An experimental study was carried out to evaluate the thermal performance of sand dune as storage material integrated in a flat solar thermal collector. The experimental apparatus is realized then installed on site. The parameter measured in this study is the temperature at different points of the collector. A graphic presentation shows the results obtained experimentally during the day of the test (winter period). The absorbing plate temperature reaches a maximum value of 97 °C and the layer of sand of 25 mm can ensure a storage of 20 minutes with a damping of thermal fluctuations of 5.2 °C. The amount of heat stored could replace the incident solar energy during the presence of clouds for 20 minutes.