Thermodynamic Design of a Pumped Thermal Energy Storage

Abstract

With regard to large-scale electricity storage systems, the concept of Pumped Thermal Energy Storage systems (PTES) has emerged in the last years. PTES systems store electrical energy in the form of thermal energy, which is later reconverted to electrical energy. Unlike pumped hydro power or compressed air energy storage, this technology allows for a site-independent installation. Compared to batteries, the durability is expected to be higher. The considered PTES system consists of a heat pump, a thermal storage system and an Organic Rankine Cycle. So far, comparable systems were mainly investigated at temperature levels below 160 ◦C using standard cycles. In this work, a pumped thermal energy storage system is investigated at significantly higher storage temperatures of 194 ◦C and 306 ◦C. After the selection of compatible working fluids and storage materials, cycle enhancements are applied to the heat pump and heat engine. A parameter variation and an exergy analysis identify the crucial components and losses. Besides the application as a pure electricity storage, the options of heat integration and extraction are considered. It could be shown that higher storage temperatures lead in general to a higher electric storage efficiency. At a storage temperature of 194 ◦C, power to power efficiencies of 59.3 % are possible when employing efficient machinery and heat exchangers. At even higher temperatures of 306 ◦C, the efficiency could not be further increased due to the lack of suitable working fluids. All simulations were conducted in EBSILON®