Introduction - Wind Energy: Renewable Energy and the Environment - page 5

FIGURE 1.6 Jacobs, 4 kW, direct current generator. It was still in use in the 1970s on a farm near Vega, Texas.
models were 110 V. The electricity was stored in batteries, and these wet-cell, lead-acid batteries
required careful maintenance for long life.
These systems with two or three propeller blades are quite different from the farm windmill,
which had a large number of blades covering most of the rotor swept area. The farm windmill is well
engineered for pumping low volumes of water; however, it is too inefficient for generating electricity
because the blade design and large number of blades means slow rotational speed of the rotor.
The wind chargers became obsolete in the United States when inexpensive electricity (subsi-
dized) became available from rural electric cooperatives in the 1940s and 1950s. After the energy
crisis of 1973, a number of these units were repaired for personal use or to sell. Small companies also
imported wind machines from Australia and Europe to sell in the United States during the 1970s.
1.1.4 G ENERATION OF E LECTRICITY FOR U TILITIES
There were a number of attempts to design and construct large wind turbines for utility use [6-11].
These designs centered on different concepts for capturing wind energy ( Figure 1.7 ): airfoil-shaped
blades with the axis of the rotor being horizontal or vertical, Savonius, and Magnus effect. With a
vertical axis there are no orientation problems of the rotor due to different wind directions.
A rotating cylinder in an airstream will experience a force or thrust perpendicular to the wind,
the Magnus effect. In 1926 Flettner built a horizontal-axis wind turbine with four blades, where
each blade was a tapered cylinder driven by an electric motor. The cylinders (blades) were 5 m long
and 0.8 m in diameter at the midpoint. The rotor was 20 m in diameter on a 33 m tower, with a rated
power of 30 kW at a wind speed of 10 m/s.
Madaras proposed mounting vertical rotating cylinders on railroad cars, which would travel
around a circular track propelled by the Magnus effect. The generators were to be connected to the