An auspicious combination: Fast-ramping battery energy storage and high-capacity pumped hydro

Abstract Pumped hydro represents the most mature energy storage technology and accounts for more than 99 % of bulk storage capacity worldwide. Nevertheless, energy storage is becoming today increasingly diversified. Battery costs have fallen massively the last years due to increased deployment and interest in storage for variable renewable energy integration. The most dramatic cost developments have been for Li-Ion chemistries, driven by the development and perspectives of the electric vehicle market. Existing or new build pumped-storage hydro power plants (PSP) provide potential for being extended by container-based battery energy storage systems (BESS) as the techno-organisational set-up can be commonly used. Apart from the technological infrastructure (high voltage installations with grid interface as well as the control, communication and monitoring systems), the required marketing and energy trading competences are available. Due to their very fast ramping capabilities, BESS are well suitable for the participation in the primary reserve (R1) market. Compared to secondary (R2) and minutes reserves (R3) markets, the R1 market promises the largest benefits for any kind of storage. By pooling of PSP and BESS, the control aggregate can make use of the advantages of the two individual technologies: the fast ramping capability of BESS and the large autonomy of PSP. In the paper, the authors discuss different modes of aggregation of PSP and BESS for their joint participation in the R1 market. Therefore, boundary conditions of possible operation on the R1 market defined by TSOs are laid down and their implications on the PSP-battery aggregate are presented. The authors show, how an aggregation of PSP and BESS can operate. Herein, the objective is to maximise the marketable reserve capacity. The contribution is based on the implementation and commissioning experience of a 12.5 MW / 13 MWh Li-Ion BESS, which enhances the reserve capacity of the existing Pfreimd hydro power plant group in Germany.