Technical Report

NREL/TP-560-46346-1 

August 2009

SunLine Transit Agency

Fuel Cell Transit Bus: 

Fifth Evaluation Report

Leslie Eudy, National Renewable Energy Laboratory

Kevin Chandler, Battelle

Link to Appendices 
National Renewable Energy Laboratory

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Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-560-46346-1 

August 2009

SunLine Transit Agency

Fuel Cell Transit Bus: 

Fifth Evaluation Report

Leslie Eudy, National Renewable Energy Laboratory

Kevin Chandler, Battelle

Prepared under Task No. FC08.7820
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iii

Acknowledgements 

This evaluation at SunLine Transit Agency 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 

U.S. Federal Transit Administration

Walter Kulyk

Christina Gikakis

National Renewable Energy Laboratory 

Keith Wipke

Terry Penney 

SunLine

C. Mikel Oglesby 

Tommy Edwards

Polo Del Toro 

Ed Gallardo

Shawn Craycraft

Karen Thomas 

Mike Hayes

UTC Power

Dave Boudreau 

Matthew Riley

Rakesh Radhakrishnan 

ISE

Paul Scott

Kevin Stone 

Dave Ticonchuk 

HyRadix 

Terry Schuster 
iv

Acronyms and Abbreviations

ASME American Society of Mechanical Engineers

AQMD Air Quality Management District

CARB California Air Resources Board

CNG compressed natural gas

DGE diesel gallon equivalent 

DOE U.S. Department of Energy 

FCB fuel cell bus

ft. feet

FTA Federal Transit Administration

GGE gasoline gallon equivalent 

HHICE hydrogen hybrid internal combustion engine 

hp horsepower 

HVAC heating, ventilation, and air conditioning

in. inches

kg kilogram 

kW kilowatts

lb. pounds 

MBRC miles between roadcalls

mpdeg miles per diesel equivalent gallon

mph miles per hour 

NFCBP National Fuel Cell Bus Program

NREL National Renewable Energy Laboratory 

PMI preventive maintenance inspection

psi pounds per square inch

RC roadcall 
v 

Executive Summary

This report describes operations at SunLine Transit Agency for a prototype fuel cell bus and five 

new compressed natural gas (CNG) buses. SunLine provides public transit services to the Palm 

Springs area of California. The Department of Energy’s (DOE) National Renewable Energy 

Laboratory (NREL) has been evaluating this fuel cell bus to document the results and help 

determine the progress of the technology toward technology readiness. This is the fifth 

evaluation report for this site, and it focuses on results and experiences from November 2008 

through June 2009. These results are an addition to those provided in the previous four 

evaluation reports. 

SunLine has operated its fuel cell bus with UTC Power’s newest version fuel cell power system, 

which was installed in April 2008. This new version of the fuel cell power system is expected to 

perform much better in respect to the number of operating hours than the previous versions. 

During the data period for the report, the fuel cell bus operated 12,529 miles and 908 hours 

(average operating speed of 13.8 mph). The totals since the new fuel cell power system was 

installed are 23,990 miles and 1,793 hours. UTC Power reports that there are no indications of 

the early power degradation that earlier versions experienced by this point. 

During the evaluation period, the hydrogen fueling station provided 4,729 kg of hydrogen at an 

average cost of $12.15 per kg including parts and labor, amortization of the equipment, and 

natural gas and utilities. SunLine indicates that the best steady-state operating point for the 

reformer system would be around $8 per kg or possibly less. The on-site CNG station provided 

fuel at an average of $1.07 per GGE.

The fuel cell bus was not available as often during this evaluation period compared with previous 

reporting periods. This lower availability was a result of two significant downtime periods that 

were not due to issues with the fuel cell system. The first was a problem with the traction 

batteries that could not be resolved quickly because of lack of funding for this project. The 

second downtime period occurred when the hydrogen fuel production system was out of service 

for an upgrade and repair. If these two incidents are factored out of the calculation, the bus had 

an availability of 74%, which is consistent with the rest of the time period after installation of the 

new fuel cell system. The fuel economy continues to be significantly higher for the fuel cell bus 

compared with the CNG buses—more than two times higher. Miles between roadcalls (MBRC) 

for the fuel cell bus has continued to be much lower than the conventional buses. The 

maintenance costs for the fuel cell bus are 1.7 times higher than the CNG buses; however, all of 

the fuel cell propulsion-system parts have been covered under warranty. 

Table ES-1 provides a summary of results for several categories of data presented in this report.
vi 

Table ES-1. Summary of Evaluation Results

Data Item Fuel Cell CNG

Number of Buses 1 5

Data Period 11/08–6/09 11/08–6/09

Number of Months 8 8

Total Mileage in Period 12,529 198,990

Average Monthly Mileage per Bus 1,566 4,975

Availability (85% is target) 51% 95%

Fuel Economy (Miles/kg or GGE) 7.14 3.39

Miles between Roadcalls (MBRC) – All 2,506 19,899

MBRC – Propulsion Only 3,132 49,748

Total Maintenance, $/mile 0.43 0.25

Maintenance – Propulsion Only, $/mile 0.16 0.05
vii 

Table of Contents

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

NREL Evaluations ...................................................................................................................... 1

Fuel Cell Bus Evaluation at SunLine .......................................................................................... 1

Hydrogen and CNG Fueling ........................................................................................................ 3

Evaluation Results ........................................................................................................................ 6

Route Assignments ..................................................................................................................... 7

Bus Use and Availability ............................................................................................................ 7

Fuel Economy and Cost .............................................................................................................. 9

Maintenance Analysis ............................................................................................................... 10

Roadcall Analysis ..................................................................................................................... 14

Demonstration Achievements and Challenges ......................................................................... 15

Achievements ............................................................................................................................ 15

Challenges ................................................................................................................................. 16

What’s Next for SunLine?.......................................................................................................... 17

Contacts ....................................................................................................................................... 18

References and Related Reports ................................................................................................ 19

SunLine ..................................................................................................................................... 19

General ...................................................................................................................................... 19

AC Transit ................................................................................................................................. 20

Connecticut Transit ................................................................................................................... 20

Santa Clara Valley Transportation Authority ........................................................................... 20
1 

Introduction

SunLine Transit Agency1 has been operating one fuel cell bus in revenue service in the Palm 

Springs, California area, since January 2006. The early operation of this bus has been 

documented in four previous evaluation reports from the U.S. Department of Energy (DOE) and 

the National Renewable Energy Laboratory (NREL).2,3,4,5

NREL Evaluations

 This report continues the evaluation 

of the fuel cell bus and five compressed natural gas (CNG) buses as a baseline.

NREL has been evaluating alternative fuel and advanced propulsion transit buses for DOE and 

the Federal Transit Administration (FTA) since the early 1990s. NREL’s first evaluation of 

hydrogen fuel cell transit buses for DOE was in 2000 and continues with this evaluation at 

SunLine. These evaluations focus on determining the status of hydrogen and fuel cell systems 

and corresponding infrastructure in transit applications to help DOE assess the progress toward 

technology readiness. NREL uses a standard data-collection and analysis protocol originally 

developed for DOE heavy-duty vehicle evaluations, and a joint evaluation plan has been 

documented for transit bus evaluations6

Fuel Cell Bus Evaluation at SunLine

. Appendix A describes NREL’s transit bus evaluation 

activities for DOE and FTA. 

SunLine Transit Agency provides public transit services to California’s Coachella Valley. 

Headquartered in Thousand Palms, SunLine’s service area of over 1,100 square miles includes 

nine member cities and a portion of Riverside County. SunLine has proactively adopted clean 

fuel technologies in their fleet, beginning with compressed natural gas (CNG) buses in 1994. 

Since then, the agency has tested many advanced technologies including buses that run on a 

blend of hydrogen and CNG, battery electric power, and fuel cells. Appendix B provides more 

information on SunLine. 

In January 2006, SunLine began demonstrating one prototype fuel cell bus jointly developed by 

Van Hool, UTC Power, and ISE Corporation. The prototype fuel cell bus features an ISE 

electric hybrid drive system with a UTC Power PureMotion7

 

1 SunLine Transit Agency Web site: 

 120 Fuel Cell Power System and 

ZEBRA batteries for energy storage. The bus is shown in Figure 1. 

www.sunline.org 2 SunLine Transit Agency, Hydrogen-Powered Transit Buses: Preliminary Evaluation Results, February 2007, 

NREL/TP-560-41001, www.nrel.gov//hydrogen/pdfs/41001.pdf 3 SunLine Transit Agency, Hydrogen-Powered Transit Buses: Evaluation Results Update, September 2007, 

NREL/TP-560-42080, www.nrel.gov/hydrogen/pdfs/42080.pdf 4 SunLine Transit Agency, Hydrogen-Powered Transit Buses: Third Evaluation Report and Appendices, June 2008, 

NREL/TP-560-43741-1, www.nrel.gov/hydrogen/pdfs/43741-1.pdf, and appendices NREL/TP/560-43741-2, 

www.nrel.gov/hydrogen/pdfs/43741-2.pdf 5 SunLine Transit Agency, Fuel Cell Transit Bus: Fourth Evaluation Report and Appendices, January 2009, 

NREL/TP-560-44646-1, www.nrel.gov/hydrogen/pdfs/44646-1.pdf, and Appendices NREL/TP/560-44646-2, 

www.nrel.gov/hydrogen/pdfs/44646-2.pdf 6 Hydrogen and Fuel Cell Transit Bus Evaluations: Joint Evaluation Plan for the U.S. Department of Energy and the 

Federal Transit Administration, NREL/MP-560-42781-1, May 2008, www.nrel.gov/hydrogen/pdfs/42781-1.pdf. 7 PureMotion is a trademark of UTC Power.
2 

Figure 1. Fuel cell transit bus at SunLine

This report includes operations at SunLine for the fuel cell transit bus in revenue service. Five 

compressed natural gas (CNG) buses operating from the same SunLine location are being used 

as a baseline comparison. Previous reports included data on SunLine’s 2005 model year Orion 

CNG buses as a baseline. For this report, we have collected data on five new CNG buses built 

by New Flyer. Over the last two years, SunLine has been replacing all of its older CNG buses as 

they reached end-of-life. The 2008 model year New Flyer CNG buses use Cummins Westport 

ISL G natural gas engines that are designed to meet 2010 emission regulations (see Figure 2). 

Appendix C provides more detail about the bus technologies included in this evaluation. 

Figure 2. New Flyer CNG bus at SunLine

This fifth evaluation report describes results and experiences with the fuel cell and CNG buses 

since the last report. The data results are focused on the period from November 2008 through 

June 2009. In April 2008, the newest version fuel cell power system from UTC Power was 

installed in the fuel cell bus. DOE and NREL have continued to collect data on the bus to 

validate performance improvements resulting from the fuel cell system update. The evaluation 

for the hybrid hydrogen internal combustion engine bus (HHICE) has concluded; however, this 

report includes the fueling data on that bus to evaluate performance of the hydrogen station. 
3 

Hydrogen and CNG Fueling 

Hydrogen fuel is supplied at SunLine by a HyRadix natural gas reformer. The fuel is 

compressed to 5,000 psi and dispensed into the buses. CNG is brought into the SunLine property 

via a high-pressure natural gas line and then compressed to 3,600 psi for delivery into the 

vehicles. Appendix D provides general descriptions of SunLine’s hydrogen and CNG fueling 

infrastructure along with maintenance facilities.

SunLine provides both hydrogen and CNG for purchase at its public dispensing island. Because 

of this, SunLine is required to track all of its fueling events in gasoline gallon equivalent (GGE) 

units to comply with state fuel-sale regulations. In the case of hydrogen, the unit used is 

typically kilograms (kg)—one kg contains essentially the same energy as a GGE for fueleconomy calculations. This report presents both GGE (kg for hydrogen) and diesel gallon 

equivalent (DGE) for hydrogen and CNG fuel consumption. The end of Appendix E shows 

energy-conversion calculations for GGE and DGE. 

Fueling Data Analysis – Figure 3 shows the average hydrogen dispensed per day into both of 

the hydrogen-fueled buses from November 2008 through June 2009. The calculation for this rate 

includes only the days in which the station dispensed hydrogen. The station was used at least 

once per day to fill at least one of the two hydrogen buses for 62% of the calendar days during 

the period. The overall average daily use was 31.3 kg per day. During this period, SunLine 

dispensed a total of 4,729 kg of hydrogen. The lower usage in December 2008 through February 

2009 was because of the fuel cell bus being out of service. Only the HHICE bus was fueled 

during that time. The lowest point for fuel use during the data period was during March 2009. 

The reformer was down most of that month for a component upgrade. This upgrade was 

necessary to address an issue discovered by HyRadix during long-term testing at other reformer 

sites. 

Figure 4 shows the distribution of hydrogen amounts dispensed per fill by bus type. The two 

buses were filled a total of 217 times during the evaluation period for a total of 4,637.6 kg.8 The 

fuel cell bus averaged 17.8 kg per fill while the HHICE bus fuelings averaged 24.2 kg per fill. 

Figure 5 shows a cumulative fueling rate histogram for the SunLine hydrogen station from 

November 2008 through May 2009. The overall average fueling rate was 1.0 kg per minute, and 

the average time for a fill was 17.7 minutes. 

 

8 This total is slightly lower than that shown for Figure 3. If the time for the fueling was not captured in data 

collection, Figures 4 and 5 exclude that fueling data.
4 

0

5

10

15

20

25

30

35

40

45

Average Daily Hydrogen Use (kg)

Figure 3. Average hydrogen dispensed per day (excluding 0 kg days)

0-5 5-10 10-15 15-20 20-25 25-30 >30 0

10

20

30

40

50

60

Fueling Amounts (kg)

Number of Events

FC1

HHICE

Figure 4. Distribution of fueling amounts
5 

0-0.25 0.25-0.5 0.5-0.75 0.75-1 1-1.25 1.25-1.5 1.5-1.75 1.75-2 >2 0

5

10

15

20

25

30

35

40

45

Fueling Rates (kg/min)

Number of Events

Figure 5. Cumulative fueling rate histogram

Hydrogen fuel costs at SunLine consist of the cost of natural gas for the reformer, maintenance 

of the station equipment, and capital cost amortization. SunLine performs the maintenance of 

the station including parts and labor. The average cost for hydrogen during the evaluation period 

was $12.15 per kg (monthly costs ranged from a low of $6.50/kg to a high of $158/kg). Lower 

use of the station (when the buses were out of service) and higher maintenance for the reformer 

during March were contributors to higher monthly costs. Figure 6 shows the monthly station use 

and hydrogen cost per kg since January 2008. DOE’s target for hydrogen cost ($3/kg) is also 

included. The figure illustrates the relationship between high hydrogen costs and low station 

use. The peak cost during the period was for the month the reformer was down for repair. The 

cost of that repair factors into the total hydrogen cost for that month. SunLine indicates that the 

best steady-state operating point for the reformer system would bring the average cost of 

hydrogen to around $8 per kg. This cost estimate is used in the cost calculations for the data 

results in the next section.
6 

$-

$10 

$20 

$30 

$40 

$50 

$60 

0

200

400

600

800

1000

1200

Cost in $/kg

Total Monthly kg

kg H2 $/kg DOE H2 cost target

$158/kg

Figure 6. Comparison of monthly hydrogen use and cost per kg

SunLine supplies CNG fuel to users in its area, and the fueling station is accessible to the public. 

The high volume of natural gas use has allowed SunLine to command a low cost as a commodity 

user. During the evaluation period, the CNG price at the dispenser for SunLine (not the public 

price) was $1.07 per GGE. This price includes all costs—natural gas, maintenance, and station 

amortization. 

Evaluation Results

The fuel cell bus at SunLine was originally placed into revenue service in January 2006. The 

focus of this evaluation report is on the most-recent operating data for the fuel cell bus and CNG 

buses. The evaluation period in this report includes data from November 2008 through June 

2009. As mentioned previously, the baseline buses used for this report were from SunLine’s 

newest order of CNG buses. Those New Flyer CNG buses began delivery in November of 2008. 

The evaluation results include operation of the selected CNG buses from November 2008 

through June 2009. (Note: Not all the CNG buses were in service for the entire month of 

November.) Appendix E provides a summary of all data. Appendix F provides a data summary 

in SI (metric) units. 

This fuel cell bus is considered prototype technology in the commercialization process. The 

analysis and comparison discussions with standard CNG buses help create a baseline to measure 

the progress of this hydrogen propulsion technology. There is no intent to consider this 

implementation of a fuel cell bus as commercial (or full revenue transit service). The evaluation 
7 

focuses on documenting progress and opportunities to improve the vehicle, infrastructure, and 

procedures. 

Route Assignments

In general, buses at the two SunLine operating locations are dispatched randomly. The overall 

system average operating speed at SunLine is 13.2 mph. The fuel cell bus has been used 

exclusively on Line 50 (average speed of 14.1 mph). In-service data for the fuel cell bus during 

the evaluation period indicate an average operating speed of 13.8 mph based on mileage and fuel 

cell system operating hours. The CNG buses have been randomly dispatched with heavy use on 

Line 111 (30% of the time—average speed of 14.3 mph) and Line 30 (16% of the time—average 

speed of 12 mph). 

Bus Use and Availability

Bus use and availability indicates reliability. Lower bus use may indicate downtime for 

maintenance or purposeful reduction of planned work for the buses. This section provides a 

summary of bus use and availability for the fuel cell and CNG buses. 

The fuel cell bus has planned service of up to seven days per week. For the fuel cell bus, total 

mileage accumulation for the evaluation period was 12,529 miles, and the fuel cell system 

accumulated 908 hours, which indicates an average speed of 13.8 mph. Since the start of 

revenue operation of the fuel cell bus, the total mileage is 76,326 with 5,820 total hours for an 

overall average speed of 13.1 mph. This average is only slightly slower than the overall 13.2-

mph average speed for all SunLine routes. 

Table 1 summarizes the average monthly mileage accumulation by bus and study group for the 

evaluation period. Using the CNG buses as the baseline, the fuel cell bus had an average 

monthly mileage 31% that of the CNG buses. This percentage is slightly less than that reported 

previously due to downtime of the reformer and significant downtime for the fuel cell bus. 

Table 1. Average Monthly Mileage (Evaluation Period)

Bus Starting 

Hubodometer

Ending 

Hubodometer

Total 

Mileage Months Monthly Average

FC1 66,662 79,191 12,529 8 1,566

603 CNG 2,752 46,798 44,046 8 5,506

604 CNG 2,574 39,783 37,209 8 4,651

605 CNG 2,683 40,869 38,186 8 4,773

606 CNG 2,554 43,977 41,423 8 5,178

608 CNG 2,522 40,648 38,126 8 4,766

Total CNG 198,990 40 4,975

Another measure of reliability is availability—the percent of time that the buses are planned for 

operation compared with the time the buses are actually available for that planned operation. 

Figure 7 shows the monthly average availability for each of the study bus groups. As shown in 

the chart, the availability goal is 85% for all buses. Availability for all of NREL’s evaluations is 

calculated by including the planned service days, which is typically every weekday. Weekends 

and holidays are included in the calculation only if the bus operated in service on those days. If a 
8 

bus does not operate on the weekend or a holiday, it is not counted as unavailable. This strategy 

applies to both the fuel cell bus and the CNG buses. 

The fuel cell bus was available 51% of the time during the evaluation period. This is much 

lower than the availability reported in the last report (76%). The bus was out of service for an 

extended period from late November 2008 through mid-February 2009. Although the bus was 

down for battery problems, the length of the downtime was because of budget issues at the 

transit agency. The repair was delayed while SunLine resolved those issues. The downtime for 

the reformer during March 2009 was another factor affecting the lower availability of the fuel 

cell bus. Removal of those three months from the calculation brings the availability up to 74%, 

which is consistent with the data from the last report. 

0

10

20

30

40

50

60

70

80

90

100

Percent Availability

FC1 CNG

Availability Target 85%

Figure 7. Availability for study bus groups

The chart shows that the CNG buses have consistently achieved availability above the 85% 

target. This is typical for new buses in service. 

Table 2 provides a summary of the availability and unavailability reasons for each of the study 

bus groups. Overall, during the evaluation period, the average availability for the fuel cell bus 

was 51%, and availability for the CNG buses was 95%. As discussed, the primary issues that 

kept the fuel cell bus out of service were downtime for traction battery replacement (64%) and 

fueling station unavailability (26%). Issues with the fuel cell system accounted for only 7% of 

the unavailability. Issues that kept the CNG buses out of service were general maintenance.
9 

Table 2. Summary of Reasons for Availability and Unavailability of Buses for Service

Category Fuel Cell Bus CNG Buses

Number Percent Number Percent

Planned Work Days 197 1,097

Days Available 101 51 1,043 95

Available 101 100 1,043 100

On-Route 98 97 988 95

Event/Demonstration 3 3 1 0

Training 0 0 3 0

Not Used 0 0 51 5

Unavailable 96 100 54 100

Fuel Cell Propulsion 7 7

ISE Propulsion 0 0

Traction Batteries 61 64

SunLine Maintenance 3 3 54 100

Fueling Unavailable 25 26

Fuel Economy and Cost

Table 3 shows hydrogen and CNG fuel consumption and fuel economy for the study bus groups 

during the evaluation period. Using the GGE fuel economy and the CNG buses as the baseline, 

the fuel cell bus had a fuel economy more than two times higher than the CNG buses. Figure 8 

shows average fuel economies for each of the study bus groups. It is interesting to note that 

these newer CNG buses have a fuel economy 8% higher than the previous group of baseline 

buses. The new buses are equipped with engines that meet 2010 emissions regulations using 

stoichiometric cooled exhaust gas recirculation combustion with a three-way catalyst. 

The fuel costs per mile for the study bus groups for the evaluation period were $1.12 per mile for 

the fuel cell bus and $0.31 for the CNG buses. The fuel cost for CNG has been much lower than 

the cost for hydrogen production. 

Table 3. Fuel Use and Economy (Evaluation Period)

Bus Mileage

(Fuel Base)

Hydrogen (kg) 

or CNG (GGE)

Miles per 

kg or GGE

Diesel Equivalent 

Amount (Gallon)

Miles per 

Gallon (DGE)

FC1 12,529 1,755.9 7.14 1,553.9 8.06

603 CNG 44,046 12,668.8 3.48 11,338.6 3.88

604 CNG 37,209 11,100.6 3.35 9,935.0 3.75

605 CNG 38,186 11,457.4 3.33 10,254.4 3.72

606 CNG 41,423 12,359.5 3.35 11,061.7 3.74

608 CNG 38,126 11,075.0 3.44 9,912.1 3.85

CNG Total 198,990 58,661.2 3.39 52,501.8 3.79
10 

0

10

20

30

40

50

60

70

80

90

100

0

1

2

3

4

5

6

7

8

9

10

Miles per kg or GGE

Avg. High Temp. (F)

FCB CNG Avg. High Temp.

Figure 8. Average fuel economy (miles per kg or GGE)

Maintenance Analysis

The maintenance cost analysis in this section is only for the evaluation period. Warranty costs 

are generally not

Total Maintenance Costs – Total maintenance costs include the price of parts and hourly labor 

rates of $50 per hour. Cost per mile is calculated as follows:

 included in the cost-per-mile calculations. All work orders for the study buses 

were collected and analyzed for this evaluation. For consistency, we set the maintenance labor 

rate at $50 per hour, which does not reflect an average rate for SunLine. This section covers 

total maintenance costs first and then maintenance costs separated by bus system. 

Cost per mile = [(labor hours * 50) + parts cost] / mileage

Table 4 shows total maintenance costs for the fuel cell bus and CNG buses. The CNG buses 

have total maintenance costs 39% lower than the fuel cell bus. The parts costs are low for the 

fuel cell bus because they are typically covered by the manufacturers for most of the propulsion 

system maintenance; however, SunLine’s mechanics do most of the work. CNG bus number 603 

had higher maintenance costs because of body damage and issues with the air-conditioning 

system. 
11 

Table 4. Total Maintenance Costs (Evaluation Period)

Bus Mileage Parts ($) Labor 

Hours

Cost ($) 

per Mile

Fuel Cell 12,529 1,275.36 82.5 0.43

603 CNG 44,046 3,328.78 171.0 0.27

604 CNG 37,209 2,153.93 163.0 0.28

605 CNG 38,186 2,438.45 148.3 0.26

606 CNG 41,423 2,427.51 145.5 0.23

608 CNG 38,126 1,518.92 136.6 0.22

Total CNG 198,990 11,867.59 764.6 0.25

Maintenance Costs Separated by System – Table 5 shows maintenance costs by vehicle 

system and bus study group (without warranty costs included). The vehicle systems shown in 

the table include the following: 

• Cab, Body, and Accessories: Includes body, glass, and paint repairs following accidents; 

cab and sheet metal repairs on seats and doors; and accessory repairs such as 

hubodometers and radios. 

• Propulsion-Related Systems: Repairs for exhaust, fuel, engine, electric motors, fuel cell 

modules, propulsion control, non-lighting electrical (charging, cranking, and ignition), air 

intake, cooling, and transmission. 

• Preventive Maintenance Inspections (PMI): Labor for inspections during preventive 

maintenance.

• Brakes

• Frame, Steering, and Suspension

• Heating, Ventilation, and Air Conditioning (HVAC)

• Lighting

• Air System, General

• Axles, Wheels, and Drive Shaft 

• Tires

For the fuel cell bus, the systems with the highest percentage of maintenance costs were 

propulsion-related, cab, body, and accessories, and PMI. The propulsion-related maintenance 

was significantly more than for the CNG buses; however, the PMI and cab, body, and 

accessories categories were essentially the same as for the CNG buses. For the CNG buses, the 

highest percentage of maintenance costs were cab, body, and accessories, PMI, and propulsionrelated. 
12 

Table 5. Vehicle System Maintenance Cost per Mile by System (Evaluation Period)

System

Fuel Cell CNG

Cost per 

Mile ($)

Percent of 

Total (%)

Cost per 

Mile ($)

Percent of 

Total (%)

Cab, Body, and Accessories 0.08 18 0.10 39

Propulsion-Related 0.16 37 0.05 20

PMI 0.06 14 0.07 29

Brakes 0.00 0 0.00 0

Frame, Steering, and Suspension 0.03 7 0.00 1

HVAC 0.00 1 0.01 5

Lighting 0.06 14 0.00 2

Axles, Wheels, and Drive Shaft 0.00 0 0.00 0

General Air System Repairs 0.02 4 0.00 1

Tires 0.02 4 0.01 4

Total 0.43 100 0.25 100

Propulsion-Related Maintenance Costs – The propulsion-related vehicle systems include the 

exhaust, fuel, engine, electric propulsion, air intake, cooling, non-lighting electrical, and 

transmission systems. Table 6 categorizes the propulsion-related system repairs for the study bus 

groups during the evaluation period (no warranty). Each of the study bus groups was under 

warranty during the entire evaluation period. Also, the fuel cell bus was maintained by the UTC 

Power engineer when the fuel cell power system required significant repairs. During the 

evaluation period of this report, the SunLine mechanics did much of the maintenance on the fuel 

cell bus themselves supported by the manufacturers; however, as mentioned above, the 

manufacturers generally supplied the parts under warranty for the propulsion system, so the costs 

for these parts are not included. 

• Total propulsion-related – The fuel cell bus had more than double the maintenance cost 

for propulsion-related maintenance compared with the CNG buses. The majority of this 

maintenance for the fuel cell bus has been labor. 

• Exhaust System – There were few or no costs for this system for the study bus groups. 

• Fuel System – Costs for the fuel system were low for both bus groups. 

• Powerplant and electric propulsion – The fuel cell bus maintenance reported here 

involved almost exclusively SunLine mechanics supporting manufacturer work on the 

bus. The preventive maintenance for the CNG buses was almost exclusively in the 

powerplant category (and none for electric propulsion). 

• Non-lighting electrical (charging, cranking, and ignition) – The fuel cell bus had some 

minor costs in this category relating to 24-volt batteries. The CNG buses mostly had 

preventive maintenance repairs in this category for spark plugs at the 24,000-preventivemaintenance cycle for each bus. 
13 

Table 6. Propulsion-Related Maintenance Costs by System (Evaluation Period)

Maintenance System Costs Fuel Cell CNG

Mileage 12,529 198,990

Total Propulsion-Related Systems (Roll-up)

Parts cost ($) 8.27 5,420.12

Labor hours 40.3 90.5

Total cost ($) 2,020.77 9,945.12

Total cost ($) per mile 0.16 0.05

Exhaust System Repairs

Parts cost ($) 0.00 0.00

Labor hours 0.0 0.0

Total cost ($) 0.00 0.00

Total cost ($) per mile 0.00 0.00

Fuel System Repairs

Parts cost ($) 0.00 183.30

Labor hours 0.0 3.5

Total cost ($) 0.00 358.30

Total cost ($) per mile 0.00 0.00

Powerplant System Repairs

Parts cost ($) 5.84 3,021.47

Labor hours 15.8 74.3

Total cost ($) 793.34 6,733.97

Total cost ($) per mile 0.06 0.03

Electric Propulsion System Repairs

Parts cost ($) 0.00 0.00

Labor hours 23.5 0.0

Total cost ($) 1,175.00 0.00

Total cost ($) per mile 0.09 0.00

Non-Lighting Electrical System Repairs (General Electrical, Charging, 

Cranking, Ignition)

Parts cost ($) 2.43 1,674.85

Labor hours 1.0 5.3

Total cost ($) 52.43 1,937.35

Total cost ($) per mile 0.00 0.01

Air Intake System Repairs

Parts cost ($) 0.00 268.73

Labor hours 0.0 0.0

Total cost ($) 0.00 268.73

Total cost ($) per mile 0.00 0.00

Cooling System Repairs

Parts cost ($) 0.00 0.00

Labor hours 0.0 3.5

Total cost ($) 0.00 175.00

Total cost ($) per mile 0.00 0.00

Transmission System Repairs

Parts cost ($) 0.00 97.92

Labor hours 0.0 1.5

Total cost ($) 0.00 172.92

Total cost ($) per mile 0.00 0.00
14 

• Air intake – The fuel cell bus had no costs in this category, and the CNG buses had only 

air filter changeouts. 

• Cooling – The fuel cell and CNG buses had low or no costs in this category. . 

• Transmission – Only the CNG buses had costs in this category for filters under 

preventive maintenance.

Roadcall Analysis

A roadcall (RC), or revenue vehicle system failure (as named in the National Transit Database9

Table 7 shows the RCs and miles between roadcalls (MBRC) for each study bus in two 

categories: all RCs and propulsion-related-only RCs. The fuel cell bus had several RCs and low 

vehicle use, which indicates the prototype nature of the technology. For the fuel cell bus, the 

four propulsion RCs were caused by the fuel cell system (3 RCs) and traction batteries (1 RC). 

The CNG buses had propulsion RCs for the engine (2 RCs), electrical (1 RC), and hydraulic leak 

(1 RC).

), 

is defined as a failure of an in-service bus that causes the bus to be replaced on route or causes a 

significant delay in schedule. If the problem with the bus can be repaired during a layover and 

the bus remains on schedule, this is not considered a RC. The analysis provided here includes 

only RCs caused by “chargeable” failures. Chargeable RCs include systems that can physically 

disable the bus from operating on route, such as interlocks (doors and wheelchair lift) and engine 

problems. Chargeable RCs do not include RCs for things such as radios or destination signs. 

Table 7. Roadcalls and MBRC (Evaluation Period)

Bus Mileage All 

Roadcalls All MBRC Propulsion Roadcalls

Propulsion 

MBRC

Fuel Cell 12,529 5 2,506 4 3,132

603 CNG 44,046 1 44,046 1 44,046

604 CNG 37,209 3 12,403 1 37,209

605 CNG 38,186 4 9,546 2 19,093

606 CNG 41,423 0 0

608 CNG 38,126 2 19,063 0

Total CNG 198,990 10 19,899 4 49,748

 

9 Federal Transit Administration’s National Transit Database Web site: www.ntdprogram.gov/ntdprogram/
15 

Demonstration Achievements and Challenges

SunLine and its project partners have gained valuable experience from operating the fuel cell 

bus. This section provides a summary of the achievements and challenges encountered during 

the demonstration. 

Achievements

SunLine’s original goal was to demonstrate this prototype 40-foot fuel cell bus in regular

revenue service for at least two years, aiding the manufacturers and the industry in testing and 

investigating what modifications were required to commercialize the technology for transit. 

Testing at SunLine’s location also provides an opportunity to evaluate how the technology 

operates in a hot, desert climate. Since that time, the agency has operated the bus for three and a 

half years, providing an excellent opportunity for the manufacturers to learn how the bus 

performs in real service and to optimize the system further to increase reliability and durability. 

• Bus Operation – The fuel cell bus went into service in January 2006. Through June 

2009, the bus had operated over 79,000 miles and accumulated 5,820 hours on the fuel 

cell system. This process has been extremely important to help the manufacturers 

determine the potential weak points in the system and make modifications to optimize 

and improve the design for the next generation of systems. 

• Fuel Economy – SunLine’s fuel cell bus achieved an average fuel economy of 7.2 miles 

per kg. This equates to 8.14 miles per diesel gallon equivalent, which is more than two 

times that of a typical diesel bus average of around 4 miles per gallon. SunLine’s newest 

conventional CNG buses average 3.79 miles per diesel gallon equivalent. Fuel economy 

for buses in transit service is highly dependent on the duty-cycle; however, this 

achievement meets the NFCBP performance target of doubling the fuel efficiency over 

conventional transit buses10

• Hydrogen Fueling – SunLine has operated a variety of hydrogen production and fueling 

technologies safely since 2000. During this demonstration, the agency had a commercial 

natural gas reformer installed and upgraded the station to increase storage capacity. 

Since January 2006, SunLine has dispensed over 26,000 kg of hydrogen into its two 

hydrogen-fueled buses (including the HHICE bus) with no major safety incidents. The 

dispenser has an average fueling rate of around 1.0 kg per minute, and fill times take less 

than 20 minutes. 

. 

• Training – SunLine’s maintenance staff have been trained to accomplish much of the 

work on the fuel cell bus; although, the fuel cell manufacturer still does most of the major 

maintenance on the fuel cell system. Agency staff assists the UTC Power engineer with 

the fuel cell system repairs and now handle the majority of the repairs of the hybrid 

system. This is a major step toward a goal of transferring all maintenance to agency staff. 

• Public Awareness – SunLine has increased public awareness of hydrogen and fuel cell 

technology through its demonstration. The agency operates the bus as much as possible 

on two of its most visible routes and participates in many events in the area. 

 

10 FTA NFCBP Solicitation Guidelines: www.fta.dot.gov/documents/Fuel_Cell_Solicitation_Guidelines_Final.doc 
16 

Challenges

The primary challenges for operating prototype fuel cell bus technology in a transit application 

are cost and reliability/durability. SunLine and its partners have worked closely to address the 

specific issues encountered and have made much progress in further developing the technology. 

• Costs – Fuel cell buses are following the typical trend as all prototype technology: capital 

costs are high in the early stages and begin to fall with increased production and further 

product development. The operating costs are also higher than that of conventional 

technology. 

• Fuel cell bus reliability/durability – The manufacturers are working with SunLine to 

increase the reliability and durability of fuel cell buses to meet transit requirements. 

Several issues were encountered during the demonstration primarily with the traction 

batteries and the fuel cell system. These issues were also encountered at the other 

demonstration sites for this bus. 

o Traction Battery Issues – Management of the ZEBRA batteries in this design 

has proved to be the biggest challenge. The hybrid design on the bus includes 

three traction batteries operating in parallel. A cell in a ZEBRA battery typically 

will fail in short circuit. A battery with failed cells has reduced voltage even 

though it still can be operated. Because the batteries operate with a direct parallel 

connection, when the number of failed cells within each of the batteries is too 

different among the three batteries, the difference causes an unbalancing of the 

state of charge (SOC). This imbalance makes it difficult to keep the batteries in 

the recommended operating range. The present SOC balancing algorithm will 

disconnect a battery temporarily to keep the SOC balanced. 

This situation may mislead over-volt errors in the propulsion system, causing a 

bus shutdown. UTC Power has been working closely with the battery 

manufacturer (MES-DEA) on the issue for some time. Because failed cells are 

related to a stress condition due to the battery use, some progress has been made 

with controller software changes to improve battery operation by refining some 

operational limits. Options for a balancing strategy are under discussion. More 

replacement batteries are kept in stock to increase the number of available bettermatched batteries and to reduce the amount of downtime of the fuel cell bus.

o Fuel Cell System Issues – UTC Power monitors the performance of the fuel cell 

power system to analyze actual performance versus predicted performance. Early 

on in the demonstration, the cell stack assemblies (CSAs) showed power 

degradation in the operation of the bus. When the power degradation of the CSAs 

falls below 90 kW to 100 kW of the original 120 kW, the system is considered to 

be at the end of its life and should be replaced. This early power degradation was 

reported with the fuel cell buses at other agencies as well, and UTC Power reports 

the problem as an issue of contamination within the CSAs causing the premature 

degradation beyond end of life (at about 800 to 1,200 hours of operation instead 

of the expected 4,000 hours or more). A new version of CSAs replaced the CSAs 

on the SunLine fuel cell bus on April 15–16, 2008. UTC Power reported that this 
17 

early power-degradation issue was resolved for these buses, and the results in this 

evaluation report support that assertion. 

What’s Next for SunLine?

This report covers SunLine’s operation of the fuel cell and CNG buses from April 2008 through 

June 2009. This is the last planned evaluation report on this bus design. Future reports will 

focus on the newer technology being introduced. 

American Fuel Cell Bus Project: Funded under the FTA’s National Fuel Cell Bus Program, 

SunLine is leading a team to develop a purpose-built fuel cell bus that meets “Buy America” 

requirements. The design features a number of advancements that are expected to result in a 

highly efficient bus. Elements include advanced energy storage and new power electronics, 

high-efficiency accessories, and the newest-generation fuel cell on a U.S.-built chassis.

Advanced Fuel Cell Bus Project: SunLine plans to demonstrate another fuel cell bus under 

funding from CARB, AQMD, and FTA. This project is currently in the planning stage and will 

be announced once negotiations with the partners are complete. 
18 

Contacts

DOE

1000 Independence Ave., SW 

Washington, DC 20585 

John Garbak, Technology Validation 

Manager, Vehicle Technologies Program

Phone: 202-586-1723 

E-mail: john.garbak@ee.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 

SunLine

32-505 Harry Oliver Trail 

Thousand Palms, CA 92276 

Tommy Edwards, Director of Maintenance

Phone: 760-343-3456 

E-mail: tedwards@sunline.org 

UTC Power

195 Governor’s Highway 

South Windsor, CT 06074 

Rakesh Radhakrishnan, 

Program Manager, Transportation Programs 

Phone: 860-727-2754 

E-mail: rakeshr@utcpower.com

Matthew Riley, Systems Engineer 

Phone: 860-727-2864 

E-mail: Matthew.Riley@utcpower.com 

ISE Corporation 

12302 Kerran Street 

Poway, CA 92064 

Paul Scott, Chief Scientific Officer 

Phone: 858-413-1742 

E-mail: pscott@isecorp.com 

HyRadix 

175 West Oakton Street 

Des Plaines, IL 60018 

Terry Schuster, Director of Sales

Phone: 630-416-7425 

E-mail: terry.schuster@hyradix.com 

Van Hool 

Bernard Van Hoolstraat 58 

B-2500 Lier Koningshooikt 

Belgium 

Paul Jenné, Automotive Relations

Phone: +32 (3) 420 22 10 

E-mail: paul.jenne@vanhool.be
19 

References and Related Reports

All NREL hydrogen and fuel cell-related evaluation reports can be downloaded from the 

following Web site: www.nrel.gov/hydrogen/proj_fc_bus_eval.html.

SunLine

Chandler, K.; Eudy, L. SunLine Transit Agency, Fuel Cell Transit Bus: Fourth Evaluation 

Report and Appendices. NREL/TP-560-44646-1, NREL/TP-560-44646-2. Golden, CO: National 

Renewable Energy Laboratory, 2009. 

NREL. SunLine Begins Extended Testing of Hybrid Fuel Cell Bus. DOE/GO12008-2610. 

Golden, CO: National Renewable Energy Laboratory, 2008. 

Chandler, K.; Eudy, L. SunLine Transit Agency, Hydrogen-Powered Transit Buses: Third 

Evaluation Report and Appendices. NREL/TP-560-43741-1, NREL/TP-560-43741-2. Golden, 

CO: National Renewable Energy Laboratory, 2008. 

Chandler, K.; Eudy, L. SunLine Transit Agency, Hydrogen-Powered Transit Buses: Evaluation 

Results Update. NREL/TP-560-42080. Golden, CO: National Renewable Energy Laboratory, 

2007. 

Chandler, K.; Eudy, L. SunLine Transit Agency, Hydrogen-Powered Transit Buses: Preliminary 

Evaluation Results. NREL/TP-560-41001. Golden, CO: National Renewable Energy Laboratory, 

2007. 

NREL. SunLine Expands Horizons with Fuel Cell Bus Demo. DOE/GO-102006-2287. Golden, 

CO: National Renewable Energy Laboratory, 2006. 

NREL. SunLine Tests HHICE Bus in Desert Climate. DOE/GO-102006-2333. Golden, CO: 

National Renewable Energy Laboratory, 2006. 

Chandler, K. Ten Years of Compressed Natural Gas (CNG) Operations at SunLine Transit 

Agency. NREL/SR-540-39180. Golden, CO: National Renewable Energy Laboratory, 2006. 

Chandler, K.; Eudy, L. ThunderPower Bus Evaluation at SunLine Transit Agency. DOE/GO102003-1786. Golden, CO: National Renewable Energy Laboratory, 2003. 

NREL. SunLine Test Drives Hydrogen Bus. DOE/GO-102003-1768. Golden, CO: National 

Renewable Energy Laboratory, 2003. 

General

Eudy, L.; Chandler, K.; Gikakis, C. Fuel Cell Buses in U.S. Transit Fleets: Current Status 2008. 

NREL/TP-560-44133. Golden, CO: National Renewable Energy Laboratory, 2008. 

NREL. Hydrogen and Fuel Cell Transit Bus Evaluations: Joint Evaluation Plan for the U.S. 

Department of Energy and the Federal Transit Administration. NREL/MP-560-42781. Golden, 

CO: National Renewable Energy Laboratory, 2008. 
20 

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

Experiences and Current Status. NREL/TP-560-41967. Golden, CO: National Renewable 

Energy Laboratory, 2007. 

AC Transit

Chandler, K.; Eudy, L. National Fuel Cell Bus Program: Accelerated Testing Evaluation Report 

and Appendices. FTA-CO-26-7004-2009.1, FTA-CO-26-7004-2009.1A. Golden, CO: National 

Renewable Energy Laboratory, 2009. 

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

Buses: Third Evaluation Report and Appendices. NREL/TP-560-43545-1, NREL/TP-560-43545-

2. Golden, CO: National Renewable Energy Laboratory, 2008. 

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

Buses: Third Evaluation Report and Appendices. NREL/TP-560-43545-1, NREL/TP-560-43545-

2. Golden, CO: National Renewable Energy Laboratory, 2008. 

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

Buses: Evaluation Results Update. NREL/TP-560-42249. Golden, CO: National Renewable 

Energy Laboratory, 2007. 

Chandler, K.; Eudy, L. AC Transit, Fuel Cell Transit Buses: Preliminary Evaluation Results. 

NREL/TP-560-41041. Golden, CO: National Renewable Energy Laboratory, 2007. 

NREL. AC Transit Demos Three Prototype Fuel Cell Buses. DOE/GO-102006-2286. Golden, 

CO: National Renewable Energy Laboratory, 2006. 

Connecticut Transit

Chandler, K.; Eudy, L. Connecticut Transit (CTTRANSIT) Fuel Cell Transit Bus: Second 

Evaluation Report and Appendices. NREL/TP-560-45670-1, NREL/TP-560-45670-2. Golden, 

CO: National Renewable Energy Laboratory, 2009. 

Chandler, K., Eudy, L. Connecticut Transit (CTTRANSIT) Fuel Cell Transit Bus: Preliminary 

Evaluation Results. NREL/TP-560-43847. Golden, CO: National Renewable Energy Laboratory, 

2008. 

NREL. CTTRANSIT Operates New England’s First Fuel Cell Hybrid Bus. DOE/GO12008-2529. 

Golden, CO: National Renewable Energy Laboratory, 2008. 

Santa Clara Valley Transportation Authority

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

Transit District, Fuel Cell Transit Buses: Evaluation Results. NREL/TP-560-40615. Golden, 

CO: National Renewable Energy Laboratory, 2006. 

NREL. VTA. SamTrans Look into Future with Bus Demo. DOE/GO-102005-2147. Golden, CO: 

National Renewable Energy Laboratory, 2005. 

 
F1147-E(10/2008) 

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SunLine Transit Agency Fuel Cell Transit Bus: 

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