Energy and thermo-fluid-dynamics evaluations of photovoltaic panels cooled by water and air

The main limit of photovoltaic (PV) systems is the low conversion efficiency of cells, which is strongly influenced by their operating temperature. As the temperature increases the short circuit current (I-sc) increases moderately, while the open circuit voltage (V-oc) decreases considerably. The cell temperature reduction is a useful methodology that could be used in order to improve the PV panels performance of both new and already installed as well. This solution is interesting especially for high irradiation level locations with high external air temperature range along the daytime, because the maximum producibility occurs when the irradiation is high and therefore, as a consequence, the cell temperature increases. Furthermore, the proposed solution could be integrated with many PV typologies, already installed as well. Thus, it represents an alternative to PVT (Thermal Photovoltaic) systems, which need DHW consumers for supplying the heat produced, otherwise the performance of the system will decrease. Various solutions adopting respectively a cooling water system and an airflow lapping the back of the panels in an open circuit is investigated to individuate the best cooling solution. Finite element software that describes with extreme detail the thermal exchange between the PV cells, the external environment and the cooling system is used in order to assess the reached temperature of the cells with different cooling system configurations calculating for each considered cases the overall thermal losses coefficient. Regarding the air cooling system configuration, which results less invasive, a comparison between the simulated and the measured, by laboratory tests, air speed has been conducted. Hourly energy simulations for the best configurations using the software TRNSYS are carried out to evaluate the annual performances. (C) 2014 Elsevier Ltd. All rights reserved.