In a previous work, fanned system collectors have been used and tested only in order to show the effects of convection heat transfer on the thermal performance, which were appreciably improved in relation to the flat-plate solar collector. Eight fanned system collectors had been selected, and had permitted to lead a first study. Four fin lengths and two spacing values between two consecutive fin rows had been chosen. The thermal performance had enhanced when the spacing was reduced. Because it could not be possible to reduce further the spacing between two consecutive interrupted fin rows and in order to enhance the thermal performance, the interaction of radiation combined to convection heat transfer have been introduced. In this effect a flat-plate and two fanned system collectors are selected. The channel back of these collectors is coated in turn by three coverings. In the first a wooden plate only which is the channel back of the collector, in the second and third time a reflecting and a black-painted covering are, respectively, used. These are put down on the channel back of collector. The black-painted coating when it is used in the three collectors gives the better improvement followed by the reflecting covering in relation to their respective collectors having uncoated channel back. The greater relative increase of thermal performance is obtained when the flat-plate collector is used and where its channel back is recovered by a black-painted coating.