Recently, many studies have reported that a curved solar air heater (CSAH) performs better than a conventional flat SAH without using any extra material. It only requires geometrical modification. The present investigation is a two-dimensional numerical study of flow, heat transfer, and entropy generation characteristics of a CSAH having a sinusoidal profile absorber plate. Reynolds number (Re) and relative roughness pitch (λ/a) have been varied from 3800 to 18,000 and 7.143 to 17.857, respectively, while keeping the value of relative roughness height (a/Dh) at 0.042. The finite volume method (FVM) and SST k–ω model have been used to solve the governing equations. The average Nusselt number and average friction factor have been calculated to find the thermo-hydraulic performance parameter (THPP), which further helped determine the optimal arrangement of the number of sinusoidal waves in the absorber plate of the SAH. The maximum value of THPP developed with the proposed setup was found to be 5.9778. Turbulent flow features have been represented in the form of contours. Correlations have also been developed for Nuavg_r and favg_r as a function of Re and λ/a. Entropy generation per unit length due to heat transfer and fluid friction has been graphically represented.