Wind energy expert Paul Gipe, author of Wind Energy Basics: A Guide to Home—and Community-Scale Wind Energy Systems, goes to great lengths outlining the differences between power and energy, and debunks the myths of wind turbine manufacturers’ unscrupulous “power ratings.” Knowing the difference between these terms, Gipe says, will inform your decisions on alternative energy, and perhaps most important these days—save you money.
According to Gipe, “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,” Gipe says, “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.”
How Does This Save You Money?
According to Paul Gipe, there are three factors in the economics and profitability of wind energy.
- The installed cost
- The amount of electricity generated
- The cost of operating and maintaining your turbines
Saving money means lowering the cost of installation and operating costs, or increasing your turbine’s productivity. You’ll make more money if the tariff for wind energy increases, too (it just did: in Vermont).
Basically, the “power” rating of a wind turbine—what manufacturers use to false market their goods—is actually an unreliable way to gauge how much energy a wind turbine will capture. Gipe says you should concentrate on the actual energy itself, and in particular the rotor diameter—which is the most reliable indicator of how much electricity a wind turbine will generate.
So when you’re shopping for your turbine, remember to ask about energy and inquire about the rotor diameter. The rotor—the most important aspect of a wind turbine—is the part right behind the blades, which facilitates the blades sweeping the air, and thereby generating energy. Bigger diameter, in this case, catches more energy from the wind. The question is, what size you need. Household-size wind turbines generate about 10kW, with rotors about 100 feet in diameter, for example, whereas large wind turbines can generate 3MW, with rotors 500 feet in diameter.
Cross-posted at Planet Green.