The city already has a program, Solarize Philly, in place to help residents install rooftop solar panels. Officials say more than 2,100 residents have expressed interest, and 186 have signed solar installation agreements. The goal is to sign up 500 residents by next year. About 80 percent of Philadelphia's rooftop space is suitable to generate solar. However, even if half of that space were devoted to solar, the city's needs would not be met.