[Solar Case Studies]
Doxford International Business Park, Oxford Solar House, Small Scale Applications,
The first speculatively constructed office building to incorporate building-integrated photovoltaics (PV) has been completed at the Doxford International Business Park, Sunderland. The building consists of a 66m long, south facing, PV façade covering 532m2. This is the largest PV façade installed in an office building in Europe to date. The façade is the main feature of the building and is inclined at an angle of 60o to the horizontal for capture of sunlight.
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The system is rated at 73kW (peak) but also encompasses passive solar techniques to minimise the buildings energy requirement. The low-energy measures include generous ceiling heights, which encourage day lighting and cross- ventilation, a well-insulated and well-sealed building envelope to minimize winter heat losses, and the provision of effective and responsive environmental controls.
A total of 352 PV modules have been integrated into the building's south-facing cladding, which incorporates alternate bands of modules and conventional glazing. The PV system meets almost 30% of the building's annual power requirements and at times when the cells produce more electricity than the building can utilise surplus is sold to the National Grid.
The total cost of the building came to approximately £4.5million after design, construction and development.
As part of a project to evaluate the potential contribution of photovoltaics to the domestic energy supply of the United Kingdom, a solar house was built in Oxford in 1994. A 4 kW photovoltaic system was integrated into the roof structure along with 5m2 of solar thermal panels. This system was used as a working example of a domestic photovoltaic installation, the house is used as a teaching and research facility managed by Oxford Brookes University.
The project began as an initiative of the house owner, a lecturer in architecture at Oxford Brookes University, who saw an opportunity to gain experience in the technology and to use this experience to teach young building designers. Built in a city location with a south-facing rear elevation, the house is designed to require the minimum of energy for heating, cooking and lighting, so as to maximize the contribution of the solar electricity supply without impairing the comfort of the occupants.. The photovoltaic system is regarded as the main electricity supply and is connected in parallel to the supply from the local grid. Energy from the solar array is consumed by the AC loads in the house and any excess exported to the local grid. When there is not enough electricity being generated the system imports from the local grid. This is a fully automatic process, completely invisible to the householder.
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The actual total photovoltaic installation comprises 48 BP Solar 585 Saturn modules with a total capacity of 4 kW p. The photovoltaic modules, four solar thermal collectors and two skylights make up the south-facing roof, which slopes at an angle of 50° to the horizontal. A supporting sub-frame creates an airspace behind the modules for ventilation.
This successful architectural integration of solar panels into the roof of a residential house produced 2700 kWh of photovoltaic electricity during the first year after its installation; 54% of the available electricity was used in the house or to charge the electric car belonging to the house owner and 46% was exported to the local grid.
The total cost of the photovoltaic system from design to commissioning was £25,000.
The costs of the key elements are given below.
Photovoltaic modules - £ 12,750
Inverter - £ 3,500
Installation - £ 8,500
Grid connection - £ 450
The Greenfields development by Maidenhead and District Housing Association has been designed by Bree Day Partnership, it is part of the Department of Trade and Industry (DTI) 100 roofs domestic PV field trial. The design of the dwellings incorporates specific solar PV framing on each of the buildings, which are orientated in a south- westerly direction and are optimised for solar gain. The project covers 15 separate homes in all with solar PV modules integrated into a specially constructed framing system that forms part of the roof design. Each home has between 1 kWp and 1.8 kWp of installed power - totalling 20 kWp. This installation has been predicted to generate 16000 kWh per annum, with a total surface area of 172 m2. The installation of the system was undertaken by normal electrical and roofing contractors, with training and supervision from Solar Century and took an average of 1 day per home. The PV systems cost £110,000 for all 15 homes.
A solar array installed on the south-facing roof of a 100 ft x 140 ft cattle barn, as part of a retrofit project, provides power for four cottages. The array is divided into four sub-arrays, each one generating power for a single cottage, each of the cottages purchases all the solar electricity generated by their associated sub-array. Electricity that doesn’t get used can be exported to the grid, with the tenants receiving payment from the supplier. The total ‘active’ area of the solar array is 180 m2 and the system size is 10.24 kWp providing 8700 kWh year. The system cost a total of £80,000.
A house in Genoa Avenue, Putney, London incorporates a roof-integrated laminate PV system. The PV array was installed on a shallow sloping roof of a three bedroom residential property. The system size is a 2.88 kWh array and the total active area of the roof is 23.4 m2.
The laminates were fitted into a framework, which was installed on the rear roof of the property. The roof has a ridge and shallow slopes facing North and South. The system has been grid connected and an export electricity meter installed to measure the units of electricity exported to the grid. London Electricity pay for each exported unit.
An Eco-house at Nottingham University for the School of the Built environment incorporates a system comprising of 132 sun slates that form a 1.56kWp photovoltaic array and is expected to have an annual yield of 1200kWh.
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