Experimental thermal performance investigation of a direct absorption solar collector using hybrid nanofluid of gold nanoparticles with natural extract of Azadirachta Indica leaves

In the last decade, direct absorption solar collector has shown tremendous potential in improving the efficiency of solar water heaters by incorporating nanoparticles. Moreover, plasmonic nanoparticles laden nanofluids have shown high absorption in the visible region due to localized surface plasmon resonance (LSPR). However, these plasmonic nanoparticles are associated with high cost, complex preparation processes, and environmental degradation over prolonged use. To overcome such issues, a hybrid nanofluid based on gold nanoparticles in Azadirachta Indica leaves extract was prepared and tested in real outdoor conditions for the very first time. The absorbance curve of the prepared hybrid nanofluid showed broadband absorption from visible to near infrared spectrum. The maximum temperature gain of about 20 °C was observed with just 2 h of sun exposure and maximum photo–thermal efficiency reached nearly 62%, which is about 12% higher than base fluid i.e. water. Further, the prepared samples were found to be highly stable without any sign of sedimentation or agglomeration under repeated sun exposure for several hours. The study results show a new class of nanofluids that can be used for attaining high thermal conversion efficiency, which are more stable and eco-friendly for such novel solar thermal technologies.