『（Abstract）
　Since the beginning of the twenty-first century the limitations of the fossil age with regard to the continuing growth of energy demand, the peaking mining rate of oil, the growing impact of CO2 emissions on the environment and the dependency of the economy in the industrialized world on the availability of fossil fuels became very obvious. A major change in the energy economy from fossil energy carriers to renewable energy. fluxes is necessary. The main challenge is to efficiently concert renewable energy into electricity and the storage of electricity or the production of a synthetic fuel. Hydrogen is produced from water by electricity through an electrolyser. The storage of hydrogen in its molecular or atomic form is a materials challenge. Some hydrides are known to exhibit a hydrogen density comparable to oil; however, these hydrides require a sophisticated storage system. The system energy density is significantly smaller than the energy density of fossil fuels. An interesting alternative to the direct storage of hydrogen are synthetic hydrocarbons produced from hydrogen and CO2 extracted from the atmosphere. They are CO2 neutral and stored like fossil fuels. Conventional combustion engines and turbines can be used in order to concert the stored energy into work and heat.

Keywords: energy carriers; hydrogen; synthetic fuels; efficiency』

1. Energy and development
　(a) Growing energy demand
　(b) The efficiency paradox
　(c) limited resources of fossil fuels
　(d) Environmental impact
　(e) Economic dependency
2. Hydrogen
　(a) Hydrogen cycle
　(b) Hydrogen production
　(c) Hydrogen storage
3. Energy density
　(a) Synthetic fuels
　(b) Energy carriers
4. Conclusion
References