A model and heat transfer correlation for rooftop integrated photovoltaics with a passive air cooling channel

Photovoltaic (PV) panels can experience undesirably high temperatures due to the heat input by that part of the absorbed solar radiation which is not converted into electricity. Regulation of the temperature rise is necessary to maintain maximum solar to electric conversion. One approach for temperature regulation, suitable for rooftop integrated PV, involves fitting an open channel beneath the PV module. The panels are cooled by radiation and free convection as ambient air rises through the channel. A scale analysis and numerical study of PV modules with a back mounted air channel provides heat transfer rates over a practical range of operating conditions and channel geometries. A generalized correlation for the average channel Nusselt number for the combined convective–radiative cooling is developed for modified channel Rayleigh numbers from 102 to 108, channel aspect ratios between 15 and 50 and inclination angles between 30° and 90°. The usefulness of a passive cooling channel to improve PV efficiency is illustrated by system analyses of typical PV modules.