An array of photovoltaic panels is supported in rows and columns spaced from one another using a foldable bi-directional span of support members. The support members include a plurality of support joists and support rails braced at an incline. Each support rail is tubular and generally rectangular, having a lower wall section with a T-slot channel for acceptance of the head of a bolt for adjustable attachment with the support joist. Also, the support rail may have a C-slot channel for retaining electrical wires. Clips are used to secure each panel to upper wall portions of underlying support rails. Each clip has a generally U-shaped gasket and is retained to a corresponding support rail through a threaded hole in a top wall of the support rail that receives a bolt or similar threaded fastener.