During the second reporting period, the SUNSON consortium advanced significantly in the development of its innovative high-temperature solar-to-electricity system, progressing through key technical and scientific milestones across the different Work Packages.
WP2 focused on developing the SUNSON-Tool, a digital decision support system that integrates physical and mathematical models of the SUNSON-Box components. The team completed multiphysical modelling of solar optics, thermal energy storage, and TPV conversion, and integrated machine learning algorithms for short- and long-term solar radiation forecasting. A multidisciplinary design optimization (MDO) module was also implemented, enabling flexible system simulations tailored to various energy demand scenarios and supporting future scale-up analysis.
WP3 addressed the solar-to-heat conversion and thermal energy storage subsystems. The modular beam-splitting optics were fully designed to generate four equal focal points for improved flux distribution in beam-down CSP configurations, and their fabrication is underway. For the thermal storage system, two Fe-Si alloy PCMs were finalized, both demonstrating high latent heat capacities (>1 MWh/m³). Crucibles made of graphite with h-BN coatings were successfully tested through 100 thermal cycles between 1100 °C and 1300 °C, showing excellent thermal and chemical stability.
WP4 focused on developing the thermophotovoltaic (TPV) generator. Thin film InGaAs TPV cells achieved 25% conversion efficiency at 1704 °C and power densities of 3–4 W/cm² at 1797 °C. However, yields remained low due to wafer size constraints. A key mitigation step involved switching to 4-inch epitaxial wafers, significantly improving yields. Integration of InGaAs TPV cells has begun, and module assembly techniques are under development.
WP5 made progress toward assembling the SUNSON-Box prototype, a highly compact and modular CSP system. The detailed mechanical and thermal design integrates a solar absorber, PCM crucible, and TPV converter within a structure optimized for thermal efficiency and operational flexibility. The prototype supports four distinct operating modes (including charge, discharge, and storage) via mechanical decoupling. Manufacturing of components is ongoing, and integration at the PSA Solar Furnace is being prepared. A dedicated movable rig and support infrastructure (e.g. argon flushing, water cooling, remote control) have been planned to facilitate full-system demonstration under concentrated solar input.
WP6 supported the technical development with ongoing sustainability and techno-economic assessments. Life Cycle Inventory (LCI) data for all subsystems were compiled, and the initial Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) evaluations were completed at TRL4. Energy and exergy analyses have been updated to reflect the latest system configurations. These results are helping guide design improvements and inform the cost-effectiveness and emissions reduction potential of the SUNSON innovations.
