The influence of frequency containment reserve on the efficiency of a hybrid stationary large-scale storage system

Abstract

Large-scale battery storage systems are predestined for balancing the fluctuating feed-in from renewable energies and supporting the electricity grid due to their high efficiency. As a result, large-scale storage has gained importance in the market for frequency support reserve (FCR). While the first LSS projects had to be planned without operational experience a couple of years ago, new LSS can benefit from the evaluation of measured field data. Especially the real-word efficiencies are key information for electricity procuring costs and arbitrage trading. To contribute filling this information gap, this paper investigates the efficiency of the hybrid LSS, its transformers, its inverters, the individual battery technologies (two types of lead-acid and three types of lithium-ion batteries) and the influence of FCR provision on efficiency. High-resolution field measurements of the hybrid 6 MW/7.5 MWh battery storage system “M5BAT” at the FCR market over several years serve as the basis. The data-based efficiency analysis reveals a high round-trip efficiency of 72.8% (with self-consumption: 66.2%) for the LSS in operation. In this context, the lithium-ion batteries have a higher round-trip efficiency of 97.4% than the lead-acid batteries with 85%. Low load on the transformers and the inverters leads to an average power-weighted power efficiency of less than 95%. The results presented can be used to model LSS and its various system components and battery technologies in order to further analyse the participation in chosen energy markets.