Tham khảo tài liệu 'wind power impact on power system dynamic part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Variability and Predictability of Large-Scale Wind Energy in the Netherlands 265 and tF3 Huibertgat Europlatform . Goerree Vlissingen .auwersi Leeuwardi Markni Lelystai de iilt Gilze-Rijen K13 Texelhors Ijmuiden M. Noordwijk Hoek v. Holland Fig. 1. Onshore coastal and offshore wind speed measurement sites in this study in combination with the surface roughness length . Walker Jenkins 1997 . The local surface roughness length however is difficult to estimate. For this reason Brand 2006 has eliminated this need. Instead two location-dependent parameters are used the friction velocity u and the average Monin-Obukhov length Lesti. The friction velocity is estimated from the 10-minute wind speed standard deviation which for most locations is available. If not for an offshore location the friction velocity is estimated from the vertical wind speed profile. The Monin-Obukhov length is estimated by the average value that follows from the positive average heat flux that has been found over the North Sea and over the Netherlands implying that the average vertical wind speed profile is stable Brand Hegberg 2004 . Given the 10-minute average wind speed p zs and standard deviation o zs at sensor height zs the estimates of the wind speed average and standard deviation at hub height zh are u esti zh pu zs ou zs zh - zs L . . esti 7 ou esti zh ou zs 1 2 where Lesti is the location-dependent average Monin-Obukhov length. If only p zs is available and provided that the location is offshore the estimates of the wind speed average and standard deviation at hub height are 266 Wind Power í í z- Pu esti zh Pu zs ln I T z z - zs L . esti 7 3 s and o__. z u esti h where u is determined from 4 í L J pu zs - In - 4 A 2 Au . I- zs 5 s L esti 5 Ì 0 and g m s2 is the gravitational acceleration and A is Charnock s constant. Averaging-time transformation A transformation from 10 to 15-minute averages is required by the design of the Dutch balancing market
