One of the main issues in the move across to zero emission trucking is that of refuelling infrastructure for alt-power vehicles, Erik Gustafson, R&D Engineer, Chart Industries, explains.
The refuelling mechanism for BEVs is readily understood; plug in the vehicle and wait for it to charge. However, the associated challenges are also both easily understood and familiar; recharging times, even with high speed chargers, are lengthy, the infrastructure is nowhere near sufficient and requires massive investment and high-speed electric vehicle recharging stations cannot be installed wherever desired, for example, proximity to a high voltage main supply must be considered.
The hydrogen model actually has a lot in common with diesel and gasoline. Fuel is distributed, typically by road, from its point of origin and stored on site at the fuelling station. The vehicle is refuelled by the driver who connects a hose from a dispenser to the vehicle. Dispensers can either be located at public stations or at a site/depot specific to a particular fleet.
Gaseous, compressed hydrogen is transported in a ‘tube trailer’, the highest capacity of which can transport about one tonne of compressed hydrogen. Liquid hydrogen is transported in insulated trailers and a further advantage here is that each trailer typically delivers around four times the amount of liquid hydrogen versus its gaseous counterpart. Both methods are proven over many years and extremely safe and effective. Almost certainly you will have passed trucks carrying liquid and gaseous hydrogen without ever realising and trucks carrying liquid gases are an everyday sight on our roads.
Fuel stations that dispense H35 and H70 have two options in how the hydrogen is stored onsite: as a compressed gas or as a cryogenic liquid. In the case of storing hydrogen as a compressed gas, additional compressors are required to boost the pressure up between the station tube storage to the onboard storage tanks.
In the case of storing hydrogen at the fuel station as a cryogenic liquid, a cryogenic pump can boost the pressure up to fill the onboard storage tanks. Since the cryogenic pump is acting upon a liquid, it inherently consumes much less energy than the compressor that acts upon a gas. Furthermore, the station with LH2 storage offers lower capital and operating expenditure than the station with compressed hydrogen storage.
LH2 refuelling stations are in development today in order to fill vehicles fitted with an LHSS. These ‘Liquid –to-liquid’ hydrogen stations receive and store LH2 to dispense directly into vehicles. Costs around an LH2 refuelling station are even lower than an equivalently sized H35 and H70 station with LH2 storage.
The investment cost and operating cost savings of an LH2 station is primarily due to the complexity of the cryogenic pump. The low-pressure LH2 dispensing pump used in an LH2 dispensing station uses a fraction of the energy and is much simpler than the H70 cryo-pump. Another advantage of using LH2 on board vehicles is the refuelling speed that can be achieved. Refuelling rates of 10kg/min or greater are easily achievable with an LH2 dispenser. To achieve a similar fuelling speed with H35 or H70 fuelling, either a very large pump/compressor is required, or a large amount of compressed storage is required, either of which leads to much higher costs.
Long-distance heavy-duty trucks are likely to utilise LH2 onboard storage in the future to maximise vehicle range and vehicle payload. It is also becoming apparent that most hydrogen refuelling stations (whether dispensing H70 or LH2) will utilise LH2 storage onsite due to the higher throughput capability and reduced costs.
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