MUSK IS THE FIRST to admit that electric cars aren't sin-free: Most electricity is produced using fossil fuels, which release carbon into the atmosphere, or with nuclear power, which has its own set of troubling issues. A Tesla will run 100 percent clean only if its electricity comes from a clean source—a solar cell, for instance. For Musk, however, this isn't a glitch in his business plan but another clean-tech opportunity: to make solar power a viable resource.

According to Musk, the solar market today is like the computer industry of the eighties. The microchip was a great invention, but until Microsoft and Macintosh found a way to bring it to the consumer, it had a limited impact. "We have dozens of solar-equipment manufacturers," he explains, "but they're so focused on ratcheting up production, in part to meet the growing demand coming from Europe, that few are working to bring their products to the average American consumer."

His newest company, SolarCity, which launched in July at solarcity.com and is scheduled to open its first retail outlet in December, in San Francisco, sells photovoltaic panels from multiple manufacturers, as well as installation and maintenance services. Among its promises: "Full-service clean-energy solutions that save you money." Says Musk, "We want to become the Dell of solar." The company's first target customers are Tesla owners, who are the type of trendsetters Musk hopes will inspire others to follow suit. For $6,500, SolarCity technicians will install a small solar-panel system on a Tesla driver's residential rooftop. "It closes the loop," says Musk. "It makes the car fully eco-friendly."

Even better, it's a foot in the door of a much bigger market: photovoltaic systems for the whole family. Solar panels powerful enough to generate electricity for an 1,800-square-foot house typically cost $12,000 to $17,000, but, as Musk explains, the investment will repay itself over eight to twelve years. In 30 years, it could generate as much as a 350 percent return on the initial purchase price—in part because public utility companies are starting to buy back privately produced solar-energy surpluses. And since going green will be increasingly essential as the future unfolds, a solar system will undoubtedly raise resale values. "In the modern world," Musk says, "clean energy production should be part of a diversified investment portfolio."

It's a new way of thinking, even for consumers who already consider themselves progressive. But as Musk sees it, we'd all be crazy not to jump on the clean-tech bandwagon. "There's more money to be made," says Musk. "It just makes economic sense."