With personnel nearly the population of Chicago and a fleet of over 500,000 aircrafts, vessels, and vehicles, the U.S. Department of Defense is a massive and energy-hungry institution.

In 2009 alone, the military consumed some 375,000 barrels of oil per day, more than three-quarters of all other countries on the planet. To put that in perspective, Nigeria-with a population of more than 140 million-consumes about the same amount.

During the decades of cheap fuel and easy access, feeding this complex system spread over 820 global installations was of little concern. In today's economic climate, however, the Department of Defense (DoD) has had to adapt its energy strategy.

"The stakes could not be higher," Navy Secretary Ray Mabus said in a statement earlier this year. "Energy reform will make us better fighters. In the end, it is a matter of energy independence and it is a matter of national security. Our dependence on foreign sources of petroleum makes us vulnerable in too many ways."

According to a recent report by the Pew Charitable Trusts, the DoD is taking aim at its annual $15 billion energy budget with a focus on efficiency and development of renewable, clean fuels-three areas that are pivotal in the race to create a more efficient fighting force and strengthen America's energy independence.

The age of domestic biofuels
As the world's largest single consumer of liquid fuels, the DoD is taking ambitious steps to source alternatives. The Obama administration recently announced a joint partnership between private-sector companies, the Department of Agriculture, U.S. Navy, and the Department of Energy to invest $510 million in biofuel production over three years.

Both the Navy and Air Force (the latter consuming over 60 percent of DoD fuel) are experimenting with biofuel alternatives based on algae and a weedy plant called camelina. Studies have shown camelina-based jet fuel to reduce net carbon emissions from planes by almost 80 percent.

Unfortunately, current biofuels production is meager compared to what the military or commercial industries might one day demand. The government's investment in the sector could be the impetus needed to turn it from fledgling to a serious player in the country's energy portfolio.

"Military use of advanced biofuels could in turn validate emerging technologies and unlock private investment in future advanced biofuels production for civilian markets," said one industry executive.

General expectations are high. The Air Force is calling for 50 percent of its domestic aviation needs to be satisfied with biofuels by 2016. The Navy's plans are similar, with a 50 percent alternative energy mix by 2020-as well as a massive fossil-fuel independent " Green Strike Carrier Group" by 2016.

As an example of just how valuable the U.S. biofuel market will be, the Navy alone estimates it will require a staggering 336 million gallons of biofuel annually by 2020. The division currently uses less than 300,000 gallons.

E is for efficiency
As with the private sector, improvements in efficiency-from bases to vehicles-is an immediate and affordable way to dramatically cut energy consumption. According to the Pew report, a DoD decision to insulate 9 million square feet of temporary structures resulted in a daily fuel savings of more than 77,000 gallons.

The greatest argument for pursuing a more efficient military, however, can be made for the amount of lives it will save. Eighty percent of the supply convoys in Iraq and Afghanistan are fuel trucks-with over 3,000 American soldiers and contractors killed in attacks associated with fuel delivery between 2003 and 2007.

"Our adversaries are increasingly employing asymmetric tactics and energy can be a soft target," Deputy Secretary of Defense William Lynn said at a Pentagon briefing last summer.

To date, the Air Force has implemented changes that include more efficient flight routes, increased use of advanced flight simulators, and development of new turbine engines that offer a 25 percent boost in energy savings.

On the ground and sea, research and development of hybrid and electric vehicles and ships is being aggressively pursued, with an eye in particular on the DoD's fleet of over 200,000 non-tactical vehicles.

In June 2011, the Department issued a request for information from all players in the electric vehicle sector for proposals and ideas on how to deploy EVs at a cost that is competitive with internal combustion engine vehicles. Gains here will eventually make huge waves in the commercial EV industry and offer tremendous savings on fuel and delivery.

Renewable solutions
Perhaps the closest ties between the DoD and the private cleantech sector come through collaborations on sustainable sources of energy. As of April 2010, over 450 renewable initiatives (including solar, wind, geothermal, and biomass) were in use or being developed on military bases.

The shift towards sustainable sources has as much to do with security as it does with budget and autonomy. With the DoD's heavy reliance on civilian utilities comes increased risk from interruptions due to natural disasters or terrorist attacks.

Investments in microgrids, which act as self-contained islands of clean energy generation and storage, are an ideal contingency plan.

"We know this technology can save fuel and maintenance time for our deployed forces," said Brigadier General N. Lee S. Price. "Through this project, we can obtain reliable data on these benefits-and lay the groundwork for successful use of microgrids in theater."

Solar photovoltaic and solar thermal technologies make up the majority of the DoD renewable energy installations and are a focal point of investment.

In September of 2011, Energy Secretary Steven Chu announced the largest domestic residential rooftop solar project in history: a $334M loan to solar power provider SolarCity that will provide "up to 160,000 rooftop solar installations on top of privately run military housing complexes at 124 military bases across 34 states."

Large scale solar projects are also in development across the U.S.-including a 500MW solar concentrator project at Fort Irwin in California.

Show and tell
Since March 2010, the DoD has held an annual ExFOB (Experimental Forward Operating Base) event offering private companies an opportunity to show off their latest advancements in "expeditionary energy capabilities."

The primary purpose of these demonstrations is to evaluate and eventually test products that can produce a more self-sufficient and mobile strike force.

According to the Pew report, up to 20 percent of a soldier's 70- to 90-pound pack consists solely of batteries. Products such as high-efficiency solar mats, next-generation lithium batteries, and fuel cells can all make a difference.

"We view ourselves as a target-rich environment," Secretary of the Army John McHugh said. "This is the right thing to do for the environment, for the taxpayer and, most important, the right thing to do for our soldiers."