Experimental & numerical investigation and optimization on a novel flat-plate PV/T system using CdfTe thin-film solar modules of sandwich structure

In flat-plate PV/T systems, there are some contradictions in the temperature requirements for the heat and electricity acquisition. The widely-used crystalline-silicon solar cells are negatively affected by the high temperature inside the PV/T collector. This paper proposes to use temperature-insensitive solar cells in PV/T and the CdTe used has the advantages of low power temperature coefficient, high photovoltaic efficiency, and low costs. Besides, the sandwich structure that CdTe cells are sealed between two pieces of glass can prevent them from the permeating of moist air. The CdTe-PV/T is experimentally tested and compared with a Poly-Si-PV/T system and it exhibits better instantaneous electrical performance at high operating temperatures and gains more electrical energy throughout the day. Then the influence of cells' coverage ratio is investigated experimentally and the result shows that a higher coverage ratio is beneficial to the electrical and energy-saving performance. Furthermore, a new quasi-steady-state mathematical model is established and verified. Parametric discussions are conducted for performance optimization. The black TPT coating with higher emissivity performs better than the selective absorption coating of the absorbing plate, contrary to the traditional PV/T collector. The heat transfer mode between the back glass and the absorbing plate is different in different thicknesses of the air gap. Reducing the thickness can effectively improve the system's performance in terms of thermal, electrical, and temperature. Then an improved CdTe-PV/T eliminating the backglass and air gap is proposed and numerically simulated. This research hopes to provide some ideas for the applicant and the optimization of CdTe-PV/T in hot climates.