The power density of the medium driving the turbine in an electric power producing unit determines the relationship between the size of the machinery and how much it produces. Water of high pressure in hydroelectric power plants and steam of high temperature and pressure in thermal plants both have much higher power density than air at atmospheric pressure and normal wind speed. For this reason, turbine-generator units in conventional power plants can have several hundred times the output of even the largest windmills and still have smaller dimensions.
In the order of a thousand large windmills with the machinery sitting on top of towers almost 100 m high are needed to produce as much power over the year as just one large turbine-generator unit in a conventional power plant. They are spread over a large area with a huge visual impact on the environment and with infinitely larger problems with assembly, inspection, maintenance, and repairs. For these reasons alone, windmills do not make much sense.
The need for large subsidies and a multitude of environmental problems other than the visual pollution are other good reasons for abandoning windmills. One such problem in Norway is windmills killing eagles along the coast. This alone has probably caused the acceptance of windmills in this country to plummet to a point where new construction has almost ceased. However, the emphasis here will be on the technical aspects.
Unreliable production due to varying wind speed is another serious problem. Windmills are also subject to excessive wear and destruction due to high wind speeds, lightning, moisture, and sometimes salt and other contaminants in the air. Stopping a windmill can not be done by turning off the wind, only by a mechanism that changes the angular position of the wings to a neutral position. If this mechanism fails or operates too slowly when the wind speed increases beyond that for which the windmill is designed, disaster is to be expected. Windmills cannot be designed to withstand runaway speed. One wing may break off and fly through the air. The huge unbalance which follows may destroy the rest.
O.W. Andersen, Norway
Life Senior Member IEEE