Experimental investigation of thermal and electrical performance of a concentrating photovoltaic thermal system enhanced with optical filter integration

Silicon-based photovoltaic (PV) cells can only convert solar radiation within the wavelength range of 370 nm to 1180 nm into electrical energy. Radiation outside this wavelength range, especially the thermal components in the infrared region, causes excessive heating on the PV surface, leading to a decrease in cell efficiency, shortening the long-term cell lifespan, and negatively affecting the overall system performance. In PV-T and CPVT systems, cooling fluids integrated into the rear surface of the PV are used to mitigate this problem by reducing the thermal load. However, this method can create thermal stress in PV cells, leading to micro-cracks and potentially reducing long-term cell durability. The alternative approach proposed in this study is the optical filtering of incoming solar radiation before it reaches the PV surface, a method known as spectral splitting. In this method, beneficial radiation corresponding to the spectral response range of the PV cells is directly transmitted to the cell through a transparent optical medium, while heat-generating thermal components are absorbed by the thermal part of the system, enabling heat recovery. This reduces the PV cell temperature and increases both electrical and thermal efficiency. In this study, a novel non-imaging concentrator structure and a CPVT system with an integrated optical filter channel are designed, and their performance is evaluated experimentally. Non-imaging concentrators offer advantages such as wide acceptance angles, the ability to collect both direct and diffuse solar radiation, no requirement for tracking systems, and uniform radiation distribution. In this respect, the system offers a simpler, lower-cost, and more applicable solution compared to traditional parabolic trough or Fresnel-type concentrators. In the proposed system, fluids will be tested through a unique optical filter channel integrated into the PV surface; the optical transmittance and thermophysical properties of these fluids will be optimized according to the spectral sensitivity of the PV cells. The aim is not only to achieve high efficiency but also to identify low-cost and field-applicable system components. The study consists of four main steps: design of the concentrating PV/T system and the optical filter channel with ray-tracing analyses and determination of their optical-thermal properties, fabrication of the experimental system, and performance evaluation under real solar irradiation in an outdoor environment.