Abstract
This paper discusses the design of the photovoltaic facade to be installed at the University of Northumbria in the summer of 1994. Photovoltaic laminates will be incorporated in rainscreen overclading on the south facing wall of the building, giving a total installed capacity in excess of 39 kWp. This project will be the first demonstration of a PV facade in the UK and provide important information on the performance of such a system in a high latitude, city centre environment

Summary
This first UK demonstration project on PV cladding involves a building typical of many requiring refurbishment. It does not represent and ideal site for PV cladding, since it is surrounded by other buildings which provide some shading during the winter season and at the extremes of the day. However, it is representative of the type of building which will become available for the installation of PV facades or roofs and which must be included in any widespread adoption of PV cladding in the future. It will also provide valuable information on the performance of a system in a northerly city centre environment, including aspects of shading reflection from surrounding surfaces, dirt accumulation, ecc. The data on the variability of output from the facade, due to variability of insolation levels in the UK climate will also give essential information on the interaction with the utility grid.
The installation of the PV facade is scheduled for the summer vacation of the University in 1994 and is expected be complete and operational by October. The project is currently in the final design stage, which has presented no significant problems to date, and is on schedule.
The project is expected to act as a focus for the development of PV cladding in the UK and, as such, is well situated for access by professionals in the building community, students from both universities in Newcastle and the general public. It has already received a large amount of publicity in the UK and will help to raise the awareness of the community regarding the role that PV on buildings can play towards the establishment of sustainable cities.

Introduction
The installation of photovoltaic modules on building facades or roofs could provide a significant proportion of the energy needs in urban areas of Europe. This is particularly true for commercial buildings, which have a daytime load and, threfore, where a reasonable match between supply and demand exists. The development of the resource from PV cladding could be a significant factor in the move towards "sustainable" cities. This paper will discuss the first major PV-cladding demonstration project in the UK and outline both the technical aspects of the project and the plans for promotion of this technology in the UK.

The project is funded by the CEC's THERMIE programme on the promotion of energy technology, together with both UK Government support and private sponsorship. The south facing facade of an existing building at the University of Northumbria will be reclad during the summer of 1994 and PV modules will be architecturally integrated into this cladding. This project will be the first of its kind in the UK and one of the largest PV cladding projects in a high latitude location. Newcastle upon Tyne being situated at a latitude of 55 °N. It is expected that this project will not only generate valuable information on the performance PV cladding in a northerly, city centre climate, but also provide a focus for the demonstration of this technology to UK architects, building engineers, town planners and the general public.

Description of the building
Northumberland Building is situated on the city campus of the the University of Northumbria, close to the city centre of Newcastle upon Tyne on the north east coast of England. The building is a five storey block, although the majority of the central ground floor is absent, providing a walkway from one side of the campus to the other. It houses several academic departments, with the accomodation being used for staff offices, teaching rooms and computer laboratories, as well as housing the central computer unit for the University. The refurbishment of the building will take place during the University vacation in the summer of 1994 and is expected to be completed by October.
The building is rectangular, with the long facades oriented approximately E-W. Both the original mosaic cladding and the concrete fixing are in poor condition and the entire existing cladding system has to be removed.
Thus, although the project involves an existing building, it is not a retrofit of photovoltaic modules to an existing facade, but rather a full integration of the modules into a new external cladding. The windows are also being replaced to provide a higher thermal efficiency than presently available. All five cladding strips will incorporate photovoltaic modules and an artist's impression of the PV-clad facade

The building is a typical example of a 1960's built academic or office building, for which the initial cladding has provided protection for over twenty years. Many tens of thousands of such buildings exist across Europe and may be expected to need recladding in the next decade.
Most of these buildings are located in urban sites and do not represent ideal conditions for the installation of modules, due to facade orientations, shading, etc. Indeed, the project building is surrounded by other University and private buildings and parts of the south facade are shaded for some portions of the day. As part of the project, the effect of partial shading on the system design and performance will be studied. For widespread implementation of PV cladding, it is essential address the issues presented by non-ideal structures in addition to determining the maximum potential of specially construct buildings.

Design
The use of an existing building constrains the design of the PV-cladding in order that it should conform with the requirements of the refurbished building. It has not been possible to incorporate any passive solar features other than the use of improved windows and a small amount of solar shading from the cladding panels. It was decided that rainscreen cladding was the best option for conventional refurbisment and, therefore, that the PV modules should be incorporated into standard rainscreen cladding for the purposes of this project.

Cladding Design
The rainscreen overcladding system extends the useful life of the building by providing protection from the elements. The outer face of the cladding, incorporating the PV laminates, will provide the major barrier to rain penetration. The advantage of the rainscreen system lies in the ventilation provided. The cladding panels are designed to provide an overlapping, back ventilated, self draining, open joint rainscreen. The system does not require gaskets, sealants or other components which may deteriorate over time. The ventilated air gap between the building structure and the rainscreen also assists in controlling the temperature of the modules.

The rainscreen is based on the Europanel system successfully used on numerous projects throughout Europe. The panels and components will be fabricated in 3mm thick aluminium and finished with a polyester powder coated paint to the required colour. The panels are designed to be hung into aluminium channel tracks, fixed to the existing concrete frame and which also serve to drain the rainwater. The fixing and bracketing system allows for building tolerances and movements, while maintaining the facade in a true plane.

The overlcadding to the south facade, incorporating PV panels, will be inclined at 13.5° to the vertical, enhancing the existing facade with the introduction of a surface feature. This also allows the facade to gain advantage from the winter sun and provides some summer shading to the windows, as the building generally suffers from overheating in the summer months.

The cladding is divided into a series of units, approximately 3.03 m x 1.36 m and each containing five PV laminates. Should any unit be damaged or future adaptation be required, the units can be individually removed from the facade. The laminates will be inset into an aluminium powder coated frame, with the face of the frame in the same plane as the face of the laminate to eliminate shading and give a flat face appearance. The PV laminates will be held in the frame by a structural silicon sealant.

PV System Design

The photovoltaic array is expected consist of 465 BP Solar Saturn high efficiency crystalline silicon PV laminates each rated at 85Wp, to give a total installed capacity in excess of 39 kWp. The PV laminates will be fitted with a 3-core arctic grade PVC flesible cable, the connection between the cable and the laminate terminals being sealed inside a solid block of epoxy resin.
Interconnection of the laminates will be carried out in junction boxes mounted on the concrete structure of the building, with five laminates per junction box and bypass diodes mounted in these boxes. three of these remote junction boxes will be connected in series to form strings of 15 laminates with a maximum power operating voltage of approximately 270V. The wiring between junction boxes is to be carried out using single core cables fitted in electrical trunking secured to the face of the existing structure on defined routes. The rear of the PV laminates, the junction boxes and the trunking may be accessed via perforated, hinged soffit panels to allow for maintenance, future adaptation or monitoring purposes.
The cables from each string of 15 laminates will run down to a central junction box situated in the ground floor plant room. Each string will have an individual isolator/circuit breaker allowing for the identification and location of faults should any occur during the lifetime of the system. The switches used are designed specifically for use in DC applications. Within the plant room, connection is made to the AC/DC converter which consists of a line commutated thyristor inverter and transformer with an input voltage of 270V, an output voltage of 415 V 3-phase aC and a power rating of 35 kW.
Connecticut will be made from the output of the inverter directly to the main busbars within the building main switchboard, thus making connection to the internal grid of the University site and indirectly to the local utility grid.
In the case of lightning strikes, experience gained in Europe ha shown that the most common problem which can occur is that caused to the control electronics of the inverter by voltage surges (1). To avoid such problems, the inverter will be protected by voltage surge suppressers.
There will aldo be a separate lightning protection system to the building.

Expected performance

The performance prediction for the building are based on computer simulations for Newcastle city centre, carried out as part of a PV-cladding resource study (2) and using solar data from FACET weather files (3). The scarcity of appropriate solar data for vertical surfaces in city centre locations and for short measurement intervals makes prediction of the detailed performance in the array difficult. However, the computer simulations suggest an typical annual solar input of about 950 kWh/m2 on a south facing vertical surface in the UK. For the present array design, this would lead to an electrical output of about 32.000 kWh/annum assuming a module efficiency of 14% and an inverter output of 30,000 kWh/annum assuming an average BOS efficiency of 90%.

Information dissemination
One of the most important aspects of such a demonstration project if the dissemination of information to people from a wide range of disciplines. In order for PV-cladding to become widespread, it must be adopted by architects and building engineers as a viable and, indeed, favoured option, the interaction with the conventional grid supply and relationships with the local suplly utility must be clarified and the PV-clad buildings must be acceptable to planning authorities and the general public. The first step in the realisation of these conditions is the provision of a focal point for the dissemination of information, such as the demonstration project now in progress in Newcastle.
The project has already attracted a high level of interest from the professional sector, including architects and engineers, and this will be encouraged through seminars and lectures. In addition, the location of the building on the University campus allows undergraduate students in a number of appropriate disciplines, including building and town planning courses, to become familiar with the technology. Architecture students from the nearby University of Newcastle are also expected to be involved in a number of complementary studies. Finally, but by no means of least importance, the central location of the project makes it possible for it to be visited by the general public. Public acceptance if essential for the widespread adoption of the technology, but its is difficult for opinions to be given without examples available for viewing. It is hoped that this building will be thr first of several examples around the UK.

Acknowledgments
The project is funded by the Commission of the European Communities. DG XVII, under the THERMIE Programme, by the UK Department of Trade and Industry and by a number of private sponsors, including Northern Electric plc, the Sir James Knott Trust and the Newcastle Building Society.
The authors would like to acknowledge the assistance of Malcolm Shaw from Ove Arup & Partners and Bryn Lord from BP Solar in the preparation of this paper.

References
1. Editorial in PV Demonstration Projects, W.B. Gillett, R. Hacker and W. Kaut, 1991, EUR 13105 EN

2. R. Hill, N.M. Pearsall and P. Claiden, ETSU Report No. S1365-P1, 1992, Energy Technology Support Unit, Harwell, UK

3. Weather data filed based on CIB SE example weather year from FACET Ltd., St. Albans, UK