Nanofluids in PV and PV/T systems: A critical review of performance, stability, thermodynamics, and emerging technologies

Photovoltaic (PV) and PV–thermal (PV/T) systems are increasingly important for sustainable energy generation. However, elevated operating temperatures reduce PV electrical efficiency and affect the thermal and overall performance of these systems. Effective thermal management is therefore essential for improving electrical output in PV systems while simultaneously enhancing heat recovery in PV/T systems. This review critically examines recent developments in nanofluid-assisted cooling for PV and PV/T systems, focusing on thermal, electrical, hydraulic, thermodynamic, and techno-economic performance, as well as nanofluid stability and emerging computational technologies. Various cooling configurations, including backside cooling plates, mini- and microchannels, jet-impingement systems, heat pipes, and advanced PV/T collectors, are discussed. Recent developments involving metal oxides, carbon-based nanomaterials, MXene, hybrid, and ternary nanofluids are critically reviewed. The literature indicates that nanofluids reduce PV/PV/T operating temperatures, improve electrical efficiency, enhance useful thermal energy recovery, and improve energy and exergy performance when nanoparticle characteristics, cooling configurations, and operating conditions are properly optimized. However, these benefits may be accompanied by increased viscosity, pressure drop, pumping power, and stability-related problems. Particular attention is therefore given to nanoparticle agglomeration, sedimentation, fouling, and long-term reliability. Recent applications of computational fluid dynamics, artificial intelligence, machine learning, and optimization techniques are also examined. Although significant improvements have been reported, long-term outdoor validation, standardized testing, and comprehensive economic and environmental assessments remain limited. Future development should focus on stable, low-cost, environmentally responsible, and scalable nanofluid-based cooling technologies for practical PV and PV/T applications.