http://www.slate.com/articles/technology/the_juice/2015/09/solar_panels_from_cps_energy_the_san_antonio_utility_s_brilliant_new_business.html

The business model surrounding rooftop solar has changed dramatically in the past decade. Several years ago early adopters had to spend a lot of money to buy expensive home systems—with no hope of recouping their investments. As prices of silicon panels came down, homeowners in the next wave could look forward to a 20-year payback period. Next, companies like SolarCity changed the game by creating the solar lease—which required no money down but a long-term financial commitment that promised to lower monthly electricity payments.