More than 500,000 people are employed in "green jobs" in California and that number is expected to ramp up in the coming years, according to a report.

The Environment California Research & Policy Center report, "Building a Clean Energy Workforce: Preparing Californians for New Opportunities in the State's Green Economy," additionally documents nearly 300 green job training programs at more than 130 institutions throughout the state.

Those programs have as many as 15,000 students enrolled annually, the report said. Bernadette Del Chiaro, the center's director of clean energy programs, said green jobs are giving the economy a boost.

"Thousands of Californians are seeking refuge from the recession via the growing green energy economy," she said. "Job training programs are a critical engine for developing the work force needed to achieve the state's environmental goals."

That may be true. But some, including economist Christopher Thornberg, figure there's some wiggle room in defining exactly what a "green" job is.

"Who the hell knows what they classify as a green job," Thornberg said. "That's what it boils down to. There are very few jobs you could say are truly green - maybe a solar panel installer ... but who else?"

The report, released last week, says that the skills required of a worker in a green job often overlap with those needed for more traditional occupations.

Many workers can transfer their existing skills to a new "green job," the study said, if they receive specialized training to fully take advantage of green job opportunities.

Electricians, for example, must perform many of the same steps when working in an efficient building as in a conventional one. But they must also be aware of the building's overall energy usage and avoid compromising its insulation or allowing air to leak in.

Likewise, a mechanic servicing an electric vehicle may require additional training to deal with more sophisticated electronics and braking. But other systems within the electric car may be identical to a conventional, gasoline-powered car.

Univoip in El Segundo installs green telephone systems that are linked directly into a company's computer network.

The technology has several advantages including a big cost savings, according to Wilson Guzman, a Univoip marketing representative.

"If a company with 100 employees moves from one location to another that could cost them $160,000 to buy and install a new phone system," he said. "But our system cost would be about $3,000."

And growth? Wilson says he's seeing it first-hand.

"We're growing faster and faster, bringing people in all the time," he said.