Artificially roughened solar air heaters have been analysed (Prasad and Saini, 1988) for fully developed turbulent flow and found to perform better both quantitatively and qualitatively compared to the smooth ones under the same operating conditions. Optimal thermo-hydraulic performance of such solar air heaters has been analysed (Prasad and Saini, 1991) and investigated (Prasad and Verma, 2000) for the maximum heat transfer and minimum pressure drop. This paper represents the experimental results on heat transfer and thereby thermal performance of artificially roughened solar air heaters for fully developed turbulent flow data collected under actual outdoor conditions. Such solar air heaters have been found to give considerably high value of collector heat removal factor (F-R), collector efficiency factor (F) and thermal efficiency (eta th) as compared to the corresponding values of those of smooth collectors. In the range of the operating parameters investigated, the ratio of the respective values of the parameters F-R, F' and eta th for the roughened collectors to the smooth collectors have been found to be 1.786, 1.806 and 1.842 respectively. (C) 2013 Elsevier Ltd. All rights reserved.