Military Embedded Systems

Portable power management for soldiers: Fuel cell hybrid system is lighter, safer


May 16, 2009

Dr. Peter Podesser

SFC Energy AG

Portable power management for soldiers: Fuel cell hybrid system is lighter, safer

A fully integrated fuel cell/battery hybrid system offers the army a safe, lightweight power source for nonstop equipment operation by soldiers in the field as an alternative to carrying extra batteries and recharging systems.

The rising deployment of electronic equipment for soldiers in the field – from night-vision goggles, laptops, and communication devices to GPS and sensors – has increased the army's need for lightweight, reliable, and portable electrical power. But there are significant technical and logistical challenges to efficiently equipping soldiers with the power they need to run this equipment.

Because their devices must be operated autonomously, soldiers typically have to carry up to 30 lbs of various primary and backup batteries, depending on the power requirements of their individual devices. This adds considerably to the weight of the equipment and provisions they also must pack. But what if soldiers could carry a single lightweight power-conversion device that is able to adapt to the power needs of all their equipment? Such a power-conversion device should enable them to use any available power source in the field – generators, field chargers, solar panels, fuel cells, and so on – to recharge their batteries.

Now, a new fully integrated, lightweight fuel cell/battery hybrid system that offers this power-conversion flexibility and enough capacity to support a 72-hour mission has been developed for defense organizations in North America and Europe. Critical missions no longer have to be interrupted for battery replacements or recharges, and important systems do not fail anymore due to empty batteries. All these factors significantly increase the soldier's safety and effectiveness.

The Direct Methanol Fuel Cell (DMFC) system – which includes a fuel cell, fuel cell cartridge, and power manager – can reduce battery weight by up to 80 percent while providing improved logistics and increased safety for soldiers.

Portable hybrid power for soldiers

These hybrid, portable DMFC systems comprise three components that work together to provide a portable, flexible, reliable power source for today's armies: the fuel cell, the fuel cartridge, and the power manager.

Component 1 – The fuel cell

Fuel cells are increasingly being viewed as a reliable, versatile power source for defense applications. They offer a range of logistical, security, and functionality advantages in the field that soldiers appreciate: They operate almost silently without producing exhaust, they are immune to extreme weather, and they produce power only when needed. Unlike batteries, which just store energy, DMFCs are actual power generators, chemically converting a fuel into electrical power in one efficient step.

In the stack, the fuel cell's power-producing heart, a mixture of methanol and water is introduced to the anode side, which is connected to the cathode by an electrical circuit (Figure 1). A patented water management system enables use of 100 percent pure methanol in the fuel cartridges. (This also helps reduce the unit's weight because pure methanol has a very high energy density.) Ambient air is pumped into the stack on the cathode side. Upon contact with a platinum catalyst, methanol releases its electrons, which flow in the direction of the cathode, thus producing power. At the same time, protons are released and penetrate the membrane to the cathode. There, the oxygen reacts with the proton and electrons to form pure water.

Figure 1: Unlike batteries, which just store energy, Direct Methanol Fuel Cells (DMFCs) are actual power generators, chemically converting fuel into electrical power in one efficient step.

During this chemical process, the fuel cell releases water in the form of water vapor and carbon dioxide. The process is environmentally friendly: The amounts of water vapor and carbon dioxide produced are comparable to the breath of a child.

Sidebar 1: SFC systems win first and third prizes in DoD competition.

(Click graphic to zoom)



The most up-to-date of these portable DMFCs – used by army organizations in the U.S. and Europe – weighs only 3.7 lbs and measures 10" x 7" x 3". It provides 25 W continual nominal power directly to electrical devices or for charging secondary batteries. Its nominal voltage is 16.8 V, and it can be adapted to other voltages. (Output voltage is 10 to 30 VDC.) Fuel consumption at 25 W is less than 0.8 grams per watt-hour, which translates into an energy density of greater than 1,250 Wh/kg – roughly 10 times the energy density of Li-ion batteries. When connected to a rechargeable battery, the fuel cell will constantly monitor the battery's charge state. Once this drops below a predefined value, the fuel cell will automatically start recharging the battery. When the battery is full, the fuel cell returns to standby mode. This continuous power generation process enables longer dismounted missions for soldiers without the need to interrupt the mission for battery replacements or recharges, and significantly reduces the battery weight they must carry.

For example, a soldier who needs 25 W during a 72-hour mission would have a total power requirement of 1,600 watt-hours. Nine military batteries such as Type BA5590 (210 watt-hours per battery) are needed to provide that energy. Each battery weighs 2 lbs, so at a minimum a soldier would have to carry 18 lbs purely to satisfy these power needs. But soldiers often carry more than one type of battery, because their devices require different voltages.

So to be assured of the necessary energy for a 72-hour mission, a soldier would have to carry approximately 30 lbs of batteries. An example of an applicable technology is the Jenny fuel cell from SFC Smart Fuel Cell, which weighs only 3.7 lbs, plus a 1-lb power manager (Figure 2). This combination, plus the hybrid solution's five 0.8-lb fuel cartridges, would reduce the weight of the soldier's power supply by 65 percent compared to primary, or nonrechargeable, batteries. Secondary, or rechargeable, batteries have even less energy density while weighing more. The hybrid fuel cell system is 80 percent lighter, on the average, than secondary batteries with equivalent power.

Figure 2: The Jenny fuel cell from SFC weighs only 3.7 lbs, plus a 1-lb power manager.

Component 2 – The fuel cartridge

DMFCs use methanol as a fuel, a liquid alcohol that is easy to store, transport, and ship – unlike the hydrogen gas used in hydrogen fuel cells. Methanol's most important property, however, is its extremely high energy density. Ten liters of methanol at a weight of approximately 18 lbs provides 11 kWh of power, a lot of energy at very low weight.

By comparison, a hydrogen tank of equivalent capacity is about five feet tall, weighs 187 lbs, and cannot be transported by aircraft. An equivalent-power battery system would weigh nearly 600 lbs.

Fuel for the Jenny fuel cell comes in convenient lightweight cartridges, each containing nearly 10 ounces of fuel at a weight of 0.6 lbs. Fuel cartridges can be easily exchanged during operation (hot swap).

Component 3 – The power manager

Part of the hybrid DMFC system, the power manager, provides excellent operational flexibility to soldiers. Measuring 1.6" x 3.4" x 5" and weighing 1 lb, it enables efficient battery charging in the field by harvesting and efficiently managing energy from virtually any energy source to provide electrical power during operation of host equipment. Possible power sources include batteries of various chemistries and states of charge, fuel cells, photovoltaic cells, typical battery chargers, or automotive battery buses.

The power manager accepts a very wide range of input voltages (operational ranges: 30 VDC nominal: 22 to 24 VDC; 12 VDC: 10 to 32 VDC), and its output voltages (operational range: 10 to 24 VDC) are compatible with virtually any electrical equipment used by army organizations like night-vision goggles, laptops, communication, and GPS devices and sensors. The power manager will automatically adjust to the required output voltage by means of an implemented cable identification feature. This allows soldiers in the field to make optimum use of any available energy source for the duration of their mission.

Hybrid power system provides army advantages

As mentioned, the DMFC hybrid system provides distinct advantages to soldiers on the ground: reduced weight, improved logistics, and increased safety.

Significantly reduced weight

With the use of the fuel cell/fuel cartridge/power manager hybrid system, the weight to be transported can be reduced by 65 percent compared to primary, nonrechargeable batteries and up to 80 percent compared to secondary, rechargeable batteries as discussed previously.

Improved logistics

Battery logistics can present a formidable challenge, as seen in the war in Iraq. Army organizations still prefer primary batteries to secondary batteries for a number of reasons: They offer long shelf life, they are easy to use, and they are immediately available without charging and priming. Their downside, however, is that once they are empty, they need to be discharged and replaced – both of which can be a challenge in critical situations. Secondary batteries can be recharged and thus reused many times, which poses less of a logistical challenge. However, severe problems arise if there are no available charge stations. With the portable power hybrid solution, however, all that soldiers need is always in their vests; with the fuel cell they have a personal power generator, and with the rechargeable battery they have power storage. Fuel for several days (25 W continuous for 72 hours: five 0.8 lb cartridges) can be easily packed and transported, making the soldier independent of logistics support.

Increased soldier safety

Direct methanol fuel cells contain no hazardous components. Defense organizations in the U.S. and Europe have rigorously tested methanol fuel to determine whether it would catch fire or explode. During these tests, rounds of different types of ammunition were fired at SFC fuel cartridges and at materials soaked in methanol. The methanol did not catch fire in any tests.

Hybrid power system keeps pace with technology

Technology has provided the army with advanced equipment for more efficient and safer field missions, but until recently the available power sources had not kept pace with those advances. DMFCs combined in a fully integrated fuel cell/battery hybrid system have enabled soldiers to take advantage of this advanced equipment while reducing the weight they are required to carry. In situations when it really counts, soldiers having their own power system with them can make a major difference. Critical missions no longer have to be interrupted for battery replacements or recharges, and important systems do not fail anymore due to empty batteries. All these factors significantly increase the soldier's safety and operability.

Dr. Peter Podesser was named CEO of SFC Smart Fuel Cell in November 2006. He has more than 20 years of management and executive experience with technology companies in Europe, the U.S., and Asia. Previous work experience includes management positions in sales and marketing for RHI AG. Peter has also served as president and CEO of EV Group and as president of Unaxis's Wafer Processing Division. He studied business administration and languages at the University of Economics and Social Sciences in Vienna, and earned a Ph.D. in Strategic Planning from the university. He can be contacted at [email protected].

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