At the recent building integrated photovoltaic (BIPV) technology platform in Brussels there was a new sense of optimism among delegates, spurred on by advances in technology, falling costs, new political support measures and increasing awareness amongst the public and professionals. But will it be enough to really launch this field? Alasdair Cameron attended the meeting.
‘The BIPV market is potentially the greatest opportunity for PV in Europe’. These were the words of Evelyn Shellekens of the European Association of Electrical Contractors (EAEC), speaking to a group of scientists, politicians and business people who had gathered from across Europe to attend the Building Integrated Photovoltaic (BIPV) Technology Platform meeting in Brussels, part of the European Union Sustainable Energy Week, a series of events held at the end of January to focus on renewable energy and energy efficiency.
Solar roof tiles on a converted building in the UK solarcentury
BIPV – the architectural, structural and aesthetic integration of photovoltaics into buildings – is one of the most exciting branches of renewable energy, allowing the incorporation of energy generation into everyday structures such as homes, schools and offices. While the hugely successful feed-in tariffs in Germany and Spain have created and sustained a large European photovoltaic industry, they have also fostered the development of multimegawatt ground-mounted arrays, and non-integrated roof-mounted systems, seen by many as a sub-optimal use of solar technology. The future, say the supporters of BIPV, is in making solar energy an everyday part of the fabric of life.
How not to do it? While effective, this type of installation may not be the best use of PV sunpower
There are many stunning examples of PV integration, but it remains the case that most PV on buildings has been a roof-mounted add-on, often with little attempt made to blend it in with its surroundings or integrate it into the design of the structure. On large buildings, much has been hidden away on roof tops, inoffensive, but also uninspiring. Such developments fail to take full advantage of the beauty of building integrated photovoltaics, and do not properly serve society. These were the sentiments echoed by Professor Stefan Behling, Head of Design at Norman Foster Architects, at the PV-SEC meeting in Barcelona in 2005: ‘In the last 15 years architecture and the PV industry have moved further apart than they were. Many of the hundred thousand roof programme buildings will come back and haunt the PV industry. They will try to sell PV to newcomers and they will reject it. The truth is the cell itself is totally innocent. Cells are beautiful, I love them. But few people take the challenge seriously and try to create examples that are beautiful.’
Not only does this situation create poor architecture, he argued, but it risks causing a backlash against PV systems in general.
A better use? The facade on the MANCAT building was inspired by the much larger CIS tower (below) daniel hopkinson
But how did this situation come about? For more than 20 years, architects and the photovoltaic industry have been talking about the potential for BIPV, but with little mainstream success. A lot of fantastic projects have been constructed, some by the world’s most noted architects, but BIPV has yet to enter the popular mindset. It seems that a number of factors have been to blame. Firstly in the early days of photovoltaics the prices were prohibitive for the wider, non-prestige market (in part because these modules are usually custom-made). Then, as support policies came into force, the PV industry began to experience an unprecedented boom, making it one of the fastest-growing industries in the world. Though the price of solar modules began to fall, the high demand for PV has given manufacturers little incentive to deal with architects and become involved in riskier and more complex projects. As producers look to fill orders in the rapidly growing market, smaller niche players have suffered. ‘The companies which have specialized in integration have seen decline’, said Stefan Behling.
Another major problem is that the building sector itself is conservative and not given to trying new and potentially risky ideas. Communication is also an issue. Traditionally there has been little interaction between roofers, glaziers and electricians on a new development, and dialogue between the photovoltaic and construction industries has also been scarce. As Evelyn Shellekens said of the BIPV industry: ‘we need to educate, to inform’.
The solar cladding on the CIS tower in Manchester, the largest vertically installed PV facade in the world solarcentury
Now things could be ready to change. Speakers at the recent BIPV platform have predicted that the combination of falling costs, new technologies, greater awareness and increasing political support mean that the time could now be right for the wider take-up of BIPV.
A time for BIPV?
There are a variety of reasons why confidence in the BIPV sector is on the rise, stemming from improvements in policy, technology and the economics surrounding photovoltaics.
Policy support for building-integrated PV
Policy measures are critical in encouraging the development of BIPV. More and more countries are now following the example set by Germany and introducing their own feed-in tariff mechanisms to boost their solar industries. Spain was one of the first to follow, and now has a modest but rapidly growing PV sector. Greece and Italy have recently followed suit, but by far the most targeted scheme is in France, which has developed a feed-in tariff aimed specifically at supporting BIPV applications. Solar electricity will receive a premium of €0.3/kWh (€0.4/kWh in the overseas départements and Corsica). The interesting bit is that the electricity will receive an additional €0.25/kWh if it is derived from BIPV installations (€0.15 in the overseas départements and Corsica). Since it was generally agreed by those attending the platform that €0.3/kWh would not be enough to encourage standard PV to grow rapidly in France, the feed-in tariff is clearly designed to foster a greater uptake of building integrated PV.
The enclosed academy in Herne, with one of the world’s largest BIPV installations scheuten solar
In addition to the feed-in tariff, France has also recently introduced a number of other measures to bolster support for PV, including tax breaks for householders installing systems, and greater rates of depreciation for corporate customers. The hope is that these incentives will lead to a rapid increase in the uptake of PV, and while no cap has been set, the figure of 160 MW by 2010 has been mentioned as a general target.
Compared with the French system, the Greek and Italian support schemes are more straightforward, and offer a payment around €0.34-0.5/kWh for solar electricity, similar to Spain and Germany. While these programmes have not been so strongly designed specifically to foster BIPV, they do contain some banding (in Italy a ground-mounted system receives less than a BIPV system, although it is not clear how integrated a system must really be) the expected rapid increase in the photovoltaic market as a whole will undoubtedly lead to a greater take up of BIPV technology.
The thin-film PV on the roof of the renovated Stillwell Avenue station in New York schott solar
In the United States, grants, tax breaks and other support measures for solar are becoming more widespread, not just in California, but increasingly the Northeastern and Southwestern States. While so far the policies do not contain any specific encouragement for BIPV, it seems likely that as in Europe they will lead to a greater take up of this technology, particularly in urban areas (for more information on BIPV in New York, see Solar Skyline, Renewable Energy World November-December 2006).
Advances in glass
In addition to increasing public and political will, there are a number of important engineering and materials breakthroughs which now make BIPV more achievable. Glass can be used to fully encapsulate solar cells – either crystalline or thin-film – and the technology in this field has progressed significantly in the last 20 years, with huge glass panels and facades becoming routine in new developments. As Alan Garnier of French glass manufacturers Saint-Gobain said: ‘glass can be used to generate electricity, and glass can be used for almost 100% of a building’s facade’, sentiments echoed by Winfried Hoffman of the European Photovoltaic Industry Association (EPIA) who said: ‘I would like to see less talk of PV in buildings, but more of solar electric glass.’
Solar skylight over a stairwell at the Ma Wan school in Hong Kong josie close
In addition to the ability to handle and produce huge sections of glass for building, new types of glass could also be useful for BIPV. Self-cleaning glass for example, can be incorporated into glass-PV modules and help to keep them free of dust and thus improve the efficacy photovoltaic cells. This is important as building integrated PV is likely to be found in some hard-to-reach places and in urban environments where dust and dirt could be a significant problem.
Solar glass can have varying degrees of transparency depending on its uses schott solar
Anti-reflective glasses increase the amount of light that reaches the cell from around 90% to 96%, improving the efficiency of the unit by at much as 3.5%. Other advances include new types of insulating glass which can help glass-glass PV to fulfil structural uses.
A number of companies are currently offering glass-glass PV, including Schott Solar, Romag (using cells from BP Solar and Q-Cells), Sharp and Scheuten Solar (using Solarworld cells), which produces custom-made modules up to 6 m2.
New types of PV
While at present crystalline silicon is the type most commonly used in BIPV applications such as solar glass and building facades (see examples below), thin-film solar has increasing potential for integrated applicationsuses.
With a few exceptions, thin-film has so far been largely restricted to large roof-top and ground mounted applications, as its lower efficiency per m2 required a greater surface area. In recent times however thin-film cells have been increasing in efficiency (some are now above 10%, compared to 4%-7% five or ten years ago) and flexibility, and can now be obtained in a variety of forms, including a range of colours, shapes and sizes. Indeed, thin-film can be mounted on any surface, including curved or flexible materials, all of which aids its integration into standard building design (see OpTIC building below). Several companies currently produce thin-film PV for BIPV applications, including Schott, Unisolar and Sharp. Unisolar produces amorphous silicon thin-film PV which can be fused to roofing materials. This type of product has been used to cover wharehouses and factories in the US such as the Coca Cola factory in LA. Sharp is currently working on a new range of thin-film BIPV modules which it will release in Japan in the summer of 2007. In the future, as the efficiencies of thin film cells continue to rise, this flexibility will become an increasing asset, and much wider deployment can be expected.
Curved photovoltaic facade on a building in Germany sunpower
Aside from the progress in thin-film systems, a number of important advances have also been made in crystalline silicon modules, allowing easier architectural integration. Kyocera, for example, markets dark blue and black modules, designed to blend with their backgrounds and improve light absorption. The same type of technology can be used to produce solar tiles or roofslates. UK-based developer Solarcentury, for example, currently makes a black 52 W monosilicon solar roof tile for new-build roof applications using SunPower cells, and also markets a grey ‘Sunslate’ from Atlantis Energy. One of the advantages of this type of solar tile is that it can often be easier to obtain permission to fit them than for standard roof-mounted models, particularly in architecturally sensitive areas (assuming they blend in of course).
Solar cladding on the MANCAT building in Manchester solarcentury
Concentrating photovoltaics (CPV) is another interesting area for BIPV applications in climates that predominantly offer direct sunshine, rather than diffuse light. CPV uses lenses or mirrors to focus sunlight onto solar cells, increasing the amount of energy obtained for a given area of silicon. While traditional CPV units have little BIPV potential given their size (they often, but not always, need a tracking mechanism) and appearance, new developments are underway which could change this. At last October’s Solar Power conference in San Jose, California, US company SunPhocus discussed plans for a new type of concentrating solar cell, using holograms instead of lenses to focus the sunlight. These holograms are very thin and can be applied in strips across the cells, allowing glass-glass PV to use a form of CPV technology, improving efficiency by 25%-40%. The product has been specifically designed for the building integrated market, and the company hopes its technology will allow high-efficiency, low cost-systems.
Glass-glass photovoltaics on the Lehrter train station in Berlin engcotec
Looking further into the future, the efficiencies of both crystalline and thin-film solar cells are continuously improving. Indeed Spectrolab recently announced that it had produced a cell with an efficiency of 40%, breaking all previous records. In time, these improvements in technology will effectively reduce the amount of space required by PV to produce a meaningful amount of electricity, increasing the BIPV options available.
In addition to increasing efficiency, it is predicted that in the future there will be significant decreases in the price of BIPV systems, in part because economies of scale should improve, and additional developments in module manufacture and installation techniques should bring prices down.
At the BIPV Technology Platform, Tjerk Reijenga of BEAR Architects (Netherlands) said: ‘There is a lot of freedom in design if you talk about building integration. There are many possibilities with PV’. From the facades of skyscrapers, to PV-windows and street furniture, the examples below help to illustrate this point. Indeed, one of the challenges to for the BIPV industry is to communicate this potential to the building sector at large. As part of this process, a new website called www.pvdatabase.org has bee launched as a joint-venture by PV-UP-SCALE and the IEA PVPS Task 10 to showcase examples of BIPV projects and photovoltaics in the urban environment.
PV facades can fulfil a vital role in buildings, not only generating electricity, but also replacing sometimes expensive facing materials (marble or granite facades for instance). Two of the best examples of photovoltaic facades can be found in Manchester in the United Kingdom (see images on page 94). The Co-operative Insurance Society (CIS) tower in the city centre, was originally built in the 1960s, but in 2005-2006 it received a complete refit, including the world’s largest vertically integrated PV system. Installed by Solarcentury using Sharp’s 80 W crystalline silicon modules, the 390 kWp solar cladding acts as a rainscreen, helping to offset the costs of other building components. The success of this project influenced the next example, the library of the new campus at the Manchester College of Art and Technology (MANCAT). Although on a smaller scale, this building also used Sharp modules as its facade, and recently won the prize for best building at the 2006 Royal Institute of British Architects / LSC Further Education Awards. (In addition to the PV facade, the MANCAT building had roof mounted PV and solar thermal, as well as a host of other sustainable features. For more information see BIPV Showcase in Renewable Energy World, November-December 2006).
As a sign of progress in this area, Schüco, one of the world’s largest providers of building facades and frames, has launched its E2 product, a fully integrated facade system for new builds.
Glass-glass panels, windows and skylights
One of the most widespread applications of BIPV is in solar windows and skylights. The recently opened Lehrter train station in Berlin contains 180 kWp of glass-glass modules from Scheuten Solar. Since the roof of the building is curved, each of the modules had to be custom built to fit within the steel frame of the building. Also in Germany, the town of Herne possesses one of the largest BIPV systems in the world. Designed by French architects Jourda et Perraudin (in co-operation with Hegger Hegger Schlieff of Kassel), the project consists of an academy, hotel, library and offices in a glass enclosure containing 1000 kWp of solar glass.
The OpTIC project in Wales, UK, with copper-indium-diselenide thin-film roof bruce cross
Further east, the Ma Wan school in Hong Kong provides an excellent example of aesthetically integrated PV in the solar skylight over the school’s stairwell. Here, polycrystalline cells have been spaced to allow 65% transparency and patterned in the edge modules to provide an attractive feature. As well as the solar skylight, the Ma Wan school has a range of roof mounted PV systems, using both crystalline and thin-film PV.
Roof spaces are ideal for solar generation, with great scope for BIPV applications. The Stillwell Avenue train station on Coney Island in New York is a perfect example. Originally built in 1919 and reconstructed in 2005, the station has been fitted out with 210 kWp of opaque amorphous silicon thin-film modules manufactured by Schott Solar. Chosen for their appearance and energy performance, the 7060 m2 array is seen by more than a million passengers a month. Steve Cohen, Product Manager at Schott summed up the project, saying: ‘Solar systems no longer have to be bulky add-ons to a structure. The Stillwell Avenue station showcases what can be done with photovoltaics today.’
Sticking with thin-film, the OpTIC building in South Wales is also an excellent example. Designed by Percy Thomas Partnership, and constructed in 2003, this project contains 85 kWp of copper-indium-diselenide PV, supplied by Shell Solar. The OpTIC building falls firmly into the category of prestige project, and was largely funded by the UK government through the Welsh Development Agency.
Solar houses in Mayersloot, Netherlands bear architects
On the domestic front, new products such as solar roof-tiles have raised the prospect of integrated solar roofs becoming widespread. These types of modules are marketed by a number of companies across Europe. One good example can be found on the Laing Development in north London. Here, nine new houses were fitted with a total of 15 kWp of grey Sunslates, small crystalline silicon modules produced by Atlantis Energy. All houses sold faster than expected and at a premium of between £5000-10,000 (€7500-15,500). It is estimated that these systems will offset around 5 tonnes of CO2 per year.
BEAR architects themselves have also developed some innovative housing projects at Mayersloot in the Netherlands. While the PV systems on these houses are roof mounted, as opposed to fully integrated, the way in which it has been done shows that the PV systems are an essential part of the design, and are also pleasing to look at.
For the future
Despite a growing number of political support schemes, excellent examples and improving technology, it is unlikely that building integrated photovoltaics can achieve widespread mainstream application in the immediate future – steady growth seems like a more reasonable expectation. In the longer term, though, it seems possible that with increased awareness and improved technology BIPV will succeed in achieving the level of deployment necessary to have yield major environmental benefits it can undoubtedly bring. More and more companies are developing products specifically designed for the BIPV market, and the growing number of examples will inspire and inform the building sector. Perhaps in the end it will simply be a natural progression. Professor Stefan Behling: ‘All these things will be overcome. In the beginning things are on their own, only when they are integrated are they of proper use to society.’
Alasdair Cameron is Assistant Editor of Renewable Energy World
Different BIPV markets
Broadly speaking, building-integrated PV can be divided into three main markets. Firstly, are the prestige buildings. These tend to be high-profile developments by major companies, governments or organizations keen to show-off their environmental credentials and cutting edge design. In these cases the clients are less likely to be concerned about short pay-back periods on their investments, as the BIPV is used as part of an overall statement.
Another major market for building integrated applications is in residential applications. Solar skylights, roof integrated systems and solar roof tiles can all fall into this category. In these cases the costs of the system are borne by the ultimate purchaser of the property and are factored in as a small part of the mortgage. Since the costs are spread over the lifetime of the property and tend to increase house prices, they represent marginal additional expense.
Next there are commercial projects. These are cases were large organizations have determined that it may be cost effective in the long-term to install BIPV in their buildings. Such developers are generally large energy users, and are found in regions with strong support for photovoltaics, either in the form of feed-in tariffs or some other programme (see below).
While the various forms of BIPV may be used in any of these markets, the design of the system chosen is likely to vary widely depending on the needs of the client. One of the key objectives in the next few years will be to move photovoltaics in buildings out of the realm of the prestige projects and more firmly into commercial and domestic applications were it can have a wider take-up.