Cycle Considerations for the Conceptual Design of a Pumped Heat Energy Storage System

Abstract

Grid-scale energy storage technologies that provide greater than ten hours of electricity at full power are a critical enabler for full penetration of renewables on electricity grids worldwide. These technologies minimize renewable curtailment, while maximizing grid security and reliability. Other energy storage solutions such as pumped hydro and compressed air energy have geological and geographical constraints that widespread adoption. Pumped Heat Electricity Storage (PHES) systems can store energy thermally in any location at the low costs necessary for displacing fossil fuels, reducing foreign fuel imports, and reducing emissions to maintain the energy security of the world. PHES systems operate in two modes, a charge mode in which the system operates as a heat pump to convert electricity into a thermal potential which is stored in a suitable storage media, and a discharge mode which uses a heat engine to convert the stored thermal energy to electricity. These systems offer a potential Round-Trip Efficiency (RTE) greater than 60%. This is a key parameter of interest for energy storage application systems, defined as the ratio between energy into the system to the energy retrieved. Efficient PHES system design represents a compromise between thermal storage temperatures, system configuration, machinery selection, and minimization of secondary losses. This paper examines design trades associated with turbomachinery, system pressure ratio, and storage temperatures and the impact on RTE for a recuperated full scale PHES system progressing through conceptual design, and wraps up with turbomachinery evaluation and selection and resulting cycle for a small-scale system demonstrator used for demonstrating PHES system startup and operational control.