TPPS: Modeling and Simulation of a Thermal Pumped Piston Storage within a Renewable Energy Supply System

Partners from TH Nürnberg: Prof. R. Schmidt-Vollus, Prof. M. Popp, M.Sc. D. Häuslein

In this reseach project a simulation model of a novel thermal pumped piston storage (TPPS) concept is developed. The TPPS is implemented within a scalable, weather-dependent, renewable energy supply system. TPPS combines potential energy storage (PES) and hot water storage (HWS) in one subsurface structure to address the challenges posed by the dunkelflaute in the power grid and the seasonal storage demands in a heat network. To investigate the storage performance in this context, a TPPS simulation model was developed, which considers the dominant processes, such as conductive and convective heat transport in the water body, displacement of the water by the moving piston, heat conduction in the piston and surrounding soil as well as thermal losses to the ambient air. Based on hourly region-specific (Central Europe) real data from 2016 to 2019 for renewable energy production and electrical consumption, optimal dimensions of grid elements are identified to minimize the required storage capacity. The scaled wind and solar power supply serve for sizing the PES and determining the amount of water in the TPPS and, thus, the heat capacity for the HWS. Depending on the residual power, the PES varies between the fully charged (top) and empty (bottom) state. The required charging or discharging water mass flow for the HWS is calculated from the solar thermal energy, heat consumption and the surplus electrical power.

A broad numerical simulation study yields the evolution of piston’s position and the spatial temperature distribution in storage and surrounding soil over time. The varied parameters cover supply area size, geometry ratios and solar thermal area. Based on these results, the time courses of electrical and thermal states of charge are derived and analyzed in detail. The simulation results demonstrate that TPPS enables the reliable supply of solely renewable energy, both for electrical power as well as heat demand.