Hybrid Power for the Frontline
Diesel-battery generators could cut troop fuel use at least by half.
The U.S. Armed Forces are heavily burdened by the financial and tactical costs of transporting fuel to the battlefield. This July, in an effort to address the problem, the United States Marine Corps will deploy a pair of diesel generators coupled with powerful batteries to frontline troops in Afghanistan. The hybrid power systems should cut by 50 to 70 percent the amount of fuel needed to generate electricity, according to the manufacturer, Earl Energy of Portsmouth, Virginia.
The generators that U.S. military camps currently use operate inefficiently because they need to handle ocassional peaks in demand. “You may have a 10-kilowatt generator that at any time is only producing 1.5 kilowatts of power to satisfy its load,” says Doug Moorehead, president of Earl Energy. “So you are wasting 8.5 kilowatts of power that you aren’t storing for later use,” he says.
The diesel-battery hybrid the company developed instead runs generators for short bursts to maximize energy utilization. Not only does this satisfy the immediate energy requirements of a camp, but the system also charges a bank of lithium-ion batteries. When the batteries are fully charged, the generator shuts off and the system begins drawing power from the batteries instead. “Generators can go from running 24 hours a day to three to four hours a day—it’s that good in some cases,” Moorehead says.
The hybrid systems to be deployed in July will combine an 18-kilowatt diesel generator, similar to those currently used in the battlefield, with a 40-kilowatt-hour bank of lithium-ion batteries. The system will also include a 10-kilowatt photovoltaic solar panel array that will further lower fuel consumption.
The entire system, including photovoltaics, sells for “over $100,000,” as compared with $80,000 to $100,000 for a similarly sized conventional generator, Moorehead says. The cost to Earl Energy for just the batteries—which have built-in safeguards against the high temperatures and dusty field conditions of Afghanistan—is $750 to $1,500 per kilowatt-hour of storage.
Moorehead estimates the system will pay for itself within seven to 12 months, depending on the cost of fuel. Bigger savings would come from using the hybrid system without the photovoltaics, which are expensive, and the company is now developing a stand-alone generator without the added solar power, he says.
Maximizing the unit’s energy efficiency requires repeatedly deep cycling the batteries—discharging them to their full capacity before recharging them. Conventional lead-acid and nickel-cadmium batteries quickly lose storage capacity if repeatedly deep cycled. The advanced lithium-ion technology in Earl Energy’s batteries allows them to last close to 4,000 cycles, or 18 to 24 months, according to the company. Moorehead developed lithium-ion battery technology for battery maker A123 Systems before joining Earl Energy.
The hybrid power system also employs energy-management software that uses complex algorithms to maximize the generator’s efficiency. Steven Minnihan, an analyst at Lux Research says this energy management, together with the power electronics that allow the system to quickly switch between generator and battery power, is very important. “Companies will speak quite freely about the chemistry of the batteries they are using, but they are very tight-lipped about the energy-management systems and power electronics,” he says. “It is becoming an increasingly important piece of intellectual property.”
The technology is competitive in the battlefield because transporting diesel fuel to the front lines in heavily armed convoys is very expensive. Moorehead, a former Navy SEAL, says delivery costs for fuel transported to the front lines in Afghanistan typically range between $20 and $40 per gallon.
Reducing fuel use on the front lines saves more than money. Ray Mabus, Secretary of the Navy, spoke of the “fully burdened” cost of fuel at a recent DOE Advanced Research Projects Agency for Energy (ARPA-E) conference in Washington, D.C. “For every 24 [fuel] convoys, we lose a soldier or a Marine [who] is killed or wounded guarding that convoy,” Mabus said. “That’s a high price to pay for fuel.”
Earl Energy hopes to begin scaling up production of its high-efficiency generator systems. According to the company, the number of fuel convoys could be cut in half if its devices are widely deployed.