A review of hydrogen delivery technologies for energy system models

UK greenhouse gas (GHG) emissions predominantly result from the combustion of fossil fuels to provide energy services in all sectors of the economy. In the future, it will be necessary to either capture the emissions or to utilise zero-carbon sources of energy. Hydrogen has been identified as a potential zero-emission energy carrier for the future, primarily for the transport sector but also for energy storage and CHP applications. Although micro-scale hydrogen production systems are being developed for domestic use by some companies, it is likely that a network of hydrogen fuelling stations would be required to supply fuel to motorists or hydrogen-fuelled vehicles would suffer the same range limitations as electric vehicles. Small-scale hydrogen production from electrolysis or biomass would be possible at fuelling stations but large plants would otherwise be required for fossil fuel feedstocks so that the CO2 by-product could be captured and stored using CCS. In the short-term, small-scale SMR could also be deployed at refuelling stations to facilitate the transition to a hydrogen economy but these would not be compatible with decarbonisation in the long-term. Hydrogen production technologies are examined in UKSHEC II Working Paper 6 (Dodds and McDowall, 2012). Hydrogen is relatively difficult to store and transport in comparison with petroleum fuels. Gaseous hydrogen (GH2) has two principle drawbacks. Firstly, the unusually low volumetric energy density of gaseous hydrogen means that the gas must be compressed to extremely high pressure to be used as a transport fuel. Secondly, the tiny molecules have a higher propensity to leak than other gases and require particularly complex storage materials. One method of avoiding these two difficulties is to compress the hydrogen into a liquid (LH2), but this is energetically-expensive and difficult to handle because LH2 boils at around –253 °C. Other forms of hydrogen, for example metal hydrides, are currently being researched but are at an early stage of development. Three methods are commonly used to deliver hydrogen to refuelling stations (Yang & Ogden 2006). GH2 pipelines require large up-front capital investments but can transport large amounts of hydrogen very cheaply over short and sometimes long distances. The most cost-effective method of delivering small amounts of GH2 over short distances is using gaseous tube trailers. Over longer distances, LH2 delivery by road tanker becomes optimal.