Performance of a photovoltaic-thermal solar collector with hollow twisted ribbon inserted in absorber tubes: A theoretical and experimental study

Photovoltaic Thermal (PVT) Solar Collector is an innovative technology that merges photovoltaic and thermal energy generation into a single device. The electrical output of PV systems suffers losses due to temperature rise, and inappropriate cooling methods lead to excessive temperature rises. The power output of conventional absorber tubes is limited due to their poor heat transfer efficiency. Absorber tube design requires optimal optimization through various improvements or advanced materials and passive perturbs to enhance heat extraction while minimizing PV system temperatures and maximizing energy generation for electricity and heating. Solution-focused improvements to this challenge will lead to the development of higher-efficiency PVT systems, achieve economic stability, and increase the adoption of hybrid solar energy. This study explores the impact of hollow twisted ribbon inserts in absorber tubes, using computational fluid dynamics (CFD) models created in ANSYS to simulate temperature variations and determine the optimum pitch ratio of the inserts. Experimental evaluations were conducted with an indoor solar simulator. Simulation results indicate that the PVT system with hollow twisted ribbon inserts maintains a lower average module temperature (47.23 °C) compared to the system without inserts (88.57 °C) at 800 W/m² and 0.04 kg/s, significantly enhancing thermal efficiency across various mass flow rates and irradiance levels. The highest energy transfer rate enhancement (30.05 %) was recorded at a pitch ratio of 0.25 and a mass flow rate of 0.06 kg/s. Experimental data show a drop in the open circuit voltage (V_oc) and an increase in the short circuit current (I_sc) at higher irradiance levels, with maximum power (P_max) ranging from 19.97 W to 20.39 W, and a mean module temperature rise to 96.21 °C, resulting in a PV efficiency decrease to 8.28 %. At 806 W/m², from 0.01 kg/s to 0.06 kg/s, the mean module temperature was reduced from 55.23 °C to 40.13 °C and increased PV efficiency from 6.97 % to 7.78 %. However, efficiency slightly declined at 0.07 kg/s, indicating optimal cooling at 0.06 kg/s.