Abstract A roughened solar air heater is developed numerically and experimentally with a novel roughness in the absorber. The roughness incorporated is a combination of rectangular and semi-circular ribs. The analysis is done to improve the thermal characteristics, considering two cases. Type A has ribs placed above the absorber, and Type B has ribs placed below it. Several operating parameters are investigated, including heat flux, Reynolds number (Re), relative obstacle relative height (h/H), ranging from 400–1000 W/m2, 4000–10000, and 0.4–1.0, respectively. The relative pitch is kept constant at 15 mm. The governing equations are simulated employing the RNG-k turbulence flow model. The results indicated that both Type A and Type B achieved significant improvements over the smooth duct. Type A exhibited a maximum Nusselt number of 4.24, while Type B achieved 3.93 in comparison with smooth ducts at Re of 10000, respectively. The thermal enhancement factor (TEF) ranges from 1.32 to 1.79 for Type A and 1.26 to 1.69 for Type B at a heat flux intensity of 1000 W/m2. Also at a relative height of 1.0, Type A demonstrated the highest TEF of 1.79 at Re = 10000 and provided a maximum exercise efficiency of 11.2%.