Abstract: A solar energy collector for use primarily in a closed-loop system has a fluid conduit of serpentine configuration which comprises a plurality of relatively thin extruded aluminum tubes, each tube having a flat top and bottom wall and lateral flat lips or flanges extending longitudinally along opposite sides thereof and coplanar with the bottom wall forming therewith a flat base for the tubes, the flanges providing means for joining the tubes by welding in an array in side by side abutment relation. Sections are formed from the flat tubing as connecting headers which are welded at both ends to pairs of adjacent tubes in staggered relation to form the continuous serpentine path for the heat transferring fluid.