DOE's Classes of Wind


The Department of Energy’s National Renewable Energy Laboratory defines the wind class at a site on a scale from 1 to 7 (1 being low and 7 being high) based on average wind speed and power density to offer guidance to potential developers as to where wind projects might be feasible. A way of quantifying on a scale the strength of the wind at a project site.

Table 1-1 Classes of wind power density at 10 m and 50 m(a)
Wind Power
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)
150 5.1 (11.5) 300 6.4 (14.3)
200 5.6 (12.5) 400 7.0 (15.7)
250 6.0 (13.4) 500 7.5 (16.8)
300 6.4 (14.3) 600 8.0 (17.9)
400 7.0 (15.7) 800 8.8 (19.7)
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.

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.


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