The Spatial and Temporal Distribution of U.S. Winds and Windpower at 80 m Derived from Measurements

This is a study to quantify U.S. wind power at 80 m (the hub height of large wind turbines) and to investigate whether winds from a network of farms can provide a steady and reliable source of electric power. Data from 1327 surface stations and 87 soundings in the United States for the year 2000 were used. Several methods were tested to extrapolate 10-m wind measurements to 80 m. The most accurate, a least-squares fit based on twice-a-day wind profiles from the soundings, resulted in 80-m wind speeds that are, on average, 1.3-1.7 m/s faster than those obtained from the most common methods previously used to obtain elevated data for U.S. windpower maps, a logarithmic law and a power law, both with constant coefficients. The implication is that U.S. windpower at 80 m is enormous and much greater than previously thought. It was found that 25.2 percent of all stations (and 44.6 percent of all coastal/offshore stations) are characterized by mean annual speeds >= 6.9 m/s at 80 m, implying that the winds over possibly one quarter of the U.S. are strong enough to provide electric power at a direct cost equal to that of a new natural gas or coal power plant. The greatest previously uncharted reservoir of windpower in the continental U.S. is offshore and near shore along the southeastern and southern coasts. The other great reservoirs, previously charted, are the north- and south-central regions. The five states with the highest percentage of stations with annual mean 80-m winds >= 6.9 m/s were Oklahoma, South Dakota, North Dakota, Kansas, and Nebraska. Other findings are (1) monthly and annual mean wind speed (and wind power) peaks in the afternoon, when electricity demand is usually high; (2) winds are Rayleigh in nature, and actual wind power at any hour of the day is close to Rayleigh wind power; (3) the standard deviation of the wind speed averaged over multiple locations is less than that at any individual location; (4) when multiple wind sites are considered, the probability of no wind power production at a given instant is substantially reduced in comparison to when one wind site is considered. In sum, a network of wind farms in locations with high annual mean wind speeds can provide a reliable and abundant source of electric power.