The transformations from hydrogen to energy and back are expensive and technologically complex. Hydrocarbons are often stored at the point of use, either as a liquid in the tanks of petrol, diesel and LPG in cars or in compressed propane tanks. The hydrogen instead is very expensive to store and / or transport with current technology. Hydrogen has a high energy density per unit mass, but poor energy density per volume compared to hydrocarbons, requiring larger tanks for its storage. Such hydrogen tanks are therefore heavier than the hydrocarbons at constant energy content. Increasing the pressure of the gas would improve the energy density per unit volume, obtaining containers less bulky, but not lighter. Compress a gas requires energy to power the compressor: a higher compression involves a greater loss of energy during the compression process.
Alternatively you could use liquid hydrogen or hydrogen snow at higher volumetric energy density. However, the liquid hydrogen requires a cryogenic storage and boils at about 20.268 K. So its liquefaction imposes a great loss of energy because energy is required to cool it up to those temperatures. Tanks must then be well insulated to prevent boiling and insulation for liquid hydrogen is usually expensive and delicate. Assuming all this solved, there remains the problem of density. Liquid hydrogen has indeed a specific energy density of about 4 times worse compared to hydrocarbons such as gasoline.
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