Optimization of reflecting materials and photovoltaics in urban environment with respect to energy balance and bioclimate

Starting point/ motivation: In PVOPTI-Ray the influence of the reflection and the radiation balance on the performance of facade-integrated Photovoltaics is analyzed in an urban complex area. At the same time, the influence of solar modules and the radiation effects of solar modules on the urban climate are considered. Reflection from the ground and surrounding buildings causes an increase of the solar radiation directed to the PV module, and entails an increase of the PV yield. Other factors which are influencing the performance of PV modules are energy flows which are having impact on both energy balance and temperature of PV modules. Human beings who are living in urban areas are just as well exposed to energy flows which can cause symptoms of thermal stress e.g. in the cause an increase of short-wave reflection. Supported by coupled urban city climate-building models and PV yield tools optimum solutions of city planning are developed with respect to the design of city canyons and the forming of its surfaces. As a result an optimized yield of façade-integrated PV plant is developed, while all bioclimatic aspects which are relevant for the well-being of humans are considered. Cities are the biggest energy consumers and they are going to be the major victims of climate change. Against this background, the ‚Solar Cities‘ issue is discussed nationally and internationally: cities that are gaining most of their energy need from the sun directly with their own rooftops and facades. Active houses and Solar Cities are thus planned in a way that they may retrieve a maximum of ‚solar harvest‘, directing their roofs and facades towards the sun avoiding shadowing to achieve a maximum solar yield. At best, black solar modules are used with low reflection and thus a high electricity yield with up to 20%. The biggest part of the absorbed solar radiation is however transformed into heat. So far there have not been developed any evaluation and simulation tools for the urban area which can estimate the effects of a broad roll-out of PV and insolation of facade surfaces in urban districts, especially on the micro-climate in street canyons. In order to adapt to climate change the US are following a contrary strategy: a city with white roofs, maximized reflective surfaces and minimized absorption of the solar irradiation of the city. Reflection from the ground and surrounding buildings causes an increase of the solar radiation directed to the PV module, and entails an increase of the PV yield. At the same time the increase of reflection can cause more thermal stress and blinding of human beings. Solar modules are reducing the reflection in urban districts and may contribute to warming the environment.