US President Barack Obama made a full-throated defense of renewable energy Monday, hitting coal-championing critics as free market hypocrites.

With one eye on a looming battle over power plant emissions limits, Obama took on fossil fuel supporters during a speech in the parched desert oasis of Las Vegas.

Framing climate change as "one of the most important issues not just of our time, but of any time," Obama said renewable energy offered a viable solution.

He made the economic case for developing green industries that provide "a steady stream of well paying jobs."

"The solar industry now employs twice as many Americans as mining coal," he claimed.

His comments come after the White House backed the first national emissions limits for power plants. That has energy firms and lawmakers in coal-rich states such as Kentucky lobbying heavily against the proposals.

He accused coal champions as being fair-weather capitalists, perhaps a subtle dig at Senate Majority Leader Mitch McConnell.

"We see the trend lines, we see where technology is taking us, we see where consumers want to go," Obama said.

"That, let's be honest, has some big fossil fuel interests pretty nervous. To the point where they are trying to fight renewable energy."

"It's one thing if you are insistent on being free market, it's another thing if you're free market until it's solar that's working and people want to buy it."

Solar power currently makes up a fraction of America's energy mix and has enjoyed government grants and subsidies to get up and running.

But Obama also said it was an example of American ingenuity.

"We can do good and do well at the same time," he said.