I am on PG&E, have the EV2-A rate, have existing 2.5kW solar and am thinking of adding more solar and a powerwall. My idea is to have the PW for backup and for rate shifting but another thread seemed to indicate that if a PG&E customer has solar and a PW, they must charge the PW only from solar. That eliminates rate shifting (i.e., charging PW during off-peak hours.) Is that correct or can I charge from the grid during off-peak hours?
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PG&E + EV2-A Rate + Solar + PW and Charging
- Thread starter SBerg
- Start date
The rate shifting that was being discussed is solar charging the PowerWalls from sunrise to 3:00pm when the EV2 Off Peak rate is $0.167/kWh and then discharging to meet the house load needs in the higher cost Partial Peak ($0.369/kWh from 3:00-4:00pm and 9:00pm-12:00am) and Full Peak ($0.479kWh from 4:00-9:00pm) periods to avoid drawing from the grid.
A 2.5kW system sounds pretty small, but it really depends on what else your house is using from 3:00pm to midnight.
As @Redhill_qik says "rate shifting" with tesla powerwalls is taking your own generated solar, storing it in the powerwalls, then using that stored power during your utilities peak energy rates.
Unfortunately you are not able to charge your powerwalls off peak from the grid at this time.
(edit: at least, not under normal circumstances. If you are willing to log into the installer interface and mess around with settings there, a member here has a way you can force powerwalls to charge from the grid, but thats very much a "on your own risk" type of thing).
Unfortunately you are not able to charge your powerwalls off peak from the grid at this time.
(edit: at least, not under normal circumstances. If you are willing to log into the installer interface and mess around with settings there, a member here has a way you can force powerwalls to charge from the grid, but thats very much a "on your own risk" type of thing).
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You can still rate shift. You'll charge your PWs during the day off peak while you you use power from the grid for your house at the off peak rate. At 3 or 4 pm you'll start discharging from the PWs depending on your SOC. If you're SOC is high, like 90% or more then it'll switch over to the PWs at 3. If it's lower, then it will start at 4 pm. If you size the number of powerwalls correctly, you'll never use peak grid power again.
kpinthebay
Member
You can set a reserve SOC level for the powerwall and the system will stop the powerwalls from draining below that SOC level during normal operations, so that way you know that you will always have that much power available for backup in the event of a power failure. But it’s kind of a balancing act. The higher you set the reserve the more power you will have available for backup, but the less power you will have for day to day operations and load shifting. The lower you set the reserve you’ll be able to do more load shifting, but you could have less power available for backup.
However, that said, if the grid fails in the morning it’s probably not too bad if the powerwalls are at a low SOC because they will only need to support your house until the sun comes up and at that point solar will take over.
As Brett said, you can play with the Resrve amount. I also change mine to backup only when a storm is coming. I don't trust PG&E
Definitely a balancing act and it depends on TOU plan that you are on. If it's PG&E E-TOU-C then you only need to meet the Peak time between 4:00-9:00pm as everything else Off-Peak at the same rate so draining your Powerwall during the night only to recharge in the morning provides no economic benefit (maybe a negative benefit due to the 90% efficiency which is offset by NBC charges). If you are on PG&E EV2 rate then you have the same 4:00-9:00pm Peak time and also 3:00-4:00pm and 9:00-12:00am Partial-Peak time to get through.
I built a spreadsheet model based on my pre-solar PG&E daily/hourly data and PVwatts daily/hourly data to be able to simulate different Powerwall reserve percentages and for my system (2x PW), usage and rates there is very little difference from a SOC of 0-60% reserve. This is likely due to my system being a net producer right now until I add an EV and replace some gas with electric.
Edit: I simulated reducing my solar production by 50% to become a net consumer and I'm seeing the same results with very little economic difference between a reserve on 0-60% on E-TOU-C and EV2 for my usage (non-EV household). I'm seeing a very big economic difference between having 2x Powerwalls and not having them (100% reserve) on the EV2 plan which would change from an annual max of $1,141 without to $578 with them set to a 50% reserve. On the E-TOU-C plan same conditions would be $607 vs $557. YMMV.
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Can you share your spreadsheet with a Google sheet link? Did you just copy paste the pge download data to run the spread sheet?
The PG&E download data is part of it (massaged to take out leap day and time change hours), the other part is the PVwatts data for my panels of which there are 4 sets as I have a really unoptimal roof and have panels in 4 different directions. The spreadsheet model works and I'm willing to share it as a Google sheet but it isn't very straightforward.
I want to spend a few hours and stand up a quick site to implement the calculations. Might find sometime this weekend after getting a tree. If you want to try the sheet as-is send me a DM and we can work something out.
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