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.