A practical and environmentally friendly way to harness solar energy is through solar air heaters (SAHs). Various techniques to enhance heat transfer have been explored to boost the thermal efficiency of SAHs. The present experimental work examined the impact of dimpled rib coarseness on the performance of a SAH with an equilateral triangular duct. Experiments were conducted under various operating conditions, including relative roughness height (e/D) ranging from 0.023 to 0.058, relative roughness pitch (L/e) from 3 to 9, relative roughness width (S/e) from 6 to 18, and Reynolds numbers from 6000 to 18000. The improvement in Nusselt number (Nu) and friction factor ( f) over a flat surface under similar operating and flow conditions has been performed. Experimental findings showed that the SAH equipped with dimple ribs achieved higher heat transfer rates compared to traditional SAH. The maximum improvement in Nu, f is 5.78, and 2.26, respectively, greater than that of a smooth SAH. The best value of performance enhancement criteria (PEC) is 4.64 which is found at e/D of 0.058, L/e of 3, and S/e of 6. The experimental findings have been used to derive empirical correlations for Nu and f .