CUTE, but Not Totally Loved

Compressor problems were the main cause of downtime for the refueling stations. They also caused consequential damage, such as contamination of the gas and the fuel tanks with oil (in Hamburg) and with graphite (in Barcelona and Perth). The risk of hydrogen embrittlement to the nozzle was considered serious enough to trigger a redesign. There was a serious enough disagreement on the root cause of the nozzle issue as to cause a complete shutdown for several weeks early in the project.

The electrolysers in Reykjavik and Hamburg experienced stress corrosion caused by a combination of high temperatures and high pressures. The natural gas reformer in Madrid experienced leakage, pipework failure and gas quality problems to the extent that it was operating at only 11 percent capacity for the year of 2004. Redesigns of the fueling hose in Perth was undertaken resulting in a capability to refuel at pressures up to 1,000 bar(g).

Emergency shutdown data for the refilling stations are revealing. The major contributor to shutdowns was a failure in the filling nozzle. Low pressure into the compressor was a factor on two occasions. Gas leakages that were detected were mostly also attributable to the dispenser. Only one reported leakage at the connection to the bus was recorded for the entire fleet across Europe. Ninety percent of ‘incidents and abnormal situations’ that were recorded were attributable to technical failure—the rest to human activities.

Regenerative Braking
The use of regenerative braking (in which the energy generated in the braking process is redistributed into the transmission for moving off again) was put forward as a major factor in fuel economy computations. Relative to conventional diesel engines, the hybrid design (through the use of battery power) and this braking capability returns a greater fuel economy than diesel. In California bus fleets with this fuel cell capability operated by SunLine and AC Transit, fuel efficiency gains of 149 percent and 67 percent more than conventional diesel were returned for trials in 2005-2006. A fuel cell fleet operated by VTA that had neither regenerative braking nor a hybrid design returned 12 percent inferior fuel efficiency.

The battery performance is being targeted for future designs. Prof. Herbert Kohler, vice president, Body and Powertrain Research at DaimlerChrysler, announced at the conclusion of the trials, “We intend to use a high-performance battery into which we can feed energy recovered from the braking process. ... The fuel cells will only have to meet the normal level of energy requirements. Peak demand will be met by the battery. This will save both volume and weight.”

The consensus view is that the buses themselves have performed better than expectations. The onsite technicians from DaimlerChrysler were thought to have provided adequate support. (This was not the experience of the Perth project, however.) Spare part supply for the buses was found to be lacking. Of the infrastructure partners, the fuel retailers (BP and Shell), it turns out, had ‘other expectations’ than those not normally in the fuel business. The gas and energy sector partners collectively expressed that the performance of the hydrogen refueling stations was “lower than expected.” Despite the documented failures throughout the trials, the troubleshooting, reporting and corrective actions procedures “have improved over time in the project.” Post-trial surveys designed to establish any sense of “regret” over the use of hydrogen refueling stations identified only two cities stating this—Luxembourg, due to the high cost of trucking in natural gas for reformation, and Madrid, because of an unreliable reformer.

78 Million Euro Investment
Perhaps, understandably, there is very little credible data on the true cost of the program. Seventy-eight million euros was invested in the overall project, of which 18.5 million euros was provided through European Commission public sector funding. The remainder was provided through the project participants, including cities, public transport operators, infrastructure partners and vehicle manufacturers. A similar public-private contribution has characterized the U.S. fuel-cell bus program.

The fuel-cell buses are heavier than existing bus technologies. The Citaro buses weighed in at 14 tons unladen; this is 2 tons heavier than an equivalent capacity CNG vehicle and 3 tons more than a diesel. The buses were also approximately 2 feet taller than regular buses—this required some adjustments to infrastructure, such as the washing facilities which had to be upgraded to accommodate the taller buses.