Impacts of non-ideal optical factors on the performance of parabolic trough solar collectors

Highlights: • Effects of non-ideal optical factors on PTC's performance were investigated. • Heat flux distribution changed by optical factors caused various thermal performance. • Cosine and end loss caused by incident angle weakened greatly collector's performance. • Temperature distribution was totally dependent on heat flux distribution. • The offset direction along positive Y-axis posed the greatest threat to receiver tube. -- Abstract: This work investigated comprehensively the impacts of non-ideal optical factors, including incident angle, sunshape and optical errors on the performance of the parabolic trough collector (PTC). Each optical factor was defined based on their geometrical principles. It was revealed that the heat flux distribution distorted by optical factors was the main cause of changing performance of the PTC. The temperature distribution was completely dependent on the heat flux distribution. The incident angle caused cosine loss and end loss, which respectively reduced the effective incident solar radiation and produced a near-zero heat flux section at one end of the absorber. Based on the effective incident solar radiation, the collector efficiency was reduced by 41.11% with the incident angle increasing from 0° to 60°. Larger circumsolar ratios produced more uniform circumferential temperature distribution, while reduced greatly the collector efficiency. The specularity error and tracking error affected slightly the receiver's safety, while the slope error reduced obviously the threat to the receiver. When specularity error was small enough (<3 mrad), further improving reflector's specular quality reduced the optical efficiency. The offset direction along X-axis caused the greatest optical loss, and that along positive Y-axis caused local overheating, threatening the receiver's safety.