Session: 03-03 Pumped Thermal Energy Storage

Paper Number: 116672

116672 - Pumped Thermal Energy Storage as Combined Heat and Power 

Pumped thermal energy storage (PTES) systems are grid batteries that use heat pumps to create both hot and cold thermal energy stores and then convert the thermal energy into electricity. PTES systems have a lower round-trip efficiency (RTE) than Li-ion batteries, but they can add thermal energy storage (TES) duration at relatively low cost after the initial cost of the heat pump and thermo-electric cycle. As such, the literature shows that PTES can be competitive at storage durations greater than six hours while providing rotational inertia to support grid stability. An ideal-gas Brayton cycle PTES configuration nominally discharges the inefficiencies of its round-trip process as heat at temperatures useful for low-grade thermal energy consumers like district and industrial heating. The nominal configuration can be modified to reject heat at warmer temperatures with reduced RTE.

This study describes an ideal-gas Brayton cycle PTES design-point performance and cost model and quantifies trade-offs between heat rejection temperature and RTE with respect to key design-point parameters. We also present a mixed-integer linear program operations model to determine PTES charge and discharge schedules to maximize net revenue from electricity purchases and sales and optionally avoided fuel costs. Then, we use the operations model to estimate the financial potential of the concept. First, we calculate the avoided cost of using fuel to generate heat assuming that 1) PTES is operated exclusively as a grid battery, 2) the heat off-taker has a backup heat source, and 3) the off-taker can absorb all rejected PTES heat at a given time. Next, we add thermal TES to the PTES heat rejection to increase the fraction of annual heat consumption that PTES can provide and recalculate the avoided fuel costs. Finally, we modify the operations model to maximize combined revenue of grid battery and avoided fuels costs and compare the resulting operating profile, heat load, and revenue to the results from the scenarios exclusively operating the PTES as a grid-battery. We repeat these analyses for different combinations of RTE vs. heat rejection temperature.

Presenting Author: Ty Neises National Renewable Energy Laboraotry (NREL)

Presenting Author Biography: Ty is a researcher at the National Renewable Energy Laboratory. His work focuses on component and system modeling of solar thermal technologies, power cycles, and thermal energy storage. Ty also leads the development of solar thermal and thermal energy storage models in NREL's System Advisor model (SAM).