Energy

Energy is a quantity, not an instantaneous rate. In home energy systems, it describes how much electricity or heat has been used, generated, stored, imported, exported or delivered over a period. The SI unit of energy is the joule, but household electricity bills, solar export records, battery datasheets and EV charging sessions usually use watt-hours or kilowatt-hours because those units pair power with time. This is different from power, measured in W or kW, which describes how fast energy is being transferred at a particular moment. A 1 kW load running for one hour uses 1 kWh of energy before losses or measurement differences. Read an energy figure with its label and measurement boundary, because import, export, battery capacity, usable storage, delivered EV charge and heat output can describe different quantities.