Architectural Integration of Photovoltaic Systems in Historic Districts. the Case Study of Santiago De Compostela

Historical buildings are often energy inefficient. Renewable energy sources can be implemented in the refurbishment projects in order to cover the high-energy consumption with sustainable sources. The paper presents the results obtained in the FP7 Project EFFESUS on the architectural integration of PV systems in the historic city center of Santiago de Compostela. In this case, one of the most challenging issue was the preservation of the original form and value of the historic district, considering the rules of local legislations and policies. According to these rules, the building stock has been classified in specific levels of constraint in order to define the compatible retrofit interventions for each level. The study has been supported by historical analysis, visual tests and heritage information of the Santiago GIS Data System. From these data the roof surfaces where the installation of PV system is deemed compatible with conservation constraints has been estimated. This study showed few degrees of freedom for the PV installation with traditional systems. On the other hand, in a historic building there are many possibilities for integrating PV systems without altering the original aspect and considering the aesthetics, physical and mechanical compatibility. The approaches developed in others European and international projects are investigated (e.g. 3ENCULT; IEA-PVPS Task 7; IEA-SHC Task 41; SuRHiB; FP7 SolarDesign, PVACCEPT) to define correct suggestions and recommendations for preserving (and in some case enhancing) the cultural value of historic districts and buildings. Next, the solar energy irradiance and irradiation maps of a specific area have been calculated, starting from the Digital Surface Model, with the module r.sun of GRASS, an open source Geographic Information System (GIS) software. From these data, the PV potential of the district has been carried out assuming a PV efficiency of 15% and 25% of losses in electricity production. The daily production data has been calculated only on filtered roofs (heritage constraints and suitable insolation level) and summed up to compare it with the consumption profile. PV production could then cover 73% of electricity needs of the district. The GIS software GRASS has been especially useful because permits to not only manage and analyze spatial data but to interpret and understand their relationships or patterns and to combine several spatial datasets obtained in this research, i.e. PV potential and historical building data.