Efforts to wean the Defense Department off of coal, oil and natural gas could do more harm than good, officials inside and outside the department concede.

During a House panel hearing Wednesday, the Pentagon's top energy official acknowledged that some renewable energy sources proposed for use at hundreds of military installations could interfere with their missions. Wind turbines, for instance, can degrade air-based and ground-based radar, while solar power-generating towers can cause interference by creating thermal images that are detrimental to sensitive testing of weapons systems, said Dorothy Robyn, undersecretary of Defense for installations and environment.

However, Robyn said there are many checks in place to make sure the department doesn't proceed with projects that interfere with training and radar.

"I don't believe any project has gone forward that creates any sort of a problem," Robyn said before the House Armed Services subcommittee on readiness.

A high-profile dispute arose last year when officials at Nellis Air Force Base, Nev., outside Las Vegas objected to agency plans to build a solar thermal power plant on federally owned land about 25 miles from the base's Nevada Test and Training Range. Base officials said the plant's 600-foot solar tower would interfere with radar used to guide flight training. SolarReserve, the California company behind the project, already had moved the planned location of the plant away from the base to mollify critics, but then base leaders called for the entire project to be scrapped.

The Defense Department brought in radar experts from the Massachusetts Institute of Technology, who conducted a six-month study of the potential impacts, Robyn said. The result was that the planned tower was moved a mile away from its proposed location.

A December report by the Government Accountability Office found that renewable energy projects may sometimes be incompatible with a military installation's need to use the land for training and other mission objectives. A Marine Corps installation visited by GAO ruled out installing on-site wind turbines to generate electricity, even though there were sufficient prevailing winds, because they would interfere with flight and firing exercises conducted in the location where the turbines would be built, GAO said.

The Pentagon does have a process for reviewing renewable energy proposals and handling disputes, yet the process is "opaque, time consuming and ad hoc," Robyn testified. Oftentimes, she said, base commanders don't learn about planned projects until they are well underway because energy companies are reluctant to divulge to their competitors what projects they're working on.

Robyn is heading up a team within the department that's working to improve the evaluation process.

"What we would like to do is come up with a more streamlined approach for projects that aren't as controversial," she said.

Robyn also said she's hopeful that advanced technologies will be developed that reduce negative impacts of renewable energy projects on military operations.