『Abstract
　The role of hydrogen in long run sustainable energy scenarios for the world and for the case of Germany is analysed, based on key criteria for sustainable energy systems. The possible range of hydrogen within long-term energy scenarios is broad and uncertain depending on assumptions on used primary energy, technology mix, rate of energy efficiency increase and costs degression (“learning effects”). In any case, sustainable energy strategies must give energy efficiency highest priority combined with an accelerated market introduction of renewables (“integrated strategy”). Under these conditions hydrogen will play a major role not before 2030 using natural gas as a bridge to renewable hydrogen. Against the background of an ambitious CO2-reduction goal which is under discussion in Germany the potentials for efficiency increase, the necessary structural change of the power plant system (corresponding to the decision to phase out nuclear energy, the transformation of the transformation sector and the market implementation order of renewable energies (“following efficiency guidelines first for electricity generation purposes, than for heat generation and than for the transportation sector”)) are analysed based on latest sustainable energy scenarios.

Keywords: Hydrogen; Sustainable energy systems; Energy efficiency』

1. Why thinking about new fuels - “business as usual” is unsustainable
2. Future uncertainties: a great range of hydrogen in world energy scenarios
3. Enhancing energy productivity: a necessary, but not sufficient condition for sustainable development
4. Case studies for German: sustainable energy systems can be financed
　4.1. Sustainable energy systems presuppose advanced efficiency
　4.2. Substantial change of electricity supply is needed
　4.3. Efficiency improvements can “buy down the costs” of renewable electricity supply
　4.4. Economics make hydrogen based on renewables a long-term option
　4.5. Interlinkages between the market introduction of future technologies and behaviour changes
5. Conclusions
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Further reading