Urban acceptability of building integrated solar systems: LESO-QSV approach

The concern for sustainable development issues together with the new EU promotion policies are finally leading to a widespread use of Photovoltaic and Solar Thermal systems in buildings. This upcoming reality is opening a new debate on the urban/architectural acceptability of such systems. In Switzerland the matter has been regulated from 2008 by the art.18-a/LAT, stating that all “carefully integrated” solar systems not attempting to the cultural or natural heritage are accepted. But this text remains ambiguous, and is differently interpreted by solar pros, building heritage administrators and city planners, actually leading to unfair decisions [1]. The presented method aims to bring objectivity to the debate, and to help dealing with the law’s two concerns: support the solar spread and preserve the urban context quality, i.e. ensure that the installed systems have an acceptable integration quality for their given environment. To assess valid and objective acceptability criteria, a few key questions must be answered : Can architectural integration quality be objectively defined? Can it be somehow quantified, and on which bases? And finally, what are the acceptability factors, and how do they interact with each other? The method faces all these questions, starting from an objective and clear definition of architectural integration quality coming from recent studies On the basis of this given definition, a list of solar system characteristics having an impact on the architectural quality is established [4][6]. The detailed evaluation of each of these characteristics in relation to the whole building design leads to a comprehensive and objective quality evaluation, summarized in a “grade” after carefully balancing the impact of each aspect. Finally a table of acceptability conditions is established on the basis of three variable local factors: - Urban context sensitivity (the quality of the architectural environment); - System visibility (close and remote visibility of the proposed system); - Socio-political context (political and energetic priorities specific to place and time). One major advantage of the method is its clarity, coming mainly from the separation of the two phases needed for the decision making process: - On one hand there is the definition and analysis of the architectural quality, carried on the sole base of architectural criteria. - On the other hand there is the assessment of the acceptability levels, variable according to specified local factors, and to be fixed by the local authorities according to the socio-political context and energetic needs.