Analysis of Heliostats' Rotation Around the Normal Axis for Solar Tower Field Optimization

The design of a solar field is one of the crucial aspects when a solar tower system is realized. In general, shading and blocking effects, which are the main causes of solar power losses, are minimized displacing the heliostats each other quite distant, with typical land coverage less than 20%, and thus, strongly limiting the construction of these plants to low value lands. A new method is proposed here to improve the collected energy for solar tower systems with high land coverage (greater than 30%), based on the chance for each heliostat to rotate about the normal passing through the center of its surface. Then, shading and blocking are minimized by optimization of the relative orientations. To this aim, a small solar field composed of 150 rectangular flat heliostats has been considered, and its performances with and without the proposed optimization have been computed and compared for a wide variety of cases. In particular, a systematic analysis is presented to study the effect of the shape of the heliostats on the solar field performance: in a series of simulations, maintaining constant the area of each heliostat, the ratio between its two sides has been varied in a range between 1 (squared heliostats) and 3 (very stretched heliostats), and optimized and nonoptimized systems have been compared. Also, the total energy collected by the solar field has been calculated for optimized and nonoptimized heliostats' orientations, considering towers of different heights. Finally, the real PS10 solar plant has been considered, demonstrating that also for an optimized, very low coverage plant (about 14%), heliostats rotation can still improve the energy collection efficiency by a non-negligible amount.