Optical Analysis of an Evacuated Parabolic Trough Receiver With a Plate Absorber

The optical efficiency of a parabolic trough receiver (PTR) is influenced by the transmittance of the glass cover and absorptivity of the absorber plate. The transmittance of beam radiation through a glazing system as a function of incidence angle can be calculated using numerical integration technique. This will allow us to determine the effective transmittance-absorptance product $(\tau a)_{eff}$ of the PTR. However, the determination of the transmittance of the glass cover is difficult since the angles of incidences of the solar radiation on the glass cover vary with the impact point. In this paper, the transmittance of the upper and the lower semi-cylindrical parts of the receiver, in addition to the transmittance of the whole receiver are calculated. The $(\tau a)_{eff}$ and its dependency on the parabolic trough orientation and absorptance of some selective surfaces is investigated. Results showed that the optical performance depends on the optical properties of the materials and the orientation of the parabolic trough collector.