You can also just change the definition of off-peak electricity. The coal grid already provides cheaper electricity at different times of day, because it's not

You can also just change the definition of off-peak electricity. The coal grid already provides cheaper electricity at different times of day, because it's not efficient to turn coal plants on and off. Right now that cheaper electricity is at night, because most electricity consumers consume during the daylight hours. So if you need a boatload of electricity and aren't too sensitive about the time, you can shift you consumption to the off-peak hours and save some money. But if you're not time-sensitive in your consumption, you can shift to the sunny daylight hours, when solar power is available. And if you're really not time-sensitive in your consumption, you can even shift consumption from cloudy days to sunny days.