Time-of-use rates and batteries: how the arbitrage works
How PG&E time-of-use pricing and a home battery interact, and how to think about charging off-peak and discharging into the 4–9 PM window.
Time-of-use pricing is what makes a home battery pay. Here is how the arbitrage works, how the daily schedule is set up, and what determines whether it is worth it on your house.
Why TOU is the whole game
Under a PG&E time-of-use plan, the same kilowatt-hour costs very different amounts depending on when you use it. Peak hours — typically 4 PM to 9 PM — are the expensive window. A battery lets you buy or generate energy when it is cheap and spend it when it is expensive. That spread is the entire economic case.
How the daily schedule works
Solar charges the battery through the middle of the day. Through the peak window the house runs off the battery instead of the grid. Overnight, at off-peak rates, the grid tops the battery back up if solar did not fully cover it. The controller runs this automatically once it is configured.
What determines your number
Your savings depend on four things: the size of the peak-to-off-peak spread on your rate plan, how much of your usage actually falls in the peak window, your battery capacity, and your array size. Two houses on the same street can land in very different places. We model yours against your real usage history rather than quoting an average.
The backup benefit
The same battery that arbitrages your rate plan also carries you through a PSPS shutoff. How long depends on your capacity and what you are running — a critical-loads sub-panel covering the fridge, internet and medical equipment stretches much further than backing the whole house including air conditioning.