Photovoltaic BIPV Systems and Architectural Heritage: New Balance between Conservation and Transformation. An Assessment Method for Heritage Values Compatibility and Energy Benefits of Interventions
2. Heritage Value Compatibility of Solar Photovoltaic Integration Assessment Method-Introduction
- Distinguishable, as the addition must be easy to notice from the original material, without disturbing the vision of the work. If this criterion is not well-fulfilled, one runs the risk of practicing a not-proper restoration by making a wrong reading of the work;
- Reversibility of the intervention that allows the removal of the intervention without altering or damaging the original parts;
- Compatibility, those materials used must not bring any constructive or aesthetic alteration to the original materials with respect to chemical-physical and mechanical properties;
- Minimum intervention, limiting the invasive actions on the historical material is preferable to respect all the information understood as historical stratifications;
- Multidisciplinary, this principle underlies the importance of collaboration to engage and interface with different specialized professionals.
- An in-depth analysis of current criteria for the assessment of the integration of solar photovoltaic BIPV systems in historic buildings and conservation areas, based on the regulations and guidance documents in neighboring countries of a specific geographical area with similar cultural and architectonic historical heritage values;
- An assessment semi-quantitative method valuable for operators or cultural heritage offices to judge energy retrofit interventions and BIPV examples of integration, based on a common framework approach;
- A methodological approach to address some barriers that will allow a further dissemination of BIPV technology in existing buildings and further market development.
3. Comparison of Directives, Regulations and Consultation Documents with Regard Solar Photovoltaic Integration
3.1. Part 1—Reference Legislation IT-CH Cross-Border Area, Binding Documents
- Coplanarity: photovoltaic modules installed on roofs, facades, balustrades and parapets of buildings must be installed coplanar to the supporting surface without substitution of material in the case of partial or total integration of the building;
- Respect of the eaves line: the module must not exceed the upper edge of the tiles by more than its thickness;
- Respect the geometry of the pitch: the position of the modules must respect the lines of the pitch;
- Compactness of the modules: limit as much as possible the separation space between the external perimeter of the modules and the residual portion of the existing roof.
3.2. Part 2—Reference IT-CH Not-Binding and Guidance Documents—Recommendations and Guidelines
3.2.1. Italy—MiBACT, Guidelines for the Improvement of Energy Efficiency in Cultural Heritage
3.2.2. Switzerland—Ticino Cantonal Guidelines
3.3. Part 3—European Guidance Documents—Standard EN 16883:2017
4. Evaluation Schedules for BIPV Heritage Compatibility and Technical Assessment of Solar Photovoltaic Solutions of Real Case Studies
- Assessment of case studies—Building schedule: BIPV heritage compatibility;
- Assessment of solar BIPV solutions—Technical schedule: BIPV functionality and energy benefits.
4.1. Information and Description Data
4.2.1. Assessment of Case Studies
- Green colour: the criteria/recommendations respect the reference definition;
- Yellow colour: assigned if the reference criteria/recommendations have been partially fulfilled;
- Red colour: the reference criteria/recommendations do not meet any of the aspects of the provisions/guidelines.
4.2.2. Assessment of Solar BIPV Solutions
5.1. Building Information and Description—Analisys of Results
5.2. Building and BIPV Assessment—Analisys of Results
- Rural building Galley, Encuivens/FR:
- Building Description: Bauernhaus Galley’s pilot project, an 1859 farmhouse, wins the Swiss Solar Award in 2018 as an example of a good energy upgrade. The terracotta-coloured photovoltaic modules were specially developed to meet the needs of protected sites. In fact, the Fribourg site is listed in the federal inventory of Swiss national heritage sites ISOS.
- BIPV System Description: The solar technology looks like a traditional roof tile with anti-reflective glass. The panels produced by the manufacturer Solarif XL, have a nominal output of 27.2 kWp. The surface area uses 250 square meters of south-facing roofing and produces 16′500 kWh/a. A highly camouflaged aluminum frame in the same colour as the panels was used.
- Single Family House, Villa Carlotta, Orselina/TI:
- Building Description: Built in 1939, this historical villa stands on a slope above Locarno near Lake Maggiore. The retrofit interventions concern the replacement of the old heating system with a better-performing one, including a BIPV system on the roof and solar collectors with vacuum tubes in the garden to achieve a high-energy standard. The original roofing of red tiles, although in good condition, has been replaced entirely by blue photovoltaic panels with high reflection, as the building and the context are not bound by any protection by cantonal law.
- BIPV System Description: The photovoltaic modules are blue in colour with a high reflection rate and standard size. Meyer Burger high efficiency crystalline solar cells are used with 18.2% efficiency in solar modules with maximum load capacity thanks to the tempered glass of 5 mm. The applied solution does not have supporting frames and uses three types of modules for a total of 117 active modules.
6. Discussion and Conclusions
- The new BIPV technology, due to its technical and constructive characteristics, is perfectly suited to the needs of new buildings, as it is able to replace technological components of the building envelope. On the contrary, the use of the mentioned solar technology, integrated in historical buildings and contexts that have a strong identity, needs to be adapted to the needs of the built environment;
- From the synoptic comparison of Swiss and Italian legislation, in force of the non-binding documents and of the guidelines, the necessity to find a compromise between conservation and energy needs promoted by the respective territorial contexts arises. For this reason, key intervention criteria have been identified to update the existing guidelines with a common normative framework;
- The assessment method proposed and discussed underlines the importance of considering the impact that BIPV technology has on the historic building and its environment, considering three macro-categories of integration (i.e., geometric, aesthetic and functional characteristics) within which the criteria highlighted by the research have been arranged;
- Moreover, comparison with the standard EN 16883/2017  confirms the need to consider the compatibility of the intervention from a point of view not only conservative or aesthetic, but also taking into account the energy aspects. The evaluation method applied to more than 35 case studies from Switzerland and Europe underlined the considerable energy contribution of BIPV systems when combined with other energy retrofit measures on the existing building envelope and facilities (e.g., internal and external insulation,
- The two examples of application of the method presented in this paper, shown in detail, represent two modes of intervention at opposite ends of the spectrum. The interventions on the rural building Galley at Fribourg attempt to mediate between conservation and energy requirements, while the Villa Carlotta building opts to optimize energy requirements as much as possible to the detriment of aesthetic and historical compatibility requirements;
- The assessment criteria applied to a broad spectrum of solar BIPV implemented in historic buildings (e.g., from listed to unlisted buildings, from rural to urban environments or conservation areas, from traditional to pre-industrial historical buildings) allow the review of different approaches, followed by interventions on a case-by-case basis, and to critically understand the motivations;
- The methodology and criteria for determining the compatibility of the interventions would be equally useful in other countries or climate zones, but would require a deeper understanding of the specific regulations and guiding criteria currently and in the future contemplated in these zones or countries. Through this analysis, it will be possible to determine the correspondence with the criteria considered in this study and whether it would be necessary to add new ones;
- The evaluation of case studies considered both the type of building (i.e., five typological schemes: 1. Courtyard buildings; 2. Blocks; 3. Towers; 4. Terraced buildings; 5. Line buildings) and different categories of possible BIPV intervention (i.e., five categories following the EN 50583:2016 standard for BIPV systems). In some cases, to assess the validity of the method, it was necessary to consider examples in other European countries because, examples of real implementation in historic buildings for all categories were not always found in Italy or Switzerland;
- Likewise, the energy assessment of the solar potential actually used by the BIPV system would prove its usefulness in those countries where a solar mapping system (solar cadastre) makes a complete and individualized building-by-building solar analysis possible, as is the case in Switzerland, Germany or Austria, for example [105,106]. Unfortunately, a more complex analysis will be required in other countries where the mentioned solar mapping tools are not well implemented. Besides, in order to compare the results with the building’s energy needs, in-depth data of the analyzed buildings have been required.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|D.lgs 28/2011 annex 3, Art. 11 |
GSE -D.P.R 31/2017 
|OPT, art.32a |
- Respect of the eaves line
- Respect the pitch geometry
- Compactness of the modules
|- Respect for lines/visibility|
- Low reflection rate
|D.lgs 28/2011-Art.4 |
- Simplified Enabling Procedure (PAS)
- Communication to the Municipality
D.P.R 31/2017 
Annex A: Landscape authorization
Annex B: No landscape authorization
Legislative Decree no. 42/2004  Art. 146, simplified landscape authorization
|LPT (SPA) |
- Art. 22
- Art. 23
- Art. 4 par. h, work subject to building license
|MiBACT ||Ticino Guidelines |
- Respect of the eaves line
- Perceptual alteration: colour, material and shape
- Non- invasiveness
- No protrusion
- Compact shape
- Low reflection
|EN 16883/2017 ||Identified Criteria|
Material: the solar panels respect the historical material in their construction, functional and technological
Fixing System: mechanical structural requirements and safe operating conditions
Reversibility: the possibility of restoring the pre-intervention condition, considering anchoring and fixing materials
Colour: the colour of the photovoltaic surface in relation to the building and the context
Texture/material: referred the pattern and transparency of the photovoltaic cells
Spatial geometry alteration: it refers the size and the respectful the lines of the building
Heating: passive and active energy input compared to the initial performance levels of the building
Shading: the ability to contribute to cooling, both from the point of view of energy production and as shading element.
Electricity/lighting: provision of the solar system to the electricity and lighting of the building
|(1) Technical/Constructive Compatibility|
- Fixing System
- Hygrothermal alteration
(2) Aesthetic Compatibility
- Spatial geometry alteration
(3) Energy/functional Compatibility
|Overview of Investigated Case Studies in Switzerland and Europe|
|(a) Rural building Galley (FR, CH): A-2, photo © solaragentur.ch; (b) Rural building Glaserhaus (BE, CH): A-2, photo © C. Martig; (c) SFH Hütterli Rothlisberger (BE, CH): A-2, photo © C. Martig; (d) Industrial building Solar Silo (BS, CH): A-2 and C-2, photo M. Zeller.|
|(e) Hôtel des Associations (NE, CH): A-3, photo© C. Martig; (f) Villa Carlotta (TI, CH): A-2, photo © 3S Solar Plus and BE Netz AG; (g) MFH Kettner (AG, CH): A-5, photo © C. Martig; (h) MFH Sanierung Viriden (TG, CH): A-2 and E-3, photo: © Viridén + Partner AG, Zürich.|
|Europe and Italy|
|(a) Multi-family house MFH Appiano (IT): A-4, photo: © EURAC; (b) Doria Castle, Porto Venere (IT): E-5, photo: © PVACCEPT; (c) Tourism Office, Alès (FR): C-2, photo: www.bipv.ch; (d) Groenholf Castle (BE): E-2, photo: © Samyn and Parners;|
|(a) Mayer Hospital, Florence (IT): D-5, photo: © CSPE (CSPE.net); (b) City Hall of Linares (ESP): B-2, photo: © Onix Solar; (c); Alzira Town Hall, Valencia (ESP): B-2, photo: © Onix Solar; (d) Béjar Market, Salamanca (ESP): B-2, © Onix Solar.|
|Intercomparison Results: Assessment of BIPV Heritage Compatibility—Building Sheet|
|Rural Bauernhaus Galley:|
The intervention meets many criteria required by current regulations and guide documents analyzed. Due to the BIPV tiles chosen, which echo the colour of the original tiles and, with a low-reflection rate, it was possible to meet the lines and the aesthetic characteristics of the building. Solar modules, although, if visible from public spaces, present a compact shape and are hardly recognizable due to the size, colour and shape chosen. However, the minimum intervention principle was not followed, as both roof pitches were used to optimize electricity production. Besides, solar technology performs constructional features, suitable to functional compatibility as a ventilation cavity underneath solar reduces steam condensation and optimizing energy yield.
The evaluation indicates that not all criteria are met. The chosen solar modules have a very different colour compared to the original roof and a high reflection rate, which does not allow a good integration with the context. The principle of minimum intervention was not pursued, as all the pitches of the roof are used to optimize electricity production but maintain the roof lines. Moreover, the elements are visible from public spaces and are easily recognizable by their chosen colour and shape. On the other hand, the energy criteria are respected. Although the intervention is not suitable for conservation needs, it contributes significantly to building energy requirements.
|Intercomparison Results: Assessment of Solar BIPV Solutions—Technical Sheet|
|Rural Bauernhaus Galley:|
The integrated BIPV system uses more than 75% of the total available roof area (262 m²). Thanks to the Swiss solar cadaster tool, it was possible to estimate a solar potential of 54,800 kWh/a. with an output of 16,500 kWh/a. Instead, the BIPV system produces only 30% of the calculated solar potential, while contributing 26% to the building’s energy requirements. In this case, aesthetic and functional characteristics were prioritized with respect to the final energy performance considering a solution compatible with the historical values of the building. Due to the design and colours of the BIPV elements, it was possible to balance aesthetic and energy requirements.
The integrated BIPV system uses more than 75% of the total available roof area (350 m²). The Swiss solar cadaster estimated the optimum figure of 60,000 kWh/y of solar potential for the entire surface area involved. With a real energy yield output of 42,264 kWh/a, the system produces 70% of the calculated solar potential, contributing 79% of the building’s energy needs. Exploiting all available roof surfaces of the building makes a significant energy contribution.
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Polo López, C.S.; Troia, F.; Nocera, F. Photovoltaic BIPV Systems and Architectural Heritage: New Balance between Conservation and Transformation. An Assessment Method for Heritage Values Compatibility and Energy Benefits of Interventions. Sustainability 2021, 13, 5107. https://doi.org/10.3390/su13095107
Polo López CS, Troia F, Nocera F. Photovoltaic BIPV Systems and Architectural Heritage: New Balance between Conservation and Transformation. An Assessment Method for Heritage Values Compatibility and Energy Benefits of Interventions. Sustainability. 2021; 13(9):5107. https://doi.org/10.3390/su13095107Chicago/Turabian Style
Polo López, Cristina S., Floriana Troia, and Francesco Nocera. 2021. "Photovoltaic BIPV Systems and Architectural Heritage: New Balance between Conservation and Transformation. An Assessment Method for Heritage Values Compatibility and Energy Benefits of Interventions" Sustainability 13, no. 9: 5107. https://doi.org/10.3390/su13095107