Solar Tower System Research Articles

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.

Heliostat Clustering for Aiming Point Strategies Optimization

The performance of solar tower systems is closely linked to the aiming point strategy of the heliostats. The optimization process of obtaining the best aiming point strategy for a field is complex and has a high computational cost. The use of the clustering technique relieves the requirements by decreasing the space of possible solutions to the problem. Results show that the application of the technique for aiming point strategy optimization reduces the time of optimization significantly.

Deep Learning Approaches for Power Prediction in Wind–Solar Tower Systems

Wind–solar towers are a relatively new method of capturing renewable energy from solar and wind power. Solar radiation is collected and heated air is forced to move through the tower. The thermal updraft propels a wind turbine to generate electricity. Furthermore, the top of the tower’s vortex generators produces a pressure differential, which intensifies the updraft. Data were gathered from a wind–solar tower system prototype developed and established at Kyushu University in Japan. Aiming to predict the power output of the system, while knowing a set of features, the data were evaluated and utilized to build a regression model. Sensitivity analysis guided the feature selection process. Several machine learning models were utilized in this study, and the most appropriate model was chosen based on prediction quality and temporal criteria. We started with a simple linear regression model but it was inaccurate. By adding some non-linearity through using polynomial regression of the second order, the accuracy increased considerably sufficiently. Moreover, deep neural networks were trained and tested to enhance the power prediction performance. These networks performed very well, having the most powerful prediction capabilities, with a coefficient of determination R2=0.99734 after hyper-parameter tuning. A 1-D convolutional neural network achieved less accuracy with R2=0.99647, but is still considered a competitive model. A reduced model was introduced trading off some accuracy (R2=0.9916) for significantly reduced data collection requirements and effort.

Impact of Temperature and Optical Error on the Combined Optical and Thermal Efficiency of Solar Tower Systems for Industrial Process Heat

Concentrating solar thermal (CST) power towers can provide high flux concentrations at commercial scale. As a result, CST towers exhibit potential for high-temperature solar industrial process heat (SIPH) applications. However, at higher operating temperatures, thermal radiation losses can be significant. This study explores the trade-off between thermal and optical losses for SIPH applications using a collection of three case studies at operating temperatures that range from 900-1,550 °C. We assume blackbody radiation to represent the thermal losses at the receiver and we use ray tracing to estimate the optical losses. The results show the impact of process temperature on the maximum attainable system efficiency, as well as the higher flux concentration requirements as the temperature increases.

Experimental development of packing structures in a gas-particle trickle flow heat exchanger for application in concentrating solar tower systems

Ceramic particles represent a viable alternative as heat transfer and storage medium in concentrating solar tower systems. The particles are heated in solar-receivers close to 1000 °C. To utilize the stored energy in the particles, an air-particle direct-contact trickle-flow heat exchanger has been identified as suitable for this task. To date, no design recommendations exist that identify an optimized packing structure capable of providing a high particle volume fraction and a uniform spatial particle density distribution for a given grain type. Consequently, an experimental selection process is presented in this work to assess various packing structures for a given grain type in a trickle-flow reactor. The experiments were conducted with countercurrent flowing air at ambient conditions and 1 mm bauxite particles. A variety of packing structures were investigated at varying media flow rates. For each flow condition, the particle volume fraction was determined, as well as the particle distribution in a separate analysis. The cold experiments yielded a clear image of a preferred packing geometry, which will be discussed in detail. The results will serve as the basis for further hot experiments and thermal performance analysis in future work, where the packing geometry can be refined iteratively if necessary.

Comparative Analysis of Solar Tower and Parabolic Trough Systems for Solar Heat in a Steel Industry

Concentrated Solar Thermal (CST) systems emerge as a promising alternative to replace fossil fuels used in industrial thermal processes due to their high energy density and dispatchability. In this study, a comparative analysis of two CST systems, Solar Tower (ST) and Parabolic Trough Collector (PTC), has been made to replace natural gas used in the steam generation process in Türkiye's largest steel production plant, located in the Mediterranean Region of Türkiye. Both the ST and PTC systems were placed in a field area of approximately 0.4 km2. The results have shown that, on a monthly basis, the PTC system could exceed the plant's thermal energy for two-thirds of the year, while the ST system could meet the plant's energy requirements for one-third of the year. This could reduce CO2 by about 12.7 and 19.1 kilo-tones for ST and PTC at LCOH of about 68.9 and 36.9 EUR/MWh, respectively.

VoCoRec

Open volumetric air receivers in solar tower systems are attractive for electricity generation as well as for process heat in chemical and other industrial applications. From the experience of past development stages, a new receiver concept was created with a conical cavity, with hexagonal cross-section for the modularity and a two-stage air heating. Several simulations have been performed. A prototype receiver module with approx. 175 kW thermal output has been manufactured and will be tested in DLR’s Synlight. For different module sizes the cost estimation for industrial fabrication was calculated as well as the performance, ranging from 89% to 78% at 700°C hot air temperature.

Numerical investigation on performance of a solar chimney power plant with different absorber configurations

AbstractA solar tower system is a nonpolluting solar thermal power plant that utilizes a combination of a wind turbine and generator to convert thermal energy generated from a solar collector into electrical energy. The study focuses on a system comprising a solar collector that transforms solar energy into thermal energy, a chimney that converts thermal energy into kinetic energy, and a wind turbine that further converts kinetic energy into electrical energy. The system's performance is evaluated through the implementation of a numerical model, which is validated by comparing it with experimental data. Four different types of meshes are tested to determine the most suitable mesh for the system. The discrete ordinate radiation model is used to solve the radiative transfer equation, and the RNG k‐𝜀 turbulence model is implemented to calculate turbulence. In a subsequent study, the effect of absorber configuration on the system's performance is investigated. Three different absorber configurations—sinusoidal, square, and triangular—are proposed, and the numerical results showed that the system's performance is affected by the absorber configuration. The velocity in the chimney inlet increases for all proposed configurations compared to the standard configuration, with the triangular configuration showing the highest velocity increase. Additionally, the newly proposed configurations enhance the thermal efficiency of the system, leading to a thermal efficiency of 12.18%, 12.2%, and 13.65% for the sinusoidal, triangular, and square configurations, respectively. Overall, the solar tower system demonstrates its potential as a clean and efficient source of electrical power.

Innovative integrated solar combined cycle: Enhancing dispatchability with a partial recuperative gas turbine and supercritical CO2 bottoming cycle, coupled with an ORC

Concentrating solar power is crucial in the future energy mix due to its ability to integrate thermal energy storage, thus providing dispatchability. One way to address the current high costs of this technology is by using higher temperatures, which can, however, lead to issues with heat transfer fluids and storage. A promising integrated solar combined cycle is here proposed to solve that current major issue. A partially recuperated gas turbine is coupled to a solar tower system using a Brayton supercritical CO2 power cycle, which recovers heat at two temperature levels. An Organic Rankine Cycle is also used to exploit the low-temperature flue gases. The performance at the design point is assessed under different solar contributions. The modulation of the thermal duty in the gas turbine recuperator allows reaching a nearly constant power production in the plant (180 MWe): 56 % coming from the gas turbine, 39 % from the CO2 power cycle, and 5 % from the ORC. The global efficiency achieved is 57.2 %. Carbon dioxide emissions range from 236 g CO2/kWhe (86 g CH4/kWhe are consumed) with the maximum solar contribution to 346 g CO2/kWhe (126 g CH4/kWh are consumed) with no solar contribution.

Design of solar cement plant for supplying thermal energy in cement production

This work describes the implementation of concentrated solar energy for the calcination process in cement production. Approach used for providing solar energy includes the utilisation of a solar tower system with a solar reactor atop the solar tower or preheater tower in a conventional cement plant. Analysis considered thermal energy substitution ranging from 100% to 50%. Solar power output of the reactor was 793 MW after considering the 45% heat loss in the reactor. The number of heliostats required for generating 793 MW solar reactor power was 15066 with a total required land surface of 1130 ha. Depending on the thermal losses i.e., 15%, 30%, and 45%, the net conversion efficiency was 44, 56, and 69, respectively. Implementing concentrated solar thermal (CST) in the calcination process of the selected conventional cement plant could save 419 thousand tons of CO2 annually. Economic analysis suggests that approach is useful when there is minimum thermal loss in the solar reactor. Payback time (PBT) and internal rate of return (IRR) for design model were 10.4 years and 5.4% when there were 45% thermal losses in solar reactor. Major challenges are regarding the conversion of laboratory equipment to industrial size, working in high-temperature environments, raw material transportation systems, and thermal storage systems.

Potential of solar thermal calciner technology for cement production in India and consequent carbon mitigation

This study describes the potential of solar thermal calciner technology and consequent carbon mitigation for Indian cement industries. Approach used to provide solar energy involves the installation of a solar tower system with a solar reactor atop the solar tower or preheater tower in a conventional cement plant. For potential estimation, locations of the clusters of cement plants with their actual annual cement production have been identified. Based on the annual actual cement production, the yearly process heating demand for the calcination process for each cement plant is estimated. Solar irradiation of each location of the cement plant is identified, and the plants with direct normal irradiation (DNI) > 1700 kWh/m2 /annum are considered. Total thermal energy saved is estimated as 133.36 PJ/annum and CO2 mitigation is estimated as 7413.73 thousand tonnes.

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF SEMICIRCULAR SOLAR UPDRAFT TOWER SYSTEM EMPLOYING POROUS COPPER METAL FOAM

The numerical and experimental study was carried out under Iraqi weather conditions to verify the improvement of the performance of the solar updraft tower system SUTS by introducing porous metal foam as a heat-absorbent plate. a semicircular basin of the solar collector was divided into two equal identical quarters. A porous foam material was fixed on one of the basins while the other basin was fixed on a traditional copper plate. The positions of the metal foam absorber plate are changed with two inclination angles (0֯ and 18֯) and the optimum position is achieved when it gives the highest thermal performance. A finite volume modeling technique is used to solve the governing equations and radiation heat transfer equations by using ANSYS Fluent. The experimental part was conducted in Baghdad / Iraq at latitude 33.3°. The presence of the metal foam absorber plate caused a significant decrease in the average temperatures of the heat-absorbent plate. The maximum airflow temperature was recorded with an inclined angle of 18◦. The metal foam as a heat-absorbent plate enhanced the efficiency and the output power of the SUTS to about 51.9% and 47.2% respectively compared to the traditional plate.

A multi-criteria performance assessment of concentrated solar power plants for site and technology selection in Egypt

The objective of this research is to investigate the implementation of two concentrated solar power (CSP) technologies in the 28 devoted locations in Egypt, in order to select the optimum site-specific CSP technology. This may be achieved by a validated thermo-economic simulation of power plants using the Sam advisory model and an investigation of the two proposed CSP technologies’ configurations to fulfill the power plant’s thermal demand. Simulations take into consideration the environmental, technical, financial, and economic aspects of the projects. Among many simulated parameters, three are considered to compare the two proposed technologies' configurations in the 28 locations utilizing geographic information system aid. Those parameters are the annual power production, the levelized cost of energy, and water consumption. A comparative analysis indicated that the solar tower requires 25% more land than the parabolic trough. The additional collecting area raised the net capital cost of the solar tower system by 15% over the parabolic trough model. As a result, the solar tower arrangement reduces the levelized cost of energy while increasing the yearly power generated and water required by the power plant. Simulation results favored the proposed solar tower configuration over the parabolic trough and recommended the implementation of such concentrated solar power projects in the central and eastern locations of Egypt.

Thermal evaluation of different integration schemes for solar-nuclear hybrid systems

Solar-nuclear hybrid systems have been proposed to meet the growing energy demand and mitigate the effects of global warming caused by fossil fuels. To achieve optimal design for these systems, an appropriate integration scheme is crucial. This article proposes three integration schemes to couple the solar system with the nuclear power plant and evaluates their performance based on energy and exergy evaluations. A reference design of the hybrid system is used, consisting of a 77.04 MWth solar tower system coupled with a 330 MWth System-Integrated Modular Advanced Reactor. Numerical results show that heating partial feedwater and saturated steam with solar energy is the best-integrated scheme, resulting in the maximum thermal efficiency and exergy efficiency for the solar-nuclear hybrid system. Comparing the standalone reactor power system to the solar-nuclear hybrid system reveals that using solar energy to heat the feedwater and saturated steam can greatly improve the energy efficiency of the power plant, increasing it to 34.97%. The solar heat to nuclear heat ratio is 25.01%, while the solar power to nuclear power ratio is as high as 44.42%, indicating effective utilization of solar heat contribution. Exergy loss distributions of the solar-nuclear hybrid system reveal that exergy losses mainly occur within the nuclear reactor and solar field, taking possession of 70% of all exergy losses.

Innovative lifetime testing protocol for high-temperature secondary reflector materials used in concentrated solar thermal energies

The actual energy market based on fossil fuels is the responsible of more than half of the greenhouse gases generated worldwide. Renewable energies play a fundamental role to lead the transformation towards an energy market less damaging for the environment. Concentrated solar thermal (CST) energy is essential to achieve this objective because it is the most profitable renewable technology to store energy in the form of heat. In recent years, solar tower (ST) systems are the most installed CST plants thanks to their high operating temperatures that allow reaching greater efficiency. Developers are presently considering the integration of secondary concentrators on the top of the tower to improve its optical and thermal behavior, and hence, to increase the performance and feasibility of the system. However, no commercial high-temperature secondary reflector materials for ST systems are marketed because their durability is currently unpredictable. In this work, a new methodology based on accelerated aging tests is developed to predict the lifetime of secondary reflector materials in short time. Additionally, operating conditions that typically take place on a ST are simulated in a solar furnace to validate the reliability of the aging tests. The protocol developed was applied to a novel secondary material recently developed. According to the results obtained for this exemplary material, the main degradation is suffered due to the high temperature during operation. The correlation was validated under representative operating conditions with deviation of 0.2% of the reflectance comparing the accelerated aging and the operating conditions tests.

Performance investigation of a solar updraft tower concept with downdraft windcatcher

In this study, a novel solar updraft tower system that combines updraft and downdraft is examined, its functional principle is explained and its performance is presented. A prototype was built at Faculty of Engineering of Trakya University in Edirne Türkiye in 2017. The concept includes counter-rotating dual drag type vertical axis turbines, wind catchers, three prismatic diffuser towers and sloped transpired solar collector. The results showed that the downdraft wind catcher integration increased annual energy production by 8 times compared to a conventional solar updraft tower. In the diffuser-shaped downdraft tower, the incoming wind accelerated up to 2.5 times. The power potential, which is 160 W for the conventional system, becomes 83 kW at a wind speed of 10 m/s and a downdraft pressure coefficient of 1.0.

Techno-economic analysis of multi-tower solar particle power plants

Solar tower systems using solid particles as heat transfer and storage medium promise to achieve, in combination with advanced power cycles, lower levelized cost of electricity (LCOE) than state-of-the-art concepts. In this study the cost potential of a multi-tower solar power plant with centrifugal particle receiver is evaluated. Most of the underlying assumptions were chosen in accordance with those specified within the US-DoE Gen3 project “G3P3”. For the power block a high-efficiency supercritical CO2 system with 100MWe was assumed. The solar subsystem is built from 12 identical solar tower modules, each with heliostat field, tower, receiver and storage. The nominal thermal power of each module is 41MWth.Since the cost assumptions for the tower and the heat exchanger (HX) are still relatively uncertain, different correlations were used representing optimistic and conservative cases. For the particle receiver two outlet temperature levels were investigated, namely 800 °C and 1000 °C.The results of the techno-economic analysis indicate a strong impact of the cost assumptions for the primary heat exchanger and the tower. With 800 °C as particle outlet temperature, the estimated LCOE range from $56.18/MWh (optimistic values for tower and HX cost) to $67.30/MWh (conservative values for tower and HX cost).Increasing the particle outlet temperature to 1000 °C results in a significant reduction of LCOE (about 12% for the optimistic cases, down to $50.46/MWh). The reason for this is the significant reduction of heat exchanger area, particle inventory and particle mass flow, resulting from the larger temperature difference in the particle system. However, operating the system at such elevated particle temperatures will require some modifications to the components that are not fully reflected in the used cost correlations yet. Nevertheless, the results propose further investigation of this option. All in all the results indicate a clear potential to achieve the SunShot goal of less than $60/MWh.

Computational analysis of passive strategies to reduce thermal stresses in vertical tubular solar receivers for safety direct steam generation

When exposed to high non-uniform heat fluxes on the receiving surface, significant temperature gradients develop in the tubes, producing thermal stress and deformations in the receivers. This paper reports a detailed investigation of the thermal and structural performance of a solar tower system that operates with direct steam generation tubes when the fins are added to the internal surface and thickness varies. Six tubes were evaluated, two without fins varying the wall thickness (5 mm and 3 mm) and four with fins under different configurations. The thermal system corresponds to a representative tube of an external tubular receiver of a central tower system. The thermal receiver operates with direct steam generation under a non-uniform concentrated solar flux with a maximum value of 0.93 MW/m2. The best configuration of the tube was with fins on the frontal surface of the tube, maintaining a receiving wall thickness of 3 mm and an adiabatic wall thickness of 5 mm. It could reduce maximum thermal gradients and temperature by 31% and 14%, respectively, maximum thermal stresses by 38%, and maintain vapor mass flow at the output (276 kg/h).

A review study on solar tower using different heat transfer fluid

The object of research is distinguishing the different heat transfer fluids (HTF) in concentrating solar power (CSP). CSP technologies are gaining more attention these years due to the fact that the world is facing significant problems, especially concerning environmental issues and the increasing electricity demand. The world countries are currently committed to mitigating climate change and limiting greenhouse gas emissions to keep the global temperature rising below 2 °C. As a result, renewable energy sources are required for power generation. One of the most widely used technologies is the solar tower, where mirrors reflect solar radiation into a central receiver on top of a tower that contains a working fluid known as heat transfer fluid. The HTF is one of the most important components in solar power tower plants used to transfer and store thermal energy to generate electricity. This study focuses on the HTF used in solar power towers and how it can affect the efficiency of the plant. The HTF discussed in this study are air, water/steam, molten salts, liquid sodium, and supercritical CO2. Among the review of HTFs in the solar tower system, the result of the research shows that the Air can reach the highest temperature while liquid sodium achieves the highest overall plant efficiency.

Experimental Analysis of Air Inlet Height Variation in a Solar Tower system Using Plate and Metal Foam Absorber

The experimental analysis is conducted under the Iraqi climate conditions to investigate the performance enhancement of a solar updraft tower system (SUTS) using the porous copper foam as an absorber plate and conventional absorber plate with absorber inclination angle of 18°. In the present work, a semicircular collector is divided into two identical quarter thermal collectors to become two identical SUTS. One of the quarter circular thermal collectors contains on the metal foam as an absorber plate, while the other quarter collector on the conventional flat copper absorber plate. In this study the air inlet height is changed of (3, 5, and 8) cm. The experimental tests carried out in Baghdad city (latitude 33.3° N). Results showed that the air inlet height variation caused to enhance the solar updraft tower performance. The highest values was recorded when the air inlet height is 3 cm using porous absorber compared to flat absorber plate. Copper material foam as an endothermic surface causes a marked decrease in average surface temperature of the plate. The maximum hourly thermal efficiency of solar collector was increased to about 41.6 % and the maximum enhancement of the power output to about 45.2 % compared with flat absorber plate.