Simplified pumped thermal energy storage using a two-way Stirling cycle

Abstract

The present work introduces a concept of pumped thermal energy storage based on the Stirling cycle. It provides a smaller sized energy storage and power conversion unit than what is typically proposed using pumped thermal energy storage systems, while offering high round-trip efficiencies despite a simple concept. Conventional systems are typically Brayton cycle based with two-tank liquid thermal storages on both the hot and the cold side. The proposed concept utilizes a single Stirling machine for both energy discharge and charge, and this is the first study where this approach is investigated. It is combined with a single-tank liquid thermal storage on the hot side and a fan and radiator combination on the cold side. Round-trip efficiencies for several storage fluids are analyzed using high-fidelity validated models, with relevant components and power losses. It is shown that round-trip efficiencies of up to 49 % at the generator are possible when using high-temperature fluids and with low-temperature synthetic fluids round-trip efficiencies of 32 % are obtained.