Solar PV - Solar PV Facades - Rainscreen Cladding
Conventional Solar PV Panels can be fixed to the external walls of buildings with brick or block exteriors, using one of the aluminium or stainless steel bracketing systems that are readily available. Purists would not consider this to be true Building Integrated Photovoltaics as, in such cases, the Solar PV Panels are merely ‘stuck on’ and do not replace an essential material that would otherwise be required in the building process
Solar PV Facades – Facade Systems
There are two main building facade systems that readily lend themselves to the incorporation of Solar PV technology: Rainscreen Cladding (Ventilated Facade) and Curtain Walling.
Increasingly, Solar PV Panels are being incorporated into the construction of new buildings as a principle source, or an ancillary source, of electrical power. Solar PV Panels can also be incorporated into existing buildings where wall cladding materials are being replaced
Solar PV Facades - Rainscreen Cladding
Rainscreen cladding systems were primarily developed in the UK for the refurbishment of high-rise concrete framed buildings, particularly apartment buildings and office blocks. Rainscreen cladding is ideally suited to new buildings but is also widely used for the renovation of older high-rise buildings with poorly performing building envelopes. Rainscreen cladding construction allows the refurbishment process to be carried out while the building is still occupied.
Solar PV Facades – Fixing Rainscreen Cladding
Rainscreen cladding forms the outer skin of a building. It is a building facade system that consists of a stainless steel sub-frame infilled with cladding panels, typically of bricks, brick tiles, terra cotta or ceramic tiles. The stainless steel cladding rails and fixing brackets are bolted onto the internal wall ready to receive the rainscreen outer layer. The system is designed so that the cladding panels stand-off from the internal insulated wall in order to create a wide ventilated cavity between the two. The cavity stops driving rain, that may penetrate the rainscreen cladding material, from adversely affecting the insulated inner wall.
Solar PV Facades - Solar PV Panels
In rainscreen cladding systems, the cladding panels are usually opaque. In such circumstances designers often opt to install conventional Solar PV Panels as they are also opaque and are generally the cheapest method of producing solar electricity.
In projects where the design brief calls for transparent or semi-transparent glass panels, toughened double or triple glazed panes with thin film Solar PV Cells can be incorporated in the rainscreen grid.
Solar PV Facades – Rainscreen Cladding
The cavity wall format of rainscreen cladding can significantly improve the efficiency of the integrated crystalline silicon Solar PV Panels. The ventilation zone behind the Solar PV Panels allows thermal currents to circulate between the back of the module and the inner wall of the building, preventing any accumulation of heat and maximising the performance of the Solar PV, even when outside temperatures are high.
Solar PV Facades - Curtain Walling Systems
Curtain walling systems are a well established technology, used in numerous prestigious projects like city centre offices and hotels. Curtain walls are assembled from non-structural elements and form the outer skin of the building. They are designed to be airtight and to resist wind and weather. Apart from their self-weight, curtain walls do not carry any vertical loading but rely for support on the building's structural floors and columns. A curtain wall sustains some horizontal wind loading which is also transferred to the main structure.
Curtain walls are lightweight and assembled using aluminium or stainless steel framing, infilled with transparent or opaque infill panels. Transparent panels are usually double or triple glazed toughened sheet glass. Opaque panels can be constructed with insulated coloured glass, ceramic tiles or insulated metal units.
Solar PV Facades - Glass Bonding
Laminated glass used in architectural products incorporates a protective resin bonding layer, typically Polyvinyl Butyral (PVB), positioned between two panels of glass. The bonding process takes place under heat and pressure. When laminated under these conditions, the Polyvinyl Butyral interlayer becomes optically clear. When sealed together the glass sandwich behaves as a single unit and looks like ordinary glass.
Solar PV Facades - Glass Sheets
In the manufacture of Solar PV Glass, the photovoltaic circuit is formed on a sheet of glass, using thin film deposition and patterning techniques. Polyvinyl Butyral and a second sheet of glass are then placed directly on the circuit. The lamination of this sandwich encapsulates the circuit, protecting it from the external environment. Electric current is extracted from the module at a sealed terminal box that is attached to the circuit and then converted to alternating current electricity (AC) by an inverter.
Solar PV Glass consists of solar cells that are built into transparent double and triple glazing units. Solar PV Glass can easily be integrated into roofs and curtain walling facade systems. Using thin film Solar PV Cells in curtain walling can result in an economical use of solar energy and encourage creative architectural design.
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