A mounting bracket arrangement for fastening a solar array to a vertical support pipe, including a generally horizontal support disk seated transversely across the pipe end to close the interior thereof, and a pair of parallel vertical bracket plates having corresponding lower edge portions each containing pairs of parallel vertical slots that define a center section and a pair of side sections. The vertical bracket plates are arranged normal to the horizontal support plate such that the center sections extend into the pipe interior via horizontal linear openings contained in the horizontal plate, and the side sections extend longitudinally externally of the horizontal support plate for connection by external fastener devices. The solar array is pivotally connected between the upper portions of the vertical bracket plates for angular adjustment relative to the support pipe.