All was well until my TOU plan changed to drop the afternoon off-peak period. Now my PW is down to 20% and not charging on full solar. Support says it is because I don't have a delta between the buy and sell prices but I have a net metering which values 1 kWh in = 1 kWh out so there is no delta. Their recommendation is that I make up numbers with at least a 15% difference and that the lower off-peak price and the higher on-peak price are not taken into account. Seems wrong.
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Powerwall, what does delta do?
- Thread starter Gwgan
- Start date
In my experience, the main thing a delta does is to make the system prefer to use solar locally rather than exporting to the grid. I agree that the suggestion doesn't sound correct. It would be helpful to know your complete rate plan configuration in the app to understand what's happening, though.
This is my current setting.
Peak 7a-8p buy price = sell price = $0.25/kWh
Off peak 8p-7a buy price = sell price = $18/kWh
My rate plan is not available in the app, I enter these manually.
Peak 7a-8p buy price = sell price = $0.25/kWh
Off peak 8p-7a buy price = sell price = $18/kWh
My rate plan is not available in the app, I enter these manually.
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I see the issue. Basically your rate plan has all solar production during peak. This means time-based control pretty much can't do any optimization since it can't charge during a cheaper period.
What are your goals for your Powerwalls? Given the current schedule, I don't think there is any way they can help reduce your peak usage during the week. At best you could charge on the weekend and then use the energy during the week, but then you'd be at your reserve until the next weekend.
What are your goals for your Powerwalls? Given the current schedule, I don't think there is any way they can help reduce your peak usage during the week. At best you could charge on the weekend and then use the energy during the week, but then you'd be at your reserve until the next weekend.
Fortunately, you included a screen shot. Thank you. What you meant was $0.25 peak, 0.$18 off peak.
You need a delta of at least 10% between the buy and the sell prices for both time periods. I would suggest 20%, I.e. buy $0.25, sell $0.20, peak, and buy $0.18, sell $0.14 off peak.
All the best,
BG
If the PWs only charge from PV, and all the PV production is peak, then as cwied observed, with true NEM the financially optimal option is to never charge the PWs. Because you can just export the PV when it is generated.
If you can charge the PWs from the grid, then the PWs can be used to time shift all peak consumption to off peak consumption, if large enough to cover a day's consumption.
Or since your weekend is all Off-Peak, you could set a reserve at say 50%, and use weekend PV production to cover some weekday Peak consumption. The PWs will spend much of the week at 50% while waiting for the weekend to recharge.
Implementing a "fake delta" will just cost you money.
Cheers, Wayne
If you can charge the PWs from the grid, then the PWs can be used to time shift all peak consumption to off peak consumption, if large enough to cover a day's consumption.
Or since your weekend is all Off-Peak, you could set a reserve at say 50%, and use weekend PV production to cover some weekday Peak consumption. The PWs will spend much of the week at 50% while waiting for the weekend to recharge.
Implementing a "fake delta" will just cost you money.
Cheers, Wayne
Thanks for the replies. This is making sense now. Net metering credits expire after a year so not using the PW at all is not the best answer either.
When we had an afternoon off peak period the PW would use some solar to charge and then start discharging during evening peak. I did not realize it was doing this because charging during off peak was considered financially advantageous.
In winter there are a couple of hours at either end of peak where there is no solar so it would be nice if PW covered those hours as well as whole rainy days using sunny day solar.
We primarily got these to cover power outages, but was trying to take advantage of TOU. It may be simpler use a fixed rate and use self power mode.
When we had an afternoon off peak period the PW would use some solar to charge and then start discharging during evening peak. I did not realize it was doing this because charging during off peak was considered financially advantageous.
In winter there are a couple of hours at either end of peak where there is no solar so it would be nice if PW covered those hours as well as whole rainy days using sunny day solar.
We primarily got these to cover power outages, but was trying to take advantage of TOU. It may be simpler use a fixed rate and use self power mode.
Remember that you lose 10% round-trip when putting power through the Powerwalls. I think backup-only makes more sense for you because if you're ending up with credits at the end of the year, you're not paying anything for electricity anyway, right? The only way self-powered helps is if you have something equivalent to California's non-bypassable charges where you pay a little for electricity imported even if it's offset by the NEM.
CrazyRabbit
Active Member
Your TOU plan effectively neutered your Powerwall, I would say purposely.
So just set it for backup only
So just set it for backup only
What actually changed is the Super Saver TOU plan I was using which had delivery rate:
off-peak 4¢, peak 23¢ with a $13.44/mo fee
has changed to:
5¢ for all periods with a $31.nn/mo fee
They intend to market this new plan to users with heat pumps and EVs with >800 kWh monthly consumption.
I got moved to the regular TOU:
¢13, ¢6.5 with the $13.44 fee
Non-TOU service is ¢8.8 with a minimum payment of $13.73 for the first 50 kWh (or ¢27.5/kWh)
Since I only pay the monthly I’ll save the ~¢30 and avoid the jump to $31
Note these prices do not include supply charges which is ¢11.8 now but with a significant raise in the works
There is also sales tax of 5.5% on total charges above 750kWh
To their credit they now offer a load management rate using a separate meter with:
Peak ¢16, off-peak ¢1.1, fee $18.77
But weekends and holidays are not off-peak: 8p-7a every day.
That’s a lot of detail but some of you may be interested in how we do things up here.
off-peak 4¢, peak 23¢ with a $13.44/mo fee
has changed to:
5¢ for all periods with a $31.nn/mo fee
They intend to market this new plan to users with heat pumps and EVs with >800 kWh monthly consumption.
I got moved to the regular TOU:
¢13, ¢6.5 with the $13.44 fee
Non-TOU service is ¢8.8 with a minimum payment of $13.73 for the first 50 kWh (or ¢27.5/kWh)
Since I only pay the monthly I’ll save the ~¢30 and avoid the jump to $31
Note these prices do not include supply charges which is ¢11.8 now but with a significant raise in the works
There is also sales tax of 5.5% on total charges above 750kWh
To their credit they now offer a load management rate using a separate meter with:
Peak ¢16, off-peak ¢1.1, fee $18.77
But weekends and holidays are not off-peak: 8p-7a every day.
That’s a lot of detail but some of you may be interested in how we do things up here.
"Peak", in his example, includes all of the time that the sun is shining, as you note.
There is no time when the Powerwalls will charge from solar, and let the house draw from the grid, the way mine does.
I don't have any delta, but Tesla follows Peak versus off-peak correctly, which doesn't help, for his case.
You could set the Powerwalls to charge from the grid, if it's not prohibited by tariff, just as you would if you had no solar PV.
That would give some leverage against using the grid during Peak.
Meanwhile I should be getting paid for storing power
Today, after forcing the batteries to charge yesterday by setting the Backup Reserve to 100% temporarily the PW started discharging with the onset of Peak so yes it does still observe the different periods. Guess I can offset grid usage on Mondays. Sadly we are explicitly prohibited from charging from the grid but the button is available and Storm Watch is an allowed exception.
I stand corrected. Called CMP to clarify that this is just a problem with the document formatting; the off-peak period still includes holidays and weekend
Really? That would make A (house) + A-LM (garage) a bit more attractive to me as it would increase charging flexibility.
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