Читать книгу Wind Energy Handbook - Michael Barton Graham - Страница 45

As indicated in the previous section, much better predictions can be made by using meteorological forecasts than by using purely statistical methods, when predictions over timescales of a few hours or days are considered. Very sophisticated meteorological forecasts are available from highly detailed simulation models of the atmosphere, fed by many recorded observations of pressure, temperature, wind speed, etc. over wide areas of land and sea.

Landberg (1997, 1999) describes the use of such models to predict wind farm output, by extrapolating the large‐scale wind predictions produced by these models down to the specific wind farm site. The geostrophic drag law and the logarithmic wind shear profile (Section 2.6.2) are used to extrapolate the wind forecasts down to ground level. Modifications to the flow resulting from the topography, the physical geography, and surface roughness conditions in the area surrounding the wind farm are then modelled by the WA^sP program (Mortensen et al. 1993). A turbine wake interaction model, PARK (Sanderhoff 1993), then takes account of wind direction in relation to the actual turbine positions to calculate wake losses, and, finally, a statistical model (as described in the previous section) combines the meteorological forecasts with recent measurements on the wind farm to give predictions of the energy output that are good enough to be useful in planning the deployment of other power stations on the network.