Optical Performance Comparison of Different Shapes of Cavity Receiver in the Fixed Line-Focus Solar Concentrating System

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To optimize the fixed-focus solar concentrating system (FLSCS) and linear cavity receiver of better optical performance, the effects of receiver parameters (geometric shape, receiver position f, receiver internal surface absorptivity αab, and end reflection plane reflectivity ρr) on the relative optical efficiency loss ηre-opt,loss, the maximum value of the local concentration ratio Xmax, and the non-uniformity factor σnon were studied in the present study. The results showed that the increases of sun declination angle δ in the range of 0–8° have a weak effect on the ηre-opt,loss. The ηre-opt,loss are 2.25%, 2.72%, 12.69% and 2.62%, 3.26%, 12.85%, respectively, when the solar hour angle ω is 0°, 30°, 60° as δ = 0° and 8° for linear rectangular cavity receiver. The Xmax mainly depends on the energy flux distribution of first intercepted sunlight on the cavity absorber inner wall. Increasing the distance between the cavity absorber inner wall and the focal line Δf can affect the Xmax. The smaller the Δf, the greater the Xmax, and vice versa. The changing trend of σnon is basically consistent with that of the Xmax. When the f is 600, 625, 650, 675, 700 mm and the ω = 0°, the σnon are 0.832, 0.828, 0.801, 0.747, and 0.671, respectively, for linear rectangular cavity receiver. This work could establish the foundation for further research on the optical to thermal energy conversion in the FLSCS.