Exergetic assessment of transmission concentrated solar energy systems via optical fibres for building applications Canan Kandilli a , Koray Ulgen a , Arif Hepbasli b, * a Solar Energy Institute, Ege University, 35100 Bornova, Izmir, Turkey b Department of Mechanical Engineering, Faculty of Engineering, Ege University, 35100 Bornova, Izmir, Turkey Received 22 December 2007; accepted 2 February 2008 Abstract Solar lighting with fibre optic bundles can be considered as a very promising option from the viewpoint of energy efficient green buildings. This study dealt with the exergetic analysis and the performance assessment of the system based on the idea of transmission concentrated solar energy via optical fibres (TCSEvOF). Although the main objective of the present study includes the solar lighting to non-daylit areas, it could be possible to transform by additional components and some modifications for other applications, such as solar power generation, solar surgery, photobioreactors, hydrogen generation and photochemical reactions and solar pumped lasers. In the analysis, the experimental data obtained from the system composed of low cost dual sun tracking offset paraboloidal dish and fibre optic bundle and installed in Ege University Solar Energy Institute, Turkey were used. Monthly average hourly exergy efficiencies of the TCSEvOF system were calculated by applying the exergetic model. Exergy efficiencies varied between 1% and 28% in daytime depending on the solar radiation values along the whole year. The seasonal average exergy efficiencies were found to be 16%, 20%, 18%, and 7% for the spring, summer, autumn and winter seasons, respectively. Average annual exergy efficiency of the system for the whole year was obtained to be 15%. Parameters affecting the performance were discussed, while some suggestions towards increasing energy and exergy efficiencies of the system for further researches were made. It is expected that the model presented here would be beneficial to everyone involved in the design and performance evaluation of solar lighting with fibre optic bundles in building applications. # 2008 Elsevier B.V. All rights reserved. Keywords: Solar lighting; Concentrated solar energy; Fibre optic bundle; Exergy analysis; Efficiency; Green buildings; Efficient buildings 1. Introduction The idea of transmission of concentrated solar energy via optical fibres (TCSEvOF) was put forward in 1980 by a group of French investigators. Owing to the unavailability of high quality optical fibres and the high cost of their design, this project limited itself to theoretical analysis only. With the present day availability of fibre-optic techniques, solar energy can be transmitted by high-quality optical fibres of large core diameter and large numerical aperture [1,2]. The systems based on the idea of transmission of concentrated solar energy via optical fibres (TCSEvOF) provide flexible options for numerous implementations such as solar lighting, solar power generation, solar surgery, photobioreactors, hydrogen genera- tion and photochemical reactions and solar pumped lasers. There are numerous studies on thermal analysis and solar power generation by TCSEvOF systems. Jaramillo et al. [3] developed a theoretical thermal study of optical fibres transmitting concentrated solar energy. It was indicated that the thermal study considered a wavelength-dependent absorp- tion coefficient of the optical fibre core in order to obtain the radiative heat flux in the fibre. Kribus and co-workers [4,5] presented a study on the potential use of optical fibres for solar thermal power generation. The main performance character- istics (numerical aperture and attenuation) and typical costs of currently available fibres were discussed. Kaushika and Reddy [6] reported the design, development and performance characteristics of a low cost solar steam generating system. Jaramillo et al. [7] carried out a theoretical and experimental www.elsevier.com/locate/enbuild Available online at www.sciencedirect.com Energy and Buildings 40 (2008) 1505–1512 Abbreviations: NA, numerical aperture (dimensionless); FOB, fibre-optic bundle; TCSEvOF, transmission of concentrated solar energy via optical fibres; EU-SEI, Ege University Solar Energy Institute; IR, infrared; UV, ultraviolet; PMMA, polymethylmethacrylat; SPC, solar parabolic cooker. * Corresponding author. Tel.: +90 232 388 40 00x5124; fax: +90 232 388 85 62. E-mail addresses: canan.kandilli@ege.edu.tr (C. Kandilli), koray.ulgen@ege.edu.tr (K. Ulgen), arif.hepbasli@ege.edu.tr (A. Hepbasli). 0378-7788/$ – see front matter # 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2008.02.021