A novel parabolic trough solar collector is presented, it has been built, and the impact of nanoparticles added to the collector's working fluid, heat transfer fluid (HTF) temperature and HTF flow rate on the collector thermal efficiency is evaluated in theory and practice. In the collector, a two-phase closed thermosiphon (TPCT) heat pipe composed of evaporation and condensation parts has been utilized to capture solar heat. The evaporation part with the length of 240 cm positioned in the center of the collector's reflector has been coated with selective coating and insulated from environment using twin wall evacuated glass tube. The condensation part with the length of 45 cm located inside a cylindrical manifold thermally insulated using glass wool transfers the vaporization latent heat of vapor existing inside the condensation part to HTF flowing inside the manifold, and heats it. To evaluate the impact of nanoparticles, distilled water and CuO - H2O nanofluid (mixture of distilled water and copper oxide) with the nanoparticles weight percentages of 0.5%, 1%, 1.5%, 2%, 2.5%, 3% and 3.5% have been used as eight working fluids. The novelty and contributions of this research work can be outlined as follows: For the first time, a novel characteristic of the built solar collector depicting its thermal efficiency versus the percent of nanoparticles available in its working fluid is found. Theoretical and experimental results presented in this study demonstrate that adding nanoparticles up to a specific percent to the working fluid enhances the thermal efficiency of the collector. But, adding more than that decreases the thermal efficiency. To assess the impact of HTF temperature and flow rate, the thermal efficiency of the built solar collector versus HTF temperature and flow rate obtained by point-by-point measurements are given that clearly verify associated theoretical results. A novel parabolic trough solar collector is presented and built. (C) 2019 Elsevier Ltd. All rights reserved.