Federal agencies are building on successful efforts to generate electricity from the sun, wind and other renewable energy sources.

Photovoltaic panels and wind turbines have proven to be reliable sources of clean energy that pay for themselves in a matter of years, managers say.

The Navy installed three wind turbines on San Clemente Island, about 50 miles off the Southern California coast, in the late 1990s to displace some of the diesel generators powering training operations there. The turbines produce 11 percent of power on the island, saving the Navy $2.3 million in fuel costs since 2001, said Bernie Lindsey, utilities and energy program manager for the Navy's Southwest region in San Diego. That has more than covered the initial $2 million investment.

"Every kilowatt hour we produce from wind is a kilowatt hour we don't have to burn diesel fuel to achieve the same power," Lindsey said.

Based on the success at San Clemente, the Navy is about to begin construction of up to nine wind turbines at neighboring San Nicholas Island that will produce 100 kilowatts each.

Some wind turbines can produce up to 2 megawatts of energy, but the Navy must limit the size and power of its turbines to avoid interfering with radar signals and other operational requirements, Lindsey said.

To meet more of its energy needs from renewable sources, the Navy is relying on photovoltaic systems that convert heat from the sun into electricity.

In the Southwest, where sunshine and land is more plentiful than other areas, the Navy is negotiating so-called power purchase agreements in which private developers would build, operate and maintain large-scale photovoltaic systems on Navy-owned land. The Navy would agree to purchase up to $200 million in power generated by the systems under 30-year contracts, helping it meet legislative requirements to increase use of renewable energy without any upfront costs.

"We want to significantly increase our renewable energy production at our facilities, but there's simply not the appropriated funding to match what our intended plans are," Lindsey said.

Under the Energy Policy Act of 2005, agencies must increase the amount of renewable energy they consume gradually through 2013. Agencies had to generate at least 3 percent of their energy from renewable sources in 2007 through 2009, increase to 5 percent in 2010 through 2012 and reach 7.5 percent in 2013.

Agencies generated 3.4 percent of their energy from renewable sources in 2008, the last year for which statistics have been released by the Energy Department.

The General Services Administration also is relying more on photovoltaic systems to help it meet renewable energy goals.

GSA is using $40 million in Recovery Act funds to build 35 acres of photovoltaic panels at the Denver Federal Center, which comprises 55 buildings home to about 7,000 employees. Panels will be mounted on building roofs, on carports and on the ground.

The PV system will generate 6 megawatts of electricity, becoming GSA's largest PV system, said Scott Connor, director of the Denver Federal Center. It will join a 1 megawatt photovoltaic system installed at the center in January 2008, which at the time was the largest PV system at a GSA-owned facility.

The two systems combined will allow the Denver Federal Center to generate half of its peak power from solar power, putting the complex well on its path to becoming the most sustainable federal campus by 2020, Connor said.

Once the additional solar arrays come online, the renewable energy produced at the Denver Federal Center will total 84 percent of all renewable energy consumed by GSA-owned buildings nationwide.

PV is a good source of renewable energy because it's easy to make an accurate prediction of how much energy will be produced by each panel, Connor said. The panels also require minimal attention. Connor said groundskeepers mow under the ground-mounted system installed in 2008 to keep grass from obscuring the panels, but otherwise they let Mother Nature handle the rest.

"It's virtually maintenance free," he said.