Research background
Conventional photovoltaic-thermal (PV-T) collectors have coupled electrical and thermal outputs, limiting the temperature of the delivered thermal energy typically to < 60 °C. Concentrating PV-T (CPV-T) collector designs can reach higher temperatures, but cell overheating from similar coupling limitations reduces their electrical efficiency. Spectral splitting—dividing the solar spectrum so that only useful wavelengths reach the PV cells—promises to break this compromise, yet to go beyond previous studies and propose advanced spectral-splitting CPV-T designs capable of breakthrough performance, it is necessary to develop fully coupled optical, electrical and thermal-fluid models validated at the collector scale.

Research content
A binational team led by Imperial College London and Tecnológico de Monterrey has modelled, designed and numerically tested a parabolic-trough spectral-splitting CPV-T (SSCPV-T) collector that integrates:
• a commercial 10× parabolic concentrator (aperture 1.088 m, focal length 0.34 m);
• a triangular primary receiver with c-Si PV cells attached to its sloped faces;
• a secondary liquid filter channel placed between the mirror and the cells, and enclosed in a glass envelope that absorbs UV/IR while transmitting the 400–1100 nm waveband optimal for c-Si PV cells.
Three filter fluids for the liquid filter channel were compared: water, Therminol-66, and an AgSiO₂-ethylene-glycol (AgSiO₂-eg) nanofluid. Fully coupled 3-D ray-tracing, electrical and CFD sub-models—each validated against literature data to within 10 %—were solved in COMSOL Multiphysics 6.1.

Key results
• At an irradiance of 1000 W m⁻², a wind speed of 1 m s⁻¹, and a filter-to-primary mass flowrate ratio of 0.2, the proposed collector delivered:
– an electrical efficiency of 15 %
– an overall, maximum thermal efficiency of 45 % (primary: 30 %; filter: 15 %)
– a filter channel outlet flow temperature of 100 °C at 5 % efficiency, allowing direct steam or process-heat applications.
• Use of the AgSiO₂-eg nanofluid filter raised the filter’s thermal efficiency to ≈ 41 %—a 25 % absolute improvement over water or Therminol-66—pushing the overall thermal efficiency to ≈ 60 %, while the electrical efficiency dropped by only ≈ 5 % absolute (≈ 10 % vs 15 %), showing effective spectral decoupling.
• Parametric studies revealed a plateau in performance above a 0.24 mass flowrate ratio, beyond which pumping penalties outweigh gains.

Research significance
By developing the first fully-validated 3-D SSCPV-T collector design tool and using this to quantifying the performance of a proposed SSCPV-T collector, the study provides designers with a validated tool and a blueprint for next-generation, high-performance total-solar-utilisation cogeneration systems. The AgSiO₂-eg nanofluid configuration is particularly attractive for industrial users prioritising high-grade heat, while the water-based design remains cost-effective for medium-temperature applications. All modelling tools and optical/thermal correlations are being released open-source to accelerate commercial uptake.
DOI: 10.1007/s11708-025-1028-y