"[The company] designs, installs, and maintains solar-energy systems fitted
to homeowners' roofs. Instead of asking for a big upfront payment, it leases
the systems. As the panels produce power, surplus electricity is sold back
to the local utility. Combined with the savings that come from using less
power from the grid, this will typically reduce the homeowner's electric
bill by enough to offset the lease payments."

http://www.technologyreview.com/energy/40352/?p1=A1