Comprising a plurality of assembled solar energy collector elements. Cold liquid is supplied at one end and water heated by the solar energy is drawn off at the other end of the device. The liquid circulates through the device in contact with an absorbent mat of intermingled fibers of dark color which is exposed to the solar radiation through at least one translucent sheet which creates a glasshouse effect. The mat guides the flow of liquid by the effect of capillarity and gravity during the heating of the liquid.