Abstract
The building of utility-scale wind farms requires knowledge of the wind speed climatology at hub height (typically 80–100 m). As most wind speed measurements are taken at 10 m above ground level, efforts are being made to relate 10-m measurements to approximate hub-height wind speeds. One common extrapolation method is the power law, which uses a shear parameter to estimate the wind shear between a reference height and hub height. The shear parameter is dependent on atmospheric stability and should ideally be determined independently for different atmospheric stability regimes. In this paper, data from the Oklahoma Mesonet are used to classify atmospheric stability and to develop stability-dependent power law fits for a nearby tall tower. Shear exponents developed from one month of data are applied to data from different seasons to determine the robustness of the power law method. In addition, similarity theory-based methods are investigated as possible alternatives to the power law. Results indicate that the power law method performs better than similarity theory methods, particularly under stable conditions, and can easily be applied to wind speed data from different seasons. In addition, the importance of using co-located near-surface and hub-height wind speed measurements to develop extrapolation fits is highlighted.
Highlights
Environmental concerns and rising fossil fuel prices have prompted rapid development in the renewable energy sector
The United States Department of Energy has examined a scenario in which 20% of the energy needs of the United States are provided by wind energy by the year 2030 [2]
The superior performance of the Mesonet-derived power law fit for the neutral and stable regimes is likely related to the varying amounts of 10- to 80-m shear experienced during these regimes (Figure 5a)
Summary
Environmental concerns and rising fossil fuel prices have prompted rapid development in the renewable energy sector. The land in the Great Plains is mostly flat and located far away from both ocean coasts This lack of complex terrain allows wind to flow unimpeded for great distances, which, in addition to the prominence of the nocturnal low-level jet, creates a vast, largely untapped potential for wind power in the Great Plains. As most standard meteorological observation sites were not designed for wind energy applications, there is a substantial lack of meteorological data at these heights [4]. Tall meteorological towers are expensive to operate and maintain, and many tall towers that have been deployed at future wind farm sites do not reach the projected turbine hub height [5].
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