Posted on 17 October 2011
Hydrogen fuelled vehicles are able to substitute for conventional light good vehicles with little compromise in duty cycle or performance in return to base delivery applications in rural and urban settings. Such vehicles are able to operate using renewable hydrogen, generated by feeding electricity generated by a biogas engine to an electrolyser, offering a model for the integration of vehicle fleets into a future renewable hydrogen economy. These are the outcomes of the trial of a hydrogen internal combustion engine light goods vehicle conducted in Stornoway, Outer Hebrides, Scotland in July-August 2010. The trial report is available to download from www.cenex.co.uk/resources.
The trial involved the use of a demonstration Ford Transit converted by Revolve Technologies to a bi-fuel petrol/hydrogen internal combustion engine (HICE) vehicle operated by Royal Mail on two delivery routes out of its Stornoway delivery office over a six week period. Hydrogen fuel was provided by Comhairle nan Eilean Siar (Western Isles Council) via its H2seed facility.
The trial period monitored by Cenex involved 19 trips (17 rural, two urban) either completely or partially fuelled by hydrogen for a total of 723 miles. The refuelling station was not available for four working days during this period due to issues with the dispensing system. Efficiency of hydrogen use on the rural route was around 19miles/kgH2, giving an extrapolated hydrogen-only range (based on a full tank of 4.5kg H2) of 85miles. By contrast, the hydrogen consumption on the urban route was 12miles/kgH2, giving an extrapolated range of 55miles.
Production of one kg of hydrogen at the H2seed facility required an estimated input of 71kWh of electricity for the electrolysis step and 97kWh for compression and dispensing; the overall system efficiency was 23%. The relative inefficiency of the production process was due to the large proportion of energy (58%) devoted to the compression step, which highlighted a known issue with compressing the hydrogen from the relatively low output pressure from the electrolyser (12bar maximum) to the high pressure storage (420bar maximum) of the refuelling station.
Assuming electricity for electrolysis and compression and dispensing was delivered by combustion of the biogas produced from anaerobic digestion (AD) at the Stornoway facility gave CO2e emissions of 155 and 239g/km from hydrogen-only operation on the rural and urban routes respectively. The CO2e emissions from this production route are due to fugitive methane emissions from the AD plant and biogas engine. The introduction of other renewable electricity sources such as wind in the system would reduce system CO2e emissions in operation to zero.