FTA Report on Worldwide H2 Bus Demonstrations Finds Better Than Expected Performance and Strong Customer Acceptance; Challenges Remain
The US Federal Transit Administration (FTA) has published a report summarizing interviews with participants in the hydrogen-powered buses trials underway in more than 20 cities around the world from 2002 to 2007. These included buses powered by fuel cells or hydrogen-fueled internal combustion engines, as well as a variety of fueling and related technologies.
The report gathers insights from demonstration participants at transit agencies in the United States, Europe, China, Japan and Australia, analyzes lessons learned, identifies key remaining challenges, and suggests potential roles for government in supporting commercialization. Among the findings were that the performance of the fuel cell stacks exceeded expectations, but the batteries and supporting components experienced significant challenges.
Most demonstrations reported better than expected performance and strong passenger acceptance. For example:
The buses performed well across a wide range of operating conditions, including hilly and flat terrain, hot, and cold temperatures, and high and low-speed duty cycles;
There were no major safety issues over millions of miles of vehicle service and thousands of vehicle fuelings;
Most participants found that drivers preferred fuel cell buses to compressed natural gas (CNG) or diesel, noting their smooth ride, ease of operation, strong acceleration, and ability to maneuver well in traffic;
Several participants noted that fuel cell bus drivers were less tired at the end of their shifts, mainly because the buses produced significantly less noise than diesel or CNG;
75% of surveyed passengers reported a quieter ride, and 63% reported a smoother ride, as compared with conventional buses;
Most participants found that the buses were easily incorporated into revenue service, with some accommodation for increased vehicle weight and height and longer fueling times; and
Most participants noted that developing fuel cell bus maintenance facilities was not as challenging as expected. However, because each site developed its own solutions, future research could capture lessons learned and develop best practices and guidelines.
According to the report, participants expressed strong enthusiasm for deploying more hydrogen buses, with most indicating a desire for larger fleets, such as 50–100 buses per site. Participants noted that the demonstrations successfully incorporated lessons learned from prior demonstrations, thus significantly advancing the technology.
Key challenges to commercialization revealed by the demonstrations were:
Vehicle Range. The most significant challenge was range. Diesel buses typically operate for 18 to 20 hours per day, over a range of about 186-217 miles (300-350 km), using one tank of fuel. At many demonstration sites, fuel cell buses required refueling after about 200 km (93-124 miles). Hybrid fuel cell systems can significantly extend range, and many participants believe that future fuel cell buses will be hybridized.
Fuel Cell Durability. Many transit agencies were surprised and favorably impressed with the steady progress made in fuel cell reliability. For example, bus availability, an indicator of vehicle reliability, was greater than 90% in the CUTE, Ecological City Transport System (ECTOS), Sustainable Transport Energy Project (STEP) and HyFLEET:CUTE fuel cell bus trials. This was higher than expected.
Fuel cell-hybrid buses, which were deployed in the United States, had a target rate of 85% availability, but experienced lower rates due to a number of issues involving the battery, hybrid drive and fuel cell. Contamination in the cell stack assembly (CSA) caused premature power degradation of the fuel cells, and was reportedly resolved when a new generation of CSAs was installed in the buses.
Participants reported that a number of fuel cell-related problems were caused by supporting components to the fuel cell. Several felt that these supporting components need additional development to be more robust, to improve lifespan, and to be sufficiently rugged for transit use. Problems included software issues, trouble with the cell voltage monitoring board, and inverter issues that forced several upgrades.
Despite significant progress, fuel cell durability must be substantially increased and/or the cost of replacement fuel cell stacks must be substantially decreased. Most participants expressed confidence that the durability challenge will be solved.
Energy Storage. Fuel cell hybrid buses are deployed in North America, at AC Transit and SunLine in California, and CTTRANSIT in Connecticut. These buses use ZEBRA NaNiCl batteries that have performed below expectation, with deployment sites reporting frequent battery system troubles. Several participants felt that battery technology is not advancing.
Battery issues have been caused by state of charge imbalances in battery cells that lead to propulsion system software over-volt errors. The technology companies and integrator have achieved some success in controlling this problem. Battery controller electronics failures have also been an issue and software changes have been made to minimize this problem.
Despite poor battery performance, many participants believed that the next generation of fuel cell vehicles will need some form of hybridization to increase range and fuel efficiency and several indicated that the next generation of fuel cell buses likely will use either lithium-ion (Li-ion) or nickel-metal hydride (NiMH) batteries.
Participants noted that batteries must be improved, and research into other energy storage systems, such as ultracapacitors and flywheels, would be valuable.
The role of HICE buses. Participants’ opinions of hydrogen-fueled internal combustion engine (HICE) and hydrogen hybrid internal combustion engine (HHICE) technologies varied from strongly supportive, to strongly opposed. A majority, however, believe that these technologies are not viable long-term options. Several participants suggested that they may serve a role as a bridge technology to fuel cell vehicles, helping in the development of a larger hydrogen infrastructure. A few were taking a wait-and-watch stance, looking for reduced cost and improved performance and reliability.
Many participants pointed out that HICE and HHICE buses are expensive to purchase and maintain and do not offer the reduced noise, zero emissions, and fuel efficiency benefits of fuel cell buses, yet face the same technical challenges of dealing with hydrogen fuel. Operating range of HICE buses is also limited, requiring buses to be refueled mid-day.
About half of participants argue that HICE and HHICE buses offer no advantages over fuel cell buses.
Bus Components. Participants reported that a number of fuel cell-related problems were caused by supporting components to the fuel cell. Several felt that these supporting components need additional development to be more robust, to improve lifespan, and to be sufficiently rugged for transit use.
Infrastructure Reliability. Many participants believed that infrastructure technology needs to progress significantly for fuel cell buses to be commercialized. Equipment failures, including nozzles, hoses and compressors, were common and buses were occasionally put out of service for weeks or months. Several participants felt that there was little or no investment being made to solve these challenges.
Hydrogen Filling Times. Currently, hydrogen fast-fills typically range between 10-30 minutes per bus, which is longer than the fueling times for diesel (2.5-10 minutes) and CNG fast-fills (4-7 minutes). As larger bus deployments are planned, the fueling time, which is a function of both the infrastructure equipment and the buses, will need to be reconsidered. Many feel that the fast-fill times will need to be reduced to accommodate more vehicles, or that fueling stations should plan for more pumps. The latter option, however, will require more investment in infrastructure and will increase the fueling stations’ footprint.
Demonstration participants envisioned two primary roles for government in future demonstrations: the development of a long-term, rather than project-specific, strategic plan for fuel cell buses and an accompanying funding commitment until commercialization is viable.
Transit operators indicated that government funding will be needed to cover incremental costs of purchasing and operating fuel cell buses through 2015, based on current commercialization timeframes. Many participants believe that government support for larger deployments (50-100 vehicles), and bigger hydrogen bus purchases, will help to bring down bus costs.
Several also believe that monetizing carbon emissions could significantly improve the life-cycle cost implications of hydrogen buses.
Participants also suggested that government should invest in hydrogen highways or other linked hydrogen infrastructure, sustainable hydrogen pathways to maximize the environmental benefits of hydrogen buses, standardizing hydrogen safety procedures for transit agencies, disseminating information on codes and standards, and developing certification standards and training curricula for maintenance technicians. Participants also would like government to direct funding for basic research and development to resolve challenges revealed by these demonstrations.
A Report on Worldwide Hydrogen Bus Demonstrations, 2002-2007 (FTA Report No. FTA-GA-04-7001-2009.01)