The integration of storage capacities is one of the key components to enable large scale integration of fluctuating renewables like photovoltaic systems and wind generators. Although the generation capacities of solar and wind are increasing year by year, e.g. the installed capacity of PV in Germany end of 2012 reached a value of approximately 30 GWp, investments for stationary storage systems are lagging behind the expectations for several economical as well as technical reasons.
Cities possess a huge – partly indirect – potential for storing energy as well as for balancing energy production and consumption in the distribution grid. A huge fraction of the necessary technologies will be used in a decentralized way, most of them integrated into buildings. At this point the concept of the so called urban hybrid energy storage comes into play: Local physical storages as well as local load and generation management components are aggregated on a district and city level and are offered as a virtual storage for the grid operator. The urban hybrid energy storage is able to react dynamically and in a very flexible way, so it can be used in addition e.g. to dynamically operated gas power plants and supports therefore the large-scale integration of fluctuating renewables.
Based on the combination of different storage technologies and load compensation measures, the urban hybrid energy storage is able to offer positive as well as negative balance energy. The urban hybrid energy storage consists of the following five components: Additional loads, dispatchable loads, electricity storages, dispatchable generation and additional generation.
One of the main objectives of the urban hybrid energy storage concept is defined by reducing the costs for necessary infrastructure measures needed by huge fractions of fluctuating renewables. The main advantage of this concept is given by the fact, that parts of this urban hybrid energy storage like heat pumps or CHP units are already state of the art and widely used and need only some additional measures like integration of thermal storages and communication infrastructure for an optimized operation.
As load balancing is already carried out in the local distribution grid by using this concept, the hybrid city storage supports the reduction of necessary infrastructure measures in the superordinate grid and investments in centralized power generation capacities.
Cost efficient intelligent storing of energy in urban hybrid energy storages is the overall objective of the Fraunhofer project “hybrid energy storage”, in which four institutes (UMSICHT, ISE, IOSBAST, ISIT) are developing advanced decentralized battery storages based on lithium-ion technologies, advanced thermal storages as well as control systems including operating control strategies enabling an optimized grid intergration.
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