A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Technical Report 

NREL/TP-560-42233 

October 2007 

Hickam Air Force Base 

Fuel Cell Vehicles: 

Early Implementation Experience 

Leslie Eudy, National Renewable Energy Laboratory 

Kevin Chandler, Battelle 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
National Renewable Energy Laboratory

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Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337

Hickam Air Force Base 

Fuel Cell Vehicles: 

Early Implementation Experience 

Leslie Eudy, National Renewable Energy Laboratory 

Kevin Chandler, Battelle 

Prepared under Task No. H270.8200 

Technical Report 

NREL/TP-560-42233 

October 2007 
NOTICE

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Acknowledgements 

This evaluation at Hickam Air Force Base would not have been possible without the support and 

cooperation of many people. The authors thank the following: 

U.S. Department of Energy 

John Garbak 

National Renewable Energy Laboratory 

Keith Wipke 

George Sverdrup 

U.S. Air Force Advanced Power Technology Office (APTO) 

Mike Mead 

Hickam AFB 15th Logistics Readiness Squadron 

Roger Storman 

Pat Lindo 

Hawaii Center for Advanced Transportation Technologies (HCATT) 

Tom Quinn 

University of Hawai’i, Hawai’i Natural Energy Institute 

Bor Yann Liaw 

Matthieu Dubarry 

Nicolas Vuillaume 

Hydrogenics 

Kevin Harris 

Norman Freeman 

Enova Systems 

Todd Martin 

HydraFLX Systems LLC 

Clark Maxwell 

Matthew Morse 

Mark Schultz 

 iii
Table of Contents 

Introduction..................................................................................................................................... 1 

Background................................................................................................................................. 1 

USAF Advanced Power Technology Office............................................................................... 2 

Hawaii Center for Advanced Transportation Technologies ....................................................... 3 

National Demonstration Center for AFVs at Hickam Air Force Base ....................................... 3 

Host Site Profile.......................................................................................................................... 5 

Fuel Cell Vehicle Descriptions....................................................................................................... 6 

Hybrid Fuel Cell System............................................................................................................. 8 

Early Vehicle Experience ......................................................................................................... 10 

Infrastructure and Facilities .......................................................................................................... 11 

Hickam Hydrogen Station Design ............................................................................................ 12 

Maintenance Facility................................................................................................................. 17 

Evaluation Plans............................................................................................................................ 18 

Vehicle Planned Use ................................................................................................................. 20 

HNEI Driving and Duty Cycle Analysis .................................................................................. 20 

What’s Next for this Evaluation?.................................................................................................. 21 

Contacts......................................................................................................................................... 22 

Acronyms and Abbreviations ....................................................................................................... 24 

References and Related Reports ................................................................................................... 25 

 iv
Introduction 

This report summarizes early implementation experience from an evaluation of two prototype 

fuel cell vehicles operating at Hickam Air Force Base in Honolulu, Hawaii. The fuel cell 

vehicles are part of a larger demonstration of advanced technologies within the United States Air 

Force (USAF), which is investigating ways to increase energy efficiency and reduce petroleum 

use. The Department of Energy (DOE), through its National Renewable Energy Laboratory 

(NREL), is evaluating these prototype fuel cell vehicles to help determine the status of the 

technology for different applications. This report describes the equipment used (vehicles and 

infrastructure) and provides details on the early experience, lessons learned, and plans for 

demonstrating the vehicles. 

Background 

The federal government is the single largest consumer of energy in the United States. Within the 

government, the Department of Defense (DoD) ranks highest in both total energy use (79% of 

total U.S. government) and petroleum consumption (nearly 92% of total)1

. Since the early 

1990s, the government has taken steps to strengthen the nation’s energy security, lower 

emissions, and reduce U.S. dependence on imported oil. Several laws have been passed 

stipulating requirements for reducing energy use and petroleum consumption. Federal agencies 

are subject to these regulations, and must develop a plan to meet the goals of each. Regulations 

include: 

• Energy Policy Act (EPAct) 1992 set statutory requirements for the acquisition of alternative 

fuel vehicles (AFVs) by federal agencies. This applies to on-road light-duty vehicles in the 

United States and Puerto Rico; exemptions are given to military tactical, law-enforcement, 

and emergency vehicles. 

• Executive Order 13149 (2000) mandate set requirements for agencies to reduce total fleet 

petroleum consumption by 20% of 1999 levels. This applies to on-road light-, medium-, and 

heavy-duty vehicles with the same exceptions as EPAct. 

• National Defense Authorization Act 2002 (NDAA) set goals of hybrid vehicle acquisition 

in DoD fleets not subject to EPAct, and expanded the alternative fuel vehicle requirements 

for DoD/EPAct subject fleets. 

• EPAct 2005 amended EPAct 1992 and adds a requirement for using alternative fuels in fleet 

dual-fuel and flex-fuel vehicles if the fuel is available within a 15 minute drive and does not 

cost more than 15% more than gasoline.

• Executive Order 13423: Strengthening Federal Environmental, Energy, and 

Transportation Management (2007) revokes Executive Order 13149 and sets requirements 

to reduce petroleum consumption by 2% annually through fiscal year (FY) 2015, and to 

increase alternative fuel use by at least 10% compounded annually through FY 2015 

compared to FY 2005 baselines.

The DoD developed a strategy to meet or exceed the objectives of these regulations. Key 

objectives of this strategy were to meet the AFV acquisition goals of EPAct, reduce petroleum 

 

1

 Energy Information Administration, Annual Energy Review 2006, http://www.eia.doe.gov/emeu/aer/contents.html 

 1
consumption by 20% through fiscal year 2005 (based on the 1999 baseline), increase average 

fuel economy of acquired light-duty vehicles, and meet hybrid light-duty vehicle acquisition 

goals of NDAA2

. DoD recognizes that switching from the current established petroleum-based 

infrastructure to one based on alternative fuels will take time and effort from government, 

industry, and the public. To address the evolutionary aspect, the DoD strategy (last revised in 

January 2003, currently four years into this strategy) is separated into three time frames: 

• Immediate solutions address the technologies already available through the General Service 

Administration (GSA), which supplies the majority of DoD’s non-tactical vehicles. 

Alternative fuel vehicles most commonly used include compressed natural gas (CNG), 

ethanol (E85), electric (low-speed vehicles), and propane. 

• Near-term (2-5 years) solutions address new technologies that are just beginning to be 

commercialized. Blends of 20% biodiesel in diesel fuel (B20) and hybrid-electric vehicles 

are the technologies of most interest. By displacing petroleum and increasing efficiency, 

these technologies can reduce DoD fossil fuel use. 

• Long-term (5-20 years) solutions address the newest technologies in the early stages of 

development. The DoD views hydrogen as a fuel of choice to meet future petroleum 

reduction goals. 

USAF Advanced Power Technology Office 

The highest petroleum consuming branch within the DoD is the United States Air Force (USAF). 

The USAF is committed to exceeding federal petroleum reduction goals using the best 

technologies currently available. As its need for energy increases, the USAF understands that 

meeting these goals will require newer, more efficient technologies to be tested and optimized. 

The DoD has a history of pushing the development and commercialization of new technologies 

to meet its specific needs. In support of bridging the gap between research and development 

(R&D) and deployment, the USAF established the Advanced Power Technology Office3

(APTO). 

APTO, headquartered at Robins Air Force Base in Georgia, is leading the effort to determine 

which technologies can meet USAF needs most efficiently in the near-term as well as exploring 

advanced technologies for the future. APTO is interested in a variety of technologies, including: 

• Fuel cells for stationary power production 

• Alternative fuels, hybrid electric propulsion, and fuel cells in transportation applications 

• Renewable sources for hydrogen production. 

In 2001, the APTO, in partnership with the High Technology Development Corporation 

(HTDC), established a National Demonstration Center for AFVs at Hickam Air Force Base in 

Hawaii. The HTDC is a state agency established in 1983 by the Hawaii State Legislature to 

facilitate the development and growth of Hawaii’s commercial high technology industry. The 

 

2

 Department of Defense Compliance Strategy for Executive Order 13149 Alternative Fuel / Hybrid Vehicle 

Requirements, Revised January, 2003, posted on the Defense Environmental Network & Information eXchange 

(DENIX) Web site: https://www.denix.osd.mil/denix/Public/Library/AFV/Reports/dod_strategy_eo13149_29jan03-

final_v3.doc

3

 The Advanced Power Technology Office Web site, http://www.robins.af.mil/units/apto.asp

 2
Hawaii Center for Advanced Transportation Technologies (HCATT4

), a division of the HTDC, 

was selected to manage this demonstration program. 

Hawaii Center for Advanced Transportation Technologies 

HCATT was originally established in 1993 as the Hawaii Electric Vehicle Demonstration 

Project. Its purpose was to represent the Hawaii Consortium in the DoD’s Electric and Hybrid 

Vehicle (EHV) Technology Program, sponsored by the Defense Advanced Research Projects 

Agency (DARPA). In this project, DARPA worked with seven regional consortia to advance the 

development of electric and hybrid technologies. 

As one of the seven consortia, HCATT facilitated partnerships between private corporations, 

non-profit organizations, federal agencies, and state agencies to develop and demonstrate electric 

vehicles. To support these projects, HCATT also created an electric vehicle conversion, 

maintenance, and service center, which included an advanced battery testing facility. The EHV 

program ran from 1993 through 1998, and helped develop components such as hybrid electric 

propulsion systems, electric motors, and advanced battery controllers. 

The DARPA project evolved into the Advanced Vehicle Technologies Program (AVP) which 

was funded through the Department of Transportation. All seven consortia continued with AVP 

funding through 2000. HCATT’s projects were focused on electric and hybrid vehicles, electric 

vehicle charging infrastructure, and advanced battery testing and life cycle predictions. It was 

HCATT’s experience with these early demonstrations that made it a perfect partner for APTO. 

National Demonstration Center for AFVs at Hickam Air Force Base 

The purpose of the National Demonstration Center is to demonstrate and validate the latest fuel 

efficient and environmentally compliant technologies for use in ground vehicle fleets, basic 

expeditionary airfield resources, and aerospace ground support equipment. The state of Hawaii 

was considered an ideal site for the National Demonstration Center. The state proactively 

encourages conservation and alternative energy, partly because of its nearly complete 

dependence on imported petroleum. Also, the island of Oahu hosts bases from each of the four 

DoD branches. This close proximity is expected to facilitate the exchange of experience in 

demonstrating these technologies, which could benefit all branches within the DoD. 

The National Demonstration Center projects depend on three primary partners: 

• APTO – provides funding and overall guidance 

• HCATT – acts as technology developer by building and managing a team to design, 

fabricate, and evaluate the technology 

• 15th Airlift Wing at Hickam – demonstrates the vehicles in various applications in and 

around the base 

Early projects funded for the National Demonstration Center were focused on all-electric, battery 

powered vehicles and fast charging infrastructure. More recent projects have begun a transition 

to fuel cell powered vehicles and equipment and the requisite hydrogen infrastructure. The first 

 

4

 HCATT website: www.htdc.org/hcatt

 3
fuel cell vehicle developed under the program was a battery dominant, hybrid fuel cell bus. The 

second vehicle developed was a fuel cell dominant hybrid step van. 

HCATT has assembled a team to develop and demonstrate the hydrogen vehicles and 

infrastructure at Hickam. Each team member receives funding under contract to HCATT. The 

project partners and their roles are described below. 

Hawaii Natural Energy Institute (HNEI)—As a research institute of the University of Hawaii 

at Manoa (UH), HNEI (www.hnei.hawaii.edu) was established by the state legislature in 1974 to 

investigate new forms of energy that would diminish Hawaii’s total dependence on imported 

fossil fuels. In 1994 the UH College of Engineering formed a team, which included HNEI, to 

participate with HCATT in the DARPA EHV program. Team member selection was conducted 

by a project evaluation panel at HTDC. HNEI has worked with HCATT since the early DARPA 

projects, developing an efficient system for collecting real-time data on alternative fuel and 

electric vehicles to help benchmark the technology. 

Additionally, HNEI possessed the requisite electrochemical expertise to provide battery 

evaluation capabilities for advanced battery chemistries. The tools developed by HNEI during 

these projects allowed the researchers to characterize the duty cycle of the vehicles using secondby-second data from multiple trips. Understanding the duty cycles for a particular vehicle 

application can aid in analyzing the performance and life for batteries and other vehicle 

components. HNEI is supporting these fuel cell vehicle projects by testing and evaluating 

advanced battery chemistries and collecting test data for performance analysis. 

Enova Systems—Headquartered in Torrance, California, Enova Systems 

(www.enovasystems.com) is a supplier of efficient, environmentally friendly digital power 

components and systems and associated engineering services. Enova designed and integrated the 

hybrid electric propulsion system for the two fuel cell vehicles included in this evaluation. 

Enova maintains a satellite office located at the HCATT facility and is providing maintenance 

for the prototype fuel cell vehicle propulsion systems throughout the demonstration. 

Hydrogenics Corporation—Headquartered in Mississauga, Ontario, Hydrogenics Corporation’s 

(www.hydrogenics.com) core business includes developing fuel cell power products such as 

fully packaged power modules and electric hybrid systems. Hydrogenics provided the fuel cells 

for the project and worked closely with Enova to integrate the fuel cell power modules into the 

vehicles. Hydrogenics will provide maintenance support for the fuel cells as necessary during 

the project. 

HydraFLX Systems—Headquartered in Austin, Texas, HydraFLX Systems 

(http://www.hydraflx.com/) is a small business research and development company with 

expertise in high pressure gaseous fuel management, and in the past has helped the USAF 

establish natural gas vehicle fueling stations at military bases throughout the United States. The 

HydraFLX System was first developed through an SBIR grant (Small Business Innovative 

Research) as part of broader goals for developing hydrogen technologies for ground support. 

The Hickam hydrogen station is a modular, fully deployable hydrogen fueling system using three 

primary modules (fuel production, pressure management, and pressure storage). HydraFLX 

developed the modules with product support from Pinnacle CNG Ltd of Midland Texas and 

 4
Teledyne Energy Systems of Hunt Valley Maryland, both of whom are supporting their first 

hydrogen vehicle fueling products. The company will be implementing technology 

enhancements to the prototype array during the coming year while supporting the initial stages of 

the larger vehicle demonstration. HydraFLX staff is responsible for all station maintenance as 

well as developing a training program for emergency responders and other Hickam staff. 

Host Site Profile 

Hickam Air Force Base is home 

to the 15th Airlift Wing 

(www2.hickam.af.mil/), the 

headquarters of the Pacific Air 

Forces, and the Hawaii Air 

National Guard. The 15th

Logistics Readiness Squadron 

within the 15th Airlift Wing is the 

host fleet for the evaluation. The 

base is situated on more than 

2,800 acres of land between P

Harbor Naval Base and the 

Honolulu International Airport. 

The runways are shared by Hickam and the airport and operate as a single airport complex under 

a joint use agreement. 

earl 

As host fleet, the 15th Logistics Readiness Squadron manages a diverse fleet of 812 vehicles 

comprised of buses, vans, sedans, stake trucks, pickup trucks, tractors and trailers, fire trucks, 

aircraft fuel trucks, forklifts, aircraft cargo loaders, aircraft servicing vehicles, tactical vehicles, 

and construction equipment. These vehicles are used in multiple applications to support 15th

Airlift Wing and transient flying missions, installation sustainment, and war readiness. The 15th

Logistics Readiness Squadron is also responsible for operating the vehicles and providing data to 

the project team for analysis. Figure 1 shows the location of the base and the surrounding area. 

 5
Figure 1. Map of Hickam Air Force Base 

Fuel Cell Vehicle Descriptions 

The fuel cell vehicles being demonstrated at Hickam were jointly developed by HCATT, Enova, 

and Hydrogenics. The first vehicle developed was a 30-foot shuttle bus, pictured in Figure 2. 

The development process for the fuel cell shuttle bus took approximately four months to 

complete. This timeframe includes design, fabrication, and integration of all of the components. 

Rather than acquire a new bus chassis, the approach was to recondition and convert an existing 

30-foot shuttle bus to an all-electric drive bus equipped with a small fuel cell system. The 

integration of the new components into the bus took about one month to complete. The design 

and development work was accomplished at Enova’s facilities in California, and Hydrogenics’ 

facilities in Canada. The actual conversion and integration of the new propulsion system into the 

bus occurred at HCATT’s facilities in Honolulu. All parties reported that this collaboration and 

process went smoothly and quickly. This portion of the project cost approximately $1 million to 

complete. 

The work was completed in January 2004 and the shuttle bus was available for service on 

February 19, 2004. The bus was put into operation on the base using its battery-only capability, 

while the hydrogen infrastructure was being planned and installed. 

 6
Figure 2. Fuel cell bus at Hickam AFB 

A second fuel cell power system was developed for a step van platform, shown in Figure 3. 

Development of the fuel cell step van began in early 2005. The approach for this vehicle was to 

acquire a standard gasoline-powered van for conversion to a fuel cell system. The team 

determined that purchasing a conventional vehicle for retrofit would be less costly than placing 

an order for an incomplete (“glider”) vehicle. The original transmission and gasoline systems 

were removed and replaced with a fuel-cell-dominant hybrid system. The system installation was 

completed in July 2006, and the step van was put though a series of shake-down tests prior to 

delivery to the fleet. 

Figure 3. Fuel cell step van at Hickam AFB 

 7
Hybrid Fuel Cell System 

Both vehicles use the same basic fuel cell hybrid system designed by the project team, with one 

main difference: the shuttle bus is battery-dominant, while the step van is fuel-cell-dominant. 

With these two strategies, the size of the fuel cell stack versus battery is reversed. The shuttle bus 

has a 20 kW fuel cell with a larger battery pack (140 Ah) for energy storage, while the step van 

has a small battery pack (42 Ah) to supplement a 65 kW fuel cell. The power system diagram in 

Figure 4 shows the energy transfer among the fuel cell hybrid system components. 

Figure 4. Propulsion system diagram 

The battery-dominant series hybrid fuel cell system that powers the shuttle bus draws primarily 

on traction batteries (gel lead acid) to provide power for propulsion. This strategy allows the bus 

to operate on battery-only power if needed. A small proton exchange membrane (PEM) fuel cell 

power module is used to charge the batteries and extend the driving range. This hybrid 

configuration and control strategy is charge depleting, meaning that the batteries will eventually 

run down even if hydrogen fuel remains. 

Given that this bus would operate primarily on base where the average speed is 25 mph, this 

approach was considered acceptable as the current draw on the batteries would not be severe and 

could be generally supported by the small fuel cell. To restore the batteries, the bus is plugged 

into an off-board charger when not in use. With a full tank of hydrogen, the typical driving range 

for the bus is around 100 miles. Depending on the operation of the bus and its efficiency, 

supplementary charging may be required every other night. The batteries can be charged by two 

different methods: a fast charge connector that plugs into a PosiCharge Unit, or a standard 220 

outlet plug that provides a slow charge and equalizes the battery pack. 

The fuel cell hybrid system that powers the step-van draws power from a 65 kW Hydrogenics 

PEM fuel cell combined with a smaller set of batteries. The configuration and control strategy is 

charge-sustaining, so the batteries do not need to be recharged to operate. However, the system 

includes a fast charge connector that plugs into a PosiCharge Unit and a standard 220 plug-in 

 8
fitting that provides an equalization of the battery pack and tops-off the charge. The estimated 

range for the step van is around 150 miles. The chassis of the van is built by Workhorse with a 

body configuration by Utilimaster. The design also includes the capability to supply distributed 

power in the field (see Figure 5). 

Outlets located inside rear door 

Figure 5. The fuel cell van is equipped with outlets to supply power in the field 

Both systems have regenerative braking. The electric drive unit (EDU) converts kinetic energy 

(energy from the motion of the bus) to electrical energy while braking, and this energy is stored 

in the traction batteries. Selected specifications for each vehicle are shown in Table 1. 

 9
Table 1. Specifications of the Fuel Cell Bus and Step-van 

System Fuel Cell Bus Fuel Cell Step-van 

Chassis ElDorado National RE-29E Workhorse/Utilimaster 

Model Year 1994 2005 

Length/Width/Height 30 ft/96 in/116 in Cargo body: 16 ft/93.5 in/85 in 

GVWR/Curb Weight 29,000 lb/22,240 lb 14,100 lb 

Number of Seats 26 Two (driver and passenger) 

Wheel Base 160 in 178 in 

Hybrid Type Series, battery dominant, charge 

depleting 

Series, fuel cell dominant, charge 

sustaining 

Regenerative Braking Yes Yes 

Fuel Cell Hydrogenics PEM fuel cell, 20 kW Hydrogenics PEM fuel cell, 65 kW 

Electric Motor AC induction motor, 120 kW max, 

85 kW continuous 

AC induction motor, 120 kW max, 

85 kW continuous 

Energy Storage Hawker EP-70/lead-acid, 28 

modules in two packs, 140 Ah 

Hawker EP-42/lead-acid, 28 

modules, one pack, 42 Ah 

Auxiliaries Electric driven 12V / 24V from 

Control Electronics Unit (CEU) Electric driven 12V / 24V from CEU 

Fuel Storage Two Dynetek cylinders, compressed 

hydrogen 

Two Dynetek cylinders, compressed 

hydrogen 

Fuel Storage Capacity 10 kg at 5,000 psi 10 kg at 5,000 psi 

Off-Board Battery Charging AeroVironment 60 kW rapid charger AeroVironment 60 kW rapid charger 

Early Vehicle Experience 

The development process for the fuel cell vehicles went extremely well because the partners 

were willing to work closely and share potentially sensitive data. Although Enova and 

Hydrogenics had not previously worked together, they were able to collaborate to design and 

build the project’s first fuel cell vehicle in record time. The modifications to the fuel cell bus 

were completed in January of 2004 and the bus was officially dedicated for service on February 

19, 2004. Because of technology challenges in getting the hydrogen fueling station installed, the 

fleet was only able to operate the bus using its battery-only mode. Despite this, the bus was 

initially assigned to limited service on a base shuttle route; however, shortly thereafter the base 

shuttle service was terminated. Following this the bus was used to transport distinguished 

visitors around base, but neither application provided sufficient usage for operational experience. 

There have been several issues with the bus since its completion. Two specific issues are 

described below. 

Air Conditioning System – One aspect of note for fuel cell and hybrid vehicles in general is that 

the systems are reported to be quieter than conventional vehicles. A potential downside of this is 

that the noise of other auxiliary systems, such as the air conditioner, becomes noticeable. This 

was the case for the prototype bus at Hickam. The bus was pulled from service to address the 

problem. The project partners traced the cause for this particular system to the air conditioner 

control strategy. Enova’s installation of a new controller and modifications to the software 

solved the problem. The control unit installed allowed separate controls for the temperature and 

fan speed. 

Voltage sensor for the fuel cell – There was a voltage irregularity that turned out to be a 

problem with the voltage sensor, and not with the fuel cell system itself. Hydrogenics personnel 

diagnosed the problem and provided a solution. Initially, an attempt was made to repair this 

 10
issue in the field rather than at the manufacturer’s plant due to the distance between the bus 

location in Hawaii and the manufacturer’s plant in Canada. However, the quality control in the 

field could not duplicate the quality control at the production lab, so the fuel cell power module 

was eventually removed from the vehicle and transported to the company for repair. The 

approach used to solve this voltage sensing problem is the result of an improved production 

process established by Hydrogenics. 

A key diagnostic feature of Hydrogenics' line of power modules is the ability to monitor and log 

real-time performance data during module operation. One such piece of data, which provides 

insight into fuel cell stack health and performance, is individual cell voltage information. 

Hydrogenics data monitoring has advanced in this area with the release of both next generation 

stack interfaces and cell monitoring hardware for this diagnostic feature. Stack interfaces on the 

fuel cell bus have been upgraded from spring-loaded pin board pick-up points, to a flexible 

printed circuit board “finger” design attached directly to the stack using conductive epoxy. The 

flexible PCB design has proven to be much more reliable in field applications and has replaced 

the spring-loaded contact pin monitoring method across all of Hydrogenics' product lines. 

Current Hydrogenics fuel cell modules also incorporate next-generation cell voltage monitoring 

electronics which are mounted directly to the stack as compared to on the frame of the fuel cell 

power module. This new design eliminates numerous components, including two secondary 

connectors and their associated wiring harness, dramatically reducing the total number of contact 

points. Eliminating this wiring harness, along with the associated connectors, daughter circuit 

boards, and separate electronics housing improves both the reliability and manufacturability of 

the electronics while enabling significant cost reductions for the complete system. 

The development and modifications for the fuel cell step-van were completed by fall of 2005. 

Because the system in the step-van is fuel cell dominant, operation in battery-only mode was not 

an option. While waiting for the infrastructure to be completed, the project team kept the van at 

the HCATT facility. During this time, Enova conducted limited operational testing to exercise 

the fuel cell. 

Infrastructure and Facilities 

For this vehicle demonstration program, the plan was to implement a temporary hydrogen 

fueling station while working on a permanent solution. Originally, the plan was to use a local 

industrial gas supplier’s tube trailer to deliver fuel to the fuel cell vehicles. The local provider 

proposing this method of support was Air Liquide Hawaii. However, barriers exist to conducting 

this type of fuel supply on the military flight lines and vehicle maintenance areas. Another 

solution proposed by Hydrogenics was to use their cutting-edge PEM electrolyzer technology to 

generate hydrogen on-site. Ultimately, the USAF asked HydraFLX to consider taking over the 

prime role based on their SBIR program experience, with the caveat that Hydrogenics be 

considered the supplier of the production system. PEM electrolyzer technology appears to be 

promising in the future, but the technical challenges remain considerable and this type of 

electrolysis continues to be in a development stage. Consequently, HydraFLX had to pursue an 

alternative solution to generating hydrogen on-site.

 11
Hickam Hydrogen Station Design 

The design of the hydrogen station at Hickam is quite unique compared to other hydrogen 

stations currently being built. To meet Air Force specifications, HydraFLX developed a 

modular, fully deployable hydrogen fueling system that conforms to USAF – 463L palletized 

airborne-deployable requirements. The individual packaged operating modules (PODs) are 

crush-proof, DOT-transportable carbon steel packages that can be easily moved by forklift and 

commercial transport. The three primary modules can fit on one standard trailer, which can be 

loaded on an aircraft for transport to any potential site. The system is designed for quick set up 

in a remote location without the need for pipelines or infrastructure. 

Although the configuration is deployable by design, there are no plans to move the component 

modules at Hickam. The equipment was installed for continued research as an outdoor 

laboratory and semi-permanent fueling support to the fuel cell vehicle demonstration program 

including future prototypes to be added. This station will be used as a model for future stations 

within the USAF. The station at Hickam cost $1.5 million, not including site preparation and 

R&D investment by some of the partners. 

Figure 6 shows the overall hydrogen station layout. The station at Hickam includes the 

following components: 

• Power Control Unit – The Power Control Unit, pictured in Figure 7, conditions and 

distributes incoming power to the other station components. A Mobile Electric Power (MEP) 

Generator is included in the station package to insure 100% deployability when not located 

near a grid power connection. The Power Control Unit provides the DC power for both of 

the electrolyzers. 

• Water Box – The water box, also shown in Figure 7, purifies the feed water for the 

electrolyzers, which allows greater purity of hydrogen to be created by utilizing ultra pure 

water. It also provides cooling water for process control. The raw water can come from any 

available source including gray water, which allows flexibility when the unit is deployed in 

the field. 

• H2FP Fuel Processor – Hydrogen gas is produced by twin hybrid Titan-series electrolyzer 

modules integrated into Teledyne’s standard HMX series electrolyzer chassis, which are 

housed together in the H2FP unit (Figure 8). These electrolyzers, which are an improved 

design from the standard commercial units, can work separately or together to produce up to 

50 kg hydrogen per day. 

• H2PM Pressure Management – The Pressure Management System is located in the H2PM 

POD as shown in Figure 8. The Pressure Management System uses a four staged intensifier 

system that can be operated on site or transported to alternate locations to assist in off site 

vehicle fills. It provides its own compression power by means of an onboard MIL-spec 

diesel engine. It can provide compressed hydrogen up to 5,000 psi with an inlet pressure 

starting at 115 psi. However, the engine is soon to be upgraded to an electric motor, taking 

advantage of the incoming grid power. With the upgrade, this design will not be transported 

off site to operate independently. 

 12
• H2PS Hydrogen Storage – There are two forms of hydrogen storage onsite at Hickam AFB. 

Each form was developed to give the Air Force the freedom it needs during the infancy of the 

deployable hydrogen program. The H2PS hydrogen storage includes units that consist of 

twelve steel DOT bottles in a vented common fill-point manifold. These units are capable of 

being filled with compressed hydrogen up to 3,000 psi. The H2PS also meets current DOT 

standards for transporting compressed hydrogen. Three of these “12 packs” have been 

provided for the station at Hickam, and since these units are portable, they can be transported 

to various locations on base to provide an on-site supply of hydrogen for fueling. These units 

also served as the interim hydrogen supply for the fuel cell bus and van while the station was 

under development/construction. 

The H2PS also includes a high-pressure storage system, which can store 3.7 kg of 

compressed hydrogen at 5000 psi. The high-pressure storage system is made up of nine 

Dynetek W150 storage vessels, with one of the nine used as intermediate storage for pressure 

management. With all of the remaining eight vessels full, the station has almost 30 kg of 

5,000 psi compressed hydrogen onsite (Figure 9). 

 

Figure 6. Hickam hydrogen station lay-out 

 13
Figure 7. The power control unit (left) and water box (right) 

Figure 8. H2FP hybrid electrolyzer (left) and H2PM pressure management (right) 

 14
Figure 9. Primary hydrogen storage (left) and portable hydrogen lift pack (right) 

Most often, hydrogen is dispensed into the fuel cell vehicles through a sequential balance 

transfer method, resulting in an approximate fill of 95%. The H2PM pressure management unit 

can be used to “top-off” or otherwise fully fill the vehicles. The vehicles are planned for use 

around the base and can be filled as needed during the day and balance transfer fueling is 

proving to be the most economical and efficient method to achieve the highest settled “fills” with 

the flexibility to fuel in unattended mode or during normal daily production runs – neither 

affecting the fueling event itself. 

The site infrastructure is based on a deployable safety system that uses an open-air design with a 

classification barrier (tilt-walls) between the station components and the fueling area. These tiltwalls are designed to be constructed on-site and easily moved and deployed as needed with the 

station (however, the Hickam installation has this wall permanently installed). The fueling area 

includes an overhead canopy to provide the users with shelter from sun and rain. The canopy 

was designed to eliminate any potential pockets where hydrogen gas could collect and cause a 

safety hazard. This design is also aided by local weather conditions which include a continual 

wind through the area. 

Hydrogen and oxygen sensors are designed for use inside the POD enclosures only, and 

additional sensors can be installed around the outdoor array if needed in the future. These 

outdoor sensors are not currently being utilized at this station for several reasons. First, the 

combination of station design and weather conditions at Hickam eliminates the potential for 

hydrogen gas to build up. Secondly, current generation hydrogen sensors also detect other 

combustible gases. The proximity of the busy airport runway results in a high level of jet 

emissions that interfere with the sensors and continually cause false alarms. 

This hydrogen station is equipped with seven emergency shutdown devices (ESD). These ESDs 

can be activated if conditions become unsafe. Activation of any of the ESDs puts the station into 

shutdown mode. Main power is removed from the station, while a low voltage backup system 

activates to maintain the logic controls. In this mode, all valves are closed to isolate hydrogen 

 15
storage vessels, and each electrolyzer automatically purges its oxygen and hydrogen generation 

vessels with nitrogen. 

The Hickam hydrogen station is considered a prototype design and HydraFLX is continuing to 

optimize and make modifications to improve several aspects of the station. Future design 

improvements planned include: 

• Electrification of H2PM Pressure Management POD – The diesel engine that currently 

supplies power to the unit is being replaced with an electric pump powering the hydraulic 

system. This is scheduled for completion in fall 2007. The purpose of this modification is 

not to remove the deployability feature – which remains intact with the MEP – but rather to 

enhance the environment of the outdoor lab operations by removing tailpipe emissions and 

operational noise levels. 

• Station Automation – will establish unattended fueling with the implementation of 

unattended balance transfers to the station’s fueling modes. This mode allows a controlled 

amount of hydrogen to be transferred while the station is either producing or not producing 

hydrogen. The upgrade will include a graphic interface that displays the status of the station 

as well as which fueling mode the station is in. A second phase of automation will allow the 

fueling operator to perform both types of fuel transfer – sequential balance transfer and 100% 

compression-assist “topping-off” of the on-board vessels when required. 

• Solar Power – The project partners are planning to install a 120 kW photo-voltaic (PV) 

system to provide more than adequate renewable energy, which will eliminate the need for 

grid power and/or the MEP military ground power unit (with the exception of back-up 

power). 

• Capture and Use of Oxygen – The electrolyzers also produce pure oxygen gas. The project 

team is exploring an efficient method of collecting the gas for use on the base. The team has 

determined that a typical USAF base averages 200-300 scf (standard cubic feet) of gaseous 

oxygen per week in the various shops and labs. The Hickam prototype station produces twice 

this amount of oxygen per hour at 99.99% purity. The MIL-spec for ABO (aviator breathing 

oxygen) is 99.5% purity. 

HydraFLX currently staffs the site with an engineer responsible for continued research activities 

and maintenance of the station. After the improvements and enhancements itemized above are 

implemented and unattended fueling completes a trial period including catastrophic scenarios 

examination, HydraFLX plans to begin training Hickam staff to fuel the vehicles. 

Early Experience with Hydrogen Fueling – The system was pre-commissioned in Midland, 

Texas, during August, 2006. The system was run for several hundred hours and through a series 

of tests to ensure each component was operating within design parameters. Once testing was 

completed, the PODs were shipped to Hawaii for final installation at Hickam. The station was 

completed by the end of October and officially dedicated in November. The November 2, 2006 

dedication ceremony was attended by Air Force and state officials, including the Governor of 

Hawaii and the Assistant Secretary of the Air Force for Installations, Environment and Logistics. 

The project partners have experienced a few issues with the infrastructure that delayed getting 

the vehicles in full service. 

 16
• Pressure Management System Component Failure – An unexpected component failure 

was experienced because a supplier failed to notify the manufacturer of a market substitution 

element. A positioning magnet inside the pressure management system failed because of its 

non-compliant material make-up. An investigation into the component failure showed the 

failed part was composed of a ferrous material which was subject to embrittlement. The 

material used in the original design was cobalt. The component manufacturer had changed 

the original design to a less-expensive alloy that was substituted unbeknownst to the pressure 

management integrator. A written examination of the problem was generated and the 

manufacturer corrected the problem with the correct magnet type for hydrogen use. 

HydraFLX completed the repair and put the system back on-line. 

• Hydrogen Leak – High-pressure fittings and components are routinely checked for vibration 

or thermal cycling leaks and thus far the station has experienced one component-to-fitting 

leak which required actual replacement of the part and fittings. The leak was detected in the 

cooling circuits between compression stages, an area which experiences the greatest range of 

thermal and pressure shock and cycling during normal operations. The audible leak was 

traced to a fitting-to-component vibration wear issue. HydraFLX was able to quickly repair 

the problem and the station was put back on line. 

Maintenance Facility 

Enova is responsible for all maintenance support on the propulsion systems of the fuel cell 

vehicles. The staff at Hickam handles all the other vehicle maintenance. The maintenance 

facility at Hickam, pictured in Figure 10, consists of an open air structure with space for up to six 

vehicles. Like the hydrogen station, the combination of an open design and local weather 

conditions was determined to be safe for use with hydrogen fueled vehicles. No modifications 

were required to allow maintenance of the fuel cell vehicles. The majority of the maintenance 

work is expected to be accomplished on the base. If necessary, Enova will transport the vehicle 

to the HCATT facility for any work that cannot be accomplished on the base. The integration of 

the fuel cell hybrid drive systems was accomplished at the HCATT facility pictured in Figure 11, 

which is fully equipped to handle any required maintenance on the vehicle systems. The facility 

is adequately ventilated, including rooftop vents to eliminate the collection of hydrogen. 

Figure 10. The open-air maintenance facility at Hickam 

 17
Figure 11. HCATT’s facilities include vehicle lifts (top left), 2 ABC 150s (top right), an 

environmental chamber (bottom left), and a chassis dynamometer (bottom right). 

Evaluation Plans 

NREL is evaluating these prototype fuel cell vehicles at Hickam as part of DOE’s Hydrogen, 

Fuel Cells & Infrastructure Technologies Program, which integrates activities in hydrogen 

production, storage, and delivery with transportation and stationary fuel cell applications. NREL 

works with fleets and industry groups to test advanced technology, heavy-duty vehicles in 

service and provides unbiased information resources for fleet managers considering these 

technologies. Information collected during the evaluation is fed back to research programs to 

help shape future work. Current DOE/NREL heavy fuel cell vehicle evaluation sites are shown 

in Table 2. 

 18
Table 2. DOE/NREL Heavy Vehicle Fuel Cell/Hydrogen Evaluations 

Fleet Vehicle/Technology Number Evaluation Status 

Shuttle bus: Hydrogenics and Enova, 

battery-dominant fuel cell hybrid 1 Shuttle bus in operation; 

U.S. Air Force/Hickam Air Force data collection started 

Base (Honolulu, HI) Delivery van: Hydrogenics and Enova, 

fuel cell hybrid 1 Van in operation; data 

collection started 

Alameda-Contra Costa Transit 

District (Oakland, CA) 

Van Hool/UTC Power fuel cell hybrid 

transit bus integrated by ISE Corp. 3 In process; preliminary 

results reported Mar. 2007 

New Flyer/ISE Corp. hydrogen 

internal combustion engine transit bus 1 SunLine Transit Agency 

(Thousand Palms, CA) Van Hool/UTC Power fuel cell hybrid 

transit bus integrated by ISE Corp. 1 

In process; preliminary 

results reported Feb. 2007 

Connecticut Transit (Hartford, 

CT) 

Van Hool/UTC Power fuel cell hybrid 

transit bus integrated by ISE Corp. 1 Bus in operation; data 

collection started 

Santa Clara Valley 

Transportation Authority, (San 

Jose, CA) and San Mateo 

County Transit District (San 

Carlos, CA) 

Gillig/Ballard fuel cell transit bus 3 Complete and reported in 

2006 

SunLine Transit Agency 

(Thousand Palms, CA) 

ISE Corp./ UTC Power ThunderPower 

hybrid fuel cell transit bus 1 Complete and reported in 

2003 

DOE and NREL are also working with the FTA to collect the same data in support of the 

National Fuel Cell Bus Program. Additional data collection and evaluation sites will be added to 

the list above as those projects get under way. 

DOE/NREL evaluation projects focus on using a standardized process5

 for data collection, 

analysis, and reporting. The objectives of the data collection are to validate fuel cell and 

hydrogen technologies for transit and other applications to: 

• Determine the status of fuel cell systems for buses and corresponding hydrogen infrastructure 

• Provide feedback for DOE and other stakeholder research and development 

• Provide “lessons learned” on implementing next generation fuel cell systems into operations. 

Data from the two fuel cell vehicles at Hickam are being collected and analyzed by NREL to aid 

in determining the status of fuel cell technology in multiple vehicle applications. Data will be 

collected from the 15th Logistics Readiness Squadron at Hickam, Enova, HydraFLX, and HNEI. 

Data parameters include: 

• Hydrogen fuel consumption by vehicle and fill 

• Mileage data and route assignments for each vehicle 

• Real-time duty-cycle data from the vehicles 

• Preventive maintenance action work orders, parts lists, labor records, and related documents 

• Records of unscheduled maintenance, including roadcalls and warranty actions by vendors 

(when available in the data system) 

 

5

 General Evaluation Plan, Fleet Test & Evaluation Projects, July 2002, NREL/BR-540-32392, 

www.nrel.gov/vehiclesandfuels/fleettest/pdfs/32392.pdf. 

 19
Additional information is being collected on the maintenance/operation experience, issues at the 

hydrogen fueling station and facilities, and lessons learned at the start-up and during operation of 

the study vehicles. 

Vehicle Planned Use 

The fuel cell vehicles have been added to the support fleet at Hickam, which includes a wide 

range of vehicles from passenger cars up to class 8 trucks and aircraft tugs. The fuel cell shuttle 

bus is being used mainly for distinguished visitor (DV) service around the base and surrounding 

area. The base has an average of 100 DVs each month, which typically equates to two to three 

trips per week. The step van is planned for package delivery service and is expected to be used 

for daily runs transporting cargo around the base. For both vehicles, log sheets are filled out for 

each use describing the general duty-cycle, mileage, and any fueling or charging time. 

HNEI Driving and Duty Cycle Analysis 

Researchers at HNEI have been investigating advanced batteries and fuel cell development for 

over 17 years. In 2001, HNEI began a project with HCATT and Hyundai Motor Company to 

conduct field testing of a fleet of battery electric vehicles. A primary goal of the project was to 

investigate battery life and performance under a variety of operating conditions. To fully 

quantify the effects of real-world operation on the vehicle systems, the researchers needed a way 

to characterize the highly variable driving cycles. HNEI developed a MATLAB-based tool that 

uses fuzzy logic pattern recognition to analyze the driving patterns in each trip. The tool uses 

second-by-second data collected from the vehicles through an on-board data acquisition device. 

The analysis of vehicle trips helps the researchers understand the percentage of time a vehicle is 

operated in each of five different driving patterns, such as stop-and-go, or highway driving. This 

understanding of the real-world vehicle use aids in determining the impacts on the overall 

system, battery, and other system components. 

An example analysis of one vehicle trip using the HNEI tool is shown in Figure 12. The road 

data on the right side of the screen shows the actual speed versus time trace (top graph). The 

separate driving pulses, which are the active driving between two sequential stops, are 

categorized based on the average speed and distance within each driving pulse. The driving 

pulse classifications for the example trip are shown in the middle graph. Once a trip is analyzed, 

it can then be normalized by the percentage of time and distance, making comparisons between 

trips possible. The normalized trip profile is shown in the lower graph of Figure 12. 

 20
Figure 12. Screenshot of MATLAB tool showing an example trip analysis 

The fuel cell vehicles at Hickam are equipped with data acquisition devices necessary for this 

driving cycle analysis. The results of the analysis will be included in future evaluation data 

reports. 

What’s Next for this Evaluation? 

The fuel cell van was put in service at Hickam in August 2007. Data on the vehicle are being 

collected and transferred to HNEI and NREL for analysis. The fuel cell bus is expected to be 

placed in service in September. NREL plans to publish a second report in spring of 2008 after at 

least six months of operational data have been collected and analyzed. The report will include 

the results of the first six months of operation and outline the fleet’s early operational experience 

with these vehicles and fueling infrastructure. 

 21
Contacts 

DOE 

1000 Independence Ave., SW 

Washington, DC 20585 

John Garbak 

Technology Development Manager 

Hydrogen, Fuel Cells, and Infrastructure 

Technologies 

Phone: 202-586-1723 

E-mail: john.garbak@hq.doe.gov

NREL 

1617 Cole Boulevard 

Golden, CO 80401 

Leslie Eudy 

Senior Project Leader 

Phone: 303-275-4412 

E-mail: leslie_eudy@nrel.gov 

Battelle 

505 King Avenue 

Columbus, OH 43201 

Kevin Chandler 

Program Manager 

Phone: 614-424-5127 

E-mail: chandlek@battelle.org 

Hickam AFB 

15 LRS/LGRV 

135 A Street 

Hickam AFB, HI 96853 

Roger Storman 

Chief, Vehicle Management Flight 

Phone: 808-448-0508 

E-mail: roger.storman@hickam.af.mil

HCATT 

531 Cooke St. 

Honolulu, HI 96813 

Tom Quinn 

Director 

Phone: 808-594-0100 

E-mail: tquinn@htdc.org

University of Hawai’i, Hawai’i Natural 

Energy Institute 

1680 East-West Road, POST 109 

Honolulu, HI 96822 

Bor Yann Liaw, Ph.D. 

Specialist, Electrochemical Power Systems 

Phone: 808-956-2339 

E-mail: bliaw@hawaii.edu

Hydrogenics 

27201 Tourney Road, Suite 201 

Valencia, CA 91355 

Kevin Harris 

Business Development & Sales Director, 

North America 

Hydrogen Power Systems 

Phone: 661-253-2593 

E-mail: kharris@hydrogenics.com

Enova 

531 Cooke St. 

Honolulu, HI 96813 

Todd Martin 

Manager, Hawai’i Office 

Phone: 808-593-1273 

E-mail: tmartin@enovasystems.com

 22
HydraFLX Systems Ltd. 

Support Offices 

P.O. Box 341842 

Austin Texas 78734 

 

Mark D. Schultz 

Director of Operations 

Phone: 800-220-9598 

Email: mdschultz@hydraflx.com

 23
Acronyms and Abbreviations 

AC alternating current 

AFV alternative fuel vehicle 

APTO Advanced Power Technology Office 

AVP Advanced Vehicle Technologies Program 

B20 biodiesel 20% 

CEU control electronics unit 

CNG compressed natural gas 

DARPA Defense Advanced Research Projects Agency 

DC direct current 

DoD U.S. Department of Defense 

DOE U.S. Department of Energy 

DOT U.S. Department of Transportation 

DV distinguished visitor 

EDU electric drive unit 

EHV Electric and Hybrid Vehicle Program 

EPAct Energy Policy Act 

ESD emergency shutdown device 

E85 ethanol 85% 

ft feet 

FTA Federal Transit Administration 

FY fiscal year 

HFCIT Hydrogen, Fuel Cells, and Infrastructure 

Technology Program 

HCATT Hawaii Center for Advanced Transportation 

Technologies 

HNEI Hawaii Natural Energy Institute 

HTDC High Technology Development Corporation 

in inches 

GSA General Services Administration 

kg kilogram 

kW kilowatts 

lb pounds 

MEP mobile electric power 

NDAA National Defense Authorization Act 

NREL National Renewable Energy Laboratory 

PEM proton exchange membrane 

psi pounds per square inch 

USAF United States Air Force 

V volts 

 24
References and Related Reports 

Eudy, L., Chandler, K., Gikakis, C., 2007, Fuel Cell Buses in U.S. Transit Fleets: Summary of 

Experiences and Current Status, National Renewable Energy Laboratory, Golden, CO, 

NREL/TP-560-41967 

Chandler, K., Eudy, L., 2007, Alameda-Contra Costa Transit District (AC Transit), Fuel Cell 

Transit Buses: Preliminary Evaluation Results, National Renewable Energy Laboratory, Golden, 

CO, NREL/TP-560-41041 

Chandler, K., Eudy, L., 2007, SunLine Transit Agency, Hydrogen Powered Transit Buses: 

Preliminary Evaluation Results, National Renewable Energy Laboratory, Golden, CO, 

NREL/TP-560-41001 

Liaw, B.Y., Dubarry, M., 2007, “From driving cycle analysis to understanding battery 

performance in real-life electric hybrid vehicle operation” Special Issue on Hybrid Electric 

Vehicles (invited), J. Power Sources, doi:10.1016/j.jpowsour.2007.06.010

Dubarry, M., Svoboda, V., Hwu, R., Liaw, B.Y., 2007, “A roadmap to understand battery 

performance in electric and hybrid vehicle operation,” J. Power Sources 

doi:10.1016/j.jpowsour.2007.06.237

Chandler, K., Eudy, L., 2006, Santa Clara Valley Transportation Authority and San Mateo 

County Transit District, Fuel Cell Transit Buses: Evaluation Results, National Renewable 

Energy Laboratory, Golden, CO, NREL/TP-560-40615 

NREL, 2006, SunLine Tests HHICE Bus in Desert Climate, National Renewable Energy 

Laboratory, Golden, CO, DOE/GO-102006-2333 

NREL, 2006, AC Transit Demos Three Prototype Fuel Cell Buses, National Renewable Energy 

Laboratory, Golden, CO, DOE/GO-102006-2286 

NREL, 2006, SunLine Expands Horizons with Fuel Cell Bus Demo, National Renewable Energy 

Laboratory, Golden, CO, DOE/GO-102006-2287 

NREL, 2005, VTA, SamTrans Look into Future with Bus Demo, National Renewable Energy 

Laboratory, Golden, CO, DOE/GO-102005-2147 

NREL, 2005, Draft Fuel Cell Transit Bus Evaluation Plan, National Renewable Energy 

Laboratory, Golden, CO 

Dubarry, M., Bonnet, M., Dailliez, B., Teeters, A., Liaw, B.Y., 2005, “Analysis of electric 

vehicle usage of a Hyundai Santa Fe fleet in Hawaii,” J. Asian Electric Vehicles 3 p. 657 

Liaw, B.Y., 2004, “Fuzzy-logic based driving pattern recognition for driving cycle analysis,” J. 

Asian Electric Vehicles 2 p. 551 

 25
NREL, 2002, General Evaluation Plan, Fleet Test & Evaluation Projects, National Renewable 

Energy Laboratory, Golden, CO, NREL/BR-540-32392 

Reports from DOE/NREL evaluations can be downloaded via the following Web sites:

Hydrogen and fuel cell related: www.nrel.gov/hydrogen/proj_fc_bus_eval.html 

Hybrid and other technologies: www.nrel.gov/vehiclesandfuels/fleettest/publications_bus.html 

 26
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Hickam Air Force Base Fuel Cell Vehicles: Early Implementation 

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This report sumarizes early implementation experience from an evaluation of two prototype fuel cell vehicles 

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