, CA
All of that said can you actually sell stored energy? As in does the Powerwall support that scenario?

Given the virtual power plant installations in Vermont and Australia, I'm sure it's possible to do it. Whether Powerwalls that aren't part of one of these aggregated systems can do it is not clear to me. I also haven't heard of anyone being successful at getting Tesla to allow grid charging in the US when a solar system is on site. My impression is that this is not something they allow.
 

ez123

Member
May 19, 2019
21
1
San Diego
As someone who has solar and is taking the credit on my Powerwall I have not tried but I believe you can ask Tesla to change your setting. Of course doing so would make you ineligible for the credit.

All of that said can you actually sell stored energy? As in does the Powerwall support that scenario?

My non-Tesla installer asked Tesla to enable grid-charging so that we could test my new Powerwall, since it was overcast at the time, but grid-charging was activated for only a few hours. I still intend to take the federal tax credit!
 

NuShrike

Member
Nov 13, 2017
459
193
SoCal
I'm sure this question has been answered many times but I can't find it; for those of you with Power Walls and time of use rate like in this picture, can you buy at the super off peak and sell at peak? Sounds too good to be true is there a catch?
View attachment 419171View attachment 419171
NO.
* at no point can you sell power sourced solely from your battery (in the USA) unless you have some form of export-agreement. With solar, most places limit your "export" to the amount your solar-panels would have exported daily.
* Tesla strictly blocks sending into the grid. There is some leakage of 30w, but over an hour, it evens out to zero.
 

Olle

Member
Jul 17, 2013
783
402
Orlando, FL
NO.
* at no point can you sell power sourced solely from your battery (in the USA) unless you have some form of export-agreement. With solar, most places limit your "export" to the amount your solar-panels would have exported daily.
* Tesla strictly blocks sending into the grid. There is some leakage of 30w, but over an hour, it evens out to zero.
Got it. But if you have a solar system larger than your consumption, can you charge up your power walls during the day and sell all the energy you won't need for the night at peak rate 4-9 pm? At 53c/kWh should be very profitable, no?
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
Got it. But if you have a solar system larger than your consumption, can you charge up your power walls during the day and sell all the energy you won't need for the night at peak rate 4-9 pm? At 53c/kWh should be very profitable, no?
Yes, that's one of the big selling points of the Powerwall. We have TOU and have virtually zero peak usage and very little part-peak usage. Nearly all of our grid usage is off-peak. We send all peak production back to the grid.

In our case, our utility doesn't pay us peak rates for energy produced so we chose to get credits instead. That offsets our off-peak grid usage at the peak and part-peak rates. These credits will be used to cover our electric usage in the winter months.
 
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cwied

Member
Jan 13, 2015
867
616
San Mateo, CA
Got it. But if you have a solar system larger than your consumption, can you charge up your power walls during the day and sell all the energy you won't need for the night at peak rate 4-9 pm? At 53c/kWh should be very profitable, no?
Actually, the answer right now is no, if my Powerwalls are representative of the US programming. The Powerwalls will never export into the grid. They will only offset house load. However, they do allow all solar to be exported during peak hours, rather than losing the amount you're using. The amount you can arbitrage currently only is the amount you usually use during peak hours.
 

NuShrike

Member
Nov 13, 2017
459
193
SoCal
Got it. But if you have a solar system larger than your consumption, can you charge up your power walls during the day and sell all the energy you won't need for the night at peak rate 4-9 pm? At 53c/kWh should be very profitable, no?
YES (with nuance)
The "peak-time" PW setting in TBC forces the battery to cover all home-power usage. That of course shunts all excess, or 100%) of solar to the grid, by the math.

However, the Utility stacked this as the 4-9pm TOU period is not a great period for solar, and you still can't technically sell any of your battery-stored power. As previously said, if the Utility audits (as PG&E seems to), your grid output is limited to what solar values THEY estimate you would've pushed out.

If you're in the grandfathered 2-8pm TOU, it's a much better deal.
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
I think I misspoke when answering @Olle earlier...but basically you charge up your Powerwalls during cheap periods and then power your house with the Powerwalls. You can then send all your solar production back to the grid during more expensive periods.

You can modify the Price Schedule (TOU periods) used by the Powerwalls so that you are powering your hour house whatever hours you like...and therefore sending excess solar production back to the grid.

Where I live, peak period is 2 pm until 6 pm. During that time, my house only uses about 4 to 6 kWh of stored energy but my system can export 50+ kWh back to the grid during that same period.
 

gnumeric

Member
Apr 17, 2018
87
64
Bay Area, California
Got it. But if you have a solar system larger than your consumption, can you charge up your power walls during the day and sell all the energy you won't need for the night at peak rate 4-9 pm? At 53c/kWh should be very profitable, no?

You can't directly export from Powerwall --> Grid, but the time-based-control setting lets you effectively do something similar.

During off-peak and partial-peak (if needed), your powerwalls will get charged from solar while powering your home from the grid.
During peak, your home gets fully powered from your powerwalls while ALL solar production is exported to the grid for maximum credits.

This is great when there is a big difference between peak and off-peak prices. For me, it's $0.49/kWh peak and $0.13/kWh off-peak. So even though my solar system is undersized relative to my usage, I can still be net negative on my NEM charges. It's been great to see my usage breakdown since getting Powerwalls.

Last month's breakdown
Peak usage: -273 kWh
Partial peak usage: -100 kWh
Off-peak usage: 573 kWh
Total NEM charges: $-23.70
 

NuShrike

Member
Nov 13, 2017
459
193
SoCal
Last month's breakdown
Peak usage: -273 kWh
Partial peak usage: -100 kWh
Off-peak usage: 573 kWh
Total NEM charges: $-23.70
Is this NEM1?

Under NEM2, monthly charges will never drop under ~$10+. Any negative NEM charges are just used for offset at annual tru-up, and then thrown away. :(
 

groovidad

Living the Dream!
Oct 19, 2018
615
460
Ewa Beach, HI
I'm not sure all electic Co.'s operate the same, in terms of PV programs(?) Here, I had a PV system installed and after, was not allowed to add more panels. I had the PWII installed this past April, under the NEM2 program. (local PV dealer, not Tesla) The electic Co. would not allow the addition of the PW or associated array to "mix" with my current PV system. So, 2 seperate systems BUT, both interface with the grid. Once my PW is fully charged, I can see energy sent to the grid by my PW array. It will also push energy to my house. To the Grid, as I understand, that energy goes to my energy "bank", to use towards my usage. Once my usage is covered for the month, the remaining in my "bank", carries over to the next months usage. At the end of the year, any overages in my bank are taken by the electric Co.

Long story to get to this but, no, I cannot sell it at premium rates or any rate for that matter, to the Ecompany. The PW will not export to the grid, as well. (That's obvious, though)
 

MorrisonHiker

S 100D 2021.4.15
Mar 8, 2015
9,437
8,588
Colorado
And you get off-peak credits for this production? That seems a terrible deal.
No. If we were to sell back the kWh, we'd only get like 1.5 cents per kWh. Because of that terrible deal, we opted for credits instead. We get off-peak credit for off-peak production, part-peak credit for part-peak production and peak credit for peak production. Basically, we get a credit value equal to the rate they would charge. That way, whenever we use the grid, we pay 8 cents per kWh (usually almost all of our grid usage is off-peak, thanks to the Powerwalls) but when we produce, we get 8 cents (off-peak), 12 cents (part-peak) or 18 cents (peak) per kWh credit.

So by producing 1 kWh in peak, it pays for for 2.25 kWh in off-peak.

In my example above, we'd earn 50 kWh * 18 cents per kWh = $9 a day during peak.
 
Last edited:

miimura

Well-Known Member
Aug 21, 2013
6,094
5,687
Los Altos, CA
Is this NEM1?

Under NEM2, monthly charges will never drop under ~$10+. Any negative NEM charges are just used for offset at annual tru-up, and then thrown away. :(
In PG&E Territory, the ~$10/mo minimum charge is not related to which NEM plan you're on. Those are the "Minimum Delivery Charges". They apply to all accounts. Sometime around 2016 these minimum charges were increased from ~$5/mo.

The calculation shown is perfectly valid for "solar energy charges" because they are added to the True-Up separately from these minimum charges. Whether you use up the negative balance in the winter or not to get full value for this credit is a separate issue.
 
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