AxiaSolar
How much battery capacity does backup power need?
Start with critical loads rather than the total building demand. List each appliance or circuit, its running power, starting surge, and hours of use during an outage.
A first energy estimate
Multiply each load in kW by its expected hours of use and add the results to estimate kWh delivered to loads. Then allow for usable battery capacity, conversion losses, reserve state of charge and future growth. The battery must also supply the highest simultaneous power demand in kW; energy capacity alone is insufficient.
For example, a 2 kW average load over five hours requires 10 kWh delivered before allowances. The final battery nameplate capacity can be higher, and real loads vary. NREL uses “hours of autonomy” as a useful behind-the-meter sizing measure. Compare this with the battery selection questions and storage solution.