1 Introduction
In developed countries, the advantages of integrated photovoltaic systems for buildings are increasing. Against the backdrop of rising global energy costs, architects and engineers are investigating new potential and cost-effective integrated solutions for the use of photovoltaics for glass curtain walls and roofs to assess the potential of BIPV.
In different developed countries that allow building owners to import surplus electricity into the public grid (photovoltaic grid), this trend is supported by the government.
According to the market price, the current price of photovoltaic power is still 2-4 times higher than the price from the public power grid. However, experts believe that photovoltaic power will be competitive under pure economic conditions within a few years.
Due to the factors of shading, building orientation or surface inclination, the technical adaptability of some building surfaces to photovoltaic power generation is limited.
Among the solutions that have been found, for example, BIPV on the structural glass of an integrated roofing system, from the perspective of architecture and solar energy conversion, adding aesthetic considerations to allow PV systems to realize their full potential. In addition, new building regulations in different countries now adopt the special safety and security features of glass only for laminated safety glass. In ceiling glass, balcony and curtain wall glass systems, laminated safety glass has to be increasingly integrated to prevent people from being damaged by broken glass.
Since the PV module itself is a special laminated glass (encapsulated solar wafer), it has its own advantages by producing PV modules with new safety and security features. The only effective interlayer for making glass the best real safety glass is the PVB membrane that is preferentially applied to safety glass production.
2. Solar Wafer Package
For photovoltaic solar modules, the current manufacturer guarantees their lifespan of at least 20 years or longer. To improve the durability of this system, many technological improvements have been made over the past few decades. One of the most important components is an encapsulation material that prevents damage to solar wafers and guarantees sustained power generation.
Due to the viscous performance of ethylene-vinyl acetate copolymer film (EVA film) during lamination, the ease of handling of the one-step laminating method, and the reliable experience of long-term application of this material, currently manufacturers are more inclined to use it as a Packaging material. Alternative materials are acrylic or polyurethane based polymeric resins. The typical component structure is shown in Figure 3. The front and back glass is usually 4mm thick tempered low-iron ultra-white glass; if you have to reduce the weight of the module, use special polyvinyl fluoride and metal coated PET as the back film.
A technical alternative to the above packaging material is a polyvinyl butyral resin (PVB) film. TROSIFOL® SOLAR is developed by Kuraray Europe GmbH (KEG). New PVB membranes launched in the PV market in 2004.
PVB has impressive records on laminated glass for its excellent properties such as optical transparency, adjustable glass adhesion, strong impact resistance, UV resistance and temperature stability.
The main difference between EVA and PVB films is that the EVA film is an elastomer that can be chemically crosslinked, while the PVB film is a non-crosslinked thermoplastic. When glass/glass photovoltaic modules are made of laminated glass containing cell sheets, they again have different performances in terms of safety and security. If an EVA film is used as an interlayer, a very thick glass is used to laminate the glass components to achieve the same safety standards as using PVB/glass alone. This means that PVB has higher penetration resistance and better post-breaking properties. These requirements must be met when the glass curtain wall or roof elements are integrated.
Therefore, PVB is slightly more expensive, allowing thinner and lighter weight glass (integrated solution) for use. The main basic specifications of TROSIFOL® SOLAR PVB are shown in Table 1. For encapsulating fragile and pressure-sensitive photo-sensitive crystalline solar cells, the viscosity and/or surface roughness of the PVB film can be adjusted to improve Evacuation of the glass interlayer in a vacuum process. For large laminated glass, it is also feasible to use a standard vacuum bag degassing step in combination with an autoclave process.
Among glass/glass components, PVB encapsulation films exhibit the following advantages over EVA films:
1) Longer shelf life (3 years vs 6 months)
2) High resistance to sagging and no edge bleeding during lamination
3) No contamination of laminator components or component parts themselves
4) Repeated lamination without cross-linking
5) Can be produced with other lamination methods that are more economical than vacuum lamination process (higher yield per cycle)
6) Long-term light and temperature stability of component systems based on laminar safety glass experience
7) Can be combined with PVB's other functions in PV module glass, such as adding soundproof PVB, color PVB according to design features
8) Meet all safety, insurance and quality standards for laminated safety glass
For photovoltaic modules consisting of an upper glass layer and a backing film (for example, a standard thin sandwich component applied to the ridge), the material has passed the compatibility test and obtained certificates and guarantees long life.
3, the use of laminated safety glass benefits
Photovoltaic modules in BIPV, for example, used in glass curtain walls, glass roofs, etc., must usually meet special safety requirements. They act like laminated safety glass, such as an integrated composite glass layer. Only PV modules encapsulated with TROSIFOL® SOLAR PVB membranes meet all requirements and national building regulations, including applications for ceiling glass, architectural glass and shedding glass. This is especially true for breakage after breakage of the glass. An overview of the specifications of this standard is shown in Table 2; Figures 4 and 5 illustrate that the penetration resistance test complies with EN12543 and EN12600.
European manufacturers of photovoltaic modules and companies supplying laminated glass have begun to sell photovoltaic glass components with safety and safety functions. The current application of lamination technology (one-step and/or two-step laminated safety glass processes) enables the production of large-size glasses and a wide variety of designs. This situation has also led to the development of new and cost-effective technologies to rapidly reduce PV module prices. For example, Ertax Solar in Amsterdam, Austria, exhibited at the 2005 International Solar Expo used TROSIFOL® SOLAR PVB membranes to achieve a surface lamination area of ​​12.5 m2 (5,100 X 2,450 mm); a combination of 560 polysilicon cells with an output of up to 1.5 kW per unit .
4. Summary
The application of Photovoltaic Building Integration (BIPV) in new and modern building curtain walls will become increasingly important. The application of TROSIFOL® SOLAR PVB membrane encapsulated solar cells opens up new multifunctional, large-area and therefore cost-effective safety and insurance The direction of the solar module system.
This development will make BIPV more attractive to architects and increase future opportunities for PV module manufacturers, construction and glass industries.
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