Installing photovoltaic modules

Photovoltaic modules must be installed so that they are exposed to the maximum amount of light. The shade of surrounding buildings, trees or the building itself, has to be avoided to maximise power production. Photovoltaic facades in the UK are optimally installed facing south or south-west. Although an optimal 30° angle of inclination is almost impossible to achieve with normal facades, it can easily be achieved in rooflights and sun shades.

There are basically four different kinds of facades and photovoltaic modules can be easily integrated into all of them.

Cold facades. A cold facade is a bracket-mounted facade in which all parts of its construction have no thermal insulation. There is no connection to the building’s warm area. The warm area is contained within the thermally insulated surfaces of the building. Cold facades are weather protected, usually by single glazed safety glass. Photovoltaic modules can simply take the place of the safety glass. Parapets are one example of a facade’s cold area. Rain screen cladding (as at Newcastle) is another.

Warm facades. These are facades which provide the functions of weather and noise protection and thermal insulation. The elements that can be used in them are either insulating panels, double-glazed windows or PV elements mounted in a proprietary facade structure. Modules can be designed to replace ordinary panels; alternatively, standard window-frame casements can used to support the modules.

Cold-warm facades. Here, there is an exchange between cold and warm areas across the facade’s gradient. The warm areas are insulated by double glazed windows and other thermal insulation.

Rooflight and glazed roof constructions. Photovoltaic modules made of semi- transparent amorphous silicon and crystalline modules with transparent interspaces can be used in those areas of the building shell where daylight is desired.

Construction options

For a photovoltaic facade to function reliably and efficiently in the long term, various requirements have to be met concerning the integration of the module, drainage, vapour pressure equalisation, cable layout, and design. The most important constructional elements here are the sectional frames used. These must: – bear the modules without stressing the modules; – be storm-resistant; – incorporate all cables; – drain off rainwater and condensation; and – create easy access to the module and its electrical system – deliver thermal and acoustic properties.

The photovoltaic modules must be positioned to ensure good passive ventilation to ensure a minimum possible operating temperature – for crystalline silicon modules the lower the temperature the higher the efficiency.

One possible facade construction is where the PV modules are secured in mullion – transom construction. The uprights (the vertical sections) are continuous and the crosspieces (the horizontal sections) made to fit. Highly elastic plastic seals are fitted between the PV module and the frame so that the module does not come into direct contact with metal.

Electrical systems and components

Coupling photovoltaic systems with the public grid is considered to have the biggest future in Europe. With these systems the photovoltaic power supply operates in parallel to the normal electricity supply to the building. In other words the building is connected to both the PV system and the mains and can use power from either source as required. If there is insufficient solar power to supply all the building needs the remainder is supplied by the mains. If there is excess solar power it may be exported to the mains. All these functions are automatic with the building occupiers unaware of any changeovers.

Installations linked to the grid have significant advantages over other approaches, namely: the highest energy yield the lowest system costs the simplest technology standard components can be used high correlation between production and consumption security of supply through link with grid.

A standard mains connected PV system consists of a photovoltaic array, a power conditioner, an inverter and control and protection equipment and any metering required.

The power conditioner, comprising an inverter with control and protection equipment is required to convert the direct current electricity generated by the PV array into alternating current for use within the building. At the same time it must ensure the quality of the power output and its synchronisation with the grid. Surplus electricity is fed via a supply meter into the public grid. If more power is needed than the solar facade can provide, it is taken from the grid and measured by a second meter.

Planning Criteria for Technical Installation

Photovoltaic power plant facades should be planned and installed by electricians or consulting engineers. They have to adhere to the usual technical standards for any electricity generating system to be connected to the electric grid.

The size of the photovoltaic facade will depend on the amount of energy needed and the suitable space available. Unnecessary costs are incurred if the installation is too large or too small. Economic benefits are at an optimum when almost all the daytime power requirements of the building are supplied by the solar facade.

In general the construction of a new industrial or commercial building, or the extensive refurbishment of an existing building is likely to require planning permission from the local planning authority. Evidence of new buildings in the last decade suggest a wide latitude will normally be allowed to designers to choose the external appearance. Particular exceptions are buildings in conservation areas or other sensitive sites. Therefore, a well designed building that includes photovoltaics should be acceptable on planning grounds. The Department of Environment has published Planning Policy Guidance Note (PPG) 22 which covers solar installations.

Regulatory Issues

Government reports on grid connected PV establish that existing standards, codes and engineering recommendations are adequate for the application of photovoltaic system design and installation. The standards applicable in the UK are increasingly being harmonised with European and international standards such as ISO and IEC. The DTI states that the wealth of experience in other countries can be adapted to suit the UK situation18. Suppliers of photovoltaic equipment are familiar with the relevant codes and standards.

Connection

There is no statutory obligation for the Regional Electricity Company to connect and purchase power from a photovoltaic building, although many other utilities in the OECD countries facilitate connection as a matter of routine. However, individual building projects are likely to be accepted given that the first two major solar photovoltaic buildings in the UK were given support from the utilities concerned. Greenpeace is working to ensure that REC's are more receptive to building integrated photovoltaics.