Above that threshold, energy increases exponentially with speed. A site with 12 mph winds can generate 70 percent more energy than a site with 10 mph winds.
Wind speeds also increase quickly with altitude. A 10 kW turbine generates 30 percent more power on a 100-foot tower than a 60-foot tower. The difference is greater if tall trees or structures block the wind or create turbulence.
Most wind turbines automatically shut down when wind speeds rise above 25 mph to avoid mechanical damage or bodily injuries. A relatively calm area with seasonal windstorms may never generate much wind capacity.
The other major consideration is the size of the turbine’s rotor blade. Like wind speed, a larger blade will generate exponentially more energy. A 10-foot blade may not look much larger than an 8-foot blade, but the “swept area” is 58 percent larger. That corresponds with a 58-percent increase in energy production per blade rotation.
The other parts of the turbine differ in quality more than output. Look for a reputable company with quality parts and avoid claims of extreme power production.
You might get a good offer on a wind turbine rated at 10 kW, but without considering several mechanical and natural factors, it is hard to determine the actual electric production capacity.
Photo: ell brown on Flickr