The output power of any PV module may be influenced by a number of factors, including the installation and environmental conditions. One of these conditions involve partial shading, where a section of a PV module is shaded due to an interruption in the direct-beam radiation from the sun. The purpose of this article is to quantify the percentage of partial shading of a given PV module within a controlled environment, correlating it to its output power. This correlation helps to reinforce the importance of allowing no shading to occur on a PV module or array. The percentage of partial shading is determined using images taken of a 10 W PV module that are processed using online imaging software. Results indicate that a partial shading percentage of 4,7 % caused by a vertical aluminum tube results in an output power reduction of 59 %. However, the results are limited to a specific string design of a PV module and to the position of the partially shaded cell. It is recommended to remove all causes of partial shading, as this impacts on current and future power generation from the PV module.