Naval Research Lab Looks to Sea, Sun for Energy
By Bob Freeman
Special to American Forces Press Service
WASHINGTON, Oct. 16, 2009 The services could more effectively power unmanned vehicles, underwater monitoring sensors, ships and aircraft if Naval Research Laboratory scientists achieve their goals of harnessing solar and sea power to fuel the military for years to come, a top NRL scientist said.
“A worldwide peak of fuel production is expected in five to 15 years, and increased demand will likely create large swings in price and availability,” Barry Spargo, head of NRL's chemical dynamics and diagnostics branch, said in an Oct. 14 interview on Pentagon Web Radio’s audio webcast “Armed with Science: Research and Applications for the Modern Military.”
“The bottom line is that we need to develop alternative power and energy because conservation and efficiency alone will fall short of meeting future needs,” he explained.
The quest for alternative fuel technologies is a top priority for the Navy, Spargo said, adding that energy research at NRL is diverse, allowing them to bring together a wide array of disciplines to address unique problems confronting alternate energy research.
“We’re conducting research in a number of areas that look really promising; however it’s unlikely that a single research area will solve the energy problems that we are facing,” Spargo said. “NRL is currently investing in synthetic fuel production at sea, enhancing fuel energy density, exploration of methane hydrates in the ocean, energy harvesting from the sea, fuel cells and batteries, power electronics and superconductors, and inertial fusion.
“Each of these research areas has significant challenges,” he added, “but certainly promising potential to help solve some of the Navy and [Defense Department’s] future power and energy needs for force mobility.”
One area of research that NRL is pursuing is the feasibility of sea-based production of hydrocarbon fuels. According to Spargo, the goal is to produce fuel in the same location where it is being consumed, specifically to support surface ships and aircraft operations from carriers at sea.
“This would give battle groups independence from fleet oilers which provide refueling needs,” Spargo explained. It also would cushion naval forces from future fuel shortfalls, he added, providing energy independence to the Navy.
Fuel synthesis would be accomplished by a catalytic conversion of hydrogen produced directly from sea water by the electrolysis of water and carbon dioxide. "It’s a complex process, but we believe that emerging scientific technology supports the development of synthetic logistic fuels," he noted.
"There are significant research and technological challenges, but the potential payoff is really high," he added.
Spargo noted that producing energy from sea water would be carbon dioxide neutral, thus not adding to the world’s carbon footprint. “This technology would be a great candidate for dual use in the civilian sector if it actually comes to fruition,” he said.
Spargo described another promising avenue of research that is investigating the potential for tapping the thermal energy stored in tropical waters.
“The energy stored in tropical waters is 300 times that of the world energy consumption. This makes the ocean the largest solar collector on Earth,” he noted.
Ocean thermal energy conversion is a potentially efficient method to convert the energy stored in tropical oceans into electricity.
“You take the surface water, which is about 80 degrees Fahrenheit, and [use it to] heat a working liquid, something like propylene, which has a vapor point below 80 degrees,” Spargo explained. “That converts the propylene liquid into a gas which drives a turbine that produces electricity. We then bring cold water up from about 3,000 feet below the surface, cool that vapor back into liquid and essentially create a cyclic process.”
Taking a more direct approach to harnessing the energy of the sun, the lab is working on flexible photovoltaic panels about four times as efficient as current solar panels. According to Spargo, the panels can be easily folded and transported, or even integrated into materials like tents and uniform covers to provide a local power source in support of expeditionary forces.
“Additionally, NRL has prototyped a photovoltaic coating that can be sprayed on surfaces, like a rock, to create on-the-fly energy sources,” he said. “You can imagine a small force spraying a rock and using it to generate electricity to power some device that they are using in the field.”
A more unusual approach to energy production is the use of certain marine microorganisms that consume carbon dioxide in the ocean and convert it into energy that can be harvested. “As part of their biochemistry, these organisms produce electricity,” he explained.
NRL has developed a number of devices that use microorganisms to power small sensors, like bottom-moored acoustic hydrophones for monitoring ship traffic, Spargo said.
“If we can produce enough energy with these devices, they could also power unmanned underwater vehicles, or at least provide a docking station where they could regenerate their batteries using electricity produced by these microbes,” he said.
The lab has expended considerable research and development into developing hydrogen fuel cells as an energy source, Spargo said. “Fuel cells are used to create electricity, and they do this by converting hydrogen and oxygen into water,” he explained.
Hydrogen fuel cells can deliver about twice the efficiency of a conventional combustion engine and when used to fuel unmanned aerial vehicles, or UAVs, they can support heavier payloads than the earlier battery-powered models.
A recent test of the prototype Ion Tiger UAV, powered exclusively by a hydrogen fuel cell, sustained continuous flight for 23 hours and 17 minutes.
“Also, they can operate in stealth because they’re not a combustion engine, which has a considerable heat signature, as well as a noise signature,” he said.
Spargo also described efforts to harvest methane hydrates from the sea floor. “They have the potential of being double the amount of recoverable and nonrecoverable fossil fuels,” he said.
Spargo admitted that there are many challenges to harvesting methane hydrates, including locating them and accessing them at such great depths, but it would be worth the effort.
“If we’re able to actually extract these from the ocean floor, there’s a potential to meet our national natural gas needs for about a hundred years,” he said.
“Energy research is a key priority for the Navy and, for that matter, all of us,” Spargo said. “I’m certain that there many exciting discoveries ahead that will help us achieve this goal of energy independence, as well as being good stewards of the environment as we operate and live in it,” he said.
(Bob Freeman works in the Office of the Oceanographer of the Navy.)