I have been mulling and lightly researching the purchase of a Powerwall (or similar) for some time in anticipation for some forthcoming TOU changes that will negatively affect the value of my solar production. Fortunately, the change to 4-9pm peak is 2.5 years away for me, but the recent power outages due to red flag weather along with the new CAL FIRE codes has got my a bit more motivated to look into options.
Stats:
9.9 KW solar
Peak production ~70 kWh summer. Half that for winter
Average day consumption just under 50 kWh including daily Model 3 charge.
Current peak is 11-4 during summer which is great ROI for solar. System generates more than daily usage and peak NEM rates are about 2:1. This helps out in the winter months when the solar generation does not cover daily usage.
Power outages in my area are rare. The thought of whole home backup is desirable and neat, but just for that there is little ROI on the purchase.
Rate arbitrage would be useful but this is an area PW isn't designed for. My neighbor has a battery solution from another manufacturer and an EV, so with his cheap EV plan, he charges both up at night super off peak, uses solar to power the house and sell excess back to the utility at a mid tier rate during the day, power his house from battery during peak until super off peak, then charge again. This ability may be useful enough that it may drive me to another solution than PW unless there's some inherent PW features that are more desirable.
Before I speak to Tesla or a third party installer, I feel I need some more knowledge on how PW can be useful in my house.
Questions:
Being that it's currently a good ROI to sell back to the utility during summer peak, is a PW useful with this rate plan?
PW must charge from the solar. It seems advantageous to charge from sunrise to 11a during the summer then sell back to the utility during peak. I cannot seem to determine via the SolarEdge web portal how long it would take to generate enough power to charge a PW. It only seems to show the output at that moment in time in KW and the reports area is lacking. Any suggestions on how to get this data?
During winter months, peak and semi peak are largely the same rate (differs by a fraction of a cent). Solar could charge PW but there may not be enough excess to sell back to the utility. While the utility acts as a big battery, I do get charged for the costs associated with transmitting the electricity used during times no solar generation. Using PW will reduce those non bypassable charges, but unsure if it's really worth it.
How does one size the PW install? Using the Tesla website it recommends 2 for my size house, but if I add EV it suggests 3. On a good solid solar day in winter, solar produces 30 kWh, house uses 10 of that, leaving 20 back to the utility. That would charge 1 PW fully and another partially. If I had 3, would one PW effectively be useless in the winter?
Forgive me if some of these questions seem elementary. When I learned that PW can't be charged from the grid if one has solar, it opened up a lot of uncertainty on how useful it may be. There isn't a lot of documentation on what level of control one may have via the software, but outside of adjusting for TOU, it seems like it's largely on autopilot (forgive me!)
Thanks for reading and offering suggestions and clarifications.
Stats:
9.9 KW solar
Peak production ~70 kWh summer. Half that for winter
Average day consumption just under 50 kWh including daily Model 3 charge.
Current peak is 11-4 during summer which is great ROI for solar. System generates more than daily usage and peak NEM rates are about 2:1. This helps out in the winter months when the solar generation does not cover daily usage.
Power outages in my area are rare. The thought of whole home backup is desirable and neat, but just for that there is little ROI on the purchase.
Rate arbitrage would be useful but this is an area PW isn't designed for. My neighbor has a battery solution from another manufacturer and an EV, so with his cheap EV plan, he charges both up at night super off peak, uses solar to power the house and sell excess back to the utility at a mid tier rate during the day, power his house from battery during peak until super off peak, then charge again. This ability may be useful enough that it may drive me to another solution than PW unless there's some inherent PW features that are more desirable.
Before I speak to Tesla or a third party installer, I feel I need some more knowledge on how PW can be useful in my house.
Questions:
Being that it's currently a good ROI to sell back to the utility during summer peak, is a PW useful with this rate plan?
PW must charge from the solar. It seems advantageous to charge from sunrise to 11a during the summer then sell back to the utility during peak. I cannot seem to determine via the SolarEdge web portal how long it would take to generate enough power to charge a PW. It only seems to show the output at that moment in time in KW and the reports area is lacking. Any suggestions on how to get this data?
During winter months, peak and semi peak are largely the same rate (differs by a fraction of a cent). Solar could charge PW but there may not be enough excess to sell back to the utility. While the utility acts as a big battery, I do get charged for the costs associated with transmitting the electricity used during times no solar generation. Using PW will reduce those non bypassable charges, but unsure if it's really worth it.
How does one size the PW install? Using the Tesla website it recommends 2 for my size house, but if I add EV it suggests 3. On a good solid solar day in winter, solar produces 30 kWh, house uses 10 of that, leaving 20 back to the utility. That would charge 1 PW fully and another partially. If I had 3, would one PW effectively be useless in the winter?
Forgive me if some of these questions seem elementary. When I learned that PW can't be charged from the grid if one has solar, it opened up a lot of uncertainty on how useful it may be. There isn't a lot of documentation on what level of control one may have via the software, but outside of adjusting for TOU, it seems like it's largely on autopilot (forgive me!)
Thanks for reading and offering suggestions and clarifications.