The US Army PortableFuel CeU ProgramBy James Stephens, US Army Communications & Electronics Command

The US Army’s programme for development of portable fuel cells is structured toexploit the potential of Proton Exchange Membrane (PEM) technology to meetthe electric power demand of the individual soldier. The Army has identified theneed for lightweight power sources to provide the individual soldier withcontinuous power for extended periods. The baseline power demand is defined atlo-20 W average, and an energy demand without resupply of 400 W h permission day. For missions that extend beyond one day, fuel cell systems providevery attractive weight and volume advantages over existing battery technologies,both primary and rechargeable. One of the key barriers to actual Army use ofportable PEM fuel cells is the absence of an appropriate source of hydrogen.Programmes presently under way promise 1000 Wh per kilogram of H,production system weight. These sources of H, will integrate into a portablepower system with high power and energy density that meets the power, energyand mission demands of the soldier.

The key document driving the Army Fuel Cell

Development programme is the Operational

Requirement Document for Landwarrior.1’1 It

clearly outlines very stringent weight goals for its

power system. Initially a 12-hour mission must

be accomplished with a system that weighs less

than I.6 pounds (0.73 kg). Ultimately this must

be accomplished with a weight allocation of just0.5 pounds (0.23 kg). The only soldier power

source - other than batteries - mentioned in the

ORD is “Fuel Cell Power Sources”.

Tradi t ional ly the Army’s portable energy

sources have been primary batteries. The

workhorse primary battery for the Army is the

BA-5590, which stores 170 Wh of energy andweighs 1 kg. More recently, rechargeable

batteries have been introduced for training

missions with an energy density of 100 Wh/kg.State-of-the-art Li-ion primary batteries rated at

300 Wh/kg are also being introduced.

One of the critical questions that must be

answered is, “What is the power demand profile for

the dismounted soldier?” A 1993 front-end analysis

of the Soldier Individual Power System[*lhighlighted two power demand profiles for the

individual soldier. The first was for an average

power demand of 50 W and 1000 Wh/day. The

second added the electric power (100 W) to

operate a microclimate cooling system. Using

batteries to power these power demands, especially

the cooling mission, is not acceptable. However,

these power demands provided the impetus to the

Army to begin investing (in 1994) in fuel cell

technology for Soldier Individual Power. Since then

the need to manage the power demand has driven

the “acceptable” power demand profile to

1 O-20 W average and 400 Wh power per mission

day. Advantages and challenges to the Army of

portable fuel cells are listed in Table 1. This Table

also identifies that there are two distinct sizes of fuelcells being considered by the Army, based on their

source of H,.

The first are small systems that are the subject of

this article. The small systems will produce less than

500 W. Their H, can be supplied from sources

other than diesel/JP8 (the single fuel to be used by

all Army systems). This potential source of H, for

small portable fuel cells will therefore be discussed

as part of this article. The Army recognises thehydrogen source as a critical technological barrier

to eventual field use. Hydrogen supply from a

pressurised tank is not logistically acceptable.

The second size of fuel cells is larger than

500 W, and must use JP8 as their source of H,.While not a part of this discussion, it is sufficient

to say that the absence of small, compact diesel

fuel processors represents the key technical

barrier to introducing large (greater than 500 W)

fuel cell systems into the Army.

Portable fuel cell systemdefinitionThe primary focus of the Army’s portable fuel

cell programme is to provide power to the

individual soldier. Opportunities for other uses,such as powering sensors and recharging

batteries, are also being explored.

Historically, all of these uses have been

battery-powered. Power systems that are more

Fuel Cells Bulletin No. 13

energy-dense than batteries are attractive to theArmy. The PEM fuel cell represents the bestI

selection from the available fuel cell

technologies.

Simply stated, the Army’s portable fuel cell

system is a small PEM fuel cell (less than 500 W)

supplied with H, from a replaceable chemical

source.

Development of portablefuel cell systemsThe various target applications and their power

requirements are shown in Figure 1. The

prototypes from two programmes that have been

completed are shown on the right-hand side.

The schematic on the right-hand side represents

the Dual Use Application Program (DUAP),

which is developing a 5-10 W fuel cell battery

hybrid that will be delivered in early 2000.

The most mature 100 W system designed by

Ball Aerospace is shown in Figure 1. This system

essentially incorporated two 50 W H-Powerstacks into one system. Self-diagnostics and

protection of the system were emphasised in the

development of the power unit. It is push.

button star t , and has produced 120 W ne(140 W gross) in our laboratory near sea level. A

8500 feet (2600 m) above sea level it ha:

produced 96 W net (122 W gross).

Many optional features are contained in thi:

prototype. An example is the RS232 contra

interface that may not be required in a specific

application. Several pounds of weight can easil)

be extracted from this system by removing

options. Also, the prototype is built using readily

available components. M a n y o f these

components - such as the air pumps and valves -

have not been optimised for size, weight 01

efficiency. The 100 W system, even with tht

improvements mentioned, is still too heavy to br

carried by the soldier as their primary powelsource. All of the testing/demonstration of thi!

system and a smaller 50 W version has been witl-

pressurised (4500 psi, 315 bar) hydrogen from 2tank.

The Fuel Cel l /Bat tery Hybrid Systen

development is presently under way, although

prototypes will not be available until January

2000. This programme is being accomplished

under the Dual Use Application Program. By

mutual agreement, the development costs arejointly shared by private industry and the US

government. H-Power will develop a system for

a commercial application, and simultaneously

develop a similar system for the military.

Significant effort has been devoted to defining

the military “power mission profile” for the Fuel

Cell/Hybrid design. Our objective was to find a

power mission profile which had a peak power

(P> to average power (pa) ratio greater than 3.

Table 2 lists the results. The two most likely

targets for the military hybrid are for the Future

Transceiver and the Physical Security Sensor.Both involve very small fuel cells, 10 W or less.

As mentioned previously, power management

techniques will be applied to drive the soldier’s

power demand down to a goal of less than 10 W.

Therefore, these 10 W or smaller hybrid fuel

cells closely match the ORD requirements. It is

clear this size can be made small and light

enough to wear. An acceptable H, supply is

required.

Hydrogen supply for smallportable fuel cellsTable 3 summarises the strategy to supply H, to

small fuel cells. The basic strategy is parallel

development of both fuel cell technology and H,

supply.One programme is evaluating high-pressure

H, storage in small glass microspheres. The

objective of this programme is to provide a very

safe supply of H,. Uniform glass spheres have

been successfully blown and charged to 7000 psi

(490 bar). The goal is 10,000 psi (700 bar).

These glass spheres would be packaged and

crushed on demand to release the H,.

Fuel Cells Bulletin No. 13

H, replacement packages of glass spheres will

weigh 1 kg and deliver 30 g of H,. This is

converted by the fuel cell into 600 Wh. The

development was performed by the Schafer

Corporat ion as a Phase II Small BusinessInnovative Research Program project. Further

development support is required to improve the

ability to mass-produce the spheres, fill them to

10,000 psi (700 bar), and commercialise the

manufacturing process.

A chemical H, source capable of providing at

least 6% of its weight as H, is the basic goal of

the joint programme listed in the bottom centre

ofTable 3. Three different chemical systems willbe baselined over the next 12 months. Table 4

compares these three different chemical systems.The intention is to demonstrate various fuel cell

systems integrated with these H, supply

chemistries.

Other H, sources of interest are from

reforming diesel fuel to H,, and direct methanol

fuel cells. Finally, H, storage in carbon graphite

nanofibres and carbon structures is listed as apotential H, storage and delivery technique for

the future.

The programme discussed above tracks very

well with the forecasts for availability of H,

supply technologies for field testing from the

1997 Workshop on Hydrogen Storage.I*l

Integrated small portablefuel cell/Hz supply systemsHere we will illustrate the impact of integrating

state-of-the-art fuel cell technology and anadvanced H, delivery system. The basic mission

is:

Power nominal: 16.0 W

Power average: 17.2 W

Power peak: 28 W

Duty cycle: 90% nominal, 10% peak

l-day mission: 4 1 5 W h

3-day mission: 1240 Wh

6-day mission: 2500 Wh

Table 5 lists the salient features of the integrated

fuel cell/H, supply system for three different

mission lengths. Each mission is accomplishedwithout resupply. Note that a hybrid fuel cell is

envisioned. This will allow the system to operate

under water, during fording operations, handle

the peak loads and provide continuous power

during H, cartridge changeover. The second

column details a system for recharging batteries.

The third column adds two rechargeable

batteries to the system weight.

Figure 2 identif ies the projected weight

advantages of fuel cells versus state-of-the-art

primary batteries (300 Wh/kg) and rechargeable

(100 Wh/kg) batteries.

The projected cost advantages of fuel cells

versus primary batteries are also interesting.Because the fuel cell is reusable, its cost can be

amortised over multiple uses. The analysis inTable 6 plans 400 uses prior to being discarded.

The cost of the H, supply is predominant.

However, the small fuel cell system is cost-

attractive even for one-day missions versus

primary battery use. The ability to extract H,

from methanol or diesel fuel will further

enhance the cost advantage of small fuel cells.

These small fuel cells may have very low

power output (a few watts) and function

within a hybrid system. Integrating the fuel

cell stack into a practical functioning fuel cell

system requires that al l of the operating

characteristics of the fuel cell be understood

and exploited to maximum advantage. Many

electric load profiles are characterised by a high

$lP, rat io . Recent tes t ing of a “nominal”

25 W stack indicated that it could be operated

at 50 W for at least two minutes without acooling fan. Eliminating the cooling fan may

be practical for certain applications. The

objective should be to integrate the minimum

number of peripheral components into the

final system.

This “minimalist” approach will reduce

parasitic load losses, system weight, and cost.

0 Primary Batteries

l Rechargeable Batteries

A Rechargeable Batteries/ FC

X Hybrid FC

r10.0

5.0

0.0

0.0 2.0 4.0 6.0 6.0

M i s s i o n L e n g t h ( D a y s )

Fuel Cells Bulletin No. 13

ConclusionsThe Army programme is focused on meeting a

soldier’s power demand:

. IO-15 W (average power).l 3040 W (peak power).l 400 Whlday.

Chemical H, sources are being developed:

l 1000 Whlkg of reactant.l For small fuel cell systems.

Direct methanol fuel cell technology is

advancing:

l Cheaper source of H,.l M o r e e n e r g e t i c s o u r c e o f H, t h a n

chemical.

Diesel fuel reforming is key to Army use of fuelcells greater than 500 W:

l Compact reformers are required.l Diesel fuel is inexpensive.l Diesel fuel is readily available to soldiers.

AcknowledgmentThis article is basedon a presenti at the

Portable Fuel Cells Conference, Luzern,

Switzerland, 21-24 June 1999. Copies of the

Conference Proceedings are available - priced at

SFr200 plus postage - from the European Fuel

Cel l Forum, P O B o x $9, C H - 5 4 5 2

Oberrohrdorf, Switzerland. Tel: +41 56 496

7 2 9 2 , F a x : +41 5 6 4 9 6 4 4 1 2 , Email:

info@efcf.com, Internet: httpl/www.efcf.coml

References1. Operational Requirements Document(Revised) for Landwarrior (LW), 3 August 1999.

2. R. Jacobs et al: “Front end analysis of soldier

individual power systems”. US Army Belvoir

Research, Development & Engineer Center,

Technical Report USA-BRDEC-TIU2541,

May 1993.

3. R. Jacobs et aL: “Portable power source needsof the future army - Batteries and fuels cells”.

Annual Battery Conference on Applications &

Advances, California State University, LongBeach, California, January 1996.

4 . W o r k s h o p o n H y d r o g e n S t o r a g e &

Generation for Medium-Power and -Energy

Applications. Sponsored by US Army Research

Office, C I A O f f i c e o f R e s e a r c h &

Development, and Department of Chemical

Engineering, Universi ty of South Carolina,

April 1997.

For more information, contact: James E. Stephens,US Army Communications & Electronics Command,Command & Control Directorate, AMSEL-RD-CZ-AP-ES-A, 10108 Gridley Road, Suite 1, Fort Belvoir. VA 22060-581 7, USA. Tel: +l 703 704 2006, Fax: +l 703 7043794, Email: jstephens@belvoir.army.mil

Fuel Cells Bulletin No. 13w