3 ms·

We're on battery-backed solar. We still have a connection to the grid, but also have a PowerWall and enough panels to generate about 10% over annual power cons

We're on battery-backed solar. We still have a connection to the grid, but also have a PowerWall and enough panels to generate about 10% over annual power consumption (this is the max that PG&E will let you install if you keep a grid connection). PG&E still plays rate-plan shenanigans. Besides the retail/wholesale stuff, they charge $10/month just for the grid connection. They're currently lobbying CPUC to raise that to $60/month. Also the "time-of-use optimized" setting in the Tesla app isn't actually that optimized. It's unaware of the retail/wholesale issue, and hence simply tries to maximize the amount you ship back to the grid in peak hours when it'd be better off minimizing total consumption. It also sometimes doesn't discharge the PowerWall as much as it could (leaving solar energy on the table), and it charges it with grid power when it could easily use solar energy. I've found it's better to just use the "Self-powered" setting, where it charges the PowerWall as soon as you have excess energy over the home consumption, starts discharging as soon as there's a shortfall, and continues until the PowerWall reaches the reserve level you set. Note that solar generation is incredibly seasonal. I'm currently generating about 25 kWh/day. In January, this is more like 4 kWh/day. So depending on your shade levels, you might have to put on 6x as many panels to be entirely grid-independent vs. grid-connected with battery backup. We're sized so that we can power a full normal workload from about Apr - Oct, which at least covers fire season, but would have to conserve significantly (i.e. forego loads of laundry and electric appliances) if we had an extended outage in winter.

kristianp 5y ago
What state are you in? Pretty northerly to have such a big drop over winter?
- nostrademons 5y ago
  CA. It's a perfect storm of factors: we're on the north side of a hill, there's a lot of tall trees to the south of us, we've got a pitched roof. In winter the sun doesn't rise on the house until almost 11 AM, and then the south roof gets dappled sunlight because of the trees until about 2 PM. Because of the shade cover, we split the panels between south and north arrays, but the north one doesn't start producing until the sun clears the rooftop, about 10:30 AM. The north array actually produces more during the winter because it gets direct sunlight and has no tree cover. In the summer, the sun is higher in the sky, so it clears the hill earlier (by 8 AM or so) and never hits the trees. Both arrays produce the full day, and the days are longer, and the sun is incident at a steeper angle anyway. My situation is a little weird, but it also applies to many urban or rural settings where you'd have a tall building or series of tall trees that block sunlight when the sun is low on the horizon, but that the sun would clear when directly overhead.

kristianp 5y ago

What state are you in? Pretty northerly to have such a big drop over winter?

nostrademons 5y ago
CA. It's a perfect storm of factors: we're on the north side of a hill, there's a lot of tall trees to the south of us, we've got a pitched roof. In winter the sun doesn't rise on the house until almost 11 AM, and then the south roof gets dappled sunlight because of the trees until about 2 PM. Because of the shade cover, we split the panels between south and north arrays, but the north one doesn't start producing until the sun clears the rooftop, about 10:30 AM. The north array actually produces more during the winter because it gets direct sunlight and has no tree cover. In the summer, the sun is higher in the sky, so it clears the hill earlier (by 8 AM or so) and never hits the trees. Both arrays produce the full day, and the days are longer, and the sun is incident at a steeper angle anyway. My situation is a little weird, but it also applies to many urban or rural settings where you'd have a tall building or series of tall trees that block sunlight when the sun is low on the horizon, but that the sun would clear when directly overhead.