Flat plate solar collectors are widely employed in applications operating at low to moderate temperatures, including domestic water heating and various industrial uses. Their thermal performance is strongly influenced by the absorber tube, through which solar energy is transmitted to the circulating fluid. Conventional designs are often limited by low convective heat transfer, which has motivated studies on geometric enhancements to improve overall efficiency. The present work examines the thermo-hydraulic characteristics of a flat plate solar air collector fitted with twisted tape inserts having various twist ratios ($\delta$ = 3, 4, 5, 6), and compares the results with a plain tube collector. Air serves as the working fluid, and simulations were carried out over a Reynolds number range of 200–2000. A three-dimensional CFD approach was employed to study critical performance characteristics, including outlet temperature, Nusselt number, friction factor, pumping power, and thermal efficiency. The results show that twisted tape collector (TTC) provide considerably greater heat transfer compared to the plain collector (PC). At Re = 1000, the Nusselt number enhancement reached 35.19%, 44.55%, 50.15%, and 54.96% for twist ratios $\delta$ = 6, 5, 4, and 3, respectively. Although this improvement is associated with increased pressure drops, the findings confirm that twisted tape inserts substantially enhance the heat transfer effectiveness of solar collectors by promoting turbulence and better fluid mixing.