Session: 30-10 Systems 2

Paper Number: 122133

122133 - The sCO2 Facility CARBOSOLA: Design, Purpose and Use for Investigating Geological Energy Storage Cycles 

Renewable energy sources are the major pathway to reduce the carbon dioxide emission in the energy sector. However, the fluctuating electricity generation of solar or wind power plants encounter mismatches between energy generation and demand as well as possible grid instability issues. For that reason, large-scale thermal energy storage (TES) systems are one of the promising solutions to overcome these issues and to allow the operation of a sustainable and reliable energy system based on renewable energy sources. A TES system converts electrical energy into thermal energy during power surplus. The thermal energy is stored and reconverted to electricity during power demand by a supercritical carbon dioxide (sCO2) power cycle. TES has many advantages, such as simplicity, low cost and reliability over alternative storage technologies. The sCO2 power cycles on the other hand offer a variety of advantages, such as a high conversion efficiency, a compact turbomachinery and a temperature glide that fits well with sensible thermal energy storages.

To further develop and assess this approach, the EU-project CEEGS (CO2 based electrothermal energy and geological storage system) deals with the development of a high-efficient, cost-effective and scalable energy storage technology. Here, transcritical CO2 cycles are integrated with underground energy storage to achieve, simultaneously, long-term CO2 sequestration and, potentially, geothermal heat extraction. During periods of excess electricity generation, the charging cycle is in operation. Here, CO2 is received from a stationary source and an electric motor drives a compressor of a heat pump system to increase the CO2 pressure from approximately 35 bar to 200 bar, while increasing the temperature from approximately 15 °C to 150 °C. The sCO2 heats up a hot-water storage while reducing its temperature to approximately 45 °C before entering an expansion turbine During the expansion the temperature and pressure are reduced to 0°C and 35 bar, and is injected in supercritical state into a geological reservoir, at more than 1 km depth. Within the reservoir, the CO2 will equilibrate with the reservoir temperature, extracting some heat. Afterwards, the CO2 cools a cold-water storage, while increasing the temperature to approximately 15 °C. The resulting Carnot Battery closes the loop with CO2 underground injection. During periods of net electricity demand from the grid, the discharging cycle is in operation. Thereby, CO2 is back-produced from the geological reservoir through the same well and is pumped through a heat exchanger, while increasing the pressure of approximately 55 bar to 190 bar. In the heat exchanger the stored thermal energy from the hot-water storage is used to evaporate and heat the CO2 up to 140 °C. The high-pressure CO2 drives a turbine to generate electricity and the pressure reduces to 55 bar. The low-pressure CO2 flows through a condenser, to be cooled and liquified down to 10 °C by the cold-water storage, before entering the pump and is reinjected in liquid state in geological reservoir through a second injection well.

The development of a proof of concept, TRL4, based on the integration of models for system, components and energy system integration, a lab demonstration on a 200 kW power scale was set up at the Helmholtz-Centre Dresden-Rossendorf. Thus, the authors will present the design of the components and the facility as well as first results from operating the cycle. Special attention is paid to the challenges during design and commissioning as well as dynamic behavior of the facility.

Presenting Author: Sebastian Unger Helmholtz-Zentrum Dresden-Rossendorf (HZDR)

Presenting Author Biography: Dr.-Ing. Sebastian Unger

- Degree in engineering - specializing in energy technology; 2014
- Qualification as International Welding Engineer; 2015
- Research assistant at Dresden University of Technology; 2015 - 2018
- Research assistant at Helmholtz-Zentrum Dresden-Rossendorf (HZDR); 2018 - 2021
- PhD/Dr.-Ing. in Energy technology and heat transfer; 2021
- Group leader/Head of Thermal Energy Technology; since 2021

Authors:

Sebastian Unger Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
Stefan Fogel Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
Peter Schütz Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
Ricardo Chacartegui Ramirez Universidad de Sevilla
Andres Carro Universidad de Sevilla
Julio Carneiro Converge! Lda
Uwe Hampel Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden University of Technology