(Business 2.0) – The Problem On a trip to Hawaii in January 2001, Randolph Gray noticed beachgoers talking incessantly on their mobile phones. But every once in a while, someone would run out to the parking lot. "They were interrupting their fun because their cell-phone batteries were dead," he says.

The "Aha!" Fascinated by solar energy as a student, Gray built a solar-powered bicycle in college. After earning a bachelor's degree in 1995, he pursued other interests but continued to follow solar technology. At the beach he thought about creating a portable charger, but then he had a better idea: Why not build a solar cell into the bags that sunbathers were already carrying?

The Payoff When he returned home to Texas, Gray bought a solar charger on eBay and sewed it into a backpack. He founded Innovus Designs in 2003 and a year later sold his first solar bag, the Reactor. Last year, Gray says, Innovus turned a small profit on revenue of about $80,000. Now he's working on a bag that can recharge laptops, and he's also pursuing an online MBA. Needless to say, there's less time for the beach.