Heliostat Field Research Articles

Technical strategy for reapplying coatings on solar tower receiver tubes using concentrated flux

Reapplying the coating is crucial to restore optimal receiver performance. However, the heat treatment must be conducted onsite since the receiver cannot be removed from the tower. This study explored effective strategies for maximizing the coating’s performance after reapplication. The impact of different aimpoint strategies on the receiver’s surface temperature was analyzed using the heliostat field and the three-dimensional receiver model. Experimental tests were conducted using a solar lamp to study temperature variation curves of coatings on different tube panels under various aiming strategies, and absorptance was then measured. The optimal recoating strategy was determined through a comprehensive analysis of the system’s power generation and its Levelized Cost of Energy across its entire lifecycle. The “image size priority” strategy led to significant temperature variations among tube panels and within each panel. In contrast, the “segmented target flux” strategy effectively minimizes temperature differences, ensuring that over 91.25 % of the receiver tube panel reached temperatures above 550 °C. Comparatively, under the “image size priority” and “segmented target flux” strategies, the coating’s absorptance at the molten salt inlet panel is lower by 1.84 % and 0.10 %, respectively, compared to the standard sample. The effectiveness of the “segmented target flux” strategy becomes more pronounced with shorter recoating intervals. The research contributes to enhancing the maintenance performance of the coating and the operational efficiency of the receiver.

Variation of Heliostat Wind Loads in a Radial Field Array Model

The design of heliostats throughout a concentrated solar power (CSP) plant are currently of uniform design, however, research into the variation in heliostat wind loading within a radially staggered field array can provide insight into potential material cost savings in heliostat field design. Experimental investigation was carried out on a field array model in the University of Adelaide large wind tunnel. A total of 64 heliostat models of size 0.1 × 0.1 m were radially arranged over four surround rows. Four 3-axis load cells were utilized to analyze field array cases of morning (0700 hours), noon (1200 hours), and evening (1700 hours) configurations. Angle calculations for beam reflection were made for the 21st March (equinox). Results show mean and peak drag force coefficients reduce with distance into the field for a 1700 hour case due to high upstream blockage. Comparing the downstream drag and lift force coefficients against each test configuration, when heliostats are at steep elevation angles, high flow blockage leads to a reduction of coefficients downstream (0700 hour and 1700 hour cases). When elevation angles are reduced (1200 hours), drag and lift coefficients increase with distance from the central tower in the downstream direction. Results also show the central tower increases load coefficients on downstream heliostats, and therefore should be considered in heliostat wind loading and field design.

DDPG‐based heliostats cluster control of solar tower power plant

AbstractThe control of heliostat is crucial for the development of solar tower power plant. Currently, most power plants use open‐loop control, which has low cost but low efficiency, closed‐loop control has high concentrating efficiency, but each heliostat requires sensors and has high cost, and Proportional‐Integral‐Derivative (PID) controller has good control effect, but the parameter adjustment is difficult and overshooting problem occurs. In this paper, we propose a DDPG‐based heliostat cluster control aimed at improving the heliostat control effect and reducing the control cost. A leader‐follower strategy is used to control the heliostat, where the whole heliostat field is divided into several groups, each group is assigned a leader heliostat, and the rest of the heliostats follow the leader heliostat to rotate. The leader acquires the control error by means of a photoelectric sensor or a camera device. The following heliographs rotate with the leader to obtain the control signal, so there is no need for sensors, which reduces the number of sensors and lowers the cost. To address the shortcomings of traditional PID, we propose a DDPG‐based PID control algorithm. The algorithm is trained to find out the optimal value at each moment, which ensures that the controller parameters are optimal at each moment. The results show that the tracking error is below 0.0001 rad for both cluster control and individual control. This ensures effective tracking performance while reducing the sensor cost. The controller based on the DDPG algorithm eliminates overshoots, reduces errors, and shortens the stabilization time by 0.5 seconds.

Integration of energy storage and determination of optimal solar system size for biomass fast-pyrolysis

This study presents a model and analysis of a heliostat field collector (HFC) system integration with fast-pyrolysis of biomass and determination of the optimal solar system size for this integrated system. Given the intermittent nature of solar energy, an auxiliary heater and a thermochemical energy storage system (TCES) are included. Four cases of HFC integration with the fast-pyrolysis process have been studied: 1) low solar radiation, 2) sufficient solar radiation, 3) high solar radiation, and 4) no solar radiation with available stored energy in TCES. The solar energy system was modeled and calculated using the Engineering Equation Solver (EES) software, while the fast-pyrolysis process and the TCES were simulated using the Aspen Plus software. A thermodynamic and economic analysis has been conducted to estimate the share of solar energy for different process configurations. Economic calculations have been conducted for three different heliostat filed areas: 4000, 8000, and 12000 m2. Solar fraction, investment and operational costs, as well as total cost were calculated for these three heliostat field areas. The results indicate that the optimum heliostat field area for the studied biomass pyrolysis plant is 8000 m2 and the average solar fraction of the required energy in summer is 0.39 and while it is 0.34 for the whole year. Simulation results considering this optimized heliostat filed area indicate that 6.27 t/h of bio-oil is produced from 10 t/h of hybrid poplar biomass. Implementing this solar-assisted system reduces CO2 emissions, increases efficiency of the system and lowers thermal energy requirement for the fast-pyrolysis process from 6MW to 3.99MW.

Quickly select heliostat candidates and design pattern-free layout using geometric projection method

Central receiver system is one of the most promising solar energy harvesting technologies, which focuses sunlight onto the receiver through heliostats to generate high temperatures for thermal cycling. The optimal layout of the heliostat plays a crucial role, but the pattern-free heliostat field layout requires multiple uses of computationally intensive shadowing and blocking efficiency, which is highly time-consuming. In this work, a new geometric projection method, Projection radius method (PRM), is proposed. It includes two aspects: (i) Quickly and effectively selecting heliostat candidates with shadowing and blocking potential by the incident and reflected ray projection radius; (ii) Designing the pattern-free heliostat field layout by employing overlap radius instead of shadowing and blocking efficiency. The results indicate that, compared to traditional methods, when designing 2650 heliostats, (i) the calculation time for optical efficiency was reduced by 63%; (ii) optical efficiency increased by 1.23%, and designing a pattern-free layout took only 2.78 h. These advancements facilitate the efficient design of large-scale pattern-free heliostat field layouts.

Heliostat field aiming strategy based on deterministic optimization: An experimental validation

In Solar Power Tower plants, the aiming strategy plays a key role in the performance and interaction between heliostat field and receiver. This work presents an aiming strategy based on a deterministic optimization that maximizes the flux uniformity and minimizes the spillage losses. The algorithm can be fed either by a flux mapping model or by the synthesis – superposition – of experimental images. Both approaches are experimentally tested at PROTEAS research facility, aiming 16 heliostats at a flat Lambertian target. In the comparison between experimental and computed flux maps, the cross-correlation coefficient exceeds 97%. The spillage loss factors are underestimated by the computations: 9.2 percentage points by the model-based and 6.7 points by the synthesis-based approach.

SolarPACES Task III Project: Analyze Heliostat Field:

In recent years, great efforts have been made to reach a consensus on heliostat testing best practices. A specific SolarPACES task was launched to provide a Heliostat Testing Guidelines document for single heliostat evaluation with a focus on prototype validation and qualification. Such guidelines are not well-suited for heliostat evaluation in operating commercial heliostat fields. The commercial implementation of the Central Receiver technology is burdened by the lack of a demonstrated cost-effective methodology to test solar fields, particularly during the commissioning and operation phases of the plant. To address heliostat characterization challenges, the SolarPACES funded Project “Analyze Heliostat Field” aims to set the basis towards a SolarPACES guideline for Heliostat Field Performance testing under a common framework. This is by means of a review of the existing methodologies, R&D and industrial stakeholders information sharing and preparation of a future quantitative comparison and validation plan. As part of the development of this project, several meetings and a workshop involving the SolarPACES community was organized to share knowledge and experience in the measurement and characterization of heliostat fields using a range of technologies and procedures. Research centers and companies from 5 different and distant countries have actively participated in these meetings, sharing their experiences, needs and interests. This paper summarizes the outcome of this international collaborative effort and the prospects for future close collaborations sustained over time.

Optical Benchmarking of a Novel Polar Bi-Focal Beam-Down Tower Concept

Small-scale modular CSP systems using polar heliostat field arrangements reduce cosine losses significantly and – by integrating a secondary beam-down reflector – enable novel receiver concepts. A novel polar bi-focal beam-down design is introduced and its optical performance is assessed with ray tracing. Albeit not fully optimized, results show that – in comparison to a single-focus beam-down system – the bi-focal system entails higher annual, DNI-weighted optical efficiency and flatter circadian profiles, beneficial for reducing peak dumping. Even higher optical performances can be reached by combining single-focus and bi-focus systems.

Variation in Reflected Beam Shape and Pointing Accuracy Over Time and Heliostat Field Position

Heliostats are typically constructed with fixed mirror shapes, which they move to varying angles to reflect sunlight onto a receiver. While heliostat facet curvatures and canting angles are selected to maximize a chosen performance criterion, these fixed shapes inevitably cannot maintain focus throughout widely varying solar incidence angles. Further, heliostat pointing accuracy generally exhibits error due to manufacturing and installation imperfections. In this paper we present a systematic study of how reflected beam shape and pointing accuracy vary with heliostat position, time of day, and time of year. We selected nine heliostats spanning the Sandia National Laboratories National Solar Thermal Test Facility (NSTTF) heliostat field, and measured their beam shape and required pointing corrections throughout the day, for six key dates spanning a solar year. We also present ray tracing analysis to aid understanding of the observed effects. The resulting data provide insight into the nature and magnitude of heliostat focus loss at various times, and clarify the nature of the problem faced when attempting to maximize heliostat field performance, especially for high-temperature industrial applications. We conclude that fixed heliostat fields canted with an off-axis strategy will lose significant performance away from the solar noon hour to which they are tuned, and that aim point corrections can vary widely, both between independent heliostats and over time for a given heiostat. This implies that multiple measurements of each heliostat are required to determine calibration pointing corrections.

Study On Operation Strategy Of CSP Peak-Regulating Power Station Based On Spot Trading Market In Gansu Province

On March 3, 2022, the National Development and Reform Commission of China and the National Energy Administration of China jointly published the Notice on Accelerating the Construction of the Electricity Spot Market. The notice indicated that the government would support the uninterrupted operation of the power spot pilot project with conditions and form a long-term and stable electricity spot market as soon as possible. These steps will help rapidly improve China's electricity spot market construction. Due to its large-scale energy storage capacity, the Concentrated Solar Power (CSP) station can be used as a peak-regulating power station to provide grid-friendly long-term peak regulating capacity and moment of inertia for the power system. When CSP stations participate in electricity spot market trading, they can optimize their operation strategy to generate more electricity during periods with higher electricity prices, thereby obtaining more profits. In this paper, a 100MW CSP Peak-Regulating Station with an 80.0hm2 reflecting area of Heliostats Field (HF) is designed in Gansu, China. In the Peak-Regulating operation strategy, the most suitable TES Capacity for this project is determined to be 15h. We take this CSP station as the research objective to optimize the operation strategy of the power station. The research results indicate that optimizing the operation strategy will increase the power station's annual electricity sales revenue by about 19.97% before the strategy was optimized when the power station participated in the real-time trading of the Gansu electricity spot market in 2022.

Notes on Measuring Concentration Ratio Distribution for a Solar Tower Using Moonlight

The authors' original concept of indirect solar flux mapping of a heliostat field measures CRD using a compact stationary array of moonlight illuminometers on the receiver aperture and a reference moonlight illuminometer on the dual-axis moon tracker. Two sets of moonlight concentration experiments (CCD camera + white target; concentrated lunar beam passing across the linear array of illuminators) were carried out on 63 heliostats at Badaling Solar Tower Power Plant in Beijing on a full moon night in 2018. How the sun and moon shapes differ for CRD as light sources on a solar dish is investigated. Solar/lunar CRDs are similar. Another lunar flux mapping model is also presented, allowing different moon shapes to estimate the solar CRD and contribute improvements in extrapolating measured lunar CRDs to a solar tower working with the real Sun by repeated smooth-filtering. In this paper, some unknown factors, effects, and improvements are carefully considered to enhance the CRD measurement accuracy of a solar tower power plant by using moonlight concentration.

Supercritical Water Gasification of Biomass on CSP Plants: Comparison of On-Sun and Off-Sun Designs

A comparative study of On-Sun and Off-Sun designs for supercritical water gasification (SCWG) of biomass on concentrated solar power (CSP) plants was here presented. In the On-Sun design, the tubular reactor was placed on a cavity receiver of a solar power tower (SPT) plant and the heat employed to produce the gasification came directly from the sun (viz. the solar radiation was concentrated, thanks to the heliostat field, onto the tube's surface). In the Off-Sun designs, the gasification of the biomass was carried out inside a heat exchanger and it was produced thanks to the heat absorbed from the hottest fluid, which can be obtained from CSP plants or electrical heating. This work numerically investigated the thermomechanical performance of both designs. The results stood out the relation between temperature-gas yield-thermal stress. In On-Sun configurations the gas yield was 5 times higher than those obtained in the Off-Sun configuration. However, the highest values of both temperature and stress may produce the failure of the reactor. This fact could be avoided in an Off-Sun reactor, since its uniform heating conditions mitigate the maximum temperature and stresses.

Design of Modular High Temperature Sodium Solar Collection Subsystems

Optimised designs of 11.7MWth solar collection subsystem modules based on high temperature (740°C) sodium central receivers are investigated. Billboard and cavity receivers mounted on steel lattice towers are considered, and radially staggered and Cartesian heliostat field layouts are compared. A billboard receiver paired with a Cartesian heliostat field layout was found to give the overall lowest levelised cost of heat (LCOH), albeit with a significantly taller tower compared to using a radially staggered heliostat field layout.

Mathematical modelling and optimizing design of heliostat field

The heliostat field is a form of solar thermal power plant, The heliostat field is a crucial component of solar thermal power plants and establishing a heliostat field is of great significance for reducing carbon emissions. and is of great significance in reducing carbon emissions This paper focuses on the mathematical modeling and optimization design problem of the heliostat field. For three different design scenarios, firstly, based on the data provided by the China Undergraduate Mathematical Contest in Modeling 2023, a geometric optical efficiency model is proposed to determine the annual average optical efficiency and output thermal power under specific heliostat field design parameters. Secondly, aiming at the optimal design parameters of the solar furnace field under the condition of rated annual average output thermal power is 60 MW\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ ext{MW}$$\\end{document}, Particle Swarm Optimization (PSO) combing with efficiency model is utilized to determine the optimal design parameters of the heliostat field. Finally, this paper uses Quasi-Monte Carlo ray tracing (QMCRT) model to perform simulations, exploring how to obtain the optimal design parameters of the heliostat field with the goals of maximizing the output thermal power and ensuring high efficiency. Furthermore, the influence of normal disturbances on the annual average annual average thermal output power is investigated.

Research on Optimization Design of Heliostat Field Based on Particle Swarm Optimization Algorithm

Research on Optimization Design of Heliostat Field Based on Particle Swarm Optimization Algorithm

Research on heliostat field design based on mesh search optimization algorithm

Research on heliostat field design based on mesh search optimization algorithm

Optimization design model of heliostat field based on gravitational search algorithm

In todays society, non-renewable resources are becoming increasingly precious, making the utilization and conversion of renewable resources more critical. Heliostat fields play a significant role in the actions taken by various countries to achieve carbon peaking and carbon neutrality. How can the installation and arrangement of heliostats maximize the annual average thermal power output per unit mirror area while achieving the rated power? This paper establishes an efficiency calculation model based on the flat-plate projection-Monte Carlo algorithm and an optimization design model of heliostat fields based on the gravitational search algorithm. The research progresses from shallow to deep, investigating methods to maximize the output thermal power under different constraints. First, it addresses the issue of maximizing the average thermal power output per unit mirror area under fixed heliostat field parameters and rated power conditions. Next, it solves the problem of maximizing the annual average thermal power output per unit mirror area under varying heliostat sizes and installation heights, with fixed rated power. Finally, it points out that the models established in this paper are applicable to complex real-world situations and can effectively improve the thermal efficiency of heliostat fields.

Performance test of a heliostat field integrated PVT solar collector using organic phase change material and carbon black additives

The rising global awareness of environmental issues has brought about a rise in the adoption of green energy throughout our daily activities in recent decades. The radiation from the sun is utilized for thermal heating, electrical generation, and agriculture by Phase change materials (PCM) integrated PVT collector. However, the lower concentration ratio of solar radiation on flat plate collectors and the lower thermal conductivity of PCMs are the major drawbacks. In this present study, a Heliostat field concentrator was designed to integrate with a hybrid photovoltaic thermal (PVT) collector for the increase of the solar irradiance, and carbon black additives incorporated stearic acid (SA) were used in the underneath PVT collector to enhance the thermal conductivity of SA as well as the thermal efficiency of the system. The performance tests were carried out for both SA with carbon black and SA without carbon black additives for varying water flow rates of 0.0025 kg/s, 0.0035 kg/s, 0.0045 kg/s, and 0.0055 kg/s. The efficiency of the PV panels ranged from 10 % to 13 %. The maximum thermal efficiency was found to be 46.56 % when using SA with carbon black for the water flow rate of 0.0035 kg/s whereas the maximum thermal efficiency was 45.45 % in the case of SA without carbon black for that water flow rate. Especially contrasted with the other flow rates throughout the investigation, the average thermal efficiency increases by 6.83 % for the flow rate of 0.0035 kg/s after integrating carbon black with PCM. The experimented results showed the outlet temperature of water in the range of 50 °C-59 °C throughout the day which is sufficient for domestic hot water applications.

Research on Optimization Design of Heliostat Field Based on Multiple Models

Research on Optimization Design of Heliostat Field Based on Multiple Models

5G as Communication Platform for Solar Tower Plants

Wiring of heliostat fields for solar tower plants is a cost factor that becomes more important as the overall cost target is decreasing. Wireless heliostats with radio communication and autarchic energy supply have therefore been proposed in the past. But none of the communication solutions investigated so far could realistically scale to commercial size plants with tens of thousands of heliostats. Moreover, the digitalization of CSP plants with numerous mobile and stationary sensor systems requires a suitable data communication, too. The new generation of mobile radio communication (5G) is capable of handling the heterogenous communication profile portfolio comprising large numbers of units with low data rates – like heliostats - and few units with very large data volume – like e.g. drone-based camera systems. The communication requirements of a typical solar tower installation are assessed in this work and a data traffic model is created for the most relevant communication channels. The various existing 5G implementations are assessed to find the most suitable solution. Different operator models for 5G are considered and their applicability in CSP target countries is discussed. A simulation test case is presented that models the radio communication traffic of a heliostat field control during a cloud passage. Finally, the experimental 5G campus network is introduced that is currently installed at the Solar Tower Jülich research plant and will be operated in the upcoming months to demonstrate the technical feasibility of 5G radio for communication in solar fields.