The United States Department of Defense (DoD) is the largest consumer of energy in the United States. Much of that energy is consumed in harsh environments to power tanks, armored vehicles, fighter jets, generators, small hospitals, command outposts and operations centers out in the field. All of these applications are critical, but costly not just in dollars but also the lives of personnel. For instance, in 2009 The Hill reported the military reportedly spent as much as $400 to deliver a single gallon of fuel to a remote Forward Operating Base (FOB) during operations in Afghanistan where, according to Operation Free, a coalition of veterans and energy experts, casualties struck one in 24 fuel convoys.
In recent years, the government has identified alternative energy use as an important means to help mitigate the expense and dangers of relying solely on fossil fuels to meet the DoD’s mission. In 2012, the White House set what is known as “25 by 25”, a policy objective that aims to reduce the amount of energy produced across the military by 25 percent by 2025. Microgrids – small-scale distributed electricity systems – are literally on the front lines of these efforts, using reciprocating engine generator sets, and harvested energy sources such as solar, wind and thermoelectricity to power critical equipment and systems in remote and harsh locations. The main benefit of the microgrid is its independence from main electrical grids found on large stationary bases and urban centers. More energy obtained from local sources – particularly harvested energy – means less greenhouse gas emissions, and less money and resources spent on fossil fuels while reducing some of the burdens of transporting and protecting that supply.
Although the benefits of renewable energy in remote, harsh locations are clear, powering critical equipment that is not tied to a main electric grid and managing that power are two substantial challenges. Deployable renewable energy systems are helping soldiers address those challenges with far more efficient operation on the battlefield than standard diesel generators, features that are evolving with the military’s increasingly demanding requirements, and rugged, modular designs for easy deployment.
An average generator on the battlefield runs at approximately 10 to 15 percent capacity, usually 24 hours a day and 365 days a year. This can cause increased maintenance on the equipment due to a condition called wetstacking, which happens when a diesel/JP-8 generator is run at light load for long periods of time. Containerized deployable energy systems, which can combine solar, wind and energy storage, can run both at maximum continuous output or at low capacity while maintaining high efficiency without issues typical of gensets such as a rapid decrease in efficiency at low usage capacity rates or wetstacking, so smart energy storage and integration are extremely valuable on the microgrid. Deployable renewable energy systems have standard footprints, and they come in sizes based on a 20-foot, ISO shipping container. For example, systems can be one-third the size of a container (Tricon) or one-quarter the size of a container (Quadcon), and so on to fit into the military’s logistics train for transport over land, sea, or air. For extreme mobility, portable, stackable, remote battery systems can power microgrid devices in the field, measuring as little as 22” x 16” x 8” (H) and weighing less than 50 pounds. The systems’ construction includes shock resistance to prevent damage during transport and handling, and they adhere to mil spec 810 G’s environmental requirements as is standard for new military equipment.
Supply and demand
Power outputs for deployable renewable energy systems can range from 2 kW or 3 kW up to 60 kW, and they must meet the military’s 3 phase standards for power generated equipment for their size. MILSPRAY’s Scorpion Energy Hunter, for instance, provides up to 18 kW (120 V, 208 V AC, 60 Hz) 3 phase. Since each piece of equipment presents different power challenges, and because renewable energy is unregulated, deployable renewable energy systems are designed to ensure power quality along with availability. The Scorpion system can handle surges to almost 40 kW to maintain its 18 kW of continuous output power and reduces fuel consumption by up to 80 percent. Harvested energy, of course, is not always available at the right time, whether wind is not blowing or the sun is not shining, so portable renewable energy systems have to ensure “balance of systems.” Supply and demand in power systems must be matched.
“You can’t just dump a bunch of solar at any given time at any ratio into a grid,” said Doug Moorehead, President of Earl Energy, whose Earlcon and FlexGen renewable power systems have been deployed in Afghanistan where a 60-kW FlexGen system reportedly saved 50 to 70 percent in fuel in microgrid environments when used in generators. “If I have excess solar available above and beyond what the loads are requiring, I’ll send that to charge the batteries. So putting regulation and control around that unregulated power source is one of the big things we do.”
Cycling and density needs determine the right battery technology
Since deployable renewable energy systems are expected to perform in rugged, high reliability applications, the same is required of the batteries these systems use to store the harvested energy. “We look at maintenance–free batteries that can handle a lot of temperature extremes – typically high temperatures and not so much low, and the ability to handle deep cycling,” says Joseph Gerschutz, Engineering Manager of MILSPRAY Military Technologies. Lead-acid chemistries are common among deployable renewable energy systems where lives depend on reliable power, and companies design them into their deployable energy systems based on their proven track record.
Lithium-ion is also very common in military applications because it offers a very broad range of chemistries with different benefits. Lithium iron phosphate is suitable for vehicle (mounted) and smaller deployable renewable energy systems (dismounted). In this case, “You’re looking to pack as much energy density into the battery as possible,” says Jeff Helm, Defense Sales Manager at Saft, “which gets you the highest kilowatt -hour per volume rating.” Saft’s Lithium-ion based ultra-portable battery storage devices are finding uses in Raytheon’s Improved Target Acquisition Systems (ITAS) – anti tank weapons systems used by the light forces – where the high kilowatt-hour per volume batteries offer benefits such as long run times versus legacy battery solutions, and the lighter weight, smaller size and enhanced capabilities means it can replace the vehicle mounted charger and the separate AC charging source.
Another chemistry, Lithium Titanate (LTO) is attractive for its cycling characteristics in high power discharge situations and equipment that can have as much as 7-8000 full depth of discharge cycles in them. “We can get a lot of power out of it, and a lot of power into it on charging to load up that generator at its optimum point with effectively a smaller battery than we would be able to do with some of the other Li-ion technologies,” said Doug Moorehead. “You sacrifice some amount of energy density for a very high rate, high power dense battery system.”
Gensets provide a reliable back-up plan
Deployable renewable energy systems are also designed to work alongside gensets — a combination of generator and an engine which can provide backup power to the end equipment, such as when the renewable energy is unavailable or the stored energy of the system cannot keep up with energy demands. “(Our) system will automatically start a connected genset which will then pick up the load for the duration that it’s on and also recharge the batteries concurrently and then automatically shut it off,” said Joseph Gerschutz. “This is done as needed.”
Saft provides an ultra-portable battery storage device – called the Advanced Deployable Renewable Energy System (ADRES)– that can be used along with generators and solar power systems to power small microgrids. The company designed an AC/DC converter into it so it can take an AC charge source and also a DC charge source from 10 V to 36 V, which means it not only can be charged from a genset but also a military vehicle, too.
While the fuel savings and carbon footprint reductions that deployable renewable energy systems help enable are important, they are secondary to the military’s objective of mission completion. Therefore, renewable energy use in the field would not be as possible as it is today without deployable renewable energy systems that have onboard energy management functionality working alongside gensets to make sure there is power to get the job done. Deployable renewable energy systems also help mission completion with modular and flexible solutions for easy configuration in the field, intuitive user interfaces such as touchscreens showing only the information the soldier needs for the situation, easy troubleshooting and programmability, and multiple inputs and outputs. Ease of use means the soldier can get back to the job at hand.
With deployable renewable energy systems providing energy surety in the field, the military can then realize the very real benefits of energy savings and safer power delivery for personnel. “When you look at…all the generators running in Afghanistan today, and you’re able to reduce 25 percent of that, you know that transportation cost savings is huge,” says Jeff Helm, “and then the casualties with logistics because of that has been documented.” As military operations shift from the harsh environment of Afghanistan and more special forces deploy to Africa, the logistics of supplying finite resources such as fuel and water will continue to be a challenge. “They have to have it, but the less of it they need and the less frequently they need to be resupplied, the far better off they are,” says Doug Moorehead. “And fuel savings is a great way to get them there.”