The U.S. Interior Department will make 16 million acres of public land rich in renewable energy resources available for defense-related projects, Interior Secretary Ken Salazar said Monday in a conference call.

U.S. Defense Secretary Leon Panetta and Salazar signed a memorandum of understanding to encourage projects harnessing solar, wind, geothermal and biomass energy resources on public lands previously restricted for military uses.

The cooperation signals another aggressive step in the Obama administration's renewable energy approach.

Salazar said 13 million acres of those lands will be in Southwestern states. As a result of the cooperation, military services are expected to deploy 1 gigawatt of renewable energy on or around their installations by 2025.

Under the Obama administration some of the largest solar projects in the world have been funded, the Department of Energy said. The administration's approach has drawn criticism as well -- Republicans accused the government of political favoritism and mismanaging public funds when solar panel maker Solyndra, the recipient of a $535 million federal loan guarantee, filed for bankruptcy last fall.

Dorothy Robyn, deputy undersecretary of defense for installations and environment, argues that the renewable projects might be a game changer in the future as traditional power grids are increasingly vulnerable to aging infrastructure and power attacks.

She said the department is testing microgrid technology, which blends different forms of renewable energy together so that grid load can be managed more efficiently.

"Together with advancing microgrid and storage technologies, renewable energy will allow military to maintain critical missions for weeks or months if the power grids go down," she said.

Robyn said military sites have back-up generators if power goes out. But she argues that these generators are expensive and not environmentally friendly. She said the Defense Department wanted to be in a position to rely on microgrid technology and renewable energy.

The military has been aggressively pursuing alternative energy resources ranging from solar projects to biofuels. Te Defense Department deployed a group of warships and fighter jets burning an expensive blend of recycled cooking grease and algae oil and petroleum in July.

However, the department's search for unconventional energy sources, especially alternative fuels, has drawn criticisms from scholars and congress members. According to a 2011 report by the Rand Corp., a non-profit global policy think tank, the military would derive no meaningful benefit from alternative fuels.

The report argues that most alternative fuel technologies are too expensive or too far away from commercial-scale use and urges the military to focus on energy efficiency instead.

Will Rogers, a fellow with the Center for New American Security, a Washington think tank, said the quest for renewables ensures that energy supply to core missions isn't susceptible to accidents and natural disasters. He said the recent power outages were proof to the necessity of having alternative sources of energy.

"Over time, they [renewable energy sources] can pay off," he said.