Solar air heaters (SAHs) are among the most common devices for converting solar energy into heat, yet their thermal efficiency is often low due to the poor heat transfer characteristics between the absorber plate and the air. Artificial roughness on the absorber plate is a promising technique for enhancing heat transfer by breaking the laminar sub-layer and creating turbulence. This paper presents a comprehensive review of various roughness geometries, including V-shaped ribs, chamfered ribs, metal grit ribs, and others, focusing on their influence on Nusselt number (Nu), friction factor (f), and overall thermo-hydraulic performance. A detailed comparison of these geometries highlights their effectiveness in different operating conditions. The paper also discusses the optimization of roughness geometry to balance heat transfer enhancement and the associated pressure drop penalty. Finally, the review identifies future research opportunities to improve the performance of solar air heaters further.