Wind energy is another form of solar energy – as the sun heats the earth, it does so unevenly. Dark landmasses heat faster than light ones. Day time heats while night time cools. Water bodies are heated by the sun at a different rate than dry earth. Since warm air is less dense than cool air, it tends to rise. All of the temperature differentials result in areas of rising and falling air that then cause horizontal air movement to fill the gap left by the rising air with the falling cooler air.
About 1 to 2 percent of all solar energy that strikes the face of the earth is converted to wind energy. That gives us a value of around 2 x 1015 Watts of power (2,000 Terawatts) available in all of the wind on earth at any given time. Obviously we can’t harness all of that energy, but considering the average worldwide power consumption was only 15 Terawatts in 2009, it’s obvious we only need to capture a small fraction of that available energy to make a big change.
Depending on the location of the wind turbines, the annual wind conditions, and proper service and maintenance, a wind farm will typically generate about 30% of its name plate capacity over the course of a year.