Today, a unit the size of a 20-foot shipping container holds enough energy to power more than 3. 200 homes for an hour, or 800 homes for 4 hours (approximately 5 MWh of energy/container, 1. 5 kW typical residential load). . How much electricity can an energy storage container store? Electricity storage containers, also known as energy storage systems (ESS), can store a vast range of electrical energy, generally measured in kilowatt-hours (kWh) or megawatt-hours (MWh). The capacity of these systems can vary greatly. . Energy capacity is the total amount of electricity that a BESS container can store and later discharge. They combine cutting-edge tech with plug-and-play convenience.