Array size with a battery
Daily production must cover daytime use plus the kWh the battery cycles each night. Divide daily kWh by sun hours and derate for array kW.
Net metering and export rates
Under low export credits, self-consuming through a battery beats exporting. Model the bill with your import rate, export rate, and fixed fee.
Adding a battery to existing solar
Confirm inverter compatibility (AC-coupled vs DC-coupled), panel capacity, and permit requirements before retrofit.
Formulas used
Array kW
daily kWh / sun hours / (1 - losses)
Worked examples
10 kWh/day, 4.5 sun hours
10 / 4.5 / 0.86 = 2.6 kW before battery charging needs.
Common questions
How much solar to charge a battery?
Add the battery's nightly kWh to daytime use, then size the array for the total.
Is solar plus battery worth it under NEM 3.0?
Low export credits make batteries more valuable: store the surplus instead of exporting it cheaply.
Sources
- Solar Energy Research National Renewable Energy Laboratory
- DSIRE Incentive Database N.C. Clean Energy Technology Center