Photo-Thermal Conversion Analysis of a Medium-Flux Direct Absorption Solar System Using Gold Nanoparticles With Natural Extract of Azadirachta Indica

Recently, direct absorption solar collector (DASC) system has emerged a new class of solar collectors with much improved solar thermal conversion potential over conventional surface-based absorption solar collectors. Further, introducing noble metallic particles like Ag, Au, Al, TiN, or Cu (at nano ranges) in the working fluids enhanced the optical properties of the working fluid and hence the overall thermal performance of such DASC systems. However, these novel thermal systems are prone to high emissive and radiative losses at high-temperature ranges. Additionally, the nanoparticles used in the working fluid are expensive, toxic after use, complex to synthesize, and mostly non-biodegradable. In the present study, a medium-flux asymmetric compound parabolic concentrator (ACPC) based concentrating DASC system has been tested over clear sky days in the months of September and October, 2022 at the composite climate of Jalandhar (latitude 31.25 deg N, longitude 75.44 deg E), India. A hybrid heat transfer fluid is prepared using Azadirachta Indica leaves' extract and blended with gold plasmonic nanoparticles (Au nanoparticles of mean sizes similar to 40 nm, mass fraction similar to 4 ppm) to improve the overall thermal performance of the concentrating DASC system. Stored energy fraction of hybrid heat transfer fluid at a depth of 2 cm reached about 74.9%, which is about 67% higher than base fluid water. The outdoor experiments showed that hybrid heat transfer fluid had about 10.4 degrees C higher temperature gains in concentrating DASC system, and the photo-thermal efficiency was enhanced up to 40% as compared to base fluid water. The study demonstrates the advantage of an eco-friendly, low cost, and highly stable hybrid heat transfer fluid as a potential candidate for a medium-flux DASC system.