A clamp for securing photovoltaic panels to a support tube of a photovoltaic panel array has a lower brace for positioning on the support tube perpendicular to the support tube. The lower brace has a central web with a pair of side walls depending from opposite edges of the web. Support shoulders are formed in the side walls. Straps have tabs on an upper end that land on the support shoulders. An upper brace has flanges for engaging upper edge surfaces of adjacent ones of the panels. At least one deflectable standoff positions the upper brace a distance from the lower brace that is selected to be greater than a thickness of the adjacent ones of the panels. Tightening bolts between the braces deflects the standoff and draws the upper brace toward the lower brace to clamp the adjacent ones of the panels between the lower and upper braces.