Artificially roughened solar air heaters perform better than the plane ones under the same operating conditions. However, artificial roughness leads to even more fluid pressure thereby increasing the pumping power. The entropy generation in the duct of solar air heater having repeated transverse chamfered rib-groove roughness on one broad wall is studied numerically. Roughness parameters, viz., relative roughness pitch P/e, relative roughness height e/D(h) relative groove position g/P, chamfer angle phi and flow Reynolds number Re have a combined effect on the heat transfer as well as fluid friction. The entropy generation is minimized and reasonably optimized designs of roughness are found. (c) 2006 Elsevier Ltd. All rights reserved.