Summarizing, this system consists of
a metallic base with an upper-level step (trapezoidal or square
profile) where all the joints to the supporting structure are
placed. Hence, a solid watertight metallic base for the water
chamber is obtained. This water chamber may be covered with
a double glazing cover similar to that of a flat solar collector,
providing a watertight chamber by simply keeping the water
level below that of the glass.