The hydrogen economy describes a national or global energy supply infrastructure which is based on hydrogen. Hydrogen has a very high gravimetric energy density of about 33 kilowatthours per kilogramm. It is around three times higher compared to gasoline and 4 times greater than that of coal.
Burning hydrogen in a combustion engine or a gas turbine produces mainly water and small amounts of different nitrogen oxides. Using hydrogen in a fuel cell produces only water vapour. Using hydrogen reduces emissions during energy usage to a near zero level.
Often forgotten: Hydrogen is not found as a gas on our planet. Hydrogen has to be produced by the use of energy before it can be converted via combustion engines, gas turbines or fuel cells. Today near 90 percent of the hydrogen stems from converting natural gas into hydrogen. 10 percent are produced by electrolysis. All these processes are based mainly on fossile fuels and release the green house gas carbon dioxide.
The solution is a solar energy based hydrogen economy or solar hydrogen economy:
- Photovoltaic cells produce electric power which drives electrolysis cells.
- solar thermal power plants -- they concentrate sunlight by a vast amount of mirrors to drive a steam turbine -- are used to produce electric power to perform the electrolysis.
- Biomass, generated with the help of sunlight, is converted into hydrogen by pyrolysis.
Another problem ist the storage of hydrogen. All methods -- pressurized or liquefied hydrogen or the storage as metal hydrate -- show low energy densities and need complex devices.
It is in question if we will establish a hydrogen economy -- methanol might be a better alternative which can be stored in simple tanks like our most widely used fuels diesel or gasoline. Methanol can also be used in direct methanole fuel cells and might take advantage of the high conversion efficiencies of these devices. The problem then is shifted to the question "How can we produce methanol by sustainable methods?"