NEW YORK (CNNMoney.com) -- To hear environmentalists tell it, investing in renewable energy won't just provide a clean source of power, it will create an explosion of new jobs.
Estimates of just how many jobs our push to go green may generate vary widely, and not all economists believe that there really will be any kind of "green job" boom.
The Apollo Institute, a group that wants the government to embark on a renewable energy project similar to the Apollo space program that put a man on the moon, expects to see three million new green jobs over the next ten years.
But the Energy and Resources Group at the University of California Berkeley thinks the boom will deliver something more along the lines of one million new jobs by 2020.
Champions of renewable energy tout the jobs angle as another reason why the government should pour money into subsidies and other incentives for the industry. But economists are split as to whether these projected jobs will ever materialize.
"You can never say for certain," said Drew Matus, a senior economist at Lehman Brothers. Still, the renewable sector is an obvious place to generate new jobs.
"New industries are where jobs are going to be created, because they are new," he said.
Matus added that what's important is whether the new jobs created in the renewable energy industry offset jobs lost elsewhere, like in oil and gas.
Supporters of renewable energy say there will be new jobs for technicians to install rooftop solar arrays and backyard windmills, jobs at manufacturers making parts for utility-scale wind and solar equipment, and jobs in agriculture, harvesting biomass.
In addition, they say, these jobs will won't get outsourced.
"We're not going to import biofuel from Saudi Arabia," said Dan Kammen, a professor in the Energy and Resources Group at the University of California Berkeley.
"The installation of solar panels is not something that can be exported," said George Sterzinger, head of the Renewable Energy Policy Project. "These are good, skilled, well-paying jobs."
Sterzinger pointed out that Midwest farmers are currently commanding a higher price for their corn thanks to the boom in ethanol, and said money flowing into the region would soar if ethanol was more widely used.
"That would just pump million and millions back into he farm communities, which would create the secondary jobs as well," he said.
But Robert Brusca, chief economist at Fact and Opinion Economics, a Manhattan consultancy, isn't convinced that ethanol production is necessarily creating new jobs.
He said lots of the new jobs in the biofuels sector could simply be filled with people shifted over from picking crops, in which case they wouldn't be new jobs at all.
"I don't understand what people are looking at to say there would be all these gains on the job front," he said. "It sounds kinda phony to me."
Brusca also said it's unrealistic to count on job gains in the solar sector, since the technology just hasn't taken off yet, adding that "green job" boosters have no way of knowing if it ever will.
"You certainly don't want to move all sorts of money into an area that's not going to be viable," he said.
Sterzinger on the other hand argues that the U.S. government should invest heavily in helping the green job sector grow.
He suggested the government take a more active role in bringing together renewable energy companies and manufacturers of other industrial equipment, so manufacturers can understand the needs in the renewable energy sector.
He also called for government-backed loans for renewable energy companies.
He said the United States could be a leading country when it came to manufacturing solar cells, but that "we're losing ground to Germany on this. You really need the polices, it's not just going to happen automatically." 
