With the Navy’s Blue Angels and their F/A-18 Hornets arrayed in a neat line behind him, Navy Secretary Ray Mabus announced that they would perform in the Labor Day Air Expo using a 50-50 mix of a plant-based biofuel and conventional fuel.

“It’s part of our process to move to alternative energy all across the Navy,” Mabus told reporters gathered on the sun-baked runway before him on Sept. 1. “The main reason we’re moving toward alternative fuels in the Navy and the Marine Corps is to make us better war fighters.”

As the nation’s single biggest energy consumer, the Pentagon has many reasons to want to diversify its fuel sources. Mabus and others say the move toward alternative energy is about national security and assured sources of supply.

In addition, with oil supplying 80 percent of the military’s energy, the impact of price fluctuations ripples quickly through the system. Each one-dollar increase in the price of a barrel of oil adds more than $30 million a year to the Navy’s energy costs, officials say.

So the Pentagon is pressing ahead with an ambitious program to change its energy use. Its spending on renewable energy increased 300 percent between 2006 and 2009, from $400 million to $1.2 billion, and it is projected to reach more than $10 billion annually by 2030, according to a report issued last week by the Pew Project on National Security, Energy and Climate.

The Defense Department has pledged to obtain 25 percent of its energy from renewable sources by 2025.

In doing so, it has provided a new target of opportunity for environmentalists and green businesses now that climate legislation has failed and renewable-energy subsidies have come under fire, most recently with the collapse of solar-panel manufacturer Solyndra.

But the Navy secretary said he is more focused on the fact that a Marine is either wounded or killed for every 50 convoys of fuel brought into Afghanistan than on cutting greenhouse gas emissions.

“That’s just too high a price to pay,” Mabus said in a phone interview Thursday, adding that when it comes to lower carbon emissions, “It’s a good byproduct, but it’s a byproduct.”

While the military’s goals promote energy independence, it remains unclear how much some of them will cut greenhouse gas emissions. Navy guidelines dictate that the advanced biofuels it will buy cannot pollute more than petroleum, but they do not say the Navy needs to cut greenhouse gas emissions by a specific amount.

Several of the Pentagon’s goals don’t apply to theaters of military operations, where it uses heavy and inefficient equipment such as tanks, some of which average less than a mile per gallon.

Ambitious savings goals

Mabus has outlined a series of ambitious goals for the Navy and Marine Corps, including ensuring that 50 percent of the services’ energy supply comes from alternative energy such as biofuels and solar power by 2020; cutting fossil fuel use by its non-combat vehicles in half by 2015; and reducing fuel consumption on ships 15 percent by 2020.

Other branches have more modest energy goals. The Air Force aims to use alternative aviation fuels for half its domestic aviation needs by 2016, for example, and cut total aviation fuel use 10 percent by 2015.

The scale of the military’s energy consumption, along with its formidable purchasing power, gives its policies tremendous impact.

And in many ways, the military is better positioned than other branches of government to address such long-term challenges as energy use and greenhouse gas emissions.

“One thing the Department of Defense is really good at is risk management and long-term strategic planning,” said Bob Barnes, a retired Army brigadier general who now focuses on the intersection between conservation, energy and national security as a senior policy adviser to the Nature Conservancy.

The Pentagon began discussions about its dependence on fossil fuels and the potential risks associated with climate change with its allies during the Bush administration, and it has continued to talk strategy with top military officers in Britain and elsewhere.

“On both sides of the Atlantic, we’ve recognized there are new sets of energy threats and challenges that we face,” said Rear Adm. Neil Morisetti, the climate and energy security envoy for Britain’s Foreign and Commonwealth Office and its Defense Ministry, during a recent visit to Washington.

Not all of the Pentagon’s renewable-energy projects have gone smoothly. This month, the Energy Department announced a conditional commitment to back a $344 million loan for a $1 billion project to install solar panels at 160,000 locations on 124 military bases throughout the country. But last week, Solar City, the company that won the contract to put in what Energy Secretary Steven Chu described as “the largest domestic residential rooftop solar project in history,” announced it would not meet the Sept. 30 loan guarantee deadline. The delay could imperil the project.

Projects under fire

Some question whether the government should be financing such projects rather than allowing the free market to determine whether the technologies succeed or fail. Jack Spencer, a research fellow at the Heritage Foundation, asked why “the Pentagon has to be compelled to engage in those programs with mandates and forced spending. . . . Leading a green revolution is not a legitimate mission for our armed forces.”

Jackalyne Pfannenstiel, assistant secretary of the Navy for energy, installations and environment, said Wednesday during a press call organized by Pew, “I think it’s fair to say every single program in the Department of Defense and the Department of the Navy needs to be scrutinized in these tight budget times. . . . I can’t say anything definitive because we’re obviously at the early stages of deciding how we will meet these budget restrictions. But I do think that energy is an incredibly important program, and recognized as such from both a war fighting and cost standpoint.”

But for the moment, these initiatives are helping clean-technology entrepreneurs who are facing a grim economy and regulatory uncertainty. Nicole Lederer, co-founder of Environmental Entrepreneurs (E2), said her group’s members have found new opportunities through defense contracts now that Congress has balked at setting national limits on greenhouse gases that would have boosted demand for low-carbon energy.

“We have turned our attention to every other possible avenue for progress,” said Lederer, whose organization partners with the Natural Resources Defense Council, an advocacy group. “When one door closed, a big window opened with the Department of Defense.”

Solazyme Inc. Chairman Jerry Fiddler, whose company produces fuel from algae, will have sold 175,000 gallons of fuel to the Navy by May 2012 through contracts with the Defense Logistics Agency, and he counts it as his firm’s biggest customer.

Pentagon officials have been explicit about their plans to help expand the market for renewables, especially in the realm of biofuels based on camelina (an oilseed also known as wild flax), algae and other sources. Last month, Mabus and Agriculture Secretary Tom Vilsack announced the administration would spend as much as $510 million during the next three years along with the private sector to produce advanced biofuels for military and commercial transport.

“We have to do this for our security,” Mabus said last week, adding that most of the new energy investments will pay for themselves in four to seven years. “The thing I want to attack the most is [that] this is some sort of fad or flavor of the moment.”