Nanofluids are embryonic fluids and promising thermal energy carrier in solar thermal applications due to their superior thermo-physical and optical properties. In present communication, an analytical expression of the characteristic equation of two different systems viz. (A) active double slope solar still coupled with series connected partially covered N photovoltaic thermal flat plate collectors (N-PVT-FPC) and operating without helical heat exchanger; and (B) active double slope solar still coupled with series connected partially covered N-PVT-FPC and operating with helical heat exchanger has been developed. Analysis has been executed for 0.25% concentration of CuO, Al2O3, TiO2-metallic nanoparticles; four number of collectors; 100 kg basin fluid (BF/NF) mass and 0.03 kg/s mass flow rate. The maximum values of instantaneous gain thermal energy efficiency (CuO 80.18%;Al2O3 71.67%; TiO2 74.92%) and instantaneous loss thermal energy efficiency (CuO 64.12%;Al2O3 59.11%; TiO2 64.77%) of the system (A) are found to be significantly higher in comparison the basefluid (gain 66.81%; loss 52.42%). The productivity of system (A) and system (B) are (CuO 32%; Al2O3 19.23%; TiO2 6.47%) and (CuO 31.49%; Al2O3 26.4%; TiO2 7.26%) respectively, higher in comparison to the case using basefluid (water). Moreover, thermal energy and exergy; and thermal exergy efficiency has been evaluated for both the systems. (C) 2016 Elsevier Ltd. All rights reserved.