Solar hybrid sulphur cycle demonstration plant (Part A): Techno-economic assessment of solar thermal plant from the European Union-HySelect project

The Hybrid Sulphur (HyS) cycle is attracting interest for decarbonising the sulphuric acid industry by integrating concentrating solar thermal (CST) technologies with the high-temperature acid splitting process. Several energy and cost studies have been performed and significant European Union (EU)-funded research projects have been implemented so far to bridge the gap towards the commercialisation of the HyS concept. However, even the concept development at the demonstration plant scale has not yet been achieved. Within the EU-HySelect project, this study presents the first demonstration-scale techno-economic assessment of the HyS plant’s solar thermal and thermochemical subsystems, utilising a detailed component-level costing approach to advance the Technology Readiness Level. The specific energy of solar SO 2 production (at purity of 79.4 wt%, compressed at 1.3 MPa) and the total solar demonstration plant costs are calculated based on Aspen Plus at 15.62 MJ/kg (or 4.34 kWh/kg) and 3.4–6.1 million € 2025 , respectively. Unlike idealised models that ignore industrial constraints, this study aligns with practical standards to realistically assess implementation potential. It identifies critical bottlenecks in CST technology and the sulphuric acid splitting reactor, highlighting key pathways for scale-up. The reported cost estimates further establish a concrete baseline for future HyS research and industrial decarbonisation strategies.