Performance enhancement methods for solar air collectors: a review of design strategies and thermal applications

Abstract Solar air collectors are widely used in solar thermal applications due to their simplicity and versatility; however, their relatively low thermal efficiency limits large-scale deployment. Although numerous enhancement techniques have been proposed, a systematic comparative evaluation of their effectiveness remains insufficient. This review aims to analyse recent studies on solar collector design strategies, including airflow pattern optimisation, absorber materials, absorber plate design, airflow channel improvements, and photovoltaic/thermal (PV/T) integration. The thermal and thermo-hydraulic performance of these approaches are comparatively evaluated, and the key mechanisms influencing thermal efficiency enhancement are clarified. The results show that structural modifications such as baffles and multi-channel designs significantly enhance heat transfer by increasing air residence time and surface area. Porous fins and optimized surface roughness improve Nusselt number and overall performance. Double-pass collectors with porous media can achieve efficiencies up to 90.8%, while integrating metal-foam phase change materials in PV/T systems yields efficiency gains exceeding 20%. The novelty of recent review lies in systematically classifying enhancement techniques, comparatively evaluating thermo-hydraulic performance across the main design categories, and identifying the key mechanisms governing efficiency improvement in solar air collectors.