Comparison of Two Sun Tracking Methods in the Application of a Heliostat Field

Abstract

The basic mathematics and structure of heliostat have remained unchanged for many decades. Following the challenge first made by Ries et al., the non-imaging focusing heliostat recently proposed by Chen et al. provides an alternative in the field of concentrated solar energy. This paper investigates the performance of a heliostat field composed of the newly proposed heliostats. In contrast to the dynamic curvature adjustment proposed in our previous work for a solar furnace, a fixed asymmetric curvature is used here with the spinning-elevation tracking method. This restriction is intended to equalize the manufacture cost of the new heliostat with that of traditional heliostats with azimuthelevation tracking and spherical curvature. Fixing the curvature results in only partial aberration correction, compared to full correction using the dynamic adjustment of curvature. Nevertheless, the case studies presented in this paper show that the new heliostat design can reduce the receiver spillage loss by 10-30%, and provide a much more uniform performance without large variations with time of day. Fig. 1 Spot size comparison between the spinning-elevation and azimuth-elevation tracking methods for June 21st. The target angle is 41.8 deg, facing angle is 10 deg to the south and the latitude is North 43 deg. Heliostat area is 25 m 2 and the slant range is 30 m.

Clay-Brick Firing in a High-Temperature Solar Furnace

“…The heliostat design includes nine mirrors, each with dimensions of 1 m × 1 m, arranged in three rows and three columns. A rotation-elevation sun tracking system is used because it produces fewer aberrations than an azimuth-elevation system (Chen et al, 2004); therefore, the heat fl ow is more uniform in time. Moreover, only M + N = six motors are required with the rotation-elevation tracking system, two for primary tracking and four for secondary tracking.…”

Storage capacities required for a solar thermal plant to avoid unscheduled reductions in output

“…It can be seen that the heliostat efficiency is lower during summer than in the other seasons, with the highest efficiency being in spring and autumn. The field efficiency was calculated for each season for each of the six sites, because the solar time depends upon the geographic location (Chen et al, 2004). The heliostat cosine efficiency is defined as Q 0 h;cos ¼ ðQ 0 s  g cos Þ.…”

“…However, the dominant component of the optical efficiency is the cosine loss, which can be calculated for any given heliostat within the field from the equation g cos = cos h i , with h i , being the incidence angle of the sun relative to the mirror surface normal, which matches that of the mirror to the receiver (Chen et al, 2004). For any given heliostat in the array, the optical efficiency, therefore, depends both on the position of the heliostat within the field and on the solar time, i.e.…”

Non‐imaging Focusing Heliostat

“…As a result, a new non-imaging focusing heliostat, that employs a clever approach to maneuver the facets in group manner for astigmatic correction has been proposed. Many research works on non-imaging focusing heliostat have been carried out by Chen et al [9][10][11][12][13][14][15], Chong et al [16][17][18][19][20][21][22] and Lim et al [23] to establish the principle and technology of the new heliostat. Overall, there are two major advancements achieved in the new heliostat compared to the conventional heliostat that has remained unchanged for many decades [24].…”

“…13 The simulated results of solar fl ux distribution for a spherical mirror with a size of 500 cm × 500 cm, focal length of 25 m and target distance of 25 m. Note that C max is maximum solar concentration and A is total image area.…”