The Obama administration has formally adopted a plan to help create large-scale solar energy plants, offering incentives for solar developers to cluster projects on 285,000 acres of federal land in the western U.S and opening an additional 19 million acres of the Mojave Desert for new power plants.

The plan places 445 square miles of public land in play for utility-scale solar facilities.

The program, announced Friday by Interior Secretary at an event in Las Vegas, will apply to new projects only and not the 17 solar facilities already awarded permits or the 78 currently in the approval pipeline.

"This historic initiative provides a road map for landscape-level planning that will lead to faster, smarter utility-scale on public lands," Salazar said.

The plan establishes 17 solar energy zones in six Western states, including 154,000 acres in California. The zones were chosen because they avoided major environmental, cultural or other conflicts. The policy encourages developers to select sites within zones by promising minimal environmental reviews and expedited permitting and a range of additional .

But developers can sidestep the zones under certain conditions. Companies may construct plants on 19 million acres designated as "variance" zones, but the government offers fewer incentives to build there. Another 79 million acres are in exclusion zones, where no is allowed.

California has 2 { times more acreage in solar zones than any other state. The state has 750,000 acres in variance areas.

Some conservation groups fought to prevent approval of utility-scale projects in the region, contending that the desert - home to scores of endangered plants and animals - was not capable of absorbing industrial-scale projects.

"We are ... disappointed to see that vital habitat for the federally threatened is still open to potential development through the variance process," said Jamie Rappaport Clark, president of Defenders of Wildlife.

Critics contend that the policies are too late, coming after years of free-for-all leasing that encouraged rampant speculation. Since leasing began, the U.S. Bureau of Land Management has been working to process more than 300 solar applications.

Many of those are for land in California's , where counties have seen the cost of private land soar and the desert given over to thousands of acres of mirrors.

Earlier this week the Interior Department announced that it had surpassed a milestone - authorizing the first 10,000 megawatts of power. The fast-tracking of solar facilities on public lands is expected to generate nearly 24,000 megawatts of renewable power by 2030, officials said.

But so far, the unprecedented urgency given to projects on public land has yielded only 50 megawatts of produced power, according to officials.

Janine Blaeloch of the group Solar Done Right supports renewable energy but said wholesale development of the desert is a mistake.

"This should all be happening on rooftops and in cities," Blaeloch said. "But that wouldn't profit the big utilities, and industry wouldn't be able to get tax breaks, so we wreck the desert instead. We aren't getting that public land back. Once it's industrialized, everything that lives there and everything we enjoy about it will be gone."