This paper presents the results of a theoretical and experimental investigation of a double exposure, flat-plate solar collector with a flat-plate reflective surface. The main role of the reflector, which is placed below and parallel to the collector, is the reflection of solar radiation on the lower absorber surface. To enable absorption from the lower absorber surface, it is necessary for the insulation mounted on the lower part of the collector box to be removed and the lower box surface replaced by a glass cover. In order to determine the feasibility of the proposed concept, theoretical and experimental investigations of a double exposure and conventional flat-plate solar collectors were carried out. The experimental tests verified the developed mathematical models of the thermal behaviour of the mentioned solar collectors. The main advantages of the proposed collector reflector system in relation to the previously investigated are: parallelism between the reflector and the collector, mirror reflective surface and mobility of the reflector in all three possible orthogonal directions. The proposed system is simpler because it consists of only one reflector. The experimental and theoretical results show that performance of a double exposure, flat-plate solar collector can be significantly higher than a conventional solar collector. The experimentally obtained relative difference of thermal power of these collectors is in the range of 41.79-66.44%, the highest achieved value of this difference in the reviewed literature is 48%. (C) 2015 Elsevier Ltd. All rights reserved.