demand

The highest requirement for power; that is, the amount of power required to satisfy the demand. There is no time element involved, and the highest requirement for power can occur in an instant. In practice, most demand meters measure the average peak demand over the 15- or 30-minute period. This definition of demand differs from the definition of energy in that energy is the usage of power over time whereas there is no time element in measuring demand. Demand is measured in kilowatts (kW) and energy is measured in kilowatt-hours (kWh).

For example, a demand for 100 kW continuous for an hour equals 100 kWh. If the demand rose to 400 kW continuously for the next hour, the demand for that hour equals 400 kWh. For the two-hour period, the demand is 400 kW because that is the highest requirement for power. The energy used is 500 kWh because that is the actual usage of power over time.