WIND POWER

According to a study done by Pacific Northwest National Laboratory, the total estimated electric energy potential of wind for the continental United States is 11 million GWh per year from regions rated as Class 3 and higher2 (Elliott et al., 1991)—a value greater than the 4.2 million GWh of electric energy generated in the United States in 2007. In energy units, 11 million GWh represents 40 EJ of energy, as compared to the 2007 domestic primary energy consumption of 100 EJ.

The domestic large-scale wind electric energy resource estimate of 11 million GWh is uncertain, however, and the actual wind resource could be higher or lower. One source of uncertainty is that the yearly wind electricity potential from the PNNL study was estimated from point-source measurements of the wind speed at a height of 50 m (Elliott et al., 1986). Modern wind turbines can have hub heights of 80 m or higher, where more wind energy resource is likely to be available. However, computer simulations of very-large-scale wind farm deployment show that an agglomeration of point-source wind speed data over large areas can significantly overestimate the actual wind energy resource base (Roy et al., 2004). Just as a large wind turbine will overshadow a wind turbine farther downwind, so a very extensive wind farm will also overshadow other wind farms downwind. Specifically, when the downwind length of the wind farm is comparable to, or larger than, the scale length of the atmosphere (approximately 50 km), then the point-source measurement extrapolation is no longer valid, and significantly overestimates the actual available wind energy resource (Keith et al., 2004).

Another consideration is that wind field deployment at levels needed to produce 5 million to 10 million GWh of electricity would entail extraction of a significant portion of the energy from the wind field of the continental United States for conversion into electric energy. Continental-scale simulations indicate that high levels of wind power extraction could, to various degrees, affect regional weather as well as climate. In addition to limiting the efficiency of large-scale wind farms, model calculations suggest that the extraction of wind energy from very-large-scale wind farms could have some measurable effect on weather and climate at the local or even continental and global scales (Roy et al., 2004; Keith et al., 2004).

More detailed meso-scale modeling and measurements are needed to clearly delineate the total U.S. extractable wind energy potential and the portion that can

2

Wind class is a measure of wind power density, which is measured in watts per square meter and is a function of wind speed at a specific height.



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