The city of Houston has agreed to purchase half its electricity from renewable energy sources, a step that makes the Texas city the nation’s largest municipal buyer of green energy. In a contract signed with Reliant Energy, Houston committed to buying more than 140 megawatts of renewable power from July 1, 2013 through June 30, 2015, locking in nearly 623,000 megawatts of clean power annually. According to city officials, the government committed $2 million — less than 1 cent per kilowatt-hour — through the purchase of renewable energy credits that will be used to fund alternative energy projects. “Houston is already known as the energy capital of the world, but we are committed to becoming the alternative energy capital of the world as well,” Mayor Annise Parker said in a statement. In addition to investing in wind energy, the city touted major solar projects at municipal sites and efforts to streamline its solar power-permitting process.