This work deals with the partial shading effect in the power curve of a PV solar array. Using a semiconductor device — MOSFET or IGBT — as electronic load added to a buck converter, it is possible to scan the power curve of a photovoltaic string and therefore empirically determine its optimum voltage, even in presence of partial shading. The aim of this paper is to give experimental details regarding the laboratory implementation of a proof-of-concept prototype meant to detect the Global Maximum Power Point. Three cases are presented that consider the partial shading effect of a PV string, with disturbances of different sizes and shapes. In the last part a novel exciting signal is presented, which allows to reduce the scanning time of the power curve. The experimental results illustrate the performance of the implemented circuit.