Thermal analysis of solar absorption heating system is considered and the influence of absorbing plate location on the performance characteristics is examined. The study is extended to include the effects of solar concentration and the Reynolds number on the performance characteristics. A numerical scheme incorporating the full radiation heating model is used in the simulations. It is found that the performance parameter increases with increasing Reynolds number. The performance parameter attains the highest value for the absorbing plate location at the mid-height of the channel for low solar concentration (C = 1). In the case of high solar concentration (C = 5), the performance parameter becomes the highest for the absorbing plate location at the top of the channel. The pump power loss parameter remains high for the absorbing plate location at the mid-heights of the channel. (C) 2013 Elsevier Ltd. All rights reserved.