Electrical energy can refer to several closely related things. It can mean:

• The energy stored in an electric field
• The potential energy of a charged particle in an electric field.
• The energy provided by electricity

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.