Numerical determination of adequate air gaps for building-integrated photovoltaics

摘要

The efficiency of photovoltaic (PV) devices is approximately inversely proportional to the cell temperature and the air gap of PV modules over or beside a building envelope can facilitate ventilation cooling of building-integrated photovoltaics. The effect of gap size on the performance of one type of PV module (with dimensions 1209 × 537 × 50 mm) in terms of cell temperature has been determined numeri cally for a range of roof pitches and panel lengths under two different settings of solar heat gains. It has been found that under constant solar heat gain, the air velocity behind PV modules due to natural convection in general increases with roof pitch angle. For a given location where solar heat gain varies with inclination from horizontal plane, however, the air velocity increases up to a pitch angle of about 60 degrees and then decreases with increasing roof pitch. The mean and maximum PV temperatures decrease with the increase in pitch angle and air gap. The mean PV temperature also decreases with increasing panel length for air gaps greater than or equal to 0.08 m, whereas the maximum PV temperature generally increases with panel length but decreases when the length of a roof-mounted panel increases from two modules to three modules and the air gap is between 0.1 and 0.11 m. Without adequate air circulation, overheating of PV modules would occur and hot spots could form near the top of modules with potential cell temperatures over 80 ℃ above ambient air temperature under bright sunshine.