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Knowing the Difference Between Power and Energy Could Save You Money

Don’t get scammed by some unscrupulous wind turbine manufacturer’s bogus “power rating”—know your terms and take control of the conversation.

The following is an excerpt from Wind Energy Basics: A Guide to Home- and Community-Scale Wind Energy Systems [1] by Paul Gipe [2]. It has been adapted for the Web.

In casual conversation, we use the terms power and energy interchangeably. But knowing the difference between the two can save you a lot of headaches—and a lot of money.

Energy is the ability to do work or the amount of work actually performed. For our purposes here, energy is given in kilowatt-hours (kWh) of electricity produced by a wind turbine or consumed in a home or business. When most people pay their utility bill, they pay for the electricity they consumed in kWh.

Power is the rate at which energy is generated or consumed, that is, kilowatt-hours per hour (kWh/h) or kilowatts (kW). One kilowatt is 1,000 watts (W). One megawatt is 1,000 kilowatts or 1 million watts.

The distinction between kilowatts and kilowatt-hours is critically important. Knowing the difference can keep you from being confused by a wind turbine’s size in kilowatts (or for very small wind turbines, watts), and how much energy, in kilowatt-hours, it will actually produce. Some unscrupulous manufacturers play upon the public’s ignorance of this distinction and give their wind turbines a very high “power rating” when the actual turbine is unlikely to deliver as much electricity as a competitor with a low power rating.

The “power” rating of a wind turbine is an unreliable and often very misleading shorthand for how much energy a wind turbine will capture.

In Wind Energy Basics the emphasis is on “energy.” The most reliable indicator of how much electricity a wind turbine will generate is its rotor diameter.