Abstract: A structure for mounting a planar array of photovoltaic panels to a roof is formed from a set of parallel spaced juxtaposed rails which are intersected by a set of parallel spaced juxtaposed runners that extend perpendicular to the rails. Both the runners and the rails are formed of sheet metal and are shaped in cross section so as to partially surround a space. Both the rails and the runners have upwardly opening apertures bordered by flanges. The flanges of the rails are coplanar with the flanges of the runners. The photovoltaic modules rest on the flanges, thereby covering the apertures and enclosing the space within the rails and the runners. This space serves as a protective raceway for the electrical interconnections and wiring. Because the entire structure is a single electrical conductor, grounding of the modules is simplified. Compared to other mounting systems, the structure is lighter in weight, simpler to install, extremely strong, and protective of the electrical interconnections.