With both M-KOPA and Eight19 models, the lights go out if the payments stop, providing an incentive to keep paying.

ECONOMIST: Solar lighting

They include Applied Solar, which also plans to build power plants for Indian cell towers, and M-KOPA, a startup created by the founders of M-PESA, the leading mobile-payment service in Kenya and Tanzania.

FORBES: Cleantech Startup Finds Poor Villagers Are More Profitable Than Mobile Telecom