Different measures for wind energy potential show very different long-term variations and trends. This seriously complicates the estimation of future long-term wind supply. Therefore, it is necessary to better understand these discrepancies and know the main causes of the reported decline. For this purpose different types of indices for the Netherlands are analysed and the influential production based index Windex-CBS is compared to different wind speed observation indices and to an index based on geostrophic wind speed.
High mutual correlations (monthly and annual) between the indices indicate that they do efficiently account for natural variability. Yet, the trends of the different indices do substantially differ from each other. The decrease of Windex-CBS is twice as large (200%) as the decrease of the wind speed based index. The trend of the difference between both indices is highly significant. This suggests that the Windex-CBS is contaminated by non-climatic or methodological factors. W-obs does not suffer from such factors and is therefore the preferred measure of wind supply.
About 80% of the decrease in W-land is explained by natural long-term variations in the wind climate. Long-term variability substantially increases the climatic uncertainty of future long-term yields. Geo-indices are potentially very useful for the quantification of the long-term variability as they do efficiently explain the natural variability of wind supply and because of the possibility to construct long time series.
A Bakker, J Coelingh, B van den Hurk. Long-term trends in the wind supply in the Netherlands
2012, 2012, EWEA