A parabolic trough solar collector(PTC)with concentration ratio of 24 was developed.By using the TracePro software

an optical model of the PTC was built.Effects of single-axis and two-axis tracking modes

azimuth and elevating angle tracking errors on the optical performance were investigated.Thermal performance of the PTC was experimentally measured as well.The results show that

the optical efficiency of the two-axis tracking was 0.813

and its year-average value was 14.3% and 40.9% higher than that of the east-west tracking mode and north-south tracking mode

respectively.The optical efficiency was affected significantly by the elevation angle tracking errors which should be kept below 0.6°.High optical efficiency could be attained by using two-axis tracking mode even though the tracking precision of one axis was degraded.The real-time instataneous thermal efficiency of the PTC reached 0.775.In addition

the linearity of the normalized efficiency was favorable.The curve of the calculated thermal efficiency agreed well with the normalized instantaneous efficiency curve derived from the experimental data and the maximum difference between them was 10.3%.This type of solar collector can be applied in middle-small scale thermal collection systems.