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Methods of hydrogen storage for subsequent use span many approaches, including high pressures, cryogenics, and chemical compounds that reversibly release H2 upon heating. Underground hydrogen storage is useful to provide grid energy storage for intermittent energy sources, like wind power, as well as providing fuel for transportation, particularly for ships and airplanes. Most research into hydrogen storage is focused on storing hydrogen as a lightweight, compact energy carrier for mobile applications. Liquid hydrogen or slush hydrogen may be used, as in the Space Shuttle. However liquid hydrogen requires cryogenic storage and boils around 20.268 K (−252.882 °C or −423.188 °F). Hence, its liquefaction imposes a large energy loss (as energy is needed to cool it down to that temperature). The tanks must also be well insulated to prevent boil off but adding insulation increases cost. Liquid hydrogen has less energy density ''by volume'' than hydrocarbon fuels such as gasoline by approximately a factor of four. This highlights the density problem for pure hydrogen: there is actually about 64% more hydrogen in a liter of gasoline (116 grams hydrogen) than there is in a liter of pure liquid hydrogen (71 grams hydrogen). The carbon in the gasoline also contributes to the energy of combustion. Compressed hydrogen, by comparison, is stored quite differently. Hydrogen gas has good energy density by weight, but poor energy density by volume versus hydrocarbons, hence it requires a larger tank to store. A large hydrogen tank will be heavier than the small hydrocarbon tank used to store the same amount of energy, all other factors remaining equal. Increasing gas pressure would improve the energy density by volume, making for smaller, but not lighter container tanks (see hydrogen tank). Compressed hydrogen costs 2.1% of the energy content〔(Energy technology analysis ). International Energy Agency (2005) p. 70〕 to power the compressor. Higher compression without energy recovery will mean more energy lost to the compression step. Compressed hydrogen storage can exhibit very low permeation.〔(Modeling of dispersion following hydrogen permeation for safety engineering and risk assessment ). (PDF) . II International Conference “Hydrogen Storage Technologies” Moscow, Russia, 28–29 October 2009. Retrieved on 2012-01-08.〕 ==Automotive Onboard hydrogen storage== Targets were set by the FreedomCAR Partnership in January 2002 between the United States Council for Automotive Research (USCAR) and U.S. DOE (Targets assume a 5-kg H2 storage system). The 2005 targets were not reached in 2005.〔(Hydrogen Storage Technologies Roadmap ). uscar.org. November 2005〕 The targets were revised in 2009 to reflect new data on system efficiencies obtained from fleets of test cars. The ultimate goal for volumetric storage is still above the theoretical density of liquid hydrogen.〔(FCT Hydrogen Storage: Current Technology ). eere.energy.gov (2011-08-26). Retrieved on 2012-01-08.〕 It is important to note that these targets are for the hydrogen storage system, not the hydrogen storage material. System densities are often around half those of the working material, thus while a material may store 6 wt% H2, a working system using that material may only achieve 3 wt% when the weight of tanks, temperature and pressure control equipment, etc., is considered. In 2010, only two storage technologies were identified as being susceptible to meet DOE targets: MOF-177 exceeds 2010 target for volumetric capacity, while cryo-compressed H2 exceeds more restrictive 2015 targets for both gravimetric and volumetric capacity (see slide 6 in 〔R. K. Ahluwalia, T. Q. Hua, J. K. Peng and R. Kumar (System Level Analysis of Hydrogen Storage Options ). 2010 DOE Hydrogen Program Review, Washington, DC, June 8–11, 2010〕). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hydrogen storage」の詳細全文を読む スポンサード リンク
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