Assessment of the potential improvement due to multiple apertures in central receiver systems with secondary concentrators

Abstract

When striving for maximum efficiencies in solar thermal central receiver systems (CRS) the use of gas turbines with bottoming cycles is inevitable. Pressurized volumetric receivers have proven their feasibility and good performance, and their integration into gas turbine cycles has been demonstrated. One disadvantage of this system is the necessity to use secondary concentrators. The sunlight has to be concentrated into the relatively small glass windows of the receiver, which leads to a limited view cone. This means that of all the possible heliostat positions around the tower, only those within the ellipse, resulting from the section boundary of the view cone with the ground plane, are usable. For small systems, for which tower costs are small, the resulting heliostat field layout is similar, with or without secondary concentrator. For large systems, which are more cost-effective, tower costs become significant, and the losses due to atmospheric attenuation and spillage dominate over the cosine losses. Thus, the purely North-oriented fields become increasingly sub-optimal. This article shall demonstrate at what power levels this problem can be alleviated by not using a single, North-oriented aperture, but up to six apertures-each of them associated with a separate heliostat field.

Optimization of multiple receivers solar power tower systems

“…see [34,6]). Having only one receiver forces to locate heliostats far from the tower, increasing atmospheric and spillage losses, as pointed out in [24,29,32]. As said in [26], the experience shows that higher conversion efficiency of solar energy to electricity can be achieved only at the high temperatures reached using multiple receivers technology, as addressed in this paper.…”

“…There exist different proposals in the literature for spatial configurations of multiple receivers: vertical [28], circular [7,14,15], same focal spot [9] and horizontal, see [29,31] and Figure 1. In our approach a horizontal distribution is considered where each receiver is characterized by its own height in the tower, aperture tilt angle, azimuth angle and aperture radius.…”

“…Different approaches of the heliostat field design have also been studied in the literature, see [4,24,26,28,29,31]. A common approach, called the field separation method, is to distinguish for each receiver a separate region, called aiming regions, where the heliostats will we placed, see [4].…”

“…A common approach, called the field separation method, is to distinguish for each receiver a separate region, called aiming regions, where the heliostats will we placed, see [4]. Different shapes are usually imposed to the aiming regions, such as concentric circular trapezoids [28] and ellipses [29,31]. However such aiming regions overlap, and it is not trivial how to decide the aiming strategy for heliostats at the intersection of the regions.…”

“…The pattern parameters are optimized and the final number of heliostats is obtained by oversizing the field, see [29]. This way, although the optimal parameters for the oversized field were obtained, there is a high risk that a strong distortion exists between the original and final configuration.…”