Optical performance and design optimization of V-trough concentrators for photovoltaic applications

Abstract

Abstract In this work, a detailed mathematical procedure to estimate collectible radiation on the base of a V-trough concentrator, to which solar cells are attached, was developed based on the imaging principle of planar mirrors, solar geometry and monthly horizontal radiation. This model allows predicting the optical performance of V-troughs with any structural and installation parameters, and optimizing the design of such concentrator. Calculation results showed that for fixed east–west aligned V-troughs (EW-V troughs, in short) with given geometric concentration factor ( C g ) and side wall reflectivity ( ρ ), the annual solar gain depended on its opening angle, tilt-angle of the aperture and climatic conditions in sites, and a set of optimal opening angle and aperture tilt-angle for maximizing annual solar gain could be obtained by iterative calculations for different opening angles and tilt-angles. It was also found that for fixed EW-V troughs with C g = 2 and ρ = 0.9, taking the site latitude as quasi optimal tilt-angle was reasonable over all area of China, 15° deviation of azimuth angle from the due south would resulted in reduction of the annual collectible radiation less than 1%, and 10° deviation of the geometric axial line from the crossing line between the horizon and the extended aperture of V-troughs resulted in the reduction of annual solar gain less than 1%. For EW-V troughs with the tilt-angle of the aperture being yearly adjusted four times at three fixed tilt-angle (3T-EW-V troughs), the annual solar gain captured by 3T-EW-V troughs with given C g and ρ in a specific site was approximately a function of the opening angle, and the optimal opening angle for maximizing annual solar gain could be simply estimated by iterative calculations for different opening angles. Compared with fixed EW-V troughs, the annual solar gain on the base of 3T-EW-V troughs increased significantly, especially for those with a large C g , and the monthly average daily solar gain was more stable over a year. This implied that several tilt-angle adjustments in a year were required to make EW-V troughs with C g > 2 efficiently concentrate radiation onto their coupling solar cells in all days of a year.