in any of these cases, the si unit of electrical energy is the joule; which is the amount of energy used by a one-watt load, such as a tiny light bulb, drawing power for one second. the unit used by many electrical utility companies is the watt-hour (wh); which is the amount of energy used by the same one-watt load drawing power for one hour. the kilowatt-hour (kwh), which is 1,000 times larger than a watt-hour, is a useful size for measuring the energy use of households and small businesses. a typical household uses several hundred kilowatt-hours per month. the megawatt-hour (mwh), which is 1,000 times larger than the kilowatt-hour, is used for measuring the energy output of large power plants.