The impact of PVP surfactant on the stability, rheological properties and performance of nanofluids for photovoltaic thermal applications: A review

Photovoltaic thermal (PV/T) systems can improve solar energy utilization by simultaneously recovering heat and maintaining photovoltaic electrical output. Nanofluids are promising PV/T coolants due to their enhanced thermal and optical properties. However, their practical application remains limited by agglomeration, sedimentation and long-term colloidal instability. Surfactants are commonly used to improve dispersion, but insufficient dosage may provide inadequate stabilization, whereas excessive addition can increase viscosity, interfacial thermal resistance and pumping requirements. Among available surfactants, polyvinylpyrrolidone (PVP) is attractive because its non-ionic polymeric structure provides steric stabilization across different nanoparticle classes. Nevertheless, the relationship between PVP formulation, nanofluid properties and actual PV/T system performance remains insufficiently established. This structured review evaluates PVP-stabilized nanofluids using a PRISMA-guided literature-selection process and evidence-based synthesis. The database search identified 1874 records, with 641 duplicates removed and 1233 unique records screened. The updated evidence total includes 79 relevant publications. The findings show that PVP performance is strongly formulation-dependent, with excessive concentration or molecular weight potentially compromising thermal and hydraulic performance despite improved stability. Importantly, only two studies directly evaluated PVP-stabilized nanofluids in complete experimental PV/T systems, highlighting a major gap between formulation-level evidence and system-level validation. This review therefore proposes an integrated evaluation framework linking colloidal stability, thermal, rheological, hydraulic, energy and exergy performance, together with a minimum reporting set and staged research roadmap for future PV/T studies. Overall, PVP should be optimized as a PV/T system-design variable rather than treated solely as a dispersion additive.