Power Electronics

Fuel-Cell/Battery Hybrid is a Leaner Portable Power Solution

An hybrid fuel-cell system has higher power density and less weight and volume, providing a more sophisticated and reliable approach than batteries alone for military missions.

Soldiers in the field require the most sophisticated portable electronic equipment to complete their missions. Meeting the power demands of such portable equipment requires technologically advanced energy systems.

Conventional battery-based power systems require soldiers in the field to carry up to 30 lbs. of various batteries to autonomously operate their electronic equipment (e.g. night-vision goggles, laptops, communication devices, GPSs, and sensors). Batteries for different devices have to be repeatedly replaced or recharged, requiring frequent interruptions to the mission that can complicate logistics as well as add weight to the soldier's equipment supply. This has intensified the need for lightweight, reliable, mobile, and portable electrical power-supply solutions.

As a result, fuel cells have become reliable power sources for mobile and portable defense applications. Direct-methanol fuel cells (DMFCs) provide logistical, safety, and functionality advantages including virtually undetectable operation. They also are immune to extreme weather, generate power only when needed, and operate almost silently without producing exhaust. Unlike batteries, which store energy, DMFCs generate power by chemically converting methanol into electrical energy.

WORKING PRINCIPLES

As shown in Fig. 1, 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. A patented water-management system enables the use of 100% pure methanol with a very high energy density in the fuel cartridges.

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 protons and electrons to form pure water.

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.

FUEL-CELL/BATTERY HYBRID

To address soldiers' growing power demands, SFC Smart Fuel Cell (SFC) (Fig. 2) developed a fuel-cell/battery hybrid system solution that offers a lightweight alternative for non-stop equipment operation. The energy network — consisting of an SFC fuel cell, fuel-cell cartridge, intelligent SFC Power Manager, and a rechargeable Li-Ion battery — is also universally compatible with current and future power-consumption requirements.

The energy source of the network, the portable Jenny fuel cell already in use by various military organizations, weighs only 3.7 lbs. and measures 10 × 7 × 3 in. It provides 25 W continuous nominal power directly to electrical devices or for charging secondary batteries. Nominal voltage is 16.8 V and can be adapted to other voltages (output voltage is 10 to 30 Vdc).

At 25 W, fuel consumption is less than one milliliter per Wh. The network produces power automatically as needed, continuously, as long as there is fuel. The fuel cell itself remains maintenance-free throughout its entire life. The only maintenance required is occasional fuel-cartridge replacement.

Fuel for the Jenny fuel cell comes in convenient 0.6-lb cartridges, each containing nearly 10 oz of fuel. Ten liters of methanol weighing approximately 18 lbs provides 10 kWh of power, a lot of energy at very low weight. Fuel cartridges can be easily exchanged during operation (hot swap).

In operation the fuel cell is barely detectable due to its low surface temperature. It has been proven to operate reliably even in extreme temperatures in deserts or cold climates, as well as at high altitudes or fully submerged underwater.

The SFC Power Manager is the second central component of the network. It is an intelligent portable power-management device that assures continuous operation of any electrical equipment carried by special-operations soldiers, as well as for charging batteries. The Power Manager enables smart energy harvesting, including an option for assigning various priorities during charging/discharging of multiple batteries and powering several devices simultaneously. It automatically recognizes the voltage demands of the individual devices and adapts the output power accordingly. The SFC Power Manager also provides a constant indication of each battery's state of charge and other parameters (SMBus Level 3). The system readily hybridizes with conventional power sources, including vehicle power, solar, and fuel cells.

HYBRID ADVANTAGES

Developed for defense organizations in North America and Europe, the fuel-cell/battery hybrid system is a flexible and intelligent solution that provides continuous operation of any electrical equipment. The combination of the fuel cell and the power-management system enables versatility. For example it can hybridize a solar-energy system and provide lightweight and reliable energy for soldiers in the field.

In the fuel-cell/solar combination, the solar panel and the Jenny fuel cell secure constant energy supply for power-consuming equipment. Based on 12 hours of sunshine and an average output rate of 50 W of the solar panel, the excess energy gets buffered in the battery. If the solar panel is unable to provide sufficient power, the Jenny fuel cell with 25 W nominal power kicks in automatically. Connected to a rechargeable battery, the SFC Power Manager constantly monitors the battery's charge state. Once this drops below a predefined value, the fuel cell automatically recharges the battery.

When the battery is full, the fuel cell returns to standby mode. In addition, the SFC Power Manager assures continuous operation of any electrical equipment carried by soldiers. It fully hybridizes available power sources, coordinates incoming energy, and can manage output up to 500 W. Moreover, it indicates energy levels of different power-consuming devices during a mission and evaluates power consumption, enabling soldiers to achieve corresponding optimization.

For example, a fuel-cell/solar combination with a Jenny fuel cell weighing 3.7 lbs. — plus two 0.8-lb. fuel cartridges — would reduce the weight of the soldier's power supply in the 96-hour mission example with three power consumers (radio, notebook, and thermal-imaging device) — by almost 70% compared to non-rechargeable batteries. The hybrid fuel-cell system is 31 lbs. lighter than batteries with equivalent power. The Table lists the energy sources, weight, and power consumption for a 96-hour mission.

SYSTEM ADVANTAGES

Significant weight reduction - With the use of the fuel-cell/battery hybrid system, the weight to be transported by soldiers in the field can be reduced up to 80% compared to conventional battery-based power systems.

Improved logistics - As a result, it simplifies logistics because conventional batteries must be discharged or replaced, which can be a challenge in critical situations. With the portable-power hybrid solution, soldiers' needs are optimized because the fuel cell automatically recharges batteries fully and the rechargeable battery stores power. Fuel for several days in lightweight cartridges is easily packed and transported, making the soldier independent of logistics support.

Ultra-high efficiency - In combination with the SFC Power Manager, the energy network represents the modern way to efficiently supply power for all sorts of missions. It is universally compatible with existing as well as anticipated future soldier equipment, and fully hybridizes available power sources.

Increased soldier safety - A fully integrated fuel-cell/battery hybrid system enables soldiers to take advantage of advanced electronic military equipment while reducing the weight of their load. Critical missions no longer have to be interrupted for battery replacement or recharging, and important systems do not fail due to drained batteries. Deploying a reliable power system can make a major difference for soldiers in the field by significantly increasing the soldier's safety, flexibility, mobility, and success.

TAGS: Content
Hide comments

Comments

  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Publish