The New Scenario for Hydrogen

With regard to energy technology, hydrogen has become rel­evant again today due to environmental problems. The ex­tensive combustion of fossil fuels such as coal, petroleum and natural gas is a large-scale intervention by mankind in­to the natural balance of the earth. The global warming pro­voked by the increasing concentration of CO2 in our at­mosphere will have threatening effects if a further rise in the average temperature cannot be kept within narrow lim­its. The EU has set an ambitious goal of 2° C above the preindustrial level for this rise [4]. Today, 0.8° of this EU goal has already occurred [4], so that many countries have es­tablished climate-protection programs. They support tech­nical alternatives to an energy supply which releases large quantities of CO2. The climate program of the German Fed­eral government stipulates a broad-based energy supply, de­pending primarily on renewable energy sources and in­cluding very ambitious CO2 reduction goals [4].

Hydrogen as an energy carrier plays a role today in two areas, owing to the increasing proportion of sustainable en­ergies in use and the more stringent requirements for en­ergy efficiency. It thus represents the bridge between sta­tionary electric power production and the transport sector:

1. For transportation, automobiles and buses can be pow­ered very efficiently and with no CO2 emissions using hydrogen and fuel cells;

2. Many renewable energy sources, especially wind ener­gy, but also solar energy, whose technical and econom­ic feasibility are at present guaranteed, generate elec­tric power in a fluctuating mode and therefore require energy storage systems. This storage could be accom­plished by using part of the wind (and solar) power generated to produce hydrogen electrolytically, and then storing it.

These two elements can be coupled in a rational way by us­ing so-called surplus power, e. g. wind power which is not needed by the power grid at the time when it is generated, for the production of hydrogen. This hydrogen can then substitute mineral fuels directly.

For heavy machinery such as trucks, construction equip­ment, locomotives, ships and aircraft, liquid fuels cannot be readily substituted, and this will continue to be true in the foreseeable future. For these uses, the energy storage den­sity of hydrogen at the current and foreseeable state of the technology is insufficient in comparison to liquid fuels. For stationary applications also, gaseous hydrogen will not play a role in the foreseeable future; here, a mature infrastruc­ture for utilizing natural gas is already in place.

Hydrogen could, however, be added at up to several per­cent to natural gas in the pipeline networks, as has been dis­cussed under the buzzword “wind hydrogen”. As an alter­native, methane production from hydrogen has been sug­gested, where hydrogen and carbon dioxide are reacted to give methane with an energy input (thermodynamically more precisely: an uptake of enthalpy) of 206 kJ/mole:

CO2 + 4 H2 о CH4 + 2 H2O.

The carbon dioxide could be provided by a future carbon capture and sequestration (CCS) scheme. This alternative in­deed makes use of an established infrastructure, but it is not energy efficient and requires the availability of concentrat­ed and purified CO2, e. g. through CO2 capture from ex­haust gases.

Methane production is in addition economically ques­tionable, since pure electrolysis hydrogen used as a fuel would be in competition with it and would have at least the value of gasoline today, 65-70 N-ct./liter of gasoline equiva­lent before taxes. Even twice this price would be justified and therefore probably acceptable to the market, since hy­drogen in fuel-cell powered vehicles is twice as energy-ef­ficient as gasoline burned in an internal-combustion engine. Thus, one could expect that a price of 1.3-14 N per liter of gasoline equivalent would be achievable for hydrogen (gaso­line has an energy content of 32 MJ/l; MJ = megajoules; l = liter). Hydrogen used for methane production and added to natural gas would be sold at the same price as the natural gas, i. e. around 1 N-ct./MJ or 32 N-ct./liter gasoline equiva­lent. Thus, the value of a pure electrolysis product would be reduced by half or even to only a quarter by a process technology which involves additional energy losses and added costs.

Updated: October 27, 2015 — 12:10 pm