The rooftops and parking lot space available at retail giants like Walmart, Target and Costco is massive. “I would have loved to see policy help incentivize rooftop solar 15 years ago instead of five years ago in the commercial space. 1 for on-site solar capacity in 2019, according to the Solar Energy Industries Association. 1 for on-site solar capacity in 2019, according to industry trade group Solar Energy Industries Association’s most recent report. It currently has 542 locations with rooftop solar — around a quarter of the company’s stores — a Target spokesperson told CNN.