Battery capacity is the total amount of electrical energy a battery can store and deliver, measured in kilowatt-hours (kWh) or ampere-hours (Ah). This fundamental specification determines how long a battery system can power a home or building under specified load conditions. Residential solar batteries typically range from 5 kWh to 20 kWh per unit.
Rating Standards
Manufacturers rate capacity at specific discharge rates and temperatures, typically 25°C ambient conditions. A battery rated at 10 kWh capacity at a 1-hour discharge rate delivers 10 kilowatts continuous power. The same battery discharged over 5 hours might deliver 12 to 13 kWh due to reduced internal heating losses. Cold temperatures reduce effective capacity by 10 to 20 percent, requiring larger installations in northern climates.
System Sizing
Proper capacity sizing requires analyzing average daily energy consumption plus emergency reserves. A household using 30 kWh daily with solar generation should install 40 to 50 kWh capacity to maintain 2 to 3 days of autonomy during cloudy weather. Industrial applications often specify capacity in megawatt-hours (MWh) for grid support, ranging from 1 to 500 MWh in utility-scale projects.