The paper presents results of an experimental study of thermo-hydraulic performance of a solar air heater with 60 degrees v-down discrete rib roughness on the airflow side of the absorber plate along with that for a smooth duct air heater. The enhancement in the thermal efficiency due to the roughness on the absorber plate is found to be 12.5-20% depending on the airflow rate; higher enhancement is at the lower flow rate. The experimental data have been generated and utilized to validate a mathematical model, which can be utilized for design and prediction of performance of both smooth and roughened air heaters under different operating conditions. The results of a detailed thermo-hydraulic performance study of solar air heater with v-down discrete rib roughness using the mathematical model are also presented along with the effect of variation of various parameters on the performance. (C) 2013 Elsevier Ltd. All rights reserved.