COMPUTER PROGRAMMING TO CALCULATE THE VARIATIONS OF CHARACTERISTIC ANGLES OF HELIOSTATS AS A FUNCTION OF TIME AND POSITION IN A CENTRAL RECEIVER SOLAR POWER PLANT

摘要

The central receiver solar power plant is composed of a large number of individually stirred mirrors (heliostats), focusing the solar radiation onto a tower-mounted receiver. In this paper, an algorithm is developed based on vector geometry to pick an individual heliostat and calculate its characteristic angles at different times of the day and different days of the year. The algorithm then picks the other heliostats one by one and performs the same calculations as did for the first one. These data are used to control the orientation of heliostats for improving the performance of the field. This procedure is relatively straight-forward, and quite suitable for computer programming. The effect of major parameters such as shading and blocking on the performance of the heliostat field is also studied using this algorithm. The results of computer simulation are presented in three sections: (1) the characteristic angles of individual heliostats, (2) the incidence angle of the sun rays striking individual heliostats, and (3) the blocking and shading effect of each heliostat. The calculations and comparisons of results show that: (a) the average incidence angle in the northern hemisphere at the north side of the tower is less than that at its south side, (b) the cosine losses are reduced as the latitude is increased or the tower height is increased, (c) the blocking effect is more important in winter and its effect is much more noticeable than shading for large fields, (d) the height of the tower does not considerably affect shading; but significantly reduces the blocking effect, and (e) to have no blocking effect throughout the year, the field design should be performed for the winter solstice noon.