Air-based photovoltaic thermal collectors: theoretical and experimental analysis of a novel low-cost prototype

In this paper the performance of an innovative low-cost flat-plate PhotoVoltaic Thermal (PVT) collector prototype is investigated. By such hybrid solar panel both electricity and thermal energy can be obtained. As commonly known, the electrical efficiency of PV cells dramatically drops as the operating temperature rises. In order to improve the PV cells efficiency avoiding the overheating, a low-cost heat extraction system was made. Specifically, the cooling system (located under the PV panel, Figure 1a) is composed of two black galvanized steel sheets, properly shaped in order to form seven air channels (Figure 1b). On the top of the structure seven fans were installed in parallel to draw air through suitable air channels. The obtained air thermal energy can be exploited for different building uses. The prototype was built and tested under different operating conditions at the University of Patras (Greece). Then, in order to carry out a deep investigation on the system, a suitable dynamic simulation model was developed for assessing the energy, economic and environmental performance analysis of the system for different weather conditions and building uses. Here, hourly weather data (TMY, IWEC, etc.) can be processed (solar radiation, air temperature and humidity, wind, etc.). The model, implemented in MatLab environment, was validated vs. the above mentioned collected experimental data and a good agreement between the simulation results and the measurements was achieved. In addition, in order to optimize the system design, a specific tool for the system parametric analysis was developed and added to the simulation code. By such tool the effects on the collector performance of the variation of different design and operating parameters (i.e. air channel depth, air mass flow rate, fans speed, etc.) can be carried out. Finally, in order to investigate the convenience of the presented prototype and the potentiality of the developed simulation tool, a suitable case study is discussed. Here, the PVT collector prototype is coupled to a heat pump for building space heating. Specifically, the air heated in the seven collector channels is supplied to the evaporator of the heat pump, increasing its energy performance and decreasing its operating costs. An office building in three different European weather zones was investigated. Useful design criteria and interesting energy and economic results were obtained.