Combining two or more energy sources, hybrid power systems are increasingly seen as the most efficient way of providing dismounted soldiers with the energy they need to operate their electronic equipment away from established power sources, for increasingly longer periods.
For forward operating bases and more extensive in-theatre installations, the same technologies on a larger scale are finding favour as a means of reducing reliance on traditional diesel generators. Led by the US military, the largest single user of liquid fossil fuels in the world, forces are working to reduce their consumption as a means of shrinking their logistic tail, and the associated loss of blood and treasure that result from attacks on re-supply convoys. “The military has a unique viewpoint on renewable energy; it uses it not to be ‘green’, but rather to increase capability and resilience,” states Phil Robinson, vice-president of Protonex Technology’s defence power systems division. “Because of this, its investment in reliable alternative energy and power management technologies has been consistent and hence effective; very unlike the commercial world where alternative energy investment is tightly linked to the price of oil.”
Dr. Peter Podesser of fuel cell specialists SFC Energy points out that long-established combinations of diesel generators and lead acid batteries are hybrid systems that are fully mature. He says that a great deal of development work has been done over the last ten years regarding hybrid systems with combinations of solar and wind power generators, batteries and fuel cells, but fielding has been slow. “To the disappointment of the users and also of industry, this adoption process has simply taken longer than anyone wanted it to,” he says. “But if you look at the defence industry, realistically it usually takes a decade to adopt new technologies.”
In part he attributes this to the changes in the nature of wars, particularly those that the West has been fighting over the last decade. These conflicts, such as the US-led operations in Iraq and Afghanistan, have been characterised by asymmetric threats encountered by isolated patrols and special forces, in which small, agile groups carrying out dismounted missions need power in a different way. “The demand structure has changed,” Dr. Podesser told Armada, “and off-grid power is a massively growing field; you usually don’t come back to a big base where there is abundant power. You have a lot of people who are out there on their own for many days, weeks, or months and they have to operate. Off-grid (power) is growing just from the structure of the threat.”
While the military has led the development of hybrid power systems in technological terms, they tend to be overtaken by the commercial and even public service sectors when it comes to implementation. Jeff Helm of Saft Batteries cites US Army and US Marine Corps work on expeditionary power systems that established the pattern for hybridisation in these applications, but are being overtaken in terms of implementation by non-military emergency response units, the oil and gas industry and others with money to spend on procurement, and a need to have portable power sources. “The military is like an incubator,” Mr. Helm observes, “but then commercialisation is done by a separate market.” He commented that the military looks to the commercial sector to drive costs down on new technologies before adopting and militarising it. “A lot of (research and development) funding never quite transitions to procurement funding.”
Dr. Podesser concurs, pointing out that between 2000 and 2010, both the US and German governments put a lot of effort into the development of portable fuel cells, much of it guided by a NATO (North Atlantic Treaty) working group of which SFC is a member, followed by the inevitable slow down after NATO largely disengaged en masse from combat operations in Afghanistan at the end of last decade. “In terms of really getting it into use, then we come back to the slow adoption of all those government based organisations … First phase development is strongly driven by military spending, but then the adoption of many of the things like solar and fuel cells, has taken place in the commercial field.”
The early military adopters of the SFC’s new portable fuel cells are the usual suspects. The first customer groups, Dr. Podesser observes, are special forces and other specialists such as forward air controllers. Such units are key elements of a force operating on the edge, carrying out a lot of specific tasks in isolated, often dismounted situations, but requiring power sources to operate equipment.
“Expeditionary power technologies, those that must be lightweight, portable, and rugged enough for use in a forward position, are the most technically challenging areas,” said Protonex’s Mr. Robinson. “The further forward the position, the more technical challenges that must be overcome. Today the military is deploying power management devices that can be carried in a rucksack, weigh less than a half a kilogram (one pound), and which use tens of thousands of lines of code to automatically assess alternative and traditional energy sources available, harvest energy from the most efficient source, convert that energy to whatever form is needed and store it in the most efficient battery or other location. Because this is all automatic, the user doesn’t need to know the difference between a volt and an amp.”
Within the US military, Jeff Helm says that the Marine Corps is leading the charge because their expeditionary nature makes reducing the logistic burden more of an imperative for them, citing as an example the Mobile Electric Hybrid Power Systems (MEHPS) which the Marines are leading. One of several important Marine Corps expeditionary energy initiatives, MEHPS incorporates solar arrays, lithium ion batteries and a generator and is being developed in ‘light hybrid’ and ‘medium hybrid’ versions.
The requirement for the five kilowatt (KW) light hybrid version includes a limit on the weight of individual components that allows either two or four people to carry them. These include a five kilowatt Advanced Medium Mobile Power Sources (AMMPS) generator and a three kilowatt Tactical Quiet Generator (TQG) and the system must be small and light enough to be carried by multiple vehicle types. The US Army wants this variant to provide at least three hours and preferably eight hours of operation in silent watch mode and use no more than 7.5 litres (2.1 US gallons) of fuel per day. The reliability requirement is for flawless operation for 500 hours.
The medium hybrid variant of the MEHPS can have components that require four to six people to lift them and must provide at least ten but preferably 15 kW from its AMMPS generator. The system must fit a Light Tactical Trailer Marine Corps Chassis (LTT-MCC). The silent watch requirement is the same three to eight hours, but as it is intended to supply more users, the fuel burn allowance is larger; the threshold of acceptability is 27.2 litres (7.2 US gallons) per day, but the objective is 22 litres (5.8 US gallons). The MEHPS programme is now in its Engineering and Manufacturing Development (EMD) phases and is scheduled to move into procurement in 2018. Among the challenges in putting this kind of system together is power conditioning, Mr. Helm told Armada, pointing to power conversion and management software that handles voltage regulators and inverters that handle the Direct Current (DC) to Alternating Current (AC) conversion.
Solar is becoming more of a commodity, Dr Podesser says. “It is really about the performance of flexible, thin-film-based solar systems that are foldable. You have to make sure it’s low in weight, but the key element there is really ruggedisation and durability so that those things survive in the field.” One supplier of such systems is US company PowerFilm, which was selected in March by the US Army and Thales to support the $49 million Universal Battery Charger (UBC) contract. The selected product is PowerFilm’s 120 W solar panel, a foldable array that supplies current to the UBC, which is designed to charge multiple battery types, enabling a squad or platoon to operate for at least 72 hours without battery re-supply in austere off-grid locations. PowerFilm says that the lightweight, durable and “extremely portable” solar panel easily folds up to fit into a soldier’s rucksack and can be rapidly deployed during halts to provide reliable, safe and secure power anywhere.
Turning to batteries, Dr. Podesser notes that the high level of development driven by military electric vehicle requirements pushing for ever higher energy and power densities raises safety issues. “Some of those novel chemistries, be they lithium ion or others, there’s still a big focus, there has to be, on the safety side because you have a tremendous amount of power density there and you don’t want it to become a threat.” With fuel cells, the drive is to make them smaller, lighter and more powerful while minimising fuel consumption and cost. The real benefits, however, come from finding the right combination.
“Batteries are an excellent solution for, let’s say, up to 24 hours. If you then combine a battery with a fuel cell and a solar array, you can reduce the overall weight of the system and still expand the operating hours because so long as you have enough sunshine, the solar panels can be the source of energy and charge the batteries, and the fuel cell is the insurance policy … Hybridisation is definitely the key that unlocks the best value for the user,” Dr. Podesser argues. “Take special forces; right now we are able to take out about 80 percent of the battery weight (from) the standard gear for special forces for four-day missions by providing an integrated solution with fuel cells, lithium ion batteries and solar systems, (a total of) nine kilograms (20lbs) of weight off their shoulders.” In a tight spot, the extra water and ammunition that this weight saving enables them to carry could save lives, he added.
Phil Robinson called solar arrays, batteries and fuel cells natural partners in a reliable, efficient hybrid system. “By adding batteries, a solar array can often provide operation (for 24 hours per day, seven days a week). However, to assure no power loss during the short days of winter, extended cloudy spells, or both at the same time, both the array and the battery bank becomes prohibitively large. By adding a fuel cell, which only comes on when the solar array can’t keep up, both the array and the battery can be sized for average, rather than extreme conditions.” There is also the question of return on investment where the amount of fuel that batteries can save drives the limit of what governments are prepared to pay for them in terms of dollars-per-kilowatt/hour.
As with many new technologies, the issues of commonality, interoperability and standardisation are increasingly exercising operators. “They want interfaces to be common, but there are no standards for any of these systems so you can’t get that economy of scale,” Mr. Robertson continues. “It’s all very customised at this point.”
Jeff Helm commented that solar energy systems have come a long way in terms of their efficiency in converting sunlight into current. On the battery side the reduction in cost and the increase in life cycle capability of lithium ion chemistries have significantly increased the available return on investment from a set of technologies that are increasingly mature and available from a wide range of suppliers.
With their high energy density, lithium batteries are enablers for off-grid energy storage and are increasingly coupled with charging systems based on solar arrays and, in some cases, small wind turbines, with small diesel generators retained as a backup, Mr. Helm said, acknowledging the competition from evolving fuel cell technology. “A lot of manufacturers are doing lithium ion chemistries and a lot doing lithium iron phosphate. Even lithium titanate oxide is commercialised by a few battery manufacturers and NMC (Nickel Manganese Cobalt) is another prominent one, so I think lithium ion battery technology is pretty mature. All manufacturers are always tuning it for certain applications,” he observes. “There are things like lithium sulphur, which gives great energy density but not great power, but for certain applications that makes sense … Lithium air is another area that people are putting a lot of research and development behind because of its energy density. Those are the kinds of battery technologies that will be coming along in the next five or ten years.”
Saft chose lithium iron phosphate chemistry for its latest 6T battery, this being a US and NATO standard form factor for ground vehicle batteries, which are increasingly being adopted for off-grid military power systems. “We have integrated it with power system companies that do the inverting to AC where they are using these lithium ion vehicle batteries for this application as well,” Mr. Helm said. “It is a nice versatile battery, it’s at a nice price point … we’ve spent a lot of time on getting the cost out.”
This emerging battery commonality between vehicles and off-grid power systems makes life easier for troops in the field. “Any time you have a unit out there they have vehicles, so they could use the vehicle battery for a military grid power system or vice versa,” Mr. Helm notes. In terms of price and energy density, Saft has moved the industry on usefully, Mr. Helm argues, if not in pure technological terms as the company used a commercially-proven lithium iron phosphate chemistry for its new 6T battery (see above). However, creating a standard battery that can be used for multiple applications is progress, he told Armada. “You can put several of them in parallel if you need more kilowatt hours,” he said. “It can take dirty DC power from ground vehicles and you don’t need a special charger.”
Looking towards the future, Mr. Helm expects operators to demand many more militarily-qualified commercial hybrid power systems to be fielded over the next five years in a bit to save on fuel costs, logistic burdens and associated risks. “I think (the military is) going to look for commercial-off-the-shelf energy storage systems, products that are already developed.”
One of SFC’s latest portable systems is the Jenny 1200, a direct methanol fuel cell rated at 50W. Cartridges in three standard sizes supply pure methanol, which provides a significant weight saving over older systems that use a blend of methanol and water. Using the Jenny 1200 to recharge batteries is the secret behind the above-mentioned weight reduction for soldiers, as it reduces the number of spare batteries that they must carry. The company also makes 500 W fuel cells, the EFOY Pro 12000 series for example, and recently launched a system with this power rating for vehicle and dismounted applications, including as a power source for surveillance systems. “We will come up with a defence version of this product in the coming twelve months,” Dr Podesser said.
SFC has also developed fuel cells that can be buried in the ground and ‘left behind’ to provide long term power for unattended ground sensors equipped with seismic detectors and/or cameras, for example, which can be left in place for up to a year without intervention. With an eye on the future, Phil Robinson pointed to an expansion in intelligent power management and energy harvesting systems, which are being evaluated by all US military branches. “As the US Department of Defence transitions from trials to full-scale deployments, the market for these technologies will increase broadly.”