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Wind Data Details

Areas designated class 3 or greater are suitable for most utility-scale wind turbine applications, whereas class 2 areas are marginal for utility-scale applications but may be suitable for rural applications. Class 1 areas are generally not suitable, although a few locations (e.g., exposed hilltops not shown on the maps) with adequate wind resource for wind turbine applications may exist in some class 1 areas. The degree of certainty with which the wind power class can be specified depends on three factors: the abundance and quality of wind data; the complexity of the terrain; and the geographical variability of the resource. A certainty rating was assigned to each grid cell based on these three factors, and is included in the Wind Energy Resource Atlas of the United States.

Table 1-1. Classes of wind power density at 10 m and 50 m(a)
Wind Power
Class
10 m (33 ft) 50 m (164 ft)
Wind Power Density
(W/m 2)
Speed (b) m/s (mph) Wind Power Density
(W/m 2)
Speed (b) m/s (mph)
1 0 0 0  
100 4.4 (9.8) 200 5.6 (12.5)
2
150 5.1 (11.5) 300 6.4 (14.3)
3
200 5.6 (12.5) 400 7.0 (15.7)
4
250 6.0 (13.4) 500 7.5 (16.8)
5
300 6.4 (14.3) 600 8.0 (17.9)
6
400 7.0 (15.7) 800 8.8 (19.7)
7
1000 9.4 (21.1) 2000 11.9 (26.6)
  1. Vertical extrapolation of wind speed based on the 1/7 power law.
  2. Mean wind speed is based on Rayleigh speed distribution of equivalent mean wind power density. Wind speed is for standard sea-level conditions. To maintain the same power density, speed increases 3%/1000 m (5%/5000 ft) elevation.

*NOTE: Each wind power class should span two power densities. For example, Wind Power Class = 3 represents the Wind Power Density range between 150 W/m2 and 200 W/m2. The offset cells in the first column attempt to illustrate this concept.