OVERVIEW | Building integrated photovoltaics (BIPV) as a viable option among renewables

In the face of the urgent need to renovate and decarbonise the existing building stock, special focus is on building skins, such as roofs and facades, to make them more efficient through innovative solutions and materials, but also to generate energy. This is essential to achieve the EU 2030 energy targets, only 11 years away.

The concept of Building integrated photovoltaics (BIPV) refers to the integration of technology, -- refers to the capacity of the photovoltaic (PV) system to be multifunctional -- aesthetics -- refers to the architectural appearance of the system -- , and energy integration, meaning the capability of a PV system to interact with the building and district energy system to maximize the local use of electricity generated.

 

The BIPV systems can be divided in three main categories:

· PV modules, with specific characteristics developed for building integration, with appealing features (such as colour, texture, shape, surface finishing, and light materials) conceived for integration in existing buildings.

· Mounting systems, to mount the PV modules on the building envelope, such as on facades, roof, and external devices.

· Energy systems, which link the PV modules to the building and district energy system to maximize the local use of the electricity generated, including storage, power conversion, power control, heating and cooling and e-mobility systems.

 

In order to promote the use of BIPV, technology development initiatives have enabled the production of databases available for practitioners to disseminate knowledge and showcase successful applications. A BIPV products database developed by Eurac Research groups existing products according to the above mentioned categories. On the other hand, a BIPV cases portal by solarfassade provides cases to support the technology transfer and continuous spread of building-integrated photovoltaics.

 

In addition, the SHC Task 41 provides an interactive collection of case studies. This task is devoted to achieving high quality architecture for buildings integrating solar energy systems, as well as improving the qualifications of the architects, assisting their communications and interactions with engineers, manufactures and clients with the vision to make architectural design a driving force for the use of solar energy.

 

At regional scale, efforts are made to develop BIPV solutions that are tailor-made for limited irradiation conditions (BIPVNO) or to bridge the gap of limited acceptance from architects through sharing knowledge and combining the competencies and create synergies between architects and specialists of the photovoltaic sector (http://www.bipv.ch/index.php/it/).

 

Several international surveys carried out among BIPV stakeholders reveal that one of the main barriers to the spread of BIPV systems is the high cost.  In fact, the economic issue is still perceived as a barrier by architects and contractors, who are the main BIPV stakeholders. On the other hand, the drastic cost breakdown of PV over recent years has decreased BIPV prices leading to cost competitiveness with standard building materials. It is thus essential to build trust of architects, investors and financial stakeholders, by showing business cases and real stories. Architects’ perception is influenced more by tangible examples and real-world experiences than by theoretical calculations.

 

Thanks to a specific initiative to promote BIPV, 16 built BIPV projects were analysed as business case studies, providing information on their final user costs. These case studies were selected among more than 40 examples collected in the South Tyrol area and they represented ordinary examples including several kinds of integration typologies (these include office, residential, agricultural, industrial, community, religious, commercial and transportation buildings) representing both private and public sector, different architectures and technologies. Such a varied sample means that the BIPV case studies have a high replication potential in other European regions. More information on the background of this project can be found in this publication Building Integrated Photovoltaic (BIPV) in Trentino Alto Adige.

 

Among this study, most of the cases (around 60%), have integrated BIPV during the building construction, while the remaining proportion represents retrofit intervention. Several architectural integrations are shown, including opaque and semi-transparent roof, warm, cold and double skin facades as well as external devices such as parapets and solar shading elements. The most predominant are façade and roof systems. And the different building typologies represent both private and public ownership, giving an overview on different approaches to BIPV, especially regarding the decision making related to economic issues.

 

In terms of costs, the same study looked at two different perspectives: the PV perspective –normalizing the cost of kWp (kilowattpeak), and the building perspective – normalizing the cost per m2. Looking at the PV perspective, results show that the cost of the analysed BIPV systems, in which the construction year was between 2004 and 2015, ranges from 2.500 €/kWp to 8.300 €/kWp, with an average of around 5.500€/kWp. This variation can be ascribed to several factors, such as the type of technological integration, the type of components used and, most important, the construction year, since the PV cost has seen an impressive decrease over the last few years.

 

In order to look at the economic matter from another perspective, the cost has been normalized to the surface of the envelope covered by BIPV (€/m2), thus using an indicator which is normally used in the building sector. The cost of the analysed BIPV systems ranges from 300 €/m2 to 1.300 €/m2, with an average of around 600 €/m2. Overall the following average values are found in Table 1.0.

 

	(A) €/kWp	(B) €/m2
Opaque cold façade	~7.900	~ 850
Semi-transparent roof-façade	~5.100	~ 500
External device	~4.900	~  500
Opaque tilted roof	~4.400	~ 600

Table 1.0. Average values for PV perspective (A) and building perspective (B) costings of BIPV projects

 

As can be seen from Table 1.0, for the €/kWp index, the cost variation can be ascribed to several factors. A crucial role is played by the PV module efficiency. For this reason, looking at this indicator might be misleading, but it is very useful to compare the BIPV system cost with standard building materials. It demonstrates that in fact, the BIPV system capital cost lays in an acceptable range and it is even cheaper than some standard passive building materials (e.g. glazed curtain walls, stone and others). This alone is of great interest when comparing with passive solutions, even without considering (a) the pay-back time period (which ranges from 4 to 11 years for the presented case studies), (b) the energy savings, and (c) the added value of an integrated façade system over its life cycle.

 

The cost variation of BIPV is widely influenced by the construction year, since the PV cost has seen an impressive decrease in recent years. A clear decreasing trend in the costs of BIPV has been found for the last decade with values of ~8.000 €/kWp and ~950 €/m2 in 2004 to ~3.300 €/kWp and ~400 €/m2 in 2015. This data makes it possible to infer that the costs of BIPV is not too far from a ground-PV solution (which is a standard non-integrated PV system). Despite these tangible examples, the economic issue is still perceived as a barrier for the widespread adoption of BIPV systems. The use of PV in architecture is nevertheless viable for many cases.

 

BIPV technology still needs to overcome some market barriers, mainly related to the flexibility in design and aesthetic considerations, lack of tools integrating PV and building performance, demonstration of long-term reliability of the technology, compliance with legal legislations, smart interaction with the grid and cost-effectiveness. In this context, several Horizon 2020 projects address such barriers.

 

The project PVSITES  aims at driving BIPV technology to a large market deployment by demonstrating an ambitious portfolio of building integrated solar technologies and systems, giving a forceful, reliable answer to the market requirements identified by the industrial members of the consortium in their day-to-day activity.

 

At the same time, the project EnergyMatching, addresses the issues related to BIPV energy integration by developing new concepts and technologies in this direction. In this context, PV integration is irrevocably destined to play an essential role in the years to come and learning from the experience gathered in realized projects, BIPV systems have the potential to play an important role in technological, aesthetic and energy integration.”.

 

Another funded project, ADVANCED BIPV, is looking at increasing the competitiveness of BIPV technology by means of developing a new generation of photovoltaic glazing. This should satisfy the well-defined market created by architectural trends, such as (a) continuous envelope surface with large glass areas between spandrels, (b) buildings whose activity demands high degrees of daylighting, and (c) projects located in earthquake and hurricane areas.

 

BIPVBOOST, on the other hand, is a project that focuses on bringing down the cost of multifunctional BIPV systems, limiting the over-cost with respect to traditional, non-PV, construction solutions and non-integrated PV modules. This will be done through an effective implementation of short and medium-term cost reduction roadmaps addressing the whole BIPV value chain and demonstration of the contribution of the technology towards mass realization of nearly Zero Energy Buildings. With huge involvement from industrial partners in the consortium, BIPVBOOST looks at pursuing a 50% reduction of the additional costs of BIPV modules in 2020, and 75% reduction in 2030, and thus result in a substantial increase of market deployment of BIPV technology.

 

Finally, Task 15 of the IEA PVPS Programme wants to create an enabling framework to accelerate the penetration of BIPV products in the global market of renewables, resulting in a level playing field for BIPV products, BAPV products and regular building envelope components, respecting mandatory issues, aesthetic issues, reliability and financial issues. The implementation of this objective is being supported by several initiatives or subtasks looking at developing databases, developing business models, demonstrations and dissemination.

 

Overall, energy integration is becoming increasingly important to meet the new building concept and its energy provision. In fact, thanks to the EU policy oriented to promote the NZEB (Nearly Zero Energy Buildings) concept and RES (Renewable Energy Sources) exploitation, buildings are becoming more than stand-alone units using energy from the grid. They are becoming micro energy hubs consuming, generating, storing and supplying energy, thus transforming the EU energy market, moving from centralized, fossil-fuel based, national systems towards a decentralised, renewable, interconnected and variable system. And the driving role of BIPV to achieve these goals is undeniable.