Tuesday, November 28, 2017
One immutable fact is that the wind doesn't blow all the time. That can never be changed. Another is that 25 to 60 percent of the time the wind is blowing, it is at a rate less than the maximum efficiency for the turbine. As a result, windmills operate at only around 33 to 40 percent of maximum production level, compared to 90 percent for coal and 95% for nuclear power.
Turbines start producing power with winds at about 8 mph and operate most efficiently with winds about 30 mph. Though higher wind speeds have more energy, turbines become less efficient at collecting it. And the machines must be shut down when a cut-off speed is reached, beyond which high winds could cause rotor blades to fly off or vibration that can shake the turbine into pieces. Turbines must not operate in wind speeds over 56 mph, and typically the cut-off speed is set at 50 mph. They also have a cut-in speed, usually 7 to 10 mph, below which the blades will not produce usable power. A complete wind energy system includes rotor, transmission, generator, storage and other devices, which all consume energy.
Wind turbines are—and always will be—unable to achieve high efficiency even under the most favorable conditions. To attain 100 percent efficiency would mean all the kinetic energy had been captured and the blades would stop rotating. The best efficiency achieved is about 47 percent, which is about as good as it can get because of a physical law known as the Betz Limit. This has been known for a hundred years. It was independently discovered by three scientists in three different countries: Albert Betz (1919) in Germany, Frederick Lanchester (1915) in Great Britain, and Nicolay Zhukowsky (1920) in Russia. Their discovery applies to all Newtonian fluids and identifies the maximum amount of kinetic energy that can be captured by windmills as 59.3 percent. But the advocates of wind power are either ignorant of this or willfully ignore it to make wind power seem feasible for achieving their goals. Wind turbines may be useful in remote locations with adequate winds where more efficient energy sources are unavailable, but they will never achieve widespread displacement of more economic energy without the waste from government subsidies and/or artificially high electricity rates for consumers.
As wind terminals proliferate, the most favorable wind locations are taken, and more and more are located in less favorable locations, with necessarily lower efficiency and higher costs. Also, the best wind locations are generally located in areas remote from the cities where most of the electricity is used. This necessitates construction of extensive distribution networks that make wind power even more uneconomic. The uneconomic realities are hidden in a labyrinth of subsidies, regulations, tax credits, consumer electricity rates, taxpayer costs, and political considerations that camouflage the true costs. In a free market—where government could not create some winners by forcing losses on others—wind power would be noncompetitive with coal, natural gas and nuclear power.