South view of the M5BAT test facility PGS E.ON ERC RWTH Aachen South view of the M5BAT test facility

Stationary energy storage will become more important in the future due to rising shares of renewable energy sources in the electricity sector which are promoted by Germany’s federal government policy called ‘Energiewende’. In this context, electrochemical storage systems are of high interest because unlike for pumped hydro storage or compressed air storage , there are no special geographic requirements and the planning and construction periods are small. Therefore, it is necessary to build up the expertise in engineering of economic designs, optimized operation control and comparative technology assessment of such storage systems and to benchmark the performance of different technologies under field conditions.

Within this project a modular Battery Energy Storage System (BESS) with five parallel battery strings of each 1.25 MW rated power will be build. This size is necessary to ensure a power output of 5 MW (even if one battery string goes offline due to maintenance). Peripheral components, such as heating, ventilation and air conditioning (HVAC), are treated as an integral part of the BESS in order to achieve an optimal system behavior in terms of cooling, heating and battery positioning.

Different battery technologies are involved in the BESS: lead-acid-, sodium-nickel-chloride- (NaNiCl) and lithium-ion-batteries are used to optimally combine the advantages of each technology. For instance, lead-acid-batteries are a relatively cheap storage technology, lithium-ion-batteries act as high-power-supplier and NaNiCl-batteries are optimally suited for power supply over a period of a few hours and are therefore eligible for applications such as load-shifting respectively in combination with the other technologies for a variety of applications with different typical discharge times. A BESS with a rated power this size, with a high modularity for the investigation of different storage technologies, is worldwide unique and acts as an important reference for the involved companies and institutions.

At first the storage operation will be conducted according to a scientific program, which allows to deduce statements about life cycle costs and techno-economical potentials. Besides the costs for the battery cells and their lifetimes, life cycle costs include costs for peripheral components for the installation of the BESS such as housing, battery management systems (BMS) and thermal management (heating, ventilation, air conditioning). These life cycle costs are intended to serve as a profound cost basis for planning and operation of BESS. Furthermore, target costs for important storage applications shall be deduced which allows to give statements about the price for balancing energy. This represents the basis for an economic operation of BESS (under consideration of the cost decline of batteries), or which regulatory incentives need to be made respectively. Also, the findings during the operation of the BESS within the project are supposed to constitute a basis for advancements of the different battery technologies.