The parabolic trough collector has a receiver formed by several single absorber tubes (13). The single absorber tubes (13) are supported by absorber tube supports (14) and surrounded by a glass tube (15). Because of different expansion behavior of the absorber tube (13) and the glass tube (15) during collector operation flexible unions (17) are foreseen between absorber tube (13) and glass tube (15). In order to use the radiation coming to the non active-area where the absorber tube supports (14) and the flexible unions (17) are installed a mirror collar (20) is installed on this area. The mirror collar (20) is able to reflect the solar radiation, which is coming from different directions, to the active absorber part of the single absorber tubes (13) also when the sun incident angle is changing.