Roofconsult Website All you need to know about building integrated photovoltaics - Part 1 by Dr Jürgen Neuwald of Kalzip Ltd
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Photovoltaics have the greatest documented technical potential for generating electricity of all the renewable energy sources in Europe. The trend is definitely in the direction of the so called BIPV – Building Integrated Photovoltaics – and these can be integrated directly as solar components with multiple functions such as sunshades, facade cladding or roofing, thus affording other green benefits. Figure 1: BIPVs as an architectural component
Photovoltaics (PV) represent an increasingly important type of renewable energy, thanks to rising interest in and demands on the environment and advances in solar technology supported by subsidised programmes.
The importance of PV in architecture is also changing, the main criteria being the desire for design freedom and a balanced appearance of the system. While PV thinking is usually strongly in the direction of tilted, framed crystalline modules, which are difficult to match with the preferences of many planners and architects, the trend today is towards architectonically integrated systems that are generally based on more modern, thin film technology.
Modern BIPV do not necessarily have to be the aspect that determines the design for architecture. Quite the contrary. Intelligent solar energy systems can be integrated in the planned construction project such that they are easily visible or hidden, depending on the customer’s wishes.In general, all roof surfaces facing southwest to southeast in central Europe are suitable for PV applications. However, BIPV can also be used for north-facing shallow-sloped roofs if the usable areas of the shells in the roof and facade are designed to ensure optimum sunlight exposure without shading. In case of doubt, computer-aided simulation can help ascertain the right solution.
Thin film modules are commonly employed in the integration of PV in buildings and compared to the better known crystalline modules, have not just a significant weight advantage. This technology is especially suitable for weak or diffused light because the usual mounting supports for the modules are no longer required.
In general, the roof is the part that is most exposed to weather and environmental influences. Classic, sustainable roof planning, with all the constructive and physical requirements in terms of waterproofing and durability, must not be neglected. Figure 2: Available solar irradiation at different orientations
Ideally therefore, well-proven roof systems should be used where the PV cells/modules are integrated into the roof skin but also where the original roof is technically separate from the PV itself
The number of metal or plastic flat or pitched roofs that satisfy this requirement is increasing but the system used should fulfill the following five criteria:
  1. The roof system is supervised and approved and its functions have been tried and tested on the market.
  2. Solutions that satisfy the relevant standards and that have technically proven themselves are available for all planning and implementation problems, especially in the case of details and connections.
  3. The functioning (or as the case may be, the failure) of the PV modules does not affect the structural and physical properties of the roof.
  4. The BIPV system demonstrably fulfills the requirements of protection class II (Electrical Safety during Assembly and Operation) and IEC 61646/IEC 61215 (Suitability and Durability of Photovoltaic Modules).
  5. The materials, construction and implementation of the roof system ensure the proper operation of the PV system over the expected PV service life. Current experience has shown this is approximately 35 to 40 years. This also means future expected maintenance or repair work should not affect the functioning of the PV system or, in the worst case, lead to a failure.
A feature shared by BIPV thin film systems used today is the favorable energy payback time. While the usual systems based on crystalline modules have an energy payback time of about 10 years, that of current thin film systems is approximately two years.The difference is based mainly on the more spared use of the primary material - silicon. In the most commonly used module type made of amorphous silicon (a-Si), the required silicon layer thickness is less than 100th of the layer thicknesses in crystalline framed cells. This property is also the reason for the malleability and flexibility of many BIPV systems.
At the same time, this characteristic means that the surface efficiency of thin film modules is usually lower than the comparable values of crystalline modules. As a result, a smaller system (ie. a lower kWp capacity) should be installed. Figure 3: Structure and components of a BIPV system
Thin film modules based on cadmium telluride (CdTe) are still not often used - they are controversial due to the use of the heavy metal cadmium and stringent safety and environmental regulations must be satisfied in the production phase.
In technical circles, copper indium diselenide (CIS) modules have long been considered as being a determining influence because higher efficiencies are being targeted for the future. Until now however, the difficulty concerning this module type has lain in setting up the very complex system technology for mass production.
Dr Jürgen Neuwald is director of new business and technology for Kalzip Ltd, for more information see
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