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.
