Hello,
I'm curious whether anyone with Powerwalls installed and a solar system has asked Tesla to install their system as if they had no solar, and if so whether Tesla agreed. This obviously wouldn't work for someone taking the ITC, as that requires charging the Powerwalls only from solar generation. But for anyone not taking the ITC, then depending on one's rate plan, it could be economically beneficial to be able to charge from the grid.
One issue is whether during island operation (power outage) the Powerwall needs to be able to monitor the solar generation via CTs in order to properly charge from it. I don't think it does, but I'm not sure.
A longer commentary on my situation is below, for anyone interested.
Cheers, Wayne
As my two Powerwalls are scheduled to be installed next month, I started to take a look at the available modes of operation and how to maximize the economic benefit from the Powerwalls. A little background:
- I'm on PG&E's EV-A schedule, which has Peak, Shoulder (Part Peak in PG&E speak), and Off-Peak rates on weekdays; and just Peak and Off-Peak on the weekend.
- I have a small solar system (2.5 kw-AC).
- I'm not currently planning to take the ITC [a close decision; as I'm an SGIP self-developer, it's 30% of the post-SGIP cost versus the extra SGIP hassle (monitoring plans) and the restriction on use (no grid charging).]
- With solar and storage, the PG&E tariff allows instantaneous discharge from the storage directly to the grid, but it restricts total annual export to the total annual production of the solar system.
So if it were possible, the most effective way for me to use the Powerwalls would be to time-shift all my consumption to Off-Peak times while simultaneously time-shifting all my solar production to Peak. On the weekend that is a pretty simple algorithm: during Off-Peak, charge to avoid exporting energy and to reach 100% at the beginning of Peak; during Peak, discharge to cover usage plus that day's full Off-Peak solar generation. Weekdays would be more complicated due to the Shoulder period, but a similar algorithm would work by forecasting the net generation expected during the Shoulder periods, and not fully charging during Off-Peak to allow absorbing the Shoulder period net generation.
Unfortunately Tesla doesn't offer this operational mode or any time-shifting of solar production. So it seems the best I can do is to time-shift all of my usage to Off-Peak. When grid charging is not prohibited the Powerwall operational mode that does this best is "No Solar TBC". That would allow all of my Peak and Shoulder generation to go directly to the grid.
I'm curious whether anyone with Powerwalls installed and a solar system has asked Tesla to install their system as if they had no solar, and if so whether Tesla agreed. This obviously wouldn't work for someone taking the ITC, as that requires charging the Powerwalls only from solar generation. But for anyone not taking the ITC, then depending on one's rate plan, it could be economically beneficial to be able to charge from the grid.
One issue is whether during island operation (power outage) the Powerwall needs to be able to monitor the solar generation via CTs in order to properly charge from it. I don't think it does, but I'm not sure.
A longer commentary on my situation is below, for anyone interested.
Cheers, Wayne
As my two Powerwalls are scheduled to be installed next month, I started to take a look at the available modes of operation and how to maximize the economic benefit from the Powerwalls. A little background:
- I'm on PG&E's EV-A schedule, which has Peak, Shoulder (Part Peak in PG&E speak), and Off-Peak rates on weekdays; and just Peak and Off-Peak on the weekend.
- I have a small solar system (2.5 kw-AC).
- I'm not currently planning to take the ITC [a close decision; as I'm an SGIP self-developer, it's 30% of the post-SGIP cost versus the extra SGIP hassle (monitoring plans) and the restriction on use (no grid charging).]
- With solar and storage, the PG&E tariff allows instantaneous discharge from the storage directly to the grid, but it restricts total annual export to the total annual production of the solar system.
So if it were possible, the most effective way for me to use the Powerwalls would be to time-shift all my consumption to Off-Peak times while simultaneously time-shifting all my solar production to Peak. On the weekend that is a pretty simple algorithm: during Off-Peak, charge to avoid exporting energy and to reach 100% at the beginning of Peak; during Peak, discharge to cover usage plus that day's full Off-Peak solar generation. Weekdays would be more complicated due to the Shoulder period, but a similar algorithm would work by forecasting the net generation expected during the Shoulder periods, and not fully charging during Off-Peak to allow absorbing the Shoulder period net generation.
Unfortunately Tesla doesn't offer this operational mode or any time-shifting of solar production. So it seems the best I can do is to time-shift all of my usage to Off-Peak. When grid charging is not prohibited the Powerwall operational mode that does this best is "No Solar TBC". That would allow all of my Peak and Shoulder generation to go directly to the grid.