Energy efficiency has become a concern for many U.S. government sectors in recent years. For instance, the Department of Energy (DOE) awarded a total of $175 million to 40 different vehicle technology projects in an effort to promote the development of lightweight, efficient vehicles. In addition, Boeing and Siemens recently announced their new alliance, which aims to improve the Department of Defense's (DOD) energy and security management. 

While these efforts seem very progressive, the DOD has increased budget pressures that may jeopardize its investment in renewable energy. According to Rear Adm. Neil Morisetti, the United Kingdom's climate and security envoy who spoke on a potential partnership between the U.K. and DOD on August 10, the cost of energy is exceeding manpower costs as far as defense budgets go. 

Despite these growing pressures, Rep. Maurice Hinchey (D-NY), co-chair of the new congressional Defense Energy Security Caucus, wrote a letter to Defense Secretary Leon Panetta on August 10 to drive the continued investment in renewable energy. Other caucus members joined Hinchey in signing the letter, such as Reps. Roscoe Bartlett (R-MD), Jack Kingston (R-GA) and the office of Gabrielle Giffords (D-AZ). 

"Recognizing the critical importance of mission energy requirements, we urge you to prioritize the department's energy policies and budgets," wrote Hinchey in the letter. "Investments in smart energy plans will not only show returns in security and mission success, but they will contribute to future cost savings and have a unique opportunity to help foster innovative and diverse energy and clean technologies to strengthen our economy."

While Morisetti noted the costs associated with renewable energy investments, he also said that it's something that cannot be pushed aside either. 

The Pentagon spent $15 billion on energy last year alone, where 75 percent of that was operational. It's expensive to move this large amount of energy around Iraq and Afghanistan where battlefields are located, and can create supply lines "that are under constant attack."

But Army Gen. David Petraeus is looking for better ways to manage fuel consumption in Afghanistan. 

"Commanders will push for rapid technology transition of new fuel savings methods to field, where appropriate, and will pursue existing, proven alternative energy options that reduce the use and transport of fuel," said Petraeus.