This study introduces a modified finned plate solar air heater (FPSAH) combined with a low-cost smart-switchable cover (SSC) for constant outlet hot air temperature. The SSC is adapted as a sun blackout shield cover with a controllable curtain roller blind which is flexible to automatically and partially shade the glazing coverage. The main objective is to manage the falling solar energy transmitted through the glazing coverage to permanently facilitate a constant outlet hot air temperature throughout the daytime. The FPSAH-SSC is studied through CFD simulations under solar irradiation values changing from 600 to 1000 W/m2 at a constant airflow rate of 0.60 kg/min. A series of simulations is performed to determine the optimal shading length of the SSC corresponding to each solar irradiation value to provide a constant outlet hot air temperature of 50 °C. Moreover, thermo-economic analyses are conducted on the proposed system to evaluate the heating power, outlet hot air temperature, average Nusselt number, energy efficiency, and cost of 1.0 kW of thermal heat. The results show that the optimal shading lengths, corresponding to solar irradiation of 600, 700, 800, 900, and 1000 W/m2, are determined to be 0.0, 4.0, 20, 30, and 40 cm, respectively. This in consequence results in a controlled outlet hot air temperature from the proposed FPSAH-SSC of 48.08, 49.85, 49.83, 50.11, and 49.84 ° °C, capable of decreasing the hot air temperatures by 8.95 %, 14.57 %, 18.7 %, and 24.44 %, respectively, compared to the case without using an SSC. Moreover, the energy efficiency reaches up to 40.62 %, while the cost of 1 kW of thermal heat is estimated at 0.0098 $/kWh, respectively. © 2025 The Authors

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