This work is a long-term, interannual, and experimental study conducted in multiple locations. It studies the effects of phase change materials (PCMs) on photovoltaic modules’ performance by reducing their operational temperature. Two PV modules were manufactured so that PCM slabs could be mechanically attached to their backside, ensuring contact with the related photovoltaic active area. Experiments were conducted in Delft, Netherlands, from 2019 until 2021 and in Catania, Italy, during the winter and start of spring of 2023. The experiment also considered two installation layouts: building integrated (Delft) and standard rack-mounted (Catania). The measurements showed that the PCM provides significant cooling under both locations, with a temperature reduction of up to 15 °C. In Delft, thermal control could be obtained for most of the sunny hours of the day, even during the summer months. In Catania, the module with PCM presented, on occasion, higher temperatures than its standard counterpart, primarily due to winter-time environmental conditions. However, the PCM provided sufficient thermal control on all conditions, ensuring increased energy yield. This increase ranged from 2.1 to 2.5 % in Delft and 1.3–1.6 % in Italy.