Modern wind farms require significant land resources to separate each wind turbine from the adjacent turbine wakes. These aerodynamic constraints limit the amount of power that can be extracted from a given wind farm footprint. We conducted full-scale field tests of vertical-axis wind turbines in counter-rotating configurations under natural wind conditions. Whereas wind farms consisting of propeller-style turbines produce 2 to 3 watts of power per square meter of land area, these field tests indicate that power densities approaching 100 Watts per square meter can be achieved by arranging vertical-axis wind turbines in layouts that enable them to extract energy from adjacent wakes. In addition, we calculated that the global wind resource available to 10-meter tall turbines based on the present approach is approximately 225 trillion watts (TW), which significantly exceeds the global wind resource available to 80-m tall, propeller-style wind turbines, approximately 75 TW. This improvement is due to the closer spacing that can be achieved between the smaller, vertical-axis wind turbines. The results suggest an alternative approach to wind farming, in which many, smaller vertical-axis wind turbines are implemented instead of fewer, large propeller-style turbines.
We conducted a series of field tests on six 10-m tall x 1.2-m diameter VAWTs on a tract of flat, vacant land in the Antelope Valley of Los Angeles County, California from June to September 2010. The turbines were a commercially available model with 4.1-m span airfoil blades and a 1200-Watt generator connected to the base of the turbine shaft. Three of the turbines rotated around their central shaft in a clockwise direction (e.g. from a top view) in winds above 3.8 m s-1; the other three rotated in a counter-clockwise direction when the wind speed exceeded the same threshold.
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