The aim of this paper is to study the influence of thermal contraction and expansion phenomenon on the behaviour of the absorber tube and its alignment along the optical focal line of a state-of-the-art parabolic-trough collector for commercial solar power plants. The study performed reveals the influence that different ranges of operating temperatures of the thermal oil used in the collectors installed in a typical commercial solar field, and other parameters such the seasonal variations of sun elevation PTC orientation, slope error, might have in the amount and distribution of the solar energy intercepted by the receiver tube. The study was carried out by means of a ray tracing method. A decrease of the intercepted solar radiation from 2.8% to up to 38% in the range of typical operating temperatures of the solar field was revealed, the decrease even exceeded the 75% when the circulating thermal oil was assumed at lower temperatures (similar to 100 degrees C). (C) 2018 Elsevier Ltd. All rights reserved.