Criteria and policies to master the visual impact of solar systems in urban environments: The LESO-QSV method

Increased use of solar collectors in buildings is necessary but poses major challenges in existing built environ ments, especially where architectural quality is an issue. The large size of solar systems at the building scale requires careful planning, as they may easily end up compromising the aesthetics of buildings, threatening the identity of entire contexts. A new method named LESO-QSV(for Laboratoire d'Energie SOlaire - Qualite Sensibilite-Visibilite) has been developed to help authorities promote solar energy use while preserving the quality of pre-existing urban areas. The vision underlining the approach is that solar integration is possible also in delicate contexts, if appropriate design efforts and adequate cost investments are made. The issue is then no longer to be in favour or against the use of solar systems in cities, but rather to define appropriate local levels of integration quality, and to identify the factors needed to initiate smart solar energy policies able to preserve the quality of pre-existing urban contexts while promoting solar energy use. The LESO-QSV method helps tackle these issues with clear and objective proposals: First it clarifies the notion of architectural integration quality and proposes a simple evaluation method, based on a set of criteria derived from pre-existing literature. Then it helps authorities set and implement local acceptability requirements, introducing the notion of architectural "criticity" of city surfaces (LESO-QSV acceptability). The concept of "criticity", at the basis of the whole approach, is defined by the Sensitivity of the urban context where the solar system is planned, combined with its Visibility (close and remote) from the public domain. The more sensitive the urban area and the more visible the system (high "criticity"), the higher the need for integration quality. In practice, authorities will be in charge to set the desired integration quality levels for each of the defined "criticity" situations, considering local specificities (energy context, available energy sources, political and social considerations, city identity and topography, among others). To help authorities set these quality expectations, the software LESO-QSV Grid has been developed. It illustrates the acceptance impact of pre-defined sets of quality requirements, using a large number of integration examples (150 emblematic cases). These detailed examples are provided to show authorities how to objectively evaluate integration quality, but they also constitute a large set of learning examples, good and bad, for architects, installers and building owners. Finally the method proposes a way to tailor solar energy policies to local urban specificities by mapping the architectural "criticity" of city buildings surfaces, and crossing this information with a city solar irradiation map (LESO-QSV crossmapping), hence completing the characterization of the building surfaces with the potentially required effort of integration.