A novel energy storage system that produces both electricity and heat at high efficiencies and takes advantage of a high temperature hot rock cavern thermal energy storage was recently introduced and designed. This study aims at evaluating the performance of the system in terms of energy and exergy efficiencies under realistic operational conditions where the storage supports a number of wind turbines over a long period. The potential value creation of the energy storage system in the local electricity and heat markets is also assessed. The Western part of Denmark with its high number of wind turbine plants and flexible electricity and heat markets have been chosen for the case study of this work. Having both forecasted and realized wind power generation as well as energy prices for the recent years, the system is designed with rigor and a smart bid strategy for the power plant equipped with the energy storage unit for day-ahead and intra-day markets is determined. The results show that the system is able to compensate the fluctuations of wind power plants, and present high annual overall energy and electricity efficiencies of 80.2% and 31.4% and exergy efficiency of 56.1%.
