Introduction - Wind Energy: Renewable Energy and the Environment - page 9

FIGURE 1.10 German wind turbines: left, 100 kW; right, 10 kW. (Photo provided by NASA-Lewis.)
develop large-scale wind turbines for producing electricity. During World War II, a series of wind
turbines in the 45 kW range were developed with direct current (DC) generators. These units pro-
duced around 4 million kWh per year during this period.
The Danes had the only successful program, which began in 1947 with a series of investi-
gations on the feasibility of using wind power, and continued until 1968 [9, pp. 229-240]. A
prototype wind turbine of 7.5 m diameter was built and remained in operation until 1960, when
it was dismantled. A wind turbine at Bogo, originally constructed for DC power in 1942, was
reconstructed for alternating current (AC) in 1952. Rotor diameter was 13.5 m with a 45 kW
generator. The results of the two experimental wind turbines were encouraging and culminated
in the Gedser wind turbine ( Figure 1.11 ) . This unit was erected in 1957, and during the period
1958-1967 it produced 2,242 MWh. It was shut down in 1967 when maintenance costs became
too high. The rotor was 35 m in diameter and the tower, 26 m height, was prestressed concrete.
The rotor was upwind of the tower, and the blades were fixed pitch with tip brakes for overspeed
control. The wind turbine had an asynchronous generator (rated power of 200 kW at 15 m/s),
which provided stall control, and it had an electromechanical yaw mechanism. Denmark and the
United States furnished money to place the Gedser wind turbine in operation for a short time
period in 1977-1978 for research, which included tests for aerodynamic performance and struc-
tural loads.
The successful program of the Danes was overshadowed by the failure of other large machines.
The machines failed due to technical problems, mainly stresses due to vibration and control at high
wind speeds. Others were economic failures. Everyone agreed there were no scientific barriers to
the use of wind turbines tied to the utility grid. In the 1960s development of wind machines was
abandoned since petroleum was easily available and inexpensive.