Comparative System Performance Analysis of Direct Steam Generation Central Receiver Solar Thermal Power Plants in Megawatt Range

Abstract

This work proposes and analyses several integration schemes specially conceived for direct steam generation (DSG) in megawatt (MW) range central receiver solar thermal power plants. It is focused on the optical performance related to the heliostat field and the arrangement of receiver absorbers, and the management of steam within a Rankine cycle in the range between 40–160 bar and 400–550 °C at design point. The solar receiver is composed of one single element for saturated steam systems or two vertically aligned separated units, which correspond to the boiler and the superheater (dual-receiver concept), for superheated steam solar thermal power plants. From a fixed heliostat field obtained after layout optimization for the saturated steam solar plant the heliostat field is divided in two concentric circular trapezoids where each of them independently supplies the solar energy required by the boiler and the superheater for the different steam conditions. It has been observed that the arrangement locating the boiler above the superheater provides a slightly higher optical efficiency of the collector system, formed by the solar field and the receiver, compared with the reverse option with superheater above boiler. Besides, two-zone solar fields provide lower performances than the entire heliostat layout aiming at one absorber (saturation systems). Optical efficiency of two-zone solar fields decreases almost linearly with the increment of superheater heat demand. Concerning the whole solar collector, heliostat field plus receiver, the performance decreases with temperature and almost linearly with the steam pressure. For the intervals of steam pressure and temperature under analysis, solar collector of saturated steam plant achieves an optical efficiency 3.2% points higher than the superheated steam system at 40 bar and 400 °C, and the difference increases up to 9.3% points when compared with superheated system at 160 bar and 550 °C. On the other hand, superheated steam systems at 550 °C and pressure between 60 and 80 bar provide the highest overall efficiency, and it is 2.3% points higher than performance of a saturated steam solar plant at 69 bar. However, if saturated steam cycle integrates an intermediate reheat process, both would provide similar performances. Finally, it has been observed that central receiver systems (CRS) producing saturated steam and superheated steam at 500 °C operating at 40 bar provide similar performances.

Techno-economic modeling and optimization of solar-driven high-temperature electrolysis systems

“…The receiver's thermal efficiency is defined as the ratio of _ Q fluid to _ Q rad . We validated our receiver model with literature data (Sanz-Bermejo et al, 2014a). The solar receiver thermal efficiency for our reference case for system 1 with a mean temperature of 727 K was 82% (see Section 4.2) which agreed with the efficiency of 81.7% reported in (Sanz-Bermejo et al, 2014a) for their superheating receiver with a mean temperature of 736 K.…”

Optimization of multiple receivers solar power tower systems

“…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.…”

Novel design of central dual-receiver for solar power tower

“…In addition, the difference in the convective heat transfer coefficient of the two sections requires different allowable heat fluxes. It has been estimated that the maximum heat flux can be imposed on the boiling and superheating sections were 650kW/m 2 and 300kW/m 2 , respectively [9]. Apparently it becomes difficult for the one-receiver configuration to control proper heat flux distribution on both sections.…”