The power generated by a wind turbine depends on both the design characteristics of the turbine and the properties of the wind resource. These parameters determine the capacity factor (ratio of average power output to rated power of the turbine). Since detailed information on the wind-speed frequency is often lacking, the shape factor (k) of the Weibull distribution is taken to be equal to 2, which may lead to significant errors. It is our aim to estimate capacity factors for shape factors between 1.5 and 3 acid for sites with average wind speeds ranging from 4 to 8 m/s. The results have been analyzed to obtain a general form for the capacity factor. Our method may be useful to turbine manufacturers in designing electronic control systems.