Hydrogen Fuel Cell Bus Technology State of the ... - NEXTHYLIGHTS

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Hydrogen Fuel Cell Bus Technology State of the Art Review 3.2 Other technical issues A number of other technical issues are relevant to bus operators when considering hydrogen vehicle purchase. These include: Noise: The noise of urban buses is a major drawback of an efficient public transport option. The main noise from a conventional bus is from the diesel engine. As the fuel cell system itself is silent, it should be possible to dramatically improve the noise levels emanating from a fuel cell bus. On many of the early fuel cell buses, various point sources of noise meant that the buses were not truly silent. In particular air compressors to pressurize the inlet air for the fuel cell stack have cause high pitched noise issues. Fuel cell system integrators envisage these issues being resolved with next generation air compressors and lower pressure stacks. Table 4 Current noise performance of basic diesel and hybrid fuel cell buses in comparison with the European noise limit in force for the external environment. The EU limit is intended for vehicles carrying more than 9 passengers and having a mass exceeding 3.5 tons. Condition EU Limit Basic diesel bus Hybrid fuel cell bus Engine power < 150kW 78db ~ 78db < 75db Source: http://ec.europa.eu/environment/noise/sources.htm; stakeholders‟ consultation Weight: The additional weight of hydrogen tanks and the fuel cell balance of systems compared to a diesel bus increase the load on the axle and can lead to restrictions in the number of standing passengers allowed. Table 5, below provides some indication of the effect of additional weight on some of the recent hydrogen buses, compared to their diesel equivalent and the effect on passenger carrying capacity. 30
Hydrogen Fuel Cell Bus Technology State of the Art Review Table 5 Typical weight and passenger capacity for diesel and hybrid fuel cell buses Typical Diesel bus (12m platform) Hybrid Fuel Cell Bus (12m platform) Kerb Weight up to 12 tonne up to 2.5 tonnes additional weight Passenger Capacity (overall) Source: Web resources, Stakeholders‟ consultation. up to 110 passengers Reduced by additional weight (up to 30 passengers less) The reduction in passenger capacity may present a problem for bus companies on very busy urban routes. However, future buses are likely to reduce this weight penalty compared with diesel buses. The main solution to reducing weight has been to reduce the hydrogen carrying capacity of the vehicle. This can be achieved with the increased efficiency of the hybridised drivetrains in next generation buses. Other weight improvements are foreseen from reduction in balance of plant weight and improvements to the overall drivetrain packaging, where hundreds of kilograms of savings have been achieved in the current generation of fuel cell buses. Refuelling time: One of the major constraints for bus operators is the refuelling time for hydrogen buses. Large bus operators typically refuel all of the buses in their depot in a short window at the end of their service at night. With depots containing over 200 buses in some cases this lead to a requirement for very rapid fill times. Fill times below 5 minutes for diesel buses are common. Filling over 30kg of hydrogen in less than 5 minutes is not currently feasible without pre-cooling the hydrogen (as the temperature increase at these high fill rates would damage the hydrogen tanks). This is a major constraint. Potential solutions are technical (e.g. cooling the hydrogen), relate to infrastructure (e.g. filling to 700 bar, to fill more hydrogen and allow less frequent fuelling) or logistical, (e.g. change depot layouts and filling patterns to allow longer filling periods). The logistical solutions are the least favoured by bus operators and will act as a barrier to entry for hydrogen vehicles unless a technical solution is developed. 31
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