Low-temperature compressed air energy storage with reversibly operable turbo- and piston machines

Adiabatic compressed air energy storage (A-CAES) is a promising storage technology to face the challenges of high shares of renewable energies in an energy system by storing electric energy for periods of several hours up to weeks. In order to reduce the investment costs and increase the flexibility of the storage system, the so called KompEx LTA-CAES® was developed by Fraunhofer UMSICHT. This new A-CAES concept is using a combination of reversibly operable turbo- and piston machines (KompEx machines). Doing so, these modules can achieve wide CAS pressure ranges (corresponding to high exergy densities) and thus can be combined with any compressed air storage volume. To realize efficient and stable operation despite a wide pressure range, a suitable control strategy of both KompEx machines is required. This paper investigates the introduced A-CAES system by a dynamic simulation, focusing on the interaction and synergy between the reversibly operable turbo- and piston machines. Results indicate that the roundtrip efficiency of this system is expected to be at the low end (55,5%) of literature values for A-CAES (52-66% for low-temperature A-CAES), which is relatively high compared to published A-CAES systems considering similar pressure ranges.