This paper describes the performance comparison of a PVT solar collector in thermosyphon closed loop mode under two different weather conditions, fully cloudy and partially cloudy scenarios. The PVT electrical and thermal performance were evaluated and compared with a same unmodified factory PV panel for both scenarios. The PVT performance was evaluated by electrical, thermal and primary energy savings efficiencies. It was found that the PVT total efficiency increased 7.28 % under the partially cloudy scenario, due mainly to the thermal energy gain. At the fully cloudy scenario this improvement was 2.12 %, which indicates that for places where present mostly cloudy conditions, the PVT enhancement will not be so significant.