Central Receiver Research Articles

Initial Performance Outlook on the Sliding Particle Receiver (SlideRec)

The next generation of central receivers is expected to reach high outlet temperatures of 800 °C and above, maintain stable operation and react to a varying incoming flux magnitude caused by hourly and seasonal variations, endure high-temperature operation, and remain cost-effective. Particle-based central receivers are being considered due to their high-temperature durability and favorable thermal properties of particle materials such as bauxite particles. This paper describes a new particle-based central receiver concept and provides an initial exploration of its performance in comparison with the existing CentRec® technology. Discrete Element Method (DEM) simulations demonstrated that a stable falling and sliding particle film can be achieved inside the SlideRec. The residence time of particle flow within the SlideRec is estimated to be higher than a falling particle receiver and similar to that of an obstructed-flow receiver. The results of the thermal model (incorporating reflective, radiative, convective and conductive heat losses) indicate that the SlideRec demonstrates a higher thermal efficiency than the CentRec® under an incoming aperture flux of between 0.1 MW/m2 and 1.7 MW/m2. The concept therefore is promising and is recommended for further experimental exploration.

Thermal stress in externally irradiated tubes of solar central receivers with a gas–particle fluidized dense suspension

One of the objectives of the new generation of concentrating solar power plants is to increase the actual temperature limit (565 °C) up to or near 1000 °C. An alternative heat transfer fluid that could help to reach this objective is the use of a fluidized dense gas–particle suspension ascending through a vertical tube. Since the predominant cause of rupture in solar receivers is the creep-fatigue damage process, which is mostly influenced by the maximum temperatures and stress experienced along the tube, the main objective of this work is to numerically study the thermomechanical behavior of a non-uniform externally irradiated tube where particles are fluidized and moves upwards. The heat transfer problem in the two media present (i.e. dense suspension of particles and tube wall) was solved separately: a Computational Particles Fluid Dynamic model solves the heat transfer in the particles, whereas a three dimensional Finite Volume model simulates the heat conduction through the tube wall to obtain the temperature profile, which serves as input to calculate the thermal stress of the tube with an analytical method. Higher thermal stresses were obtained for an absorbed power of 250 kW/m2 (σVM,max=219MPa) compared to that for an absorbed power of 500 kW/m2 (σVM,max=72MPa) due to the lower temperature difference between the front and rear sides of the tube caused by the more pronounced increase of the radiative losses in the front side of the tube compared to that at the rear side. The thermomechanical behavior of a particle receiver was compared to that of a molten salt receiver. For an incident solar flux of 500 kW/m2, the particle receiver reduced the maximum thermal stress by 73% compared to the molten salt receiver. However, the tube’s maximum temperature exceeded the working limit for stainless steel tubes. In order for the receiver to survive heat fluxes characteristic of solar power plants, research into technological solutions that allow to improve the effectiveness of the heat transfer rate from the tube to the particle flow is necessary.

A theoretical thermodynamic investigation on solar-operated combined electric power, heating, and ejector cooling cycle driven by an ORC turbine waste heat, tri-generation cycle system

The current study investigated a solar thermal power plant to simultaneously produce multiple energy outputs, including electric power, process heating, and cooling. This integrated approach aligns with the concept of a tri-generation system, where three different forms of energy are produced from a single source. The study involves a parametric analysis, where the impact of each influencing parameter including, turbine inlet temperature, and turbine inlet pressure is systematically varied with DNI ranging from 600 W/m2 to 1000 W/m2 to understand its effects on both first-law and second-law efficiencies. Further, the exergy analysis shows the irreversibility's occur within the system. Notably, the central receiver and heliostat are identified as major sources of exergy loss. The comparison to a combined power and heating (CPH) cycle without an ORC-ejector indicates that the additional technologies significantly contribute to improving the system's performance, approximately 3.97 % and 2.3 % for both efficiencies, respectively.

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.

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.

Case Studies and Parametric Analysis of Heliostat Performance with a Tradeoff-informed Technoeconomic Analysis Metric

Abstract The Heliostat Consortium (HelioCon) was launched in 2021 to advance heliostat technology. This work presents a collection of baseline case studies for the technoeconomic analysis (TEA) of candidate heliostat improvements for concentrating solar power (CSP) and concentrated solar thermal (CST) systems that employ central receivers. The case studies we develop include a large-scale CSP plant, a smaller, modular CSP plant, and a small CST plant used for industrial process heat. In this work, we propose a novel metric for TEA of a plant component technology that recasts relative changes in levelized system costs into component-specific capital cost budgets. This measure, which we refer to as the equivalent breakeven installed cost, is the maximum budget for the technology component that leads to improved levelized costs. Finally, we perform a parametric analysis to show the impact of candidate technologies on levelized cost of heat and, by extension, equivalent breakeven installed cost.

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.

Integrated solar system for hydrogen production using steam reforming of methane

Integrating renewable technologies has emerged as a promising option in pursuing sustainable and efficient energy solutions. The primary source of industrial hydrogen is steam methane reforming (SMR); however, this process is based on fossil fuels with massive carbon byproduct emissions. The solar thermal tower appears to be a suitable renewable source for powering SMR by providing high temperature heat to drive the process reactions. This approach aims to harness the abundance of solar energy for natural gas reforming to produce hydrogen at minimum environmental impact. This research establishes the viability of combining external central receiver concentrated solar power with SMR integrated with thermal energy storage (TES), revealing general insights into the system energy and exergy performance. The analysis of the current system is performed using the thermodynamic and thermochemical approaches to conduct a parametric study. A 543 MW central receiver is first modeled with a high-temperature molten salt as a working fluid. The SMR process model is then developed, considering both reforming and shift reactions, and solved using Engineering Equation Solver (EES). The subsystem models are validated before being integrated into the overall system model. The performance of the SMR reactor is found to affect the overall system performance considerably. The results also show that when increasing the temperature above 760 ° C, no remarkable improvement in the reforming process is observed. In contrast, the higher the temperature in the water gas shift reactor, the lower the system's performance. Moreover, the impact of wind velocity on the overall system is considered due to the large central receiver surface area. The overall system performance in terms of energy, exergy, and effectiveness is evaluated for one day of operating through charging and discharging operations. In charging mode, the overall energy and exergy efficiencies are 46.5% and 57.2%, respectively, while the overall effectiveness is 61.8%; on the discharging operation, the overall energy efficiency and effectiveness have a similar definition with a value of 82.4% and the overall exergy efficiency achieves a value of 78.7%. Additionally, the amount of hydrogen produced at a central receiver of 543 MWth capacity is about 7.3 kg/s at a 2.1 steam-to-carbon ratio. This integration mitigates a minimum of 12 kg/s of CO2 emissions that would be generated due to methane combustion.

Thermal Desalination Through Forward Osmosis Coupled With CO2-Mixture Power Cycles for CSP Applications

This work, performed in the framework of the H2020 EU project “DESOLINATION”, analyses the coupling between CSP plants using transcritical power cycles with CO2-mixtures and an innovative thermal desalination technique based on Forward Osmosis. Calculations are presented for a large scale CSP plant with central tower receiver and direct storage with solar salts in Dubai, adopting the mixtures CO2+SO2 and CO2+C6F6 in the power cycles. The heat rejected from the cycle condenser is recovered directly by the FO plant, where the draw solute is heated up from 40 °C to 76 °C, to allow for the regeneration of the draw solution used in the forward osmosis membrane. The thermo-responsive polymer adopted is PAGB2000, already considered in literature as a promising option. Results show a very effective synergy between the electricity and the freshwater production: high yearly solar to electric efficiencies are possible (around 19%), with a low freshwater specific thermal consumption (around 100 kWhth/m3). The proposed desalination method is more effective than a conventional MED system (with + 50% of yearly freshwater produced), while a larger solar field (+ 28% in surface area) is necessary for a PV+RO plant to produce annually both the energy and freshwater produced by the CSP+FO plants.

Solar receiver endurance assessment under non-conventional operation modes

Central receiver endurance in solar power tower plants is a critical aspect to ensure their viability. In this work, two receiver configurations, with and without flow path crossover, are compared in thermal and mechanical performance. Considering their thermomechanical limits during operation, results show that panels in the crossover configuration would endure from 1.22 to 2 times that in the no-crossover, just marginally penalising its thermal efficiency. Additionally, two plant operation strategies are compared: continuous operation and nighttime strategy. The former results in 1.89-times more damage but roughly a 1.9-times increase in energy output, obtaining a practically constant trade-off between damage and energy generation for these two strategies. Lastly, the effect of considering either a linear or bilinear (interaction point set at 0.05,0.05) creep/fatigue damage interaction is explored. While producing more conservative results, linear interaction error is below 3 % in the most critical receiver regions. Such a low discrepancy is caused by the creep-damage dominance over fatigue in the most critical regions. Other areas show heavier creep-fatigue interaction, resulting in larger error, but these areas obtain times to failure much longer than expected receiver lifespan.

Evaluation of a concentrated solar power-driven system designed for combined production of cooling and hydrogen

The current technique of hydrogen generation and cooling production raises climatic problems, which calls for the investigation of cleaner alternatives. No research has been conducted to propose and analyze a solar thermal power cycle-based water electrolysis for on-site production of hydrogen and the detailed exergy analysis of a series flow double-effect absorption chilling machine employed for large solar cooling. In this regard, a helically coiled tube embedded central receiver is used in the heliostat field for the simultaneous production of solar cooling and green hydrogen to meet the increasing needs of energy and fuel sustainably. The combined system is composed of four sub-systems including a heliostat field, LiBr–H2O operated series-flow double effect absorption refrigeration cycle (DEARC), organic Rankine cycle (ORC), and proton exchange membrane (PEM) electrolyzer. The system was examined from energy and exergy perspectives in the Engineering Equation Solver (EES) using library data of REFPROP for obtaining the thermodynamic properties of working fluids. The results of the thermodynamic model for the combined system are validated. Furthermore, the effect of ambient temperature, solar irradiation, and type of ORC working fluid on the hydrogen and cooling production, and the overall energy and exergy efficiency of the combined system are examined. A computational fluid dynamics simulation applying ANSYS-FLUENT was used to examine how coil curvature ratio and coil torsion affect solar heat transfer fluid (SHTF) pressure and temperature leaving the receiver. The coil curvature ratio affects temperature increase more than coil torsion. Solar heat transfer fluid outlet temperature increases by 36.9 % when the coil curvature ratio increases from 0.063 to 0.095 at direct normal irradiations (DNI) 1200 W/m2, input temperature of 92°C, and coil torsion of 0.032. The response of the cogeneration cycle to varying operating parameters is examined. Application of R141b as the ORC fluid results in a large increase of cooling exergy efficiency from 14.98 % to 63.48 % when the ambient temperature is increased from 15 °C to 45 °C whereas the exergy efficiency of the combined system is marginally improved. The exergy distribution presents for ORC operating on R141b, out of 100 % input solar exergy, 16.42 % is generated as hydrogen exergy and 13.67 % cooling exergy, 66.79 % is the exergy destroyed, and the rest 3.12 % is exergy loss. Exergy analysis is utilized to identify the sources of losses in useful energy within the components of the system considered and provides a more realistic and meaningful assessment than the traditional energy analysis. The results justify a need for the promotion of exergy analysis through policy decisions in the context of the global energy and environment crisis.

On the feasibility of overnight industrial high-fidelity simulations of CSP technologies on modern HPC systems

In the last decades, computational fluid dynamics (CFD) has become a standard design tool in many fields, such as the automotive, aeronautical, and renewable energy industries. The driving force behind this is the development of numerical techniques in conjunction with the progress of high-performance computing (HPC) systems. However, simulation time remains the most limiting factor for large-eddy simulations (LES) to be adopted in the industry. A consensus exists that, to be feasible, LES simulations should be completed overnight In this context, this work assesses the feasibility of overnight LES simulations on GPU-accelerated supercomputers with TFA, our novel in-house code, which relies on a symmetry-preserving discretisation for unstructured collocated grids that, apart from being virtually free of artificial dissipation, is shown to be unconditionally stable. The study cases will be taken from central receivers used in concentrated solar power (CSP) plants, and a comparison with open-source CFD codes will be made.

IoT-Based Manhole Monitoring System

As cities grow, the complexity of their sewage systems also increases, making manual monitoring methods obsolete. To address this, a system based on the Internet of Things (IoT) has been developed. This system uses sensors to monitor conditions in manholes in real-time and send data to a central receiver. Any issues are automatically alerted for quick intervention by concerned authorities.

High-resolution spectral atmospheric attenuation measurement for solar power plants

One of the main challenges in solar tower renewable technologies is measurement of solar radiation attenuation at the plants at surface level. This paper describes an improved version of the optical spectrum analysis method for measuring solar radiation attenuation in real time at solar tower plants, as presented in a previous work. The new hardware design and calibration process are explained in detail. This new system has a resolution of 0.25 nm in the VIS range and a precision of 0.5% in real time, improving over the state of the art for the measurement of spectral atmospheric attenuation. These specifications allow the assessment of the contribution of different attenuation factors at surface level, such as absorbance peaks (Na, H, H2O) or scattering and the search for correlation with different weather conditions. They also enable experimental validation of atmospheric extinction simulation methods and their parameters. This work also includes the results of a 6 month-long campaign of solar weighted atmospheric extinction measurements at Atlantica's operating central receiver solar plant PS10 at Sanlúcar la Mayor (Seville, Spain). Fluctuations in the daily averaged transmittance greater than 10% are observed, which shows the importance of monitoring this parameter during the operation of solar plants.

Pathways to IEC Standards for Heliostat Design Qualification and Site Acceptance in Central Receiver CSP Applications

This paper surveys the existing landscape of standards relevant to heliostats, identifies their gaps, and proposes a path forward to a comprehensive set of heliostat guidelines, technical specifications, and standards under the framework of International Electrotechnical Commission (IEC) TC 117. Gaps in existing guidelines and standards are surveyed using a three-tiered taxonomy: component-level, heliostat-level, and field-level. At each level, the gap analysis is followed by a proposal for a coordinated path forward on the development of standards. At the component level, advances in the understanding of wind loading should inform a technical specification for drives and structures. Reflectors require consolidation of measurement guidelines into existing standards documents. Communications & controls require technical standards to inform their selection and secure implementation. At the heliostat level, IEC 62817 (solar trackers) adequately characterizes drive systems, structures, and electronics, but requires adaptation to heliostats’ use patterns, operating modes, and expected life cycles. IEC 62817 does not address heliostat beam quality and pointing accuracy, but the process for determining both is elaborated in the SolarPACES Guideline for Heliostat Performance Testing. This SolarPACES document requires two main modifications: adaptation to IEC language and inclusion of testing after heliostats which have undergone accelerated weathering and mechanical cycling (to understand performance degradation). At the field level, IEC 62862-4-2 addresses the function and control of heliostat fields but does not cover the statistically rigorous testing of heliostat groups, or field performance factors like security and soiling. The addition of documents under IEC-62862-4 is proposed to address this gap.

Global Methods for Calculating Shading and Blocking Efficiency in Central Receiver Systems

This paper presents three new methods for calculating the shading and blocking efficiency in Central Receiver Systems (CRSs). All of them are characterized by the calculation of multiple useful and total reflecting areas without the need to resort to parallel calculation in the CPU or GPU, and by low computation times and minimum errors. They are being specially designed for implementation in codes focused on heliostat field design and optimization in CRSs. The proposed methods have been compared against two outstanding “individual” methods (homology and Boolean operations), in addition to a reference case based on the Monte Carlo ray-tracing (MCRT) technique. The results indicate that one of the proposed methods presents reduced error values and high computational speed, even relaxing the restrictions on candidate filtering. At the same error level, the global method is up to 7.80 times faster than the fastest individual method (homology) and up to 194 times faster than the method based on the MCRT technique. The causes of the main errors of each method are also analyzed.

Development and Evaluation of a MQ-5 Sensor-Based Condition Monitoring System for In-Situ Pipeline Leak Detection

The condition monitoring system for an in-situ pipeline is an innovative concept that uses MQ-5 sensors to detect fuel leaks in pipelines and relay concentration data to a receiver station. The essence of the monitoring process is to ensure the safety and security of engineering properties and lives. The project addresses the crucial requirement for rapid detection of fuel leaks to avoid environmental problems, economic losses, and safety risks connected with pipeline circulation. The goal is to create a leak detection monitoring system. The project required the design and execution of four transmitter stations, each responsible for detecting fuel leaks at various places along a small-scale pipeline and transmitting concentration data to a central receiver station. The system's response time, a critical performance parameter for this project, was measured by timing how long it took for an alert to arrive at the receiving station after the transmitter detected a leak. This time was measured at three distances between the transmitter and receiver stations: 1m, 2m, and 3m. Multiple measurements were taken at each distance, and the average response time was computed. The results showed that as the distance between the stations increased, so did the reaction time. The average response time at 1m was 3.37 seconds, whereas, at 2m and 3m, it was 3.856 seconds and 4.198 seconds, respectively. A t-test inference was performed to check that there was a distinct difference between the response times for each distance, and a significant difference was detected. The built system effectively demonstrated its ability to detect fuel leaks, and the observed response times offered useful information about the system's performance at various distances. This technology demonstrates the potential to improve pipeline transportation safety and efficiency by enabling early identification of fuel leaks.

Techno-Economic Analysis of Central Receiver Plants According to the Optical Error of the Solar Field

Among the concentrated solar power technologies (CSP), the central receiver (CR) technology is the most promissing to achieve the lowest levelized cost of energy (LCOE) and the one expected to play one of the major roles in the energetic mix in the next years. For that purpose, succesful CR projects are needed, starting by the contruction and erection of a reliable heliostat field that fulfils its design specifications. In this work, the loss of energy production and the consequently rise of LCOE is investigated as function of the optical error of the heliostats. For that, a reference CR plant is defined in which the heliostat field layout and the receiver are optimized to collect the maximum annual energy. An aiming strategy is also implemented to obtain more realistic results. For instance, for a reasonable deviation of about 40-50% compared to the optical reference error, the annual collected energy can drop to a considerable 5%.

Design Basis Document / Owner’s Technical Specification for Nitrate Salt Systems in CSP Projects

Work has begun on a Design Basis Document / Owner’s Technical Specification for parabolic trough and central receiver power plants using nitrate salt as the heat transport fluid and the thermal storage medium. A principal topic of recent interest is the failures of the hot salt tanks in central receiver projects. The paper outlines a hypothesis for the source of the failures, and discusses a range of possible solutions.

A Method for Projecting Cloud Shadows Onto a Central Receiver Field to Predict Receiver Damage

This work demonstrates methods of mapping high-spatial-resolution direct normal irradiance (DNI) data from satellites, Total Sky Imagers (TSIs), and analogous data sources onto a heliostat field for characterizing the spatial and temporal variation of the incident flux on a central receiver tower during cloud transient events. The mapping methods are incorporated into an optical software module that interfaces with CoPylot–SolarPILOT’s python API– to provide computationally efficient optical simulation of the heliostat field and the solar power tower. Eventually, this optical model will be incorporated into optimization models whereby a plant operator can understand the effects of cloud transient events on overall power production and receiver lifetime due to creep-fatigue damage and therefore make better informed decisions about receiver shutdown events. By more accurately modelling the effects of cloud events on receiver flux maps, this work may determine the magnitude and frequency of thermal cycling on receiver tubes and panels using actual or realistic cloud shapes instead of averaged DNI values–which may undercount the total cycle number. This work may also prevent unnecessary plant shutdowns due to overly precautionary control strategies and characterize the relative impact of various cloud types on receiver life. We plan to eventually integrate this methodology into the System Advisor Model (SAM) to improve performance model accuracy during periods of cloudiness. In this paper, we demonstrate generating DNI maps and mapping them to a solar field in CoPylot using 10 m resolution data from publicly available Sentinel-2 satellite data over the Crescent Dunes plant.