An EA-6B Prowler from the Salty Dogs of Air Test and Evaluation Squadron 23 flies Sept. 16, 2011 over Southern Maryland. The plane uses a biofuel blend of JP-5 aviation fuel and camelina oil. The Department of Defense, a huge consumer of petroleum, is trying to develop biofuels on a large scale as an alternative. Republicans in Congress have voted the program out of an authorization bill, saying oil and even coal can meet the military's needs. - 

Sarah Gardner: Talk about betting: The U.S. military's certainly been betting on alternative energy the past couple year. And this month, the Navy shows off what it calls its Great Green Fleet. We're talking ships and warplanes running on 50 percent alternative biofuels.

But there's pushback in Congress from lawmakers who object to the cost, and from biofuels competitors who want are vying for defense dollars. Scott Tong reports from the Marketplace Sustainability Desk.

Scott Tong:The Navy’s demo is part of a broader effort to cut the military’s addiction to petroleum -- for tanks, ships, planes, generators, air conditioning in the desert. Geoff Dabelko is with the Woodrow Wilson Center think tank.

Geoff Dabelko: We count on them to anticipate, to game out, to look at even low-probability events. And one of those is changes in our access to fossil fuels.

Planes and vehicles use liquid fuels, so solar and wind don’t help much. So we’re left with biofuels from plants, algae, woodchips. And right now, they struggle to compete with crude oil. On a per-drop basis, crude packs an unbelievable amount of energy.

Robert Rapier: Mother Nature did all that.

Biofuels entrepreneur Robert Rapier is with Merica International.

Rapier: The heat and pressure has converted it into a very energy-dense liquid fuel. That’s the main reason why biofuels will always have a hard time competing with petroleum.

And that’s before you get to the politics of green energy. Texas Republican congressman Mike Conaway added language to a military bill. It bans the Navy from buying more expensive fuels, like biofuels.

Mike Conaway: We don’t have the money to be wasting on this publicity stunt. It’s just about wasting money that we don’t otherwise have, when we are trying to trim $487 billion out of the defense budget.

Conaway also penned a provision letting the Pentagon buy fuels with a dirtier greenhouse footprint. That opens the door to fuel from coal. Congressional staffers say the coal lobby’s been “pushing hard.” Also in: oilsands crude from Canada – subject of the Keystone XL pipeline fight. Cindy Schild is with the American Petroleum Institute.

Cindy Schild: We support anything that can limit restrictions on bringing in additional supplies from Canada.

The revenge of the fossil fuels is embedded in a bill passed in the House, and one the Senate takes up this summer. Still, even if biofuels get whacked, it’s just one military energy program. Most others, including solar batteries for Marines on the front lines, stay fully charged. In Washington, I’m Scott Tong for Marketplace.

Follow Scott Tong at @tongscott