This paper presents an exergetic analysis of a downward flat plate collector, an unglazed selective absorber collector and an artificial rough surface collector. The analysis is based on mass, energy and exergy balance equations. The results show that for the Reynolds number of Re = 4000, the daily exergy output rate varies inversely with the mass flow rate per unit area, while the exergy efficiency of the artificial rough surface collector is four times greater than that of a conventional solar air heater. In addition, there is maximum dimensionless exergy loss in the downward flat plate collector already having the smallest thermal efficiency.