title: Experimental investigation of the power production cycle in a CO2 based electrothermal energy and geological storage system
Creators: name: Unger, Sebastian
name: Fogel, Stefan
name: Schütz, Peter
name: Chacartegui Ramirez, Ricardo
name: Carro, Andres
name: Farkas, Márton
name: Schmidt-Hattenberger, Cornelia
name: Hampel, Uwe
Publisher: name: DuEPublico: Duisburg-Essen Publications online, University of Duisburg-Essen, Germany
Year: 2025
Subjects: subject: transcritical CO2
subject: electrothermal energy storage system
subject: geological storage cycle
subject: experimental investigation
subject: 620

description: The European Commission aims at achieving a net-zero greenhouse gas emissions economy until 2050. For this reason, renewable electricity generation is expected to increase up to 69% by 2030. However, the intermittent nature of solar and wind power generation requires sustainable storage systems, in order to compensate for the mismatch between energy supply and demand. Large-scale thermal energy storage in combination with supercritical carbon dioxide (sCO2) power cycles is a promising solution to address this issue. The EU-project CEEGS (Novel CO2-based Electrothermal Energy and Geological Storage System) aims to develop a highly efficient, cost-effective and scalable energy storage technology. When excess renewable electricity is available, a compressor drives a heat pump cycle to increase temperature and pressure. The hot CO2 heats a hot water storage and cools down before entering an expansion turbine. The low-temperature CO2 cools a cold-water storage tank before entering the compressor. In the discharge cycle, CO2 is pumped from the geological reservoir into the surface components and gets heated by the stored thermal energy through a heat exchanger, before entering the turbine to generate electricity. The low-pressure CO2 is liquified by entering a condenser, which is cooled by the cold-water reservoir, and pumped back into the subsurface reservoir through an injection well to extract heat from the subsurface. In order to demonstrate the transcritical cycle of the CEEGS concept and to validate the surface components, a 20 kW demonstrator was designed, built and operated at the Helmholtz-Zentrum Dresden-Rossendorf. In the present contribution, the design of the facility and the operation of the discharge cycle at CO2 temperature and pressure of up to 250 °C and 235 bar will be presented and discussed. The safety and measurement concept of the facility is presented. The design of the main components, such as the high-temperature heat exchanger (HXW), the low-temperature heat exchanger (HXI) and the CO2-pump, as well as the cycle behavior are presented. The experimental results show a lower Reynolds number at higher cycle pressures, due to the more closed valve position. Particular attention is paid to the performance of the high-temperature heat exchanger in terms of overall heat transfer coefficient. Convective heat transfer on the CO2 side plays a dominant role in the thermal resistance of the heat exchanger. The thermal efficiency of the cycle during discharge is strongly influenced by the maximum cycle pressure. In fact, at higher pressures, higher cycle efficiency is achieved due to greater expansion work. The experimental results will be used by the project partners to validate the numerical models. Future experimental campaigns will investigate the dynamic operation of the facility.
description: Conference Proceedings of the European sCO2 Conference6th Edition of the European Conference on Supercritical CO2 (sCO2) for Energy Systems: April 09–11, 2025, Delft, The Netherlands, p. 306