Abstract: Two identical header tube members are fitted to opposite ends of an absorbing member with a plurality of internal channels for circulation of a heat transport fluid to form a collector element. Each header has a header tube which is spaced from a header base plate by a tube saddle. The perimeter of the element includes a flange for joining it together with other, identical elements. Any number of such elements may be joined together to form a continuous, watertight sheet. Where the header tubes of adjoining elements connect, their spacing from the base plate leaves a passageway under them between adjacent tube saddles. Water can run off the surface through the passageway in the direction of slope of the surface upon which the sheet of elements is installed.