Cosine Efficiency Distribution of Heliostats Field of Solar Thermal Power Tower Plants

Mathematical model of cosine efficiency of heliostats field of solar thermal power tower plants was established, while the distribution of cosine efficiency of traditional and rotating heliostats field for latitude of 40.4deg in the northern hemisphere defined by essential staggering layout with no blocking radial spacing was analyzed. The results show that, at given condition, the incident angles for traditional tracking heliostats during equinox are comparatively smaller, and from 8 a.m. to 16 p.m., the zone of higher cosine efficiency moves from northwest side to northeast side, and the distribution at 12 o´clock is quite similar to that of the average level of whole working hours, choosing equinox noon as layout point for the traditional heliostats field is therefore a good first choice. However, the rotating heliostats field is more powerful in concentrating solar energy for higher cosine efficiency at almost any individual hours than that of the traditional field. While in common, the average cosine efficiency distribution of the traditional and rotational field is symmetrical along the north direction to the tower, while the collective performance is better for those heliostats with less azimuthal angles and with shorter distance to the receiver. Based on this principle, placement and maintenance strategy of heliostats should be made so as to collect more solar energy.