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

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 α_ab, and end reflection plane reflectivity ρ_r ) on the relative optical efficiency loss η_re-opt,loss, the maximum value of the local concentration ratio X_max, and the non-uniformity factor σ_non 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 η_re-opt,loss . The η_re-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 X_max 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 ∆f can affect the X_max . The smaller the ∆f, the greater the X_max, and vice versa. The changing trend of σ_non is basically consistent with that of the X_max . When the f is 600, 625, 650, 675, 700 mm and the ω = 0^◦, the σ_non 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.