Eco-friendly functionalized MWCNT/TiO₂ hybrid nanofluids for enhanced thermal management and energy harvesting in photovoltaic systems

• Eco-functionalized CT-MWCNT/TiO₂ nanofluids for PV cooling • OHPs combined with TiO₂-coated reflectors for dual benefits • 0.2 wt% nanofluid lowered thermal resistance significantly • PV efficiency and exergy improved by over 18% • Sustainable techno-economic and environmental performance Photovoltaic (PV) performance decreases under high solar irradiance due to overheating, making effective thermal management crucial. This study experimentally evaluates a novel passive hybrid system that combines oscillating heat pipes (OHPs) for cooling with TiO₂-coated aluminum reflectors for optical concentration and self-cleaning. The working fluid is an eco-friendly hybrid nanofluid of clove-treated multi-walled carbon nanotubes (CT-MWCNTs) and TiO₂ nanoparticles dispersed in deionized water, offering high thermal conductivity, long-term stability, and surfactant-free preparation. Seven outdoor configurations were tested to separate thermal and optical effects. The 0.2 wt% CT-MWCNT/TiO₂ nanofluid significantly reduced OHP thermal resistance, while TiO₂-coated reflectors enhanced solar input and maintained optical efficiency by resisting fouling. The integrated system increased PV electrical and exergy efficiencies by over 18% compared to a reference module, with favorable techno-economic performance. Although the nanofluid introduced a slight rise in CO₂ emissions, the overall environmental impact per kWh decreased due to higher energy yield. To our knowledge, this is the first experimental demonstration of a PV–OHP system that simultaneously uses eco-functionalized CT-MWCNT/TiO₂ nanofluids and self-cleaning TiO₂-coated reflectors, offering a scalable and sustainable approach for advanced solar energy harvesting.