COMPARATIVE EXPERIMENTAL CHARACTERISATION BETWEEN AN ASYMMETRIC COMPOUND PARABOLIC PHOTOVOLTAIC CONCENTRATOR AND A FLAT NON-CONCENTRATING SYSTEM T K Mallick 1 , P C Eames 2 , T J Hyde 3 Centre for Sustainable Technologies School of the Built Environment, University of Ulster, Newtownabbey, NI, UK, BT37 0QB, Email: 1 tk.mallick@ulster.ac.uk , 2 pc.eames@ulster.ac.uk , 3 t.hyde@ulster.ac.uk Tel: 1 + 44 2890 368568; 2 +44 2890 368244, 3 +44 2890 368235 B Norton Dublin Institute of Technology, Aungier Street, Dublin-2, Ireland Email: president@dit.ie , Tel: +353 1 402 7135; fax: +353 1 402 7099: ABSTRACT: A comparative experimental characterisation of a prototype asymmetric compound parabolic photovoltaic concentrator with its non-concentrating counterpart was performed at the University of Ulster, Northern Ireland (54º36´ N, 5º37´ W). The concentrator increased the maximum power point by 60% (i.e. the power ratio was 1.60) for a theoretical concentration ratio of 2.0 for the same incident solar radiation when compared to a similar non- concentrating PV panel. This value is less than the design factor of 2, and was a result of higher back plate temperatures and due to ohmic losses in each individual interconnection between the solar cells. The concentrator achieved an average optical efficiency of 80% and an average fill factor of 50%, while the non-concentrating PV panel had an average fill factor of 55%. The concentrator had only a 8°C higher solar cell operating temperature when compared to the non-concentrating system. Keywords: Photovoltaic Concentrator, Building Integration, Optical efficiency 1 BACKGROUND Optical design was used to develop a low concentration asymmetric compound parabolic photovoltaic system suitable for building façade integration in the UK. The air-filled asymmetric concentrator collects up to 70% of the diffuse solar radiation in addition to the direct solar radiation [1]. The concentrator is made with two different parabolic mirror sections that have acceptance angles of 0° and 50° and is suitable for northern European locations. The system is however suitable for any location it mounted at the correct inclination. To reduce the quantity of reflector materials, system weight and cost, the concentrator was truncated [2] by 54% leading to a geometrical concentration ratio of 2.01. The concentrator has an optical efficiency of up to 85.85% and collection efficiency of 100% for a wide range of solar incidence angles [3]. Analysis of the system design was undertaken using a ‘comprehensive unified’ model [4] for optics and heat transfer [5], [6]. The work presented in this paper details a comparative experimental characterisation of the asymmetric compound parabolic photovoltaic concentrator [5] and a similar non-concentrating PV system. 2 SYSTEM DESCRIPTION The experimentally characterised system is shown in Fig.1. The concentrator system consists of a 3mm thick aluminium back plate, to which an array of 6mm thick aluminium reflector supports are attached. A 0.15mm thick stainless steel reflector substrate covered with a 68 micron thick mirror reflector was glued to the reflector supports. The solar cells were attached to the rear aluminium plate via an intermediate layer of EVA. Both PV systems consist of forty half-size (50mm × 125mm) BP Saturn solar cells with eight strings of five cells connected in series. Each PV string could be isolated to allow the PV strings to be monitored using different series and/or parallel combinations. The detailed design and fabrication of both PV systems has been reported previously [5]. The experiments were carried out near Belfast in Northern Ireland (54°36'N, 5°37'W). The electrical performance and temperatures were monitored for over thirty days for both systems. Press moulding could be used for commercial manufacture of the reflector system ensuring reflector costs are low with a subsequent significant reduction in PV panel costs. To avoid moisture ingress seals similar to those used for double glazing could be employed [7] with a desiccant included in the sealed system to absorb any moisture. 3 OUTDOOR EXPERIM ENTAL PROCEDURE The outdoor experimental performance of the flat non-concentrating system and the concentrator were Figure 1: Flat non-concentrating and asymmetric compound parabolic photovoltaic concentrators under outdoor experimental characterisation at the University of Ulster. 19th European Photovoltaic Solar Energy Conference, 7-11 June 2004, Paris, France 738