4E performance evaluation and optimization of a photothermal system to utilize full-spectrum solar energy

The paper presents a solar thermal system that harnesses full-spectrum solar energy by guiding visible wavelengths through optical fibers for illumination and converting nonvisible wavelengths into recoverable heat. A 4E analysis method (including energy efficiency, exergy, environmental, and economic aspects) is proposed, combining experimental measurements with numerical simulations to assess performance. Experimental results show average thermal efficiencies of 40.6 % in summer and 35.6 % in autumn, with corresponding electrical efficiencies of 24.2 % and 11.3 %. Thermal efficiency and overall energy efficiency of the system decline as airflow rate increases, whereas electrical efficiency remains constant.Meeting a 400 lux requirement, the system saves 127 kWh of electricity and reduces CO2 emissions by 293 kg annually. Economic analysis shows unit lighting cost reductions of 50.2 % versus focused fiber illumination and 42.3 % versus fiber-PV hybrids. CFD simulations indicate that adding straight-channel fins (up to 4.7 cm) raises inlet–outlet temperature differences by up to 8.32 °C and achieves a peak Nusselt number of 87.9, though gains diminish at higher airflow rate. These findings demonstrate the system's potential for energy-efficient, cost-effective, and low-carbon building lighting and heating applications.