Solar Tower Research Articles

Performance assessment of solar tower collector based integrated system for the cogeneration of power and cooling

Integrating solar energy systems is an essential measure in advancing worldwide sustainability objectives and offers a sustainable, environmentally friendly approach to reducing greenhouse gas emissions and pollutants. To this direction, the proposed system integrating solar tower collector, supercritical CO2, organic Rankine cycle, and single effect absorption refrigeration cycles shows potential as an efficient and sustainable solution for meeting energy and cooling demands. A detailed thermodynamic evaluation has been performed to gain valuable understanding of the energy and exergy performance, enabling the assessment of thermal and exergy efficiencies, exergy destructions, and heat losses. Results show that this study found the thermal efficiency of the proposed system to be 47.35 % for R245fa, 48.59 % for R123, and 52.32 % for toluene. In addition, the exergy efficiency was obtained at 40.99 % for R245fa, 42.41 % for R123, and 46.67 % when toluene is used as a working fluid. With all investigated working fluids of organic Rankine cycle, toluene achieved the highest thermal and exergy efficiency of the proposed power-cooling cogeneration system, while R245fa achieved the lowest energetic and exergetic performance. Among the various ORC working fluids investigated under operating conditions, toluene demonstrated the highest turbine power output (3202 kW), whereas R245fa exhibited the lowest turbine power output (2804 kW). The refrigeration output for all ORC working fluids studied was found to be 988.8 kW. Additionally, the primary contributor of exergy destruction rate in the proposed system was determined to be the solar tower receiver, contributing 73.24 %, 67.80 %, and 66.19 % to the total for the toluene, R123, and R245fa working fluids, respectively.

Energy and exergy analysis of a new solar hybrid system for hydrogen, power and superheated steam production

This study investigates the amalgamation of solar tower technology and thermal energy storage (TES) within the framework of a supercritical carbon dioxide (S-CO2) Brayton cycle, a copper-chlorine (Cu-Cl) hydrogen production cycle, and a heat recovery steam generator (HRSG) to generate superheated steam. The various subsystems have been merged to enhance overall energy efficiency significantly, ensure uninterrupted operation, and minimize exergy loss. Energy and exergy analyses have been carried out to assess the prerequisites and effectiveness of each subsystem, highlighting the thermodynamic benefits of integration. Engineering Equation Solving Software (EES) was employed to solve the integrated system model and assess the thermodynamic properties provided by the EES library. Results showed that in the basic design mode, exergy destruction in the solar tower, S-CO2 Brayton cycle, and Cu-Cl cycle are 9930 kW, 7111 kW, and 9735 kW, respectively. The system produces 4226 kW of power, 2697 kW of heat, and 0.04971 kg/s of hydrogen. The overall energy and exergy efficiency of the power plant are 17.48 % and 18.72 %, respectively. These findings demonstrate that this integrated system can address key gaps in the literature by presenting a novel combination of solar power-driven Cu-Cl hydrogen production and superheated steam generation. The proposed system contributes to advancing renewable, efficient, and uninterrupted energy production.

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.

Remote Measurement of Heliostat Reflectivity with the Backward Gazing Procedure

Concentrated solar power is a promising technique enabling renewable energy production with large scale solar power plants in the near future. Estimating quantitatively the reflectivity of a solar concentrator is a major issue, since it has a significant impact on the flux distribution formed at the solar receiver. Moreover, it is desirable that the mirrors can be measured during operation in order to evaluate environmental factors such as day/night thermal cycles or soiling and ageing effects at the reflective surfaces. For that purpose, a backward gazing method that was originally developed to measure mirror shape and misalignment error was developed. The method operates in quasi real-time without disturbing the heat production process. It was successfully tested at the Themis solar tower power plant in Targasonne, France. Its basic principle consists in acquiring four simultaneous images of a Sun-tracking heliostat, captured from different observation points located near the thermal receiver. The images are then processed with a minimization algorithm allowing the determination of the reflectance and slopes errors of the mirrors. In this communication, it is shown that the algorithm allows one to get quantitative reflectivity maps at the surface of the heliostat. The measurement is fully remote and is used to evaluate surface reflectivity that depends on optical coatings quality and soiling effects. Preliminary results obtained with a Themis heliostat are presented. They show that reflectivity measurements can be carried out within repeatability about ± 5% Peak-to-Valley (PTV) and 1% RMS. Ways to improving these numbers are discussed in the paper.

Comparison of Aiming Point Strategy Algorithms and Their Assessment for Volumetric Solar Receivers

The present work summarizes the work done within the scope of CATION, CHLOE, and HECTOR projects related to the aiming point strategies optimization algorithms applied to volumetric solar receivers. Several optimization methods have been applied in the literature for optimizing the aiming strategy of solar power tower plants. However, the use of these algorithms for the requirements of volumetric solar receivers and solar fuel applications has not been accomplished. Herein, the problem is formulated as a constrained optimization problem whose objective function is a combination of the total power on the receiver surface and the flux homogeneity. A comparison of the results is presented in this work. It will be seen that TABU search and SA algorithms are the most efficient in terms of computation time and, in addition, the first one shows very good results in power and spillage. The rest of the mentioned algorithms are much slower and, in general, the results are slightly worse.

Model Predictive Control and Service Life Monitoring for Molten Salt Solar Power Towers

A two-component system for control and monitoring of solar power towers with molten salt receivers is proposed. The control component consists of a model predictive control application (MPC) with a flexible objective function and on-line tunable weights, which runs on a Industrial PC and uses a reduced order dynamic model of the receiver’s thermal and flow dynamics. The second component consists of a service-life monitoring unit, which estimates the service-life consumption of the absorber tubes depending on the current mode of operation based on thermal stresses and creep fatigue in the high temperature regime. The calculation of stresses is done based on a detailed finite element study, in which a digital twin of the receiver was developed. By parallelising the model solver, the estimation of service-life consumption became capable of real-time operation. The system has been implemented at a test facility in Jülich, Germany, and awaits field experiments. In this paper, the modeling and architecture are presented along simulation results, which were validated on a hardware-in-the-loop test bench. The MPC showed good disturbance rejection while respecting process variable constraints during the simulation studies.

Solar Field and Receiver Model Validation of the Next-CSP MW-Scale Prototype

This study presents a comparison of both modelling and experimental results obtained on the solar field and the receiver of the MW-scale particle driven CSP unit implemented at the Themis solar tower (France) in the framework of the Next-CSP H2020 European project. At partial load, ~900 kW, the simulated data concerning the incident power at the receiver aperture are consistent with the measured values with less than 5% difference from the experimental results. The difference is higher for the particle temperature and the thermal efficiency as a function of particle mass flow rate. It ranges between 12 and 98°C for measured particle temperature of 430 and 300°C respectively. For the thermal efficiency, the difference varies strongly with the experiments from approximately 12% to 50% (relative). The main cause of discrepancy between the experimental and the calculated results is attributed to the heterogeneity of the solar flux distribution on the receiver tubes.

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.

Analysis and Optimization of a s-CO2 Cycle Coupled to Solar, Biomass, and Geothermal Energy Technologies

This paper presents an analysis and optimization of a polygeneration power-production system that integrates a concentrating solar tower, a supercritical CO2 Brayton cycle, a double-flash geothermal Rankine cycle, and an internal combustion engine. The concentrating solar tower is analyzed under the weather conditions of the Mexicali Valley, Mexico, optimizing the incident radiation on the receiver and its size, the tower height, and the number of heliostats and their distribution. The integrated polygeneration system is studied by first and second law analyses, and its optimization is also developed. Results show that the optimal parameters for the solar field are a solar flux of 549.2 kW/m2, a height tower of 73.71 m, an external receiver of 1.86 m height with a 6.91 m diameter, and a total of 1116 heliostats of 6 m × 6 m. For the integrated polygeneration system, the optimal values of the variables considered are 1437 kPa and 351.2 kPa for the separation pressures of both flash chambers, 753 °C for the gasification temperature, 741.1 °C for the inlet temperature to the turbine, 2.5 and 1.503 for the turbine pressure ratios, 0.5964 for the air–biomass equivalence ratio, and 0.5881 for the CO2 mass flow splitting fraction. Finally, for the optimal system, the thermal efficiency is 38.8%, and the exergetic efficiency is 30.9%.

Experimental study on the effects of integrating phase change material with a solar updraft tower

AbstractThe solar updraft tower power plant presents a promising renewable energy solution but faces limitations in thermal efficiency and energy production during nonsunny hours. This study addresses a critical gap in the literature by investigating the integration of latent heat storage systems utilizing paraffin wax as phase change materials (PCMs) to enhance solar updraft tower (SUT) performance. Two identical small‐scale SUTs were constructed, both using the same tank configuration; however, the PCM device was filled with paraffin wax as a PCM, while the non‐PCM device contained only atmospheric air. Three scenarios were explored, featuring varying PCM tank heights of 2, 4, and 6 cm (the full capacity of the PCM tank). Results indicated that, from 3 p.m. until sunset, the PCM‐integrated SUT in Case 3 (with 6 cm of PCM) achieved the best performance, with an average absorber temperature rise of 25°C, compared with 12°C for the non‐PCM device. During the same period, the average air velocity at the tower neck, where a wind turbine could be installed, was 1.21 m/s for the PCM device, versus 0.82 m/s for the non‐PCM device. Notably, the nocturnal operating time extended significantly with PCM use, rising from 90 min for the 2 cm case to 125 min for the 6 cm case. In contrast, the non‐PCM device exhibited no operational time after sunset. This research not only demonstrates the effectiveness of PCM in improving the thermal performance and operational longevity of SUTs but also introduces a novel tank configuration that allows for flexible PCM integration, representing a significant advancement in the development of more efficient SUT systems.

Optimizing Concentrated Solar Power: High‐Temperature Molten Salt Thermal Energy Storage for Enhanced Efficiency

ABSTRACTMolten salts (MSs) thermal energy storage (TES) enables dispatchable solar energy in concentrated solar power (CSP) solar tower plants. CSP plants with TES can store excess thermal energy during periods of high solar radiation and release it when sunlight is unavailable, such as during cloudy periods or at night. This capability allows these plants to provide reliable, dispatchable power, ensuring a continuous electricity supply to the grid. This paper examines the challenges and opportunities of utilizing higher‐temperature molten salt formulations to enhance power cycle efficiency. Drawing on existing literature, performance analysis of existing power plants, and novel simulation results, we project the expected technological improvements by the end of this decade. By using 15 h of TES and a higher temperature MS formulation, with heat transfer fluid hot temperatures of 700°C, and a power cycle 350 bar 700°C of efficiency 48%, the annual electricity production from a 115 MW power plant in Daggett, California is 688 GWh, the total installed cost is $684 m while the 25‐year LCOE is 6.37 c/kWh.

From ideal to realistic compact hybrid PV-CSP systems: A technoeconomic evaluation

Compact PV/CSP hybrid systems, based on the integration of both PV and CSP technologies within a single power plant, have been attracting interest in recent years, because of their potential to lower the cost of solar electricity and minimize the land footprint required. However, the objective evaluation of these technologies is complicated by the fact that they involve two separate converters, each delivering a different form of energy (dispatchable for CSP, non-dispatchable for PV). We propose here an original evaluation and optimization approach based on 3 techno-economic indicators quantifying (1) the overall conversion efficiency of these systems compared to their standalone CSP counterparts, (2) the energy production balance between PV and CSP, and (3) the extra manufacturing cost compared to standalone CSP systems. These different indicators are evaluated for two families of hybrid systems (PV Topping and PV Mirror) and for 3 geometries of concentrating optics (Linear Fresnel Lenses, Parabolic Troughs and Solar Towers). One originality of our approach lies in its ability to determine the optoelectronic properties of PV cells likely to lead to the best hybrid performance, taking into account whether or not they are able to reach their own theoretical limits. Another original feature is that the hybrid systems considered in our analysis are compared with CSP equivalents which have been independently optimized. It is shown that the integration of realistic solar cell technologies whose performances deviate significantly from their theoretical limits notably restricts the range of operating conditions for which hybrid systems could outperform their standalone CSP counterparts. We conclude this work by discussing a number of key challenges that need to be overcome in order to develop more competitive and efficient hybrid systems.

Reinforcement learning for heliostat aiming: Improving the performance of Solar Tower plants

Solar Tower (ST) systems use heliostats to concentrate solar radiation onto a tower-mounted receiver. Optimizing the aiming strategy for these heliostats over the receiver remains a critical challenge due to the dynamic nature of solar radiation and the need to maximize energy capture while ensuring operational safety. This paper introduces a novel, model-free deep Reinforcement Learning (RL) approach to optimize heliostat aiming strategies, utilizing the Soft Actor–Critic (SAC) algorithm. This advanced RL method enhances the traditional Actor–Critic framework with two neural networks. The proposal dynamically adjusts the aiming points across the receiver surface in real time, trying to improve the overall performance of the ST plant. The strategy was simulated and evaluated over a full operational year and compared with traditional methods. The results show an increase of more than 8.8% in yearly absorbed power, a significant improvement that directly enhances performance and contributes to better economic outcomes for the technology. This technique also eliminates the need for constant human intervention and is applicable to both existing and future plants.

The potential role of concentrated solar power for off-grid green hydrogen and ammonia production

This paper investigates the potential role of concentrated solar power (CSP) in off-grid green electrolytic hydrogen and ammonia production using an open-source techno-economic assessment optimisation model. The green ammonia plant comprises a flexible Haber-Bosch loop, an electrolyser park, a desalination plant, storage systems (thermal, electrical, and hydrogen), and a power supply optionally including wind power, solar photovoltaic (PV), and CSP (solar tower or parabolic trough collectors). Various system configurations and cost assumptions are tested to evaluate when CSP technologies are economically viable for green fuel production. Results demonstrate that CSP and thermal energy storage (TES) technologies can play a minor but useful role in providing nighttime power supply to the ammonia plant, in combination with onshore wind power and electrical storage. Solar PV with 1-axis tracking remains the primary power provider, and the optimal system always includes large-scale hydrogen storage. In the cheapest configuration, the LCOA reaches 646 €/tNH3. With an 80% reduction in CSP and TES costs, CSP technology becomes a major player in power production. In scenarios where hydrogen storage is not feasible and the ammonia plant lacks full flexibility, a 20% cost reduction (to 2750 €/kW) is enough for them to become major power providers.

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.

ACWA Power’s CSP Performance Models

CWA Power develops, owns, and operates several CSP projects, including the largest one in the world. One of the primary objectives for companies in the Concentrated Solar Power (CSP) sector is to lower the electricity costs associated with CSP plants. This goal extends not only to existing operational plants but also to future projects. Enhancing plant performance is a key pathway to achieving this cost reduction. CSP performance models play a pivotal role in this journey by allowing us to analyse different configurations, changes, or modifications without the necessity of their physical implementation. In 2015, ACWA Power made a strategic decision to develop its own CSP performance models. This move aimed to enhance ACWA Power’s competitiveness for upcoming projects while also supporting operational plants by identifying avenues for performance improvement. The decision was made to create models for the two prevailing CSP technologies: Parabolic Trough with thermal oil as the heat transfer fluid (HTF) and molten salt storage system, as well as solar tower with molten salts.

An efficient 3D tube-level flux-thermal model of external tubular receivers in solar power tower systems

Accurate and efficient radiative flux simulation and thermal analysis of liquid tubular receivers are essential for safe and stable operations of solar power tower systems. However, the complicated structure and photothermal processes on these receivers pose significant challenges for simulation. Although existing models have made great simplifications, the simulation results are still inefficient and inaccurate. To address these issues, a novel and universal 3D flux-thermal model is proposed. Firstly, a flux model is proposed via a tube-level Monte Carlo ray tracing method based on GPU parallel computing, enabling real-time and accurate radiative flux density distribution simulation for each absorber tube. Secondly, a high-resolution multi-tube thermal model is proposed, providing accurate 3D thermal analysis for each absorber tube. Through pre-factorization and highly parallelized designs, the proposed thermal model achieves a 600 times acceleration in efficiency, even with tens of millions of discrete elements. Finally, the novel flux-thermal model is validated against publicly published measured data from Solar Two, indicating a mean deviation of only 0.1% and a root mean square error of 0.006, demonstrating its high accuracy. Furthermore, the proposed flux-thermal model reveals complex and asymmetrical flux and temperature distributions on the absorber tube, in contrast to the symmetrical distributions obtained by the simplified models. Such inaccuracies in the simplified simulations may cause operational misjudgements and affect system safety potentially. Therefore, the proposed 3D tube-level flux-thermal model provides an accurate and efficient solution to radiative flux simulation and thermal analysis, enhancing the safe and stable operation of solar power tower systems.

A solar air receiver with porous ceramic structures for process heat at above 1000 °C – Heat transfer analysis

Abstract Concentrated solar energy can be used as the source of heat at above 1000 °C for driving key energy-intensive industrial processes, such as cement manufacturing and metallurgical extraction, contributing to their decarbonization. The cornerstone technology is the solar receiver mounted on top of the solar tower, which absorbs the incident high-flux radiation and heats a heat transfer fluid. The proposed high-temperature solar receiver concept consists of a cavity containing a reticulated porous ceramic (RPC) structure for volumetric absorption of concentrated solar radiation entering through an open (windowless) aperture, which also serves for the access of ambient air used as the heat transfer fluid flowing across the RPC structure. A heat transfer analysis of the solar receiver is performed by means of two coupled models: a Monte Carlo (MC) ray-tracing model to solve the 3D radiative exchange and a computational fluid dynamics (CFD) model to solve the 2D convective and conductive heat transfer. Temperature distributions computed by the iteratively coupled models were compared with experimental data obtained by testing a lab-scale 5 kW receiver prototype with a silicon carbide RPC structure exposed to 3230 suns flux irradiation. The receiver model is applied to optimize its dimensions for maximum efficiency and to scale up for a 5 MW solar tower.

Life cycle assessment of typical tower solar thermal power station in China

In light of the growing environmental awareness and the sustainable development consideration in energy policies, the environmental impacts of concentrating solar power (CSP) have attracted significant attention. Considering that the site selection of CSP stations and databases used for evaluation has an important impact on the environment, the objective of this study is to assess the impact of concentrating solar power tower (CSP-T) station with thermal storage devices in the geographical context of China from environmental perspective by the life cycle assessment (LCA) method. To achieve this goal and ensure the reliability of the research results, a 2 × 50 MW capacity, double tank solar nitrate energy storage, and 12-h energy storage time CSP-T station in Dunhuang, Gansu, was selected. In addition, its model was constructed using the eFootprint online platform, assessing the environmental impacts of the CSP-T station according to the cradle-to-grave system boundary. Moreover, the impact assessment was performed in terms of key metrics, such as energy payback time (EPT), carbon cost of electricity (CCOE), carbon flow analysis, and environmental benefits of energy conservation and emission reduction. The results showed that the production stage is the most significant source of environmental impact in the life cycle of the CSP-T station, with the condensing system and heat storage system contributing 50.17 % and 47.64 % respectively. It can be found that the EPT of the CSP-T station is estimated at 4.88 years, accounting for 16.25 % of the operation cycle of the thermal power station, and varies depending on the station's location. It can be reduced to 3.19 years in places such as North Africa with abundant light intensity. Furthermore, the CCOE of the CSP-T station is 0.04 kg CO2/kWh. Overall, CSP-T station has over 95 % environmental benefits for energy conservation and emission reduction for most indices compared to thermal power station. Although the Chemical Oxygen Demand (COD) index is slightly lower, it still reaches 82.67 %. To promote the ecological development of the CSP-T station in China, this study usually includes a brief comment or relevant improvement recommendations after each comparative analysis.

Energetic and Exergetic Analyses of a Double-Pass Tubular Absorber for Application in Solar Towers

Abstract The present research integrates the concept of double-pass (DP) flows with high-temperature solar receivers to introduce an innovative design aimed at minimizing heat losses and optimizing performance. The new DP system was developed using a tubular absorber derived from billboard solar tower technology and operated with air as the heat transfer medium. Computational fluid dynamic models are developed based on an experimental campaign conducted at a solar furnace facility. The computational analyses indicated that employing the DP design instead of single-pass (SP) absorbers results in an average enhancement of energy and exergy efficiency by 35% and 225%, respectively, across all test conditions. However, this enhancement is accompanied by an average increase in pressure drop of ∼60%. The detailed exergy analysis also revealed the contribution of each term in the exergetic performance, identifying the exergy destruction between the sun and the absorber as the primary source, accounting for an average of ∼65% of the total inlet exergy for both SP and DP absorbers. Consequently, the DP presents itself as a promising alternative design for future solar tower configurations, offering improved Nu numbers up to ∼50% in air-based solar systems.