Introduction - Wind Energy: Renewable Energy and the Environment - page 4

The farm windmill proves that wind energy is a valuable commodity, even though the size is small.
For example, there are an estimated 30,000 operating farm windmills in the Southern High Plains of
the United States. Even though the power output is low, 0.2-0.5 kilowatts (kW), they collectively pro-
vide an estimated output of 6 megawatts (MW). If these windmills for pumping water were converted
to electricity from the electric grid, it would require around 15 MW of thermal power at the generating
station and over $1,000 million for the transmission lines, electric pumps, etc. This does not count the
dollars saved in fossil fuel with an energy equivalent of 130 million kilowatt-hours (kWh) per year
(equivalent to 80,000 barrels of oil per year). Because many of these windmills are 30 years old or
older and maintenance costs are $250-400 per year, farmers and ranchers are looking at alternatives
such as solar water pumping rather than purchasing new farm windmills.
In 1888, Brush built a windmill to generate electricity, which was based on the rotor (large
number of slats) and tail vane of a large farm windmill. The wooden rotor (17 m diameter) was
connected to a direct current generator through a 50:1 step-up gearbox to produce around 12 kW in
good winds. The unit operated for 20 years; however, the low rotational speed was too inefficient
for the production of electricity. For example, a wind turbine with the same-diameter rotor would
produce around 100 kW.
1.1.3 W IND C HARGERS
As electricity became practical, isolated locations were too far from generating plants and transmis-
sion lines were too costly. Therefore, a number of manufacturers built stand-alone wind systems for
generating electricity (Figures 1.5 and 1.6), based on a propeller type rotor with two or three blades.
Most of the wind chargers had a direct current generator, 6 to 32 volts (V), and some of the later
FIGURE 1.5 Windcharger, 100 W, direct current, with flap air brakes. At USDA-ARS wind test station,
Bushland, Texas.