Techno-economic and environmental assessment of nanofluid integration in different solar water heating systems

Solar collectors represent one of the most established and extensively utilized technologies for harnessing solar energy. In recent years, growing attention has been devoted to enhancing their efficiency through the incorporation of nanofluids, although significant progress in this area remains challenging. In this study, a comprehensive feasibility assessment of nanofluid integration into three commercial solar water heating systems (SWHSs), namely the flat plate solar collector (FPSC), the evacuated tube collector (ETC), and the compound parabolic collector (CPC) is conducted under the climatic conditions of Tunisia and Saudi Arabia. Simulation outcomes reveal that the incorporation of nanofluids significantly enhances the overall performance of solar water heating system, thereby shortening the payback period (PP) to approximately 4.45 years for Tunisia and 3.34 years for Saudi Arabia. The integration of nanofluids also contributed to a reduction in CO 2 emissions of up to 0.49 tons per year when used with electric auxiliary heaters. Hourly and daily analyses of system behavior confirmed stable operational performance, with collector thermal efficiencies reaching 60.62 % and a daily solar fraction exceeding 56.86 % during the coldest month at both locations. These findings demonstrate the potential of nanofluids to improve the techno-economic and environmental sustainability of solar water heating systems in diverse climatic regions.