Experimental investigation of cavity flow under building integrated photovoltaic panels using thermography and particle image velocimetry

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.

An extensive experimental investigation demonstrates the impact of cavity airflow underneath photovoltaic (PV) panels integrated in the roof assemblies of buildings. The benefit of underside ventilation is seen in terms of an increased efficiency of photovoltaic panels due to lowering their operating temperature, resulting in less turn-off times as well as an improved hygrothermal and durability behavior of the panels. We perform an extensive measurement campaign of the surface temperature using infrared thermography and of the airflow using particle image velocimetry. A novel setup was developed consisting of a building model with a mock PV panel and a solar simulator placed inside a large-scale atmospheric wind tunnel. A solar simulator is positioned in the tunnel to provide a range of various radiation intensities over the panels and the approaching upstream wind is well controlled in the wind tunnel. The top surface temperatures and air speeds above and below the panel are monitored simultaneously. It is shown that, in general, the airflow within the cavity is faster compared to the free upstream air velocity, resulting in an increased heat exchange between the PV and the air cavity and a reduction of the PV surface temperatures. A stepped open arrangement of panels is shown to be more effective in reducing the surface temperatures comparing to a flat arrangement. The results also show the presence of different interacting flow phenomena: natural convection due to irradiation, forced convection due to the upstream wind, cavity ventilation and surface convection, as well as the presence of complex 3D flows patterns (e.g. lateral eddies), which contribute to a highly non-uniform surface temperature distribution over the PV modules.