For the last few years, much of the innovation around solar technology has been aimed at generating more electricity from sunlight. But a new crop of entrepreneurs is working to use the sun more efficiently by using its heat, as well as its light, for individual business, factories and, perhaps one day, even homes. These companies say that providing both electricity and heat reduces the amount of time it takes customers to recoup their investments. "It's a single system that provides the greatest impact on a homeowner's energy bill," says Sam Weaver, CEO of heat and power solar startup Cool Energy.