Potential disadvantages aside, the United States has a good number of wind turbines installed, totaling more than 9,000 MW of generating capacity in 2006. That capacity generates in the area of 25 billion kWh of electricity, which sounds like a lot but is actually less than 1 percent of the power generated in the country each year. As of 2005, U.S. electricity generation breaks down like this:
- Coal: 52%
- Nuclear: 20%
- Natural gas: 16%
- Hydropower: 7%
- Other (including wind, biomass, geothermal and solar): 5%
Source: American Wind Energy Association
The current total electricity generation in the United States is in the area of 3.6 trillion kWh every year. Wind has the potential to generate far more than 1 percent of that electricity. According to American Wind Energy Association, the estimated U.S. wind-energy potential is about 10.8 trillion kWh per year -- about equal to the amount of energy in 20 billion barrels of oil (the current global yearly oil supply). To make wind energy feasible in a given area, it requires minimum wind speeds of 9 mph (3 meters per second) for small turbines and 13 mph (6 meters per second) for large turbines. Those wind speeds are common in the United States, although most of it is unharnessed.
When it comes to wind turbines, placement is everything. Knowing how much wind an area has, what the speeds are and how long those speeds last are the crucial deciding factors in building an efficient wind farm. The kinetic energy in wind increases exponentially in proportion to its speed, so a small increase in wind speed is in fact a large increase in power potential. The general rule of thumb is that with a doubling a wind speed comes an eight-fold increase in power potential. So theoretically, a turbine in an area with average wind speeds of 26 mph will actually generate eight times more electricity than one set up where wind speeds average 13 mph. It's "theoretically" because in real-world condition, there is a limit to how much energy a turbine can extract from the wind. It's called the Betz limit, and it's about 59 percent. But a small increase in wind speed still leads to a significant increase in power output.