Academies publish position paper on the future power supply

10. December 2015

There are various reasonable options how the power supply can be stabilised in the age of renewable energies. There are alternatives to almost every technology, almost all can be replaced at reasonable additional costs. One exception, however, are gas power plants that can be flexibly fired with various gases: They constitute the backbone of any stable energy system of the future. This is the result of a position paper which was elaborated by an ESYS Working Group and was published today by acatech – National Academy of Science and Engineering, the German National Academy of Sciences Leopoldina and the Union of the German Academies of Sciences and Humanities.

Due to the weather, the power generation from wind and photovoltaics is volatile. So-called flexibility technologies are necessary to balance the ensuing fluctuations. To achieve this end, there are several sound possibilities: From flexibly dispatchable power plants, to storage systems or the balancing of power demand and power feed-in (demand-side management). The challenge is to identify the technologies that combine stability, sustainability, cost efficiency and social acceptability. A Working Group of the Academies’ Project ESYS has developed a special calculation model enabling the comparison of around 130 different constellations. The position paper “Flexibility concepts for the German power supply in 2050” sums up the most important results, the details of which can be found in a comprehensive analysis.

The calculations show: There are numerous possibilities how the energy system could be designed, all at comparable power generation costs. Due to the continuing price erosion, wind power and photovoltaic plants will become the most important power generation technologies. However, in the long term, there is virtually no getting around flexible gas power plants. “They will increasingly be operated with biogas, hydrogen or synthetic methane”, explains Prof. Dirk Uwe Sauer (RWTH Aachen, co-chair of the ESYS Working Group). “New power plants should therefore be engineered with variable firing, enabling the gas sector to successively switch from natural gas to fuels producing less carbon emissions.” This would also be a way of reliably bridging periods of up to three weeks with little wind and solar radiation.


Even with 100 percent renewable energies, a stable and affordable power supply is possible. Wind power and photovoltaic plants could, for instance, be supplemented by biogas plants or solar thermal or geothermal thermal power plants. These are flexibly dispatchable and could bridge even several weeks with little wind. However, the advantages and disadvantages should be carefully weighed:

  • The cultivation of energy crops is an important option, but environmental impacts as well as possible competition with food crops and other uses must be considered.
  • Solar thermal power plants have a smaller ecological footprint, but are only profitable in very sunny regions. In order transport the power from southern Europe or North Africa to Germany, the trans-European grids would have to be significantly expanded – which can be a challenge both in terms of costs and regarding the citizens’ acceptance.
  • Geothermal energy affects the environment and surrounding areas comparatively slightly, but is rather expensive as a means of power generation and therefore more suitable for heat generation.
  • A system with considerably more wind and photovoltaic plants than are necessary to cover the annual power demand (installed overcapacity) would need hardly any additional power plants. In this case, long-term storage devices can bridge longer periods with little wind.

The most cost-efficient means of compensating for short-term fluctuations in the power feed-in are demand-side management measures. In future, batteries in electric vehicles and photovoltaic systems in households will be the standard and can serve as storage units that are charged in times of power surpluses. Household appliances can likewise be operated according to the power supply situation. Long-term storage is only viable if carbon emissions are reduced by more than 80 percent. Otherwise, it is more cost-effective to feed power surpluses from wind and photovoltaic plants into the thermal market or to curtail the excess.

More than 100 experts from academia and industry took part in the Working Group chaired by Peter Elsner (Fraunhofer Institute for Chemical Technology) and Dirk Uwe Sauer. They evaluated the technologies and assessed their progress by 2050 as well as the expected costs. A team headed by Manfred Fischedick (Wuppertal Institute for Climate, Environment and Energy) analysed energy scenarios with different power requirements and shares of wind and solar power. All this data served as a basis for the model calculations.

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