Pergamon Energy Convers. Mgmt Vol. 35, No. 7, pp. 575-582, 1994 Copyright © 1994 Elsevier Science Ltd 0196-8904(93)E0007-8 Printed in Great Britain. All rights reserved 0196-8904/94 $7.00+ 0.00 EFFECT OF OPTICAL ERRORS ON FLUX DISTRIBUTION AROUND THE ABSORBER TUBE OF A PARABOLIC TROUGH CONCENTRATOR A. THOMAS 1 and HALIL M. GUVEN z qnstrumentation and Services Unit, Indian Institute of Science, Bangalore-560 012, India and 2Department of Mechanical Engineering, San Diego State University, San Diego, CA 92182, U.S.A. (Received 1 December 1992; received for publication 26 October 1993) Abstract--Using simulation techniques, the effect of optical errors on the flux distribution around absorber tubes of Parabolic Trough Concentrators (PTCs) were investigated. It is found that the total optical error has profound effect on the intercept factor, as well as on the optical efficiency of PTCs. Parabolic trough concentrator Optical efficiency Flux distribution Gaussian distribution Intercept factor INTRODUCTION The reflected solar radiation from the reflecting surface of a single axis tracking parabolic trough concentrator (PTC) (Fig. 1) falling on its absorber is circumferentially non-uniform [1]. For a given geometry of a PTC, the intensity of the flux distribution and the optical efficiency of the PTC are largely determined by its optical errors which are due to the diffusivity of the mirror materials, contour errors of the reflector, displacement of the absorber tube with respect to the focal line, and tracking errors. The total effect of all these errors is termed "effective sunshape" [2]. In the statistical error analysis, these errors are assumed to follow an independent stochastic process, and their occurrence is represented by a normal distribution. The distribution of energy directed towards the receiver is, thus, obtained by convolution calculations. Therefore, the angular intensity function of the effective sunshape (Ie~) can be expressed as a normal distribution, as shown in equation (1): where Ie~r(z) - a~o,~/'-~ 2 \ O'to~ J I z = angular aperture (radians) Ib = beam solar radiation (W/m 2) a,o, = reflected energy distribution standard deviation = angular shift of the mean of the distribution 2 2 "~ 2 2 O'~'ot : O'su m "-I-(20"slope) + + O'trac k 0"mirror + O'displaceme m • A study has been undertaken to investigate the effect of optical errors on the flux distribution around the absorber tube of a PTC. COMPUTATION OF FLUX DISTRIBUTION The optical model and the computer program developed by Guven [3] have been used for simulation studies which calculate the flux distribution pattern of solar power deposited on the absorber tube of a PTC. The model uses a ray trace technique to project the effective sunshape given by equation (!) on to a circular absorber tube, as shown in Fig. 2. 575