Roofconsult Website All you need to know about building integrated photovoltaics - Part 2 by Dr Jürgen Neuwald of Kalzip Ltd
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In Part 1, Dr Neuwald covered the various ways in which BIPVs can be applied. In this the second part we look at the structure of those systems, how they are implemented, the costs and return on investment.
BIPV systems function in a similar way to the usual bolt on roof systems which are implemented using conventional crystalline module technology.
The PV cells which account for approximately 75% of the system costs are connected in series to form strings of laminates producing direct current when exposed to sunlight.
The strings are then routed to a combination box which gathers the whole array together and contains a circuit breaker, fuses and – if necessary –a circuit breaker for the lightning protection system.
The combination box is usually installed near the PV modules and should be easily accessible. While they are not required in every case, their use is recommended due to the reasons mentioned above.
The inverter is the control centre of the PV system, accounting for approximately 10% of the total costs of the system. Inverters not only convert the direct current into grid compliant alternating current, they also use voltage/amperage regulation to control the system at varying amounts of solar irradiation. In technical jargon, this is called Maximum Power Point (MPP) tracking. For this reason, it must be ensured that roof extents with different orientations and pitch are connected to separate inverters.
The solar energy that is generated is first used by the building and then fed into the National Grid. In the UK, the Department of Trade and Industry’s latest funding scheme for renewables, the Low Carbon Buildings Programme (LCBP) was relaunched in May 2007.
Through this, funding is available for householders, with a maximum of £2,000 per kW of installed capacity, subject to an overall maximum of £2,500 or 50% of the relevant eligible costs, whichever is the lower. For the public sector there are grants available with a maximum of £1 million or 40 to 50% of total costs excluding VAT.
However, in many cases the operator of a PV system is not satisfied with merely having a feed counter.The most up to date monitoring systems permit remote diagnostics and continuous function monitoring of the individual components and which inform the operator of faults by, for example, text messages or an acoustic signal. Large scale displays, which are popular with clients, are intended to monitor the effectiveness of the system for the operator and increase occupant awareness.
In the planning phase of a BIPV system, the suitability of the individual roof and facade surfaces should first be checked in terms of irradiation aspects. Shadowing of roof surfaces, such as can occur with prominences or free form surfaces, should be avoided. Furthermore, minimum pitches may need to be taken into account to ensure adequate water run off depending on the roof system.
Even though this sounds complicated – especially in terms of irradiation aspects – it is actually very simple with state of the art software. In case of doubt, please contact our technical services department to determine the relevant design parameters and for free annual yield calculations.
To do this, suitable inverters and wiring concepts are determined so costs can be specified and optimised at an early stage.
Furthermore, approved planners of electrical systems and building technicians should be involved as early as possible to reduce costs that accrue later during implementation and prevent any duplicate planning work. In particular, local authority policies can affect the system layout.
It is recommended that the local power utility company also be contacted during the planning phase and permission obtained, along with the technical specifications for inputting the PV system into the National Grid.
Due to the roof integration, the duties of roofers and electricians overlap during implementation. However, the roofer or the facade constructor may undertake the string interconnection of the modules and guide the additional cables into the building.
To do this, they need to use special allinsulated snap-fit systems such as those that are used in all commercially available BIPV modules. Within the building, the qualified electrician usually does the rest of the work. He is solely responsible for mounting the generator junction boxes, especially in the area of the inverters and the alternating current interconnections.
The complete roof or facade, including the BIPV, is usually tendered as one trade – the roof or facade constructor, with the help of subcontractors, then undertakes the entire job up to commissioning. Modern high quality BIPV systems can run without maintenance but this does not include scheduled inspections of the inverters and visual checks of the PV cells for excessive dirt or debris build up.
Research has shown that the operation and maintenance costs of a commercial office building over a 25-year lifetime can be up to five times the initial capital cost of construction. The reduced running costs provided by a PV system therefore need to be included in an economic efficiency calculation. Maintenance contracts with the company that carries out implementation provide certainty in this regard. These can usually be combined with periodic maintenance work on channels, skylights and so on.
A frequently asked question involves cleaning work or removal of snow in winter. In this regard, losses due to dirt are usually included in the yield calculations but these do not include permanent deposits of rotting leaves or of snow.
Even if the system were to be completely covered by snow during winter, the annual yield would be reduced by only about 10% because the winter months are also the period with the lowest solar irradiation.
System efficiency
Due to the integration of the roof system with PVs, not only are building material costs reduced but significant savings in terms of the mounting costs can be achieved, especially since BIPV does not require additional assembly components such as brackets and rails.
Due to the fact that BIPV with thin film technology has higher specific surface area requirements than conventional crystalline systems, the executable system output per unit area is usually lower.
Due to the lower construction costs and the usually higher specific yields however, the investment security is often higher.
BIPV systems provide many opportunities for innovative architectural design and they are generally less expensive than the usual add on systems. But planning and system selection must always satisfy the structural and physical requirements of the building shell. Selection is helped by the multitude of fully developed and tested systems available on the market today.
Additional information on the planning and implementation of BIPV via an extensive database on the basics of PVs as well as practical examples can be found at
Flexible solutions for creative solar architecture are contained within an updated Kalzip solar brochure that contains information on the different systems available, when and how they can be installed, general design considerations, and technical information on the advantages of amorphous thin film technology.
Dr Jürgen Neuwald is director of new business and technology for Kalzip Ltd, for more information see
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