A Diagnostic Model for Estimating Winds at Potential Sites for Wind Turbines

Abstract

Terrain features and variations in the depth of the atmospheric boundary layer produce local variations in wind, and these variations are not depicted well by standard weather reports. We have developed a diagnostic model that computes local winds for use in estimating the wind energy available at any potential site for a wind turbine. The method uses the terrain heights of an area surrounding the site and a series of wind and pressure reports from the nearest four or five National Weather Service stations. An initial estimate of the winds in the atmospheric boundary layer is made and these winds are then adjusted to satisfy the continuity equation. In this manner the flow is made to reflect the influences of the terrain and the shape of the boundary-layer top. We applied the method to seven sites in the United States for 1977. For four of the sites, we determined the sensitivity of the model to the values assigned to several parameters used in the computation. Suitable values of the parameters were selected by comparing the corresponding simulations to wind measurements that were made at the sites by the Department of Energy through its Pacific Northwest Laboratory. For the other three sites, simulations were made without adjusting the model. Seasonal and annual average wind speeds and frequency distributions were generated from the simulated 3 h u and v components. The simulated annual average speeds for the seven sites differ from measured values by amounts ranging from 0.1 to ?1.8 m s?1, with an average absolute deviation of 0.7 m s?1. This level of accuracy is sufficient for determining whether particular sites merit the installation of wind-measuring equipment. Validation that wind energy is adequate to justify wind-turbine installation must be provided by site wind measurements for a period of one year or more.