The article deals with the performance of an absorber tube along with thermal performance enhancer of a flat plate solar water heater. The objective of the present work is to augment the convective heat transfer coefficient by increasing the effective area of flow between the heat transfer liquid and the contact surface with a negligible increase in pumping power. The present study involves modeling of the flat plate solar water heater with validation by experimental results. Two geometrical profiles namely rectangular and square internal fins were used as thermal performance enhancers in this investigation. The thermal performance enhancer is engaged frictionally with the absorber tube and it is kept parallel to the heat transfer fluid flow path. The performance factors are analyzed, and the results show that rectangular thermal performance enhancer gives more energy and exergy efficiency when compared with square thermal performance enhancer with an augmentation in the convective heat transfer coefficient with the minimum rise in pumping power. The rectangular thermal performance enhancer has the lowest entropy generation and exergy destruction as compared to the smooth tube and square thermal performance enhancer. The impact of economic and environmental for different heat transfer liquid inlet temperature is presented. The rectangular thermal performance enhancer has a low simple payback period and energy payback time compared to the smooth tube and square thermal performance enhancer. © 2019 Elsevier Ltd