When Greg Johanson first had the idea to give the hybrid car a bit of solar electrical energy, he didn't know what a challenge that curved roof would present.

Johanson's company had to embed the solar cells into fiberglass and custom mold it.

Tapping the roof, Johanson called the Prius the "worst vehicle" for testing his concept.

"I have a habit of doing things backward," he said. "If we could make the worst vehicle work, the easy vehicle should be easy."

The company soon will be producing solar panels for Toyota's Rav4 EV and Highlander, two vehicles with very flat roofs.

Johanson is president of Solar Electrical Systems, which creates and installs home and business solar systems. Known for his tinkering, Johanson — who co-designed the first entirely solar-powered vehicle — launched Solar Electrical Vehicles as a sister business in 2005 to focus on bringing solar power to hybrid cars.

Since then, Solar Electrical Vehicles has sold about 130 conversion kits for the Prius. The system drinks up solar power and uses motorcycle batteries hidden in the rear well to supplement the manufacturer's battery.