Performance Assessment of Different Roof Integrated Photovoltaic Modules under Mediterranean Climate

Many countries, for aesthetic purposes, offer economic advantages (tax deductions, incentives, etc..) for the installation of building integrated photovoltaic modules (BIPV), with water-tightness capability and adequate mechanical resistance in order to substitute tile covering or part of it. Nevertheless, poor or absent ventilation under BIPV panels could cause them to overheat and reduce their efficiency. It is well established that the presence of an air gap between a photovoltaic (PV) module and roof covering facilitates ventilation cooling under the device and consequently reduces cell temperature and improves its performance. In this study, we investigated the thermal performance of PV modules installed in a real scale experimental building over a traditional clay tile pitched roof in Italy for almost one year (from August 2009 to June 2010). One PV module was rack-mounted over the roof covering with a 0.2 m air gap; the others were fully integrated and installed at the same level of the roof covering (one with an air gap of 0.04 m, the other mounted directly in contact with the insulation). Temperature and heat flux measurements for each panel, and environmental parameters were recorded. Experimental results demonstrate that even though the rack-mounted PV module constantly maintains cell temperature below that of the other full-building integrated modules, due to the presence of a higher air gap, the difference in the energy produced by the PV modules estimated for the entire monitoring period is less than 4%.