For a class project at Northwestern, Aaron Hall developed a business plan for Borrego Solar Systems, a family friend's struggling solar power company. He got top marks -- yes, from his professor, but perhaps more importantly, also from the company's owner, who was so impressed he let the 20-something economics student put the plan to work in 2001.

Hall, who now runs the El Cajon, Calif.-based company, has turned Borrego into an alternative energy powerhouse, boosting annual revenue by more than 1,000 percent since 2004 and setting it on course to earn a projected $60 million by the end of the year. He turned 29 in February.

"This is our time," says Hall, a numbers guy who once made cash on the side gambling with other people's money. "I saw the writing on the wall back in 2001, and now global warming and energy independence is on everyone's mind."

What's certain is that before Hall took over, Borrego was in serious trouble. Having launched in 1980 -- when Hall was just a toddler -- the company had since lost nearly all its clients and had not made any sales in years. When Hall stepped in, the main office in San Diego consisted of a desk and single computer.

"It was basically a complete start-up," he says. "I had to go to Office Depot for pens and paper."

He also had to borrow about $20,000 from his dad. Still, Hall knew he was on to something. As part of his class project, he had tried to contact all his competitors in the San Diego solar power industry. None of them responded. To Hall's mind, that meant they were too busy to answer the phone, or simply lacked the sufficient infrastructure to run a successful business. Either way, Hall saw an opportunity.

For the first few months, the company operated out of his parent's house. At one point, neighbors threatened to sue when 18-wheelers began dropping off industrial equipment in the driveway.

When it came to meeting prospective clients, Hall brought along Borrego's original owner. "I was 21, and no one wanted to sign an $80,000 contract with me," Hall says. "Having someone with industry experience behind me helped convince people that we were a serious business." 

As the company grew client by client, Hall began adding staff, including an older brother who initially refused a job offer -- after all, who would want to work for their kid brother? -- yet later signed on with enthusiasm.

Under its young CEO, the company became the first solar energy firm to use Google Adwords. And as brand awareness spread, Hall says his age went from being a disadvantage to a boon. "We had several big clients by that point, and when they found out how old I was it was a 'wow' -- but a good 'wow.'"

These days, Borrego has a half dozen outlets in California, which recently enacted a billion-dollar grant program aimed at encouraging residents to install solar energy panels. To date, it's built and installed some 800 solar panel systems for homes, businesses, and public buildings.

The company has also expanded operations in New England, where its 50 installation -- including a local radio station and a public water treatment plant, among other facilities -- offset as much as 2.4 million pounds of carbon dioxide emissions, what it describes as the equivalent of planting 1,000 trees.

Back in California, the band Cake plans to power its Sacramento recording studio entirely with Borrego's rooftop solar panels for its sixth album. It might not be the most complex installation or the biggest contract, but Hall's excited anyway.

"It's really cool," he says, a subtle hint to his young age. "I love that band."