Performance - Wind Energy: Renewable Energy and the Environment - page 152

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figure 8.2 Average capacity factor for wind turbines in California, wind farms. (Data from California
Energy Commission.)

By 1990 there were 1,500 MW installed in California, and they produced 2.68 TWh, enough to
power the residential needs of San Francisco [5]. Kenetech, formerly U.S. Windpower, still had the
largest number of units and largest installed capacity. The size of the wind turbines increased from
100 kW to 750 kW. In 2008, California wind farms were producing over 4 TWh/year, around 1.5%
of the total electric production, and the size of new wind turbines had increased to megawatts.
The annual capacity factor is an average from operational wind turbines (Figure 8.2). In 1990,
the better projects had capacity factors in the twenties, and for the third quarter, Kenetech had a
value of 40% and Bonus had a value of 39%. An example of the problem with capacity factor is
demonstrated by Fayette, which at one time had the second largest installed capacity; however, the
capacity factor for Fayette was very low, 5%, as these turbines were overrated (90 kW, 10 m diam-
eter). The vertical-axis wind turbines of Flowind also had a low capacity factor, 10%. The annual
capacity factor increased to 30% with the new, larger wind turbines (Figure 8.3). The specific out-
put, kWh/m 2 , varied from low values to over 1,000 kWh/m 2 ( Table 8.1 ) .

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1996 2003

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Turbine Size, kW

figure 8.3 Capacity factor by range of wind turbine sizes, California.