Solar

Building the future: New possibilities for thin films in building integrated PV

Issue 5 and Volume 10.

Silke Krawietz summarizes the outcome of her research project on behalf of UNESCO that explores the future architectural potential of building integrated photovoltaics (BIPV), in particular thin film PV technologies. The project combines the interests and motivations of architects and of solar researchers and manufacturers. Exploration of the characteristics of thin film technologies currently on the market and the kind of technology that high-profile architectural projects require formed the basis for the scientific research.

The rapidly growing importance of renewable energy technologies, in particular PV, makes them a critical focus for research. So far, wafer-based PV technology has been the industry standard, while thin film technology, which uses polycrystalline silicon film deposited on low-cost substrates, particularly glass, is already available in the market. Research to improve thin film technology continues. The most important research recently conducted has been helping to allow technology to transition from the first-generation, based on silicon wafers, to the second generation, in which a low-cost substrate supports thin films, as in the case of polycrystalline silicon film on glass. The wafer-based approach requires material in quantities that limit the potential for cost reduction and, hence, the long-term impact of the technology. It is expected that a mature second generation will replace first-generation technology over the coming decades. The change to thin-film dominance is considered inevitable, even though demand for first-generation technology will still remain. The advantages of second generation technologies include the lower price of modules and a more pleasing appearance. It is, for example, possible to produce semitransparent thin film modules (as is the case with first generation technology).

The integration of photovoltaics in buildings is a key to the future of PV technology. Architects and engineers are willing to integrate PV into their overall design projects and concepts. We know that architects are restricted to selecting PV technologies that are on the market. Further research into building integrated PV is also required to achieve the aims of architects and designers, which is to enhance the use of this technology in their buildings. The increased use of this technology in building integrated PV (BIPV) and research into thin films is expected to be ongoing in the medium and long terms to reduce the costs of the technology in such applications.

For thin films, high efficiency is the key to reducing the cost per rated watt of product in the long term. Third-generation PV maytriple efficiencies and hence significantly reduce costs of thin-film cells and modules.

BIPV potential

The possible uses of thin film PV in BIPV are wide ranging. And what important architectural and engineering characteristics must it have to make it suitable in BIPV? As the efficiency of thin-film cells continues to rise, their flexibility of use in BIPV will increase, making them a great asset. PV researchers are aiming for greater efficiency. Architects want to use PV in new applications and integration methods and want PV modules with improved aesthetics for specific projects. The solar industry is looking for cost-effectiveness in PV.

The needs of BIPV

What module and design features would high-profile architects find attractive in second-generation technology, and what further development would be required to make it even more financially competitive? What is the potential for large-scale application and building integration of the second generation of PV? The costs of thin-film technology make it more competitive with standard building materials. Table 1 summarizes the characteristics of first and second generation PV technology.


 

Desired characteristics

A summary follows of the main points that high-profile architects and engineers made in this research about how the development of PV modules should progress, in particular thin-film modules, and about what characteristics they would like to see in BIPV:

  • More variation in colour of and pattern on PV modules.
  • In the design of PV modules, more flexibility in the shape and dimensions of semitransparent panels. This would give architectural projects the opportunity to use PV in a greater range of applications.
  • Higher efficiency is needed for large-scale use.
  • More information about and the common development of new products is desirable. Interdisciplinary collaboration by architects, engineers and the PV industry on new products and the photovoltaic characteristics of PV panels that are under development – and research into them – might be the key to creating inventive applications in architecture and might enlarge the market for BIPV significantly. Some architects have criticized the nature of the available information about the potential of existing products and their ranges of applications.
  • Reduction of PV costs is essential for the expanded use of BIPV in high-profile projects. This is the main argument for enhanced BIPV use in architectural projects.
  • Life cycle assessment should be improved. Products should be more durable and have fewer technical problems over the 25 years that is typical of their operating lives.
  • Enhanced interdisciplinary research in collaboration with the PV industry into new PV products and modules (their design, characteristics, colours, patterns, new forms of integration) is needed. This has not yet happened to a great extent between architects, engineers, the PV industry, PV researchers and PV designers.
  • Greater BIPV variability from the PV modules side. This would increase the integration possibilities of the products.
  • Better collaboration in the field of legal standards for the integration of PV modules and products (standards for safe integration of glass and PV modules).
  • Reduction of the energy losses incurred through problems in storage, through inverters and through inaccurate planning of the integration (for example shadowing of modules).
Overall results of the project

The project has found that high-profile international architects and engineers and the leading research institutes in the field of PV want to see further development of second generation photovoltaics in BIPV that will introduce new design features and technical characteristics that will make them competitive materials to use by the PV production industry.

The project aimed to explore the potential for architectural application of new PV technology. It also aimed to exploit technology developed at the Centre of Excellence for Advanced Silicon Photovoltaics and Photonics at the University of New South Wales in Australia, under the leadership of Professor Martin A. Green. It also aimed to integrate its findings into the university’s teaching programme and support education for sustainability in the medium and long terms.

The project and it’s results can be directly integrated into technology education and the teaching sector. The outcome can be made available to a large number of engineers, architects and scientists through the connection with UNESCO and other related international programmes.

Further results

Exploration of the potential use of second generation, thin film photovoltaic technology in architecture has not yet been explored in the field of BIPV from the point of view of architectural expectations of this technology. The results of the project show how innovative it was and underline the importance of interdisciplinary collaboration between architects, industry and engineers. It shows that further development and detailed research is needed into the use of thin film PV technology in BIPV, and into what new design features it should have based on the needs of international architects and engineers. There should also be analysis of what steps have to be taken to make this technology competitive on the market.

Dr Silke Krawietz is Interim Professor at the Faculty of Architecture, University of Catania, Italy, and a teacher. She is also a specialist in BIPV, in the newest PV technologies and in renewable energy in architecture and engineering. She will soon publish a manual about BIPV for architects and engineers. She has various roles at the Italian Industry Association, including speaker and advisor on energy efficiency and on the use of renewable energy in buildings.
e-mail: [email protected]


Background to the BIPV research project

The architects that took part in the project included Foster and Partners; PTW-Peddle Thorp and Walker Architects, and Alberto Breschi. The engineers included Battle McCarthy and Arup.

In various meetings, overall ideas were explored, including selected reference projects of the various architects (planned, ongoing and past projects), projects that use first generation PV and second generation PV and a planned large-scale project, the Beijing Olympic Swimming Centre.

Part of the project included a meeting of high-profile architects, engineers and industry partners in London. Participants were the author and representatives of Richard Rogers Partnership, Battle McCarthy Engineers, BDSP Engineers and industry representatives from Schott Solar of Germany. The topics discussed included the architectural potential of thin film PV for BIPV.


Endesa headquarters

A good example of first generation BIPV integration is in Endesa’s headquarters in Madrid, Spain, designed by architects Kohn Pederson Fox and engineering firm Battle McCarthy. In addition to an overall eco-friendly design, the project contains photovoltaics in the glass roof of the huge atrium.

Integrated design measures have been taken to reduce the building’s dependence on mechanical systems and extraneous energy use. An ambitious efficiency target has been set of 30% reductions compared with a normal building of this size. The 4600 m2 atrium roof has been designed to receive standard sized, semitransparent PV panels progressively procured during the building’s life up to a potential 4600 m2 of panels.


BIPV used in the roof of the atrium at Endesa’s headquarters in Madrid, Spain

 


External view of Endesa’s HQ battle mccarthy, © kohn pederson fox architects

 


LA courthouse building

The Los Angeles Federal Courthouse integrates thin film photovoltaics. The architects and chief engineer Battle McCarthy incorporated eco-friendly features into the initial design of the building so that it could serve as a landmark in sustainable building. The building was oriented so that a large PV system could be placed on the south wall. A ground-source heat pump system in the foundations will provide cooling. Internally, the design of the central atrium allowed natural ventilation and daylight for the courtrooms and public spaces. Perkins & Will designed the building, which in 2003 received the Architectural Review Future Project Prize MIPIM.


BIPV integration into the facade of the Los Angeles courthouse © perkins & will architects

 


Railway station for high-speed trains in Naples, Italy

Another recent project that is using BIPV is the station for high-speed trains in Naples, Italy, designed by Zaha-Hadid Architects in collaboration with Max Fordham Engineers. Construction will end in 2008.


Internal view of the station for high-speed trains in Naples, Italy © zaha-hadid architects

 


Beijing Swimming Centre for the 2008 Olympics

The Beijing 2008 Games aquatic centre aims to meet international standards for competition while maximizing social and economic benefits. The centre will provide public multi-function leisure and fitness facilities before and after the games. The design aims to make the building visually striking, energy efficient and ecologically friendly.

Integration of PV into the building had been planned but had to be abandoned because the characteristics that the architect PTW and engineer Arup wanted from the PV technology and the construction material, such as the desired semitransparent effects and the thermal properties of the construction material, could not be met by available technology. Even in this modern high-technology project in which the client looked favourably on renewable energy and in which the newest building materials were used (such as high-tech EFTE cushions for cladding the building), the PV technology was unable to match the characteristics needed for it to be integrated into the project.


Watercube, Olympic Swimming Centre, Beijing © ptw architects, sydney, australia