A gasoline-powered generator can supply electricity to a remote U.S. Marine outpost in Afghanistan, powering everything from laptops to communications equipment. And the noise from that generator can be a dead giveaway to Taliban forces searching for Americans.

So when Marines tout the effectiveness of quiet, solar-powered generators, it's not because they feel all warm and fuzzy about Earth Day. They say the equipment makes them safer in a combat zone.

"A lot of our enemies can follow us around by the noise of our generators," said Marine Col. Bob Charette, director of Expeditionary Energy in the Marine Corps.