Wind energy is expected to make up about 4.6 percent of total U.S. electric power generation by 2015, totaling about 77,000 megawatts of wind power capacity nationwide, U.S. Energy Information Administration data show. That’s up from 3 percent in 2012, when total U.S. wind power generation capacity was about 60,000 megawatts. One megawatt of wind power is enough energy to provide electricity to roughly 300 homes. A new interactive map featured on the U.S. Department of Energy’s website shows how fast all those wind farms were constructed. The first panel in the map shows the nation’s first wind farm going online in southern California in 1975, producing enough electricity to power 4,149 homes. Flash forward 20 years to 1995, and there were 54 wind farms across the country, mostly in California, powering 349,000 homes. By 1999, wind farms were coming online throughout west Texas, Minnesota, Wisconsin, Iowa, Colorado and Wyoming. As of 2012, there were more than 45,000 wind turbines in 39 states and Puerto Rico, providing enough electricity to power about 15 million homes.