Green synthesizing carbon-based hybrid nanofluids has the potential to drive innovation in both renewable energy technologies and nanomaterial applications. In this regard, the current experimental work focuses on enhancing the thermal performance of flat-plate solar collectors (FPSCs) using working fluids made of nanocomposite materials via an eco-friendly technique (clove). Conventional methods of synthesizing nanofluids frequently involve using hazardous chemicals, raising concerns about the environment and human health. This experimental work examined the energy efficiency, exergy efficiency, and hydrothermal performance of FPSC using clove-treated carbon nanotubes/titanium dioxide (CT-MWCNTs/TiO2) nanocomposites by the ratio of (60 to 40 ) dispersed in distilled water (DW). The test conditions were in the following ranges: hybrid nanofluid in different weight concentrations (0.025, 0.05, 0.075, and 0.1 wt), different flow rates (0.3, 0.6, 0.9, and 1.2 L/min), heat flux intensities (400, 600, 800, and 1000 W/m2) and inlet temperature (30, 35, 40, 45 °C). The experimental results revealed that, the maximum enhancement in the energy efficiency (20.6 ) and exergy efficiency (22.9 ) were achieved at 0.1 wt and 1.2 L/min, relative to the base fluid. In addition, the solar collector size was reduced by 20.5 due to using a hybrid nanofluid. To conclude, the hybrid nanofluid outperformed the mono nanofluids regarding overall thermal evaluations. The novel hybrid nanofluids generally showed promising results for managing and conserving energy applications. © 2024 Elsevier Ltd