A review on recent development of thermal performance enhancement methods of flat plate solar water heater

The present review focusses on the recent developments in the thermo-economic performance of solar water heating systems regarding the design, modification of thermo-physical properties of heat transfer fluids, integrated thermal energy storage and hybrid systems of flat plate solar collectors (FPSC). Enhancement of design factors and convective heat transfer coefficient between the fluid and absorber tubes are the most desirable factors to improve the overall performance of solar collectors. In addition to various performance parameters, numerical heat transfer relations for the evaluation of energy/exergy efficiency enlisted to determine the performance of the different enhancement methods. At lower twist ratios of absorber flow inserts, the heat transfer enhancement achieved from 13.03% to 25.25% more than that of the larger twist ratios. The use of nanofluids increased the energy and exergy efficiency of FPSC up to 24% and 30%, respectively. The review article provides an eagle's view of the recent developments, practical techniques, economic importance, requirement of solar water heating, and barriers in utilizing solar energy for water heating applications to all the stage holders of solar energy. The hybrid solar photovoltaic/thermal system (PV/T) is a useful technology for economic benefits and higher efficiency of the heating system. The research gap and areas requiring attention are discussed towards the improvement of deployment of FPSC.