CHICAGO - SEPTEMBER 01: Solar photovoltaic panels generate electricity at an Exelon solar power facility on September 1, 2010 in Chicago, Illinois. The 10-megawatt facility located on the city's south side is the largest urban solar installation in the United States. The 32,292 panels can generate more than 14,000 megawatt-hours of electricity per year, enough to meet the annual energy requirements of up to 1,500 homes.
