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Energy Systems and Technologies for the Coming Century ...

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Figure 9: The annual mean power density at 50 m <strong>for</strong> <strong>the</strong> Columbia Gorge test regionbased on annual mean wind-speed <strong>and</strong> variance modelling. Winds derived fromgeostrophic winds from CFSR data.Figure 10: The annual mean power density at 50 m <strong>for</strong> <strong>the</strong> top 10-percentile (windiest1/10 th of <strong>the</strong> area) <strong>for</strong> <strong>the</strong> Columbia Gorge test region based on annual mean wind-speed<strong>and</strong> variance modelling. Winds derived from geostrophic winds from CFSR data.To apply <strong>the</strong> estimated spatial variance of wind speed, wind data pertaining to <strong>the</strong> largetest areas is required. For this <strong>the</strong> purpose Climate Forecasting System reanalysis(CFSR) data was used, Saha et al (2010). The data is available at 0.5 degree resolution<strong>and</strong> hourly. For this exercise geostrophic winds were calculated <strong>for</strong> year 2000 using 6-hourly data, <strong>for</strong> each of <strong>the</strong> 50 x 50 km blocks. The winds were trans<strong>for</strong>med to 50 mabove surface level winds, using <strong>the</strong> geostrophic drag law <strong>and</strong> mean surface roughness<strong>for</strong> each 50 x 50 km block.Wind power density is given by[Eq. 1]Where u is wind speed <strong>and</strong> ρ is density. Per<strong>for</strong>ming Reynold’s decomposition <strong>for</strong> <strong>the</strong>time <strong>and</strong> space variation of wind speed, one obtains a time <strong>and</strong> space mean wind powerdensity given by[Eq. 2]Risø International <strong>Energy</strong> Conference 2011 Proceedings Page 222

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