Heat recovery potential and electrical performances in-field investigation on a hybrid PVT module

The aim of the present study is the characterization of PVT modules electrical performance in real operating conditions, as well as the investigation of thermal recovery via a cooling circuit integrated with a third generation PV module. The approach combines both theoretical and experimental tools: a MatLab® simulation model provides a reliable theoretical basis, whose validation is performed on experimental evidences from in-field PV module tests. The model represents the module energy balance, under unsteady operating conditions; a full set of measurements allowed to validate the theoretical approach, thus offering the possibility to evaluate the effects of both variable outdoor air temperature and pressure and wind speed. Water-cooled PV modules electrical performance increases by as much as 33%, with respect to the situation in which no cooling is performed and up to a 20% electric efficiency is achieved, with a 2.0 L/min water flow rate on the back. A major drawback is that thermal recovery for cogeneration purposes is not effective, due to a low thermal gradient (10 K maximum) on the water. When a 10 mm thick glass cover was integrated in the PV module along with a frame to reduce wind circulation over exposed surfaces, a 100–500 W thermal recovery on a day basis could be achieved. Furthermore, a 15–30 K increase in water temperature assures about the higher quality of the recoverable heat. The suitability of organic fluids instead of water to reduce the power absorption by the pump, is addressed as the most effective way to increase PVT electric output: the absorption with R236fa and R245fa is a 60% and 75% lower than with water, respectively. The novelty of the present study lies in the dual theoretical and experimental approach, leading to a validated non-steady-state mockup, easily adjustable to extend the analysis to PV modules arrays for residential applications. Furthermore, the use of an infrared camera, typically confined to post-manufacturing quality control, allows here a continuous monitoring of the module thermal field, key to evaluate the temperature effect on the module performances both in steady and unsteady conditions.