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5.2 Estimating annual energy production

If the mean annual wind speed at a site is known, or can be estimated, the following formula (Beurskens and Jensen, 2001) can be used to make a rough initial estimate of the electricity production (in kilowatt-hours per year) from a number of wind turbines:

Annual energy production equation
Figure 13 Annual energy production equation

This formula should be used with caution because it is based on an average of the characteristics of the medium- to large-scale wind turbines currently available. It also assumes an approximate relationship between annual mean wind speed (ideally, the mean speed at turbine hub height) and the a frequency distribution of wind speeds that may not be accurate for an individual site. It also does not allow for the different power curves of wind turbines that have been optimized either for low or high wind speed sites.

If it is not possible to carry out wind measurements at a proposed site, or where a preliminary analysis is required prior to installing instrumentation, there are techniques that can give an approximate estimate of the wind speed characteristics of a site. You’ll study these in the next section.

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