In last two decades, metallic particles of nano-sizes
(~10 -9m) are tested profoundly in
volumetric absorption solar collectors (VASC) due to their excellent
optical properties and broadband absorption in entire solar spectrum.
However, availability, ease to synthesise, toxicity, and
non-biodegradable nature of these nanofluids are some of the challenges
that still needs attention of scientific community for future
commercialisation of this technology. Further, based on literature
review, very limited studies are available for understanding the
performance of integrated energy storage VASC system using nanofluids.
Considering all these issues, a hybrid nanofluid of gold nanoparticles
in Azadirachta Indica leaves extract has been synthesised by
chemical route. The prepared hybrid nanofluid has shown good absorption
in 400-700nm wavelength range and hence high photo-thermal conversion
efficiency for VASC. Further, commercial available paraffin wax is used
as phase change material (PCM) in thermal energy storage (TES) and
further integrated with VASC to analyse thermal performance of system
even after sunshine hours. The real-time experiments were conducted
using different working fluids and at three mass flow rates i.e. 0.5
lpm, 1 lpm and 2 lpm, respectively during mild
winter days under tropical climate of India. The study revealed a
photo-thermal efficiency enhancement of about 17.1% when hybrid heat
transfer fluid was used in VASC system with TES as compared to base
fluid water without TES. Further, a maximum zero loss efficiency of
83.8% was estimated at optimal mass flow rate of 2 lpm for TES
integrated VASC system.