Why a battery roughly doubles what a roof earns
Same kWh, different hour. The maths behind the calculator.
The calculator on the home page gives a battery a lot of credit. Here is why.
Same power, better hour
A 7 kW roof in Sacramento exports about 500 kWh of surplus a month. Sold as it is made, mostly between eleven and three, it fetches an average of around $0.13. That is $65.
Put a 13 kWh battery in the loop and about 350 of those kWh get shifted into the evening peak, where the average is closer to $0.23. The remaining 150 still sell at midday. The total is about $100 from the shifted power plus $20 from the rest, before the fee.
Plus what the battery sells on its own
On cloudy days the battery can charge from the grid overnight and still sell into the peak. That adds a few dollars a week in most regions and a lot more during heat waves.
The catch
A battery costs money. Whether it pays back depends on your local prices, your incentives and how long you plan to stay. The calculator gives you the payout side; the state pages give you the incentive side.