Photovoltaic modules (PV) are tested in the industry in standard conditions and their characteristics are given in the datasheet. After installation on the site, its performance is not evaluated separately of the other parts of the PV generator. Nevertheless some discrepancies of the expected generation and the measured ones are verified. To deal with these discrepancies it is worth characterizing the module on the site and acquire data in an easy and inexpensive way. This paper presents a proposed characterization system as well as its application. A module test was performed on a site located in Brazil. At these latitudes it is common to have high amount of ultraviolet components. The characterization system measures separately the ultraviolet component, as well as the visible and global irradiations. The results obtained are analyzed and the effect of the UV variation is observed, proving the importance of doing this characterization on site after implementation of the PV system.