BESS sizing depends on the load profile, peak demand, electricity tariff, backup duration, solar generation profile, available space, grid connection limit, operating strategy, and project budget. A proper sizing study should review historical electricity data and define whether the main goal is cost saving, backup power, or renewable integration.

kW measures power, or how much electricity the system can deliver at one time. kWh measures energy capacity, or how much electricity the system can store. For example, a 125 kW / 261 kWh BESS can deliver up to 125 kW of power and store 261 kWh of energy.