Performance Evaluation and Optimization of a Concentrating Photovoltaic/thermal System Using Ag@Al2O3 Core-Shell Nanofluid As Spectral Splitting Medium

Spectral beam splitting technology offers a potential solution for limited solar conversion efficiency and local overheating of photovoltaic panels in centralized photovoltaic/thermal (CPV/T) system. In this work, an Ag@Al2O3 core-shell nanofluid-based spectral splitter is integrated into a thermally decoupled system equipped with a compound parabolic concentrator to address spectral mismatch and overheating in CPV/T. A numerical framework is constructed that couple finite-difference time-domain simulation for predicting the optical properties of nanoparticles, a radiative transfer model for the transmittance of nanofluids, and a three-dimensional conjugate heat transfer model coupled with photovoltaic electrical performance. With the spectral matching factor as the objective, a multi-parameter co-optimization is performed over the silver core diameter, shell thickness, particle mass fraction, and optical path length. The optimal nanofluid is selected, and its combined thermal and electrical performance is evaluated under 4 suns. Results indicate that the silver core diameter governs localized surface plasmon resonance, with absorption dominates below 40 nm, while scattering increases with rise of the diameter, accompanied by higher-order modes. The Al2O3 shell redshifts the resonance peak and provides chemical protection. Multi-parameter optimization yields an optimal design with 30 nm of silver core diameter, 5 nm shell thickness, 66 ppm mass fraction of nanofluid, and 19 mm optical path, yielding a spectral matching factor of 0.3916, achieving electrical efficiency of 12.82%, thermal efficiency of 67.76%, and total exergy efficiency of 17.76%. This work provides a systematic design framework for spectrally tunable, nanofluidbased CPV/T systems.