Power is the rate of doing work or producing or expending energy. Electrical power is measured in watts (W). A kilowatt (kW) is 1,000 watts. A megawatt (MW) is 1,000,000 watts. A gigawatt (GW) is 1 billion (109) watts. In relation to other sources of power, 1 W is equal to 1 joule (J) per second.