A mounting system for mounting photovoltaic panels on a support structure. The mounting system comprises photovoltaic panel frames in which the photovoltaic panels are mounted, panel support rails, and mounting brackets or cross beams for supporting the panel support rails. The panel frames have inwardly extending panel frame extensions on their back side. The panel support rails are mounted on the support structure with either pivoting brackets or cross beams. In either case, the support rails have pairs of stationary clamps and movable clamps with clamp lips that engage the panel frame extensions of the panel frames.