PV-roof-integrated systems vs. best- and worst-cases

The popularity of PV -facade and -roof integrated systems still remain at small scale compared to fast growing PV on-roof systems. One of the most significant obstacles is the technical barrier (electrical, thermal and mechanical behaviours). With the national research project MULTIELEMENT supported by BMU, the electrical, thermal and mechanical measurements have been performed under long term outdoor conditions. The evaluations show, that the heat-flux to internal room over solar irradiation increases by the roof tilt angle. Furthermore the fluctuation of temperature caused by weather conditions does not have a significant impact on the total energy yield, whereas temperature influence on sunny days is noticeable. For the wind direction from south-east to south-west, directly towards the module surface, the temperature of the bottom PV module is lower than the one at the top of the PV array (~ 2-4 °C) due to chimney effect. For the wind direction from north-east to north-west, wind from backside of PV array, the operating temperature of PV module at bottom may be higher up to 6°C compared to that at the top of the field due to cooling effect from turbulences at the top edge of the roof. The average energy yield of the bottom module is about 1% higher compared to the top module. In comparison to the free-standing PV module, these energy yields of PV roof-integrated system exhibit only -0.9% to -1.8% for bottom and top modules of PV array, respectively. At the same time, the energy yield of the worst-case scenario module (fully thermal isolated module) shows -4% compared to the free-standing PV module.