The paper describes the results of a study undertaken by the German "Power Engineering Society within VDE (ETG)". Different stakeholders took part in the Task-Force "Energy Storage" in order to evaluate the needs and possibilities of electrical energy storage in future power supply systems. This paper is focussed on the results with regard to distribution systems and includes the possible impact of mobile storage systems in a vehicle-to-grid approach.

EC Directives (EC in SEC 85/3, 2008; EP, EC in COM 19, 2008) give individual targets in emission reduction and renewable energy share to the member states of the European Union. Germany is obligated to reduce its green house gas emissions by 14 % until the year 2020 related to the year 2005 and to increase its share of renewable energy in the final energy consumption to 18 %. For electrical energywhich is the main topic of this paperthe portion of electricity based on renewable energy sources (RES) is projected to increased from 15 % in 2008 to 40 % until 2020 (Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit, 2012). Because of the short period of time, this ambiguous target represents a big challenge in development of adequate renewable generation. The high shares of wind or PV in the supply system necessitates to expand the storage capacities, extend the transmission and distribution grids and improve flexible operation of the entire energy system, star ting with generation and ending with demand side. Long term scenarios of electricity generation and demand in Europe until 2040 can be found in Eurel (2012). To maintain the high standard of security of supply in the German grid, a Task Force of VDE has investigated the needs to balance the German energy system under the aspect of high penetration of RES. For the analysis of the consequences for the non-renewable power generation, a simulation model of the German energy system had been elaborated, which considers the development of RES shown in the reference scenario (VDE AT40, 2012), for the following development of RES until the year 2020: wind 60 GW, PV 60 GW, run-of-river hydro 5 GW (constant) and biomass 7 GW. In total the installed power of RES might achieve 130 GW. Considering the coincidence of RES generation, it will touch the grid load many times over the year and to a small extend overshoot the existing demand. The system simulations show, that the thermal fleet will be facing load gradients of up to 15 GW/h over 1 h in the year 2020. These high gradients will need flexible thermal power plants, which will be able to respond to fast changing

The necessity of the wide use of renewable generation is nowadays self evident. However, the corresponding technologies like wind, PV or fuel cells are still being developed. Thus far, they have not reached the break even point and must be supported by different economic (subventions) and regulatory (priority) frameworks. The VDE/ ETG 1 studied this problem in the scope of a Task Force (TF)on Smart Distribution in order to identify the need for new mechanisms, which should be mapped during the next German Renewable Energy Law (EEG) revision. In this paper the authors, who are members of the abovementioned TF, present the methodology of the investigations and discuss new proposals concerning the EEG revision.

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