Optical efﬁciency study of PV Crossed Compound Parabolic Concentrator Nazmi Sellami ⇑ , Tapas K. Mallick ⇑ Mechanical Engineering, School of Engineering & Physical Sciences, Heriot-Watt University, Edinburgh Riccarton EH14 4AS, UK highlights " The efﬁciency of a static concentrator has been investigated for PV application. " An optical model using ray trace technique and MTLAB program has been elaborated. " A prototype of the CCPC was made and tested in indoors conditions. " The experimental results validate the optical model. article info Article history: Received 9 February 2012 Received in revised form 13 July 2012 Accepted 29 August 2012 Available online 6 October 2012 Keywords: CPC Building integration Photovoltaics Optical modelling Ray trace abstract Static solar concentrators present a solution to the challenge of reducing the cost of Building Integrated Photovoltaic (BIPV) by reducing the area of solar cells. In this study a 3-D ray trace code has been devel- oped using MATLAB in order to determine the theoretical optical efﬁciency and the optical ﬂux distribu- tion at the photovoltaic cell of a 3-D Crossed Compound Parabolic Concentrator (CCPC) for different incidence angles of light rays. It was found that the CCPC with a concentration ratio of 3.6 represents an improved geometry compared to a 3-D Compound Parabolic Concentrator (CPC) for the use as a static solar concentrator. The CCPC has a maximum optical efﬁciency of 95%, in line with the optical efﬁciency of the 3-D CPC, with the added advantage of having a square entry and exit aperture. A series of prelimin- ary experimental measurements were taken on a setup of nine solar cells. The experimental results pro- vide validation of the MATLAB code developed, showing a deviation of 12 ± 2% from the simulation results, thus conﬁrming that the code can be used to investigate different concentration ratios of the CCPC. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction With the growing problems surrounding global warming, researching various renewable energy technologies has become a necessity. Currently there is a huge amount of interest in concen- trating solar energy to generate electricity. Conventional solar pho- tovoltaic (PV) systems for integration to buildings are not cost effective; the high cost of PV systems is mostly associated with the solar cells. The cost of these modules could be reduced by increasing the output per unit solar cell and this could be done by replacing expensive solar cells with a low cost optical material (concentrator). In general, the price of concentrating photovoltaic (CPV) is lower than ﬂat plate systems and as a result many projects have been carried out to ﬁnd ways for lowering the manufacturing cost using various types of solar concentrators to develop a CPV system [1]. Furthermore, the CPV can be even more efﬁcient when used in hybrid photovoltaic/thermal system applications which produce electricity and hot water simultaneously [2,3]. Many ideas of designing speciﬁc geometry for concentrating PV systems have been proposed since the birth of non-imaging optics in the 1970s [4]. Example of these include the design of an asym- metric compound parabolic concentrator for PV application; which enables the capture of a large part of the diffuse solar radiation in addition to the direct component [5]. One of the most studied solar concentrators is the 2-D CPC trough (Fig. 1); it is the most efﬁcient solar concentrator because of its characteristics of collecting and concentrating all the rays within a speciﬁed acceptance angle [6]. The most recent study by Su et al. introduced a novel lens-walled CPC having a larger acceptance angle and an optical efﬁciency of more than 0.4 compared to the mirror CPC [7]. Building integration PV systems require a static concentrator collecting maximum solar radiation; the 2-D CPC trough represents a solution but with limi- tations in concentration and in solar radiation collection. The 3-D CPC represents an improvement on the 2-D CPC trough; the geometrical concentration ratio is increased and therefore the size of the solar cells used is reduced. The circular-sectional 3-D 0306-2619/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2012.08.052 ⇑ Corresponding authors. Tel.: +44 131 4548083 (N. Sellami), tel.: +44 131 451 4379 (T.K. Mallick). E-mail addresses: ns190@hw.ac.uk (N. Sellami), t.mallick@hw.ac.uk (T.K. Mallick). Applied Energy 102 (2013) 868–876 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy