Artificial roughness in the form of repeated ribs is one of the effective way of improving the performance of a solar air heater ducts. Various studies have been carried out to determine the effect of different artificial roughness geometries on heat transfer and friction characteristics in solar air heater ducts. The objective of this paper is to review various studies, in which different artificial roughness elements are used to enhance the heat transfer coefficient with little penalty of friction factor. On the basis of correlations developed by various investigators for heat transfer coefficient and friction factor, an attempt has been made to compare the thermohydraulic performance of roughened solar air heater ducts. It has been found that lot of experimental and analytical studies reported in the literature. (C) 2012 Elsevier Ltd. All rights reserved.