Hybrid solar collectors based on Bragg-mirror spectral splitting for simultaneous heat and electricity generation

• Spectral-splitting PVT collectors enable electricity and heat co-generation. • A dielectric Bragg mirror separates solar spectrum for dual energy harvesting. • Thermal absorber reaches 209.1 °C and solar cell is only 36.6 °C. • Bragg-mirror spectral splitting enables effective thermal-electrical decoupling. Spectral-splitting photovoltaic-thermal (PVT) solar collectors offer a pathway for simultaneous electricity and high-temperature heat generation from solar energy. In this study, we experimentally investigate a PVT solar collector incorporating a dielectric Bragg mirror as a spectral-splitting optical reflector. The solar collector spectrally separates the solar spectrum by reflecting part of the spectrum (< 870 nm) to a concentrated gallium arsenide (GaAs) photovoltaic cell and transmitting the rest of the spectrum (> 870 nm) to a solar thermal absorber. The resulting spectrum splitting achieves a reflectance of 91.4 % above the GaAs bandgap and a transmittance of 79.7 % below it. Under concentrated illumination (geometric factor of 100) and based on the total incident solar energy (full-spectrum performance), the GaAs cell has an electrical efficiency of 6.5 % operating at 36.6 °C, while the solar thermal absorber achieves a thermal capture efficiency of 8.8 % at 80 °C. The stagnation temperature of the solar thermal absorber, measured experimentally without heat extraction, reaches 209.1 °C. Both electrical and thermal efficiencies remain limited, primarily due to optical losses arising from misalignment and interference-related reflection losses. The Bragg mirror exhibits negligible absorption and self-heating, confirming its suitability for spectral splitting under concentrated illumination. While such optical losses remain challenges for both the indoor prototype and potential outdoor implementations, this work highlights a strategy for enhancing hybrid solar energy utilisation.