LAUSR

Abstract Stationary compound parabolic concentrators (CPC) are usually oriented in the east–west direction and tilted towards the equator for efficient radiation concentration. However, the slope ( β ) of roofing structure integrated with CPCs may be not equal to site latitude ( λ ) in buildings, thus asymmetric CPCs (ACPC) should be used. In this work, geometric characteristics and optical performance of ACPCs integrated onto roofs of buildings are investigated. To perform this work, a mathematical procedure, in which three and four reflections within ACPCs with flat-plate (ACPC-1) and tubular (ACPC-2) absorbers are respectively considered, is suggested and validated by ray-tracing analysis. Analysis shows that the geometric concentration of ACPCs on a south-facing roof tilted at an angle ( α = λ - β ) relative to the site latitude is not only dependent on angular extent (2 θ a ) of solar rays required for acceptance on the cross-section of linear ACPCs, but also dependent on the geometry of absorbers and α . Calculation results indicate that given θ a , the geometric concentration ratio ( C t ) of horizontally truncated ACPC-1 decreases with an increase of α but that of ACPC-2 increases. Compared to similar symmetric CPC, an appropriately designed ACPC not only reduce the use of reflector materials but also increase the annual collectible radiation ( S a ). It is found that as compared to similar symmetric CPC, for ACPC-1 with θ a = 35 .5° and ρ = 0 . 9 , 7° and 10° of | a | result in reduction of S a less than 1%, and 2%, respectively; whereas for ACPC-2, 10° and 15° of | a | result in reduction of S a less than 1%, and 2%, respectively.