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.
The terms "electrical energy" and "electric power" are frequently used interchangeably. However, in physics, and electrical engineering, "energy" and "power" have different meanings. Power is energy per unit time. The SI unit of power and electricity is the watt. One watt is a joule per second. In other words, the phrases "flow of power," and "consume a quantity of electric power" are both incorrect and should be changed to "flow of energy" and "consume a quantity of electrical energy."