Wind resource evaluation is a critical element in projecting wind turbine performance at a given site. The energy available in a wind stream is proportional to the cube of its speed, which means that doubling the wind speed increases the available energy by a factor of eight. Furthermore, the wind resource itself is seldom a steady, consistent flow. It varies with the time of day, season, height above ground, and type of terrain. Proper siting in windy locations, away from large obstructions, enhances a wind turbine's performance.

 

In general, annual average wind speeds of 5 meters per second (11 mph) are required for grid-connected applications. Annual average wind speeds of 3 to 4 m/s (7 to 9 mph) may be adequate for non-connected electrical and mechanical applications such as battery charging and water pumping. Wind resources exceeding this speed are available in many parts of the world. A useful way to evaluate the wind resource available at a potential site is the wind power density.