Session: Poster Session

Paper Number: 162804

Fundamental Thermodynamic Insights on Compressor Train Design for Indirect-Heating Solar D-Caes 

The decarbonisation of the energy sector increasingly depends on renewable energy sources (RES) such as photovoltaics and wind due to their environmental and economic advantages. However, the intermittency of these sources poses challenges to grid stability, particularly with the rising electricity demand driven by the electrification of industries and mobility. This is aggravated by the limited capacity of the existing infrastructures to transport and distribute electricity, hence the lack of capacity to manage the massive amount of electricity foreseen to be produced during dayhours. To address these issues, energy storage solutions capable of managing excess electricity are essential.

Compressed Air Energy Storage (CAES) is a promising solution that stores energy (exergy) as high-pressure air. Excess electricity drives a compressor train, storing compressed air in underground caverns or above-ground tanks. The stored energy is later recovered by discharging the air through an expander train to provide electricity back to the grid. Despite a round-trip efficiency (RTE) below 100%, CAES leverages price differences in the energy market to remain economically viable.

This study evaluates the ASTERIx-CAESar concept using a fundamental thermodynamic approach focused on exergy analysis. It specifically examines how compressor train design affects the plant's RTE. The compressor train converts electrical energy into two forms of exergy: mechanical (pressure-related) and thermal (temperature-related). The balance between these forms depends on factors such as the number of compression stages with intercooling (approaching isothermal behaviour), the final storage pressure, and the polytropic efficiency.

Efficiently recovering thermal exergy is crucial to maximising system performance. This exergy is preserved only if it can be effectively captured and stored in a low-temperature thermal energy storage (LT-TES) unit. Failure to do so significantly reduces the overall RTE. Unlike commercial diabatic CAES (D-CAES) concepts, which rely on direct-firing with natural gas, the ASTERIx-CAESar concept employs indirect heating using solar-heated air streams. However, using thermal energy from the compressor train to preheat air discharged from the compressed air storage (CAS) unit introduces trade-offs, as it may limit the effective use of high-temperature thermal energy storage (HT-TES). These competing thermal interactions are analysed to identify optimal configurations.

Additionally, the study explores the potential of recovering lost exergy by converting it into electricity using an Organic Rankine Cycle (ORC). This additional recovery pathway offers an opportunity to further enhance system efficiency.

This analysis aims to inform the design of the compressor train for indirect-heating solar D-CAES systems. By applying a methodology based on fundamental thermodynamics that incorporates irreversibilities across system components, the study seeks to maximise exergy utilisation to improve overall system performance.

Presenting Author: Pablo Rodríguez-Dearriba University of Seville

Presenting Author Biography: Pablo Rodríguez de Arriba is a PhD student in Energy Engineering at the University of Seville. His thesis focuses on the techno-economic optimisation and integration of innovative CO2-based technology for Concentrated Solar Power applications. His research activity focuses on unconventional working fluids, renewable energies, ORC, WHR and economic evaluations.

Authors:

Pablo Rodríguez-Dearriba University of Seville
María-Dolores Quirós-Gotarredona University of Seville
Francesco Crespi University of Seville
David Sánchez University of Seville