FACTBOX: Green energy at U.S. military bases

(Reuters) - The U.S. Department of Defense is trying to cut its energy use to save money and seeks to have 25 percent of its energy come from renewable sources by 2025.

Here are some examples of energy-saving efforts in use or development at three bases in the U.S. West:

PORTABLE RENEWABLE POWER

--THEPS, or Tactical Hybrid Electric Power System, is a portable renewable power station in development at Fort Irwin in California's Mojave Desert. THEPS will one day provide electricity during national emergencies, or electrify remote villages around the world.

As big as a standard, 20-foot (6-metre) shipping container, THEPS would be airlifted by helicopter or pulled by trucks. THEPS insulated boxes will in several years help power remote military posts, cutting the need for risky and expensive refueling convoys.

-- INSULATING FOAM

The Army sprays big canvas tents that house troops in Iraq and Afghanistan and at training bases including Fort Irwin. The tents cost about $70,000 each and it costs about $72,000 to spray them with foam.

At Fort Irwin last week, with the temperature outside was 115 F (46 C), the temperature inside a tent with foam insulation was 74 degrees Fahrenheit (23 Celsius) without being air-conditioned, while a tent without the foam insulation was 20 degrees (6.66 C) hotter.

The cost of insulating the tents with foam pays for itself in savings on diesel fuel in 35 days.

-- SOLAR POWER PLANT

The biggest photovoltaic solar panel array in the United States covers 140 acres at Nellis Air Force Base in Nevada. At peak production, it provides about 25 percent of the base's power needs.

GEOTHERMAL POWER PLANT

-- The Coso Geothermal Field serves the China Lake Naval Air Weapons Station near Death Valley and the Mojave Desert in California. It generates 270 megawatts of power, enough to power about 175,000 California homes.

(Reporting by Bernie Woodall; Editing by Patricia Zengerle)