Solar Thermal Power System Research Articles

Study of parabolic trough collector with crucial analysis on controller and estimator with variable mirror efficiency

Solar Thermal Power (STP) plants are a crucial technology for converting solar energy into electricity. Among the STP, the Parabolic Trough Collector (PTC) is one of the integral parts of STP systems for electrical power generation. Maximizing PTC performance is a challenge due to dynamic and unpredictable solar radiation and environmental disturbances, such as cloud cover and dust accumulation. The optical efficiency parameter of the PTC is critical for calculating the desired heat gain, which is difficult to measure in real-time, necessitating sophisticated control and estimation strategies for optimal heat regulation. This study introduces two control mechanisms for the PTC system and comparing their efficacy. A classical PI controller supplemented by Static Feed-Forward (SFF) control demonstrates improved performance with an optimal transfer function model. In contrast, Nonlinear Model Predictive Control (NMPC) excels in disturbance rejection and setpoint tracking, considering operational constraints. The NMPC controller notably outperforms the PI controller with SFF in performance metrics, with the Integral Time Squared Error (ITSE) decreasing by approximately 99% across case studies. Also, in the case of heat gain, NMPC controller exhibits percentage increases when compared to the PI controller. Furthermore, since the measurement of optical efficiency is essential, but due to difficulty in the measurement for various reasons, the estimator is used as a virtual sensor to estimate those optical efficiency. The unmeasured states and parameters, including optical efficiencies of the PTC, are estimated using Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) techniques, with UKF exhibiting superior accuracy. However, considering the average computation time, EKF is preferred for real-time applications.

Comprehensive assessment and energetic-exergetic performance optimization of a new solar thermal electricity system based on Scheffler-type receivers combined with screw-type volumetric machines

This study explores the potential of a novel solar-powered cascade Rankine cycle system based on Scheffler-type receivers combined with screw expanders. Specifically, in this solar power system, steam is generated in the Scheffler-type receiver, which proves to be well performing compared with other technological solutions to exploit solar energy, due to satisfactory efficiency of the focal receiver that is able to curtail heat losses, even at high evaporation temperatures. Subsequently, steam expands in the screw machines which, unlike conventional steam turbines, are specially fitting in energy conversion with vapor-liquid mixes in the field from tens to hundreds of kW. In the present study, comprehensive assessment of this renewable energy power system is thoroughly conducted in a large range of operating states. For this purpose, specific numerical models and basic criteria fixed for the screw expanders and Scheffler receivers part-load behavior are combined with thermodynamic formulations established for energetic-exergetic performance optimization of the entire solar thermal electricity plant. Hence, parametric optimization of the major thermodynamic factors involved at part-load operating situations is conducted to enhance the energetic and exergetic efficiencies of the designed solar thermal power system.

Development of a Novel High Temperature Continuous Particle Mass Flow Measurement Device for Particle-Based CSP Applications

Particle-based concentrating solar power (CSP) technology is one of the generation three (Gen3) CSP technologies that has potential for lowering the levelized cost of electricity produced by this solar thermal power systems. Commercially available ceramic particles, which are rated for high temperature applications up to 1200 °C, were selected for this study. This medium is commonly used as an energy carrier or heat transfer medium in Gen3 CSP research and development efforts [1]. Prior studies at the National Solar Thermal Test Facility (NSTTF) have investigated and evaluated various mass flow measurement methods, and a simple gravimetric temporal load measurement method was chosen as the best candidate for the research purpose [2]. This mass flow measurement method is a batch process and is not a viable solution for commercial-scale power generation applications based on cost, space, process control, and practical system integration factors. In-line and continuous particle mass flow measurement will play an integral role in efficient and cost effective Gen3 CSP particle technologies. Process parameters, including energy absorbed by the particles, receiver efficiency, temperature dependent flow phenomena, and general high temperature measurement reliability are all rely on repeatable and accurate measurement of particle mass flow under various operating conditions. Ceramic particles, like those used in this application, are not conventionally used as an energy carrier. A novel concept for continuous particle mass flow at a wide range of operating temperatures is currently under development and planned to be tested at the NSTTF, called the Particle In-LinE (PILE) mass flow sensor.

Effect of multi‐tubes and eccentricity on melting performance of honeybee wax thermal energy storage system: A comprehensive numerical study and experimental validation

AbstractWhen it comes to solar thermal power systems, a latent heat energy storage unit is one possible solution to the imbalance in supply and demand. On a shell‐tube type heat storage system, computational and experimental research was done to determine how to charge a heat storage system using honeybee wax‐biodegradable phase change material. This paper examines the impact of single, double, and triple inner heat transfer fluid tubes on the melting properties of bee wax in relation to vertical and horizontal eccentricity. Through the experimental examination of a lab‐scale prototype, the computational model was verified. A computational model was used to investigate the impact of eccentricity on different configurations for the melting process. Utilizing multiple tubes significantly shortened the charging time, according to the system analysis. In a vertically downward direction, melting time reduced as eccentricity increased. Compared to the single tube concentric case, the maximum melting time reduction for the single‐, double‐, and triple‐tube cases was 63.7%, 67.0%, and 68.34%, respectively.

Frequency regulation in solar PV-powered thermal power system using FPA-PID controller through UPFC and RFB

Frequency regulation in solar PV-powered thermal power system using FPA-PID controller through UPFC and RFB

Startup characteristics of the large length–diameter ratio high-temperature heat pipe

Large length–diameter ratio high-temperature sodium heat pipes (HTSHPs) are uniquely structured heat-transfer devices with significant application potential in high-temperature solar thermal power and small-scale nuclear systems. This study tested HTSHPs' startup characteristics examining various parameters. Results indicate that the transition temperature for flow transition is 564 K, and the continuous flow transition temperature is 722 K. Heat pipes at 15 % fill ratio are adaptable across various inclination angles, whereas those at 25 % and 35 % fill ratios show optimal startup at smaller angles (15°, 30°), with decreasing startup time as angle increases, notably significant at 45°.The start-up time refers to the duration from the initiation of heating to the point when all the normal operational temperature points of the HTSHP reach the continuous flow transition temperature during the condensation section. During the experiments, heat pipes with a large length–diameter ratio exhibit heat transfer instability, temperature oscillation and local overheating. Reducing the fill ratio and inclination angle effectively reduces the probability of temperature oscillation and local overheating. This study proposes a novel method for optimizing temperature oscillations in heat pipe design, offering pioneering insights and experimental data crucial for specialized high-temperature heat pipe research.

Design and behaviour estimate of a novel solar and fuel cell complementary driven supercritical-CO2 cycle thermal system

Solar-integrated fuel cell systems are widely regarded as an effective means of saving energy and reducing emissions, given their ability to decrease reliance on fossil fuels. However, solar thermal power systems are intermittent, whereas fuel cell waste heat power generation has continuous power output. The paper proposes a novel solar and molten carbonate fuel cell complementary driven supercritical-CO2 cycle system. The performance of multi-energy complementary driven supercritical-CO2 cycle and system operation mode conversion is being investigated. The complementary operation mode ensures the continuous output of the proposed system through the switching of the solar module and the fuel cell module. The result indicates that the fuel cell module operates for 23.5 % of the time in a year, resulting in a reduction of the storage tank volume by 14,723 m3 and a decrease of the fixed heliostat area by 108,237 m2. The efficiency of the supercritical-CO2 cycle individually is 43.1 %, and with the addition of the waste heat utilization subsystem, the cycle efficiency of the proposed system reaches 50.89 %. Furthermore, the levelized cost of electricity for the proposed system is 0.1861$/kWh, and the research results can serve as a reference for the design of complementary energy systems.

Numerical research on performance of new structure centrifugal compressor for supercritical CO2 power systems

The supercritical carbon dioxide (sCO2) power cycle system is a potential thermoelectric conversion system with the advantages of high efficiency and compactness, which can be used in the fields of solar thermal power, nuclear power, and other thermal power systems. The compressor is one of the important machines in sCO2 power systems. To improve the performance and reduce the condensation risk of sCO2 centrifugal compressors, a new structure sCO2 centrifugal compressor is proposed in this paper, which has a partial-cover impeller and self-circulation-channel casing (PISC). The internal flow of the compressor with the new structure is analyzed by the CFD method. The flow and condensation in sCO2 centrifugal compressors with the PISC structure and that with the semi-open impeller and traditional casing (SITC) are compared. The results show that the PISC sCO2 compressor has an inhibiting effect on the condensation at the compressor inlet location, reducing the condensation volume to approximately 82% of that of the original structure under design conditions. The total pressure ratio and isentropic efficiency of compressors are simulated, and the result shows that the minimum stable mass flow rate is reduced by about 13% by introducing the new PISC structure into the sCO2 centrifugal compressor, and the maximum isentropic efficiency is increased from 83.5% to 84.4% compared to that of the SITC compressor. A new design idea for the impeller and sCO2 compressor structure is provided in this paper. The research results can be applied to sCO2 compressors and improve the performance and stability of sCO2 power cycle systems.

Power load analysis and configuration optimization of solar thermal-PV hybrid microgrid based on building

Solar thermal power system and photovoltaic coupled system can supply electric energy based on renewable solar energy. To explore the optimal configuration of hybrid microgrid driven by solar energy and to achieve a stable and sufficient electric power supply for the distributed energy system, this paper configures a solar thermal-photovoltaic hybrid microgrid and compares the performance of several microgrids based on the power load analysis of the building. The working fluid and the microgrid configuration are determined based on the performance evaluation of single and hybrid microgrids. The effect of solar irradiation on economic and environmental performance is analyzed under the meteorological data of Xi'an and Lhasa in China. Furthermore, the configuration optimizations of a hybrid microgrid based on the actual load and basic load of the building are carried out to examine the performance of the system. Results indicate that economic and environmental performances are sensitive to solar irradiation. More than 50 % of the area of solar thermal collector can be saved for Lhasa compared with Xi'an. Solar thermal-photovoltaic hybrid microgrid with battery can decrease carbon emission and avoid dependence on the external power grid.

Numerical study on the stress and thermal performance of a supercritical CO2 solar conical cavity receiver

Solar thermal power systems rely on high-temperature cavity receivers. Guaranteeing the effective and secure operation of a receiver involves researching the impacts of various geometric parameters and operating conditions on its thermal performance and mechanical qualities. To examine the impacts of diameter, curvature, and various operating conditions on the thermal and mechanical performance of a receiver, a coupled thermal–mechanical model was created and assessed. The findings showed that the spiral coiled tube's thermal stress distribution is very nonuniform. Thermal efficiency declines and maximum stress rises from 74.9 MPa to 171.87 MPa as the diameter increases from 10 mm to 30 mm. The thermal efficiency rises when the curvature goes from 1/190 to 1/130, but the stress rises as well. The outlet temperature drops by 73.46 K after 5 min of cloud cover; cloud cover and startup conditions will result in rapid variations in stress and temperature on the coiled tube wall, endangering the receiver's safe function and shortening its lifespan.

Performance evaluation of a novel photo-thermal-electric hybrid system

Solar thermal power systems are promising electricity generation technology; however, their thermal efficiency is low due to the installed tilt angles and heat losses of solar collectors. Herein, a novel photo-thermal-electric hybrid system that integrates a tilt angle-independent and efficient evacuated U-tube solar collector with a thermally regenerative electrochemical cycle is theoretically conceptualized to evaluate its effectiveness. By developing a mathematical model, analytical expressions for performance indicators as well as the conditions delivering electricity of the hybrid system are deduced. Regardless of tilt angle, calculations indicate that the power density, energy efficiency and exergy efficiency can reach 82.99 W m−2, 8.30 % and 7.61 %, respectively. The hybrid system is less efficient than common silicon photovoltaic cells but is more efficient than some photovoltaic/thermal systems. Exhaustive parametric studies reveal that decreasing thermally regenerative electrochemical cycle internal resistance, ambient temperature or liquid flow rate in evacuated U-tube solar collector and increasing temperature coefficient or evacuated U-tube solar collector inlet temperature can enhance the hybrid system performance. Gradient-based local sensitivity analyses identify that the internal resistance and temperature coefficient of the electrochemical cycle are, respectively, the most and least sensitive variables. A practical case study predicts the hybrid system performance under local weather conditions.

Co-Optimization of Distributed Energy Resources Under Time-of-Use Pricing Frame

Abstract Distributed energy resources (DERs) have been considered as a promising solution due to the benefits on efficiency and environmental sides. However, despite the rapid development of distributed energy resources and technologies, the share of distributed energy generation is still small in comparison to that of traditional generation. Time-of-use (TOU) pricing can be an important incentive strategy to encourage the penetration of distributed energy resources. In this paper, a multi-objective optimization considering the time-of-use pricing impacts is proposed to determine the optimal configuration and capacity of distributed energy resources involving different technologies, including solar photovoltaic (PV), solar thermal collector (STC), combined heating and power system (CHP), and integrated energy storage (ES). The distributed energy resources are designed to satisfy the electric and thermal load of commercial buildings (large hotels and medium offices) partially or entirely. The proposed multi-objective optimization is utilized to configure the optimal combination of distributed energy technologies as well as the system capacity to reduce both the cost and environmental impact of the system in different locations. Results show that the proposed optimization method can achieve a trade-off between system cost and environmental impact based on the existing time-of-use pricing structure.

Improvement of the classical artificial neural network simulation model of the parabolic trough solar collector outlet temperature and thermal efficiency using the conformable activation functions

The outlet temperature and the thermal efficiency predictions of the PTSC are essential parameters in the solar thermal power system. Therefore, it is crucial to have a prediction model that can predict its spatiotemporal behavior to the greatest extent possible. For that, the present study provides improved models of the classical ANN model by using ELU, swish, softplus, logsig, and tansig functions through the exponential transfer function to improve the outlet temperature prediction performance and thermal efficiency of PTSC. The PTSC’s outlet temperature simulation showed that the ANN model of topology 6-2-1 with the conformable swish transfer function (cswish) was the best model among nine other studied models, with an R2 and Radj2 of 0.9988, and MAE of 0.0052. The simulation of PTSC’s thermal efficiency proved that the conformable functions logsig, tansig, ELU and the classical ELU function involved in the ANN model for 6-3-1 achieved better results with approximately 95% precision. With the non-integer activation functions, was reduced a neuron in the hidden layer, which leads to the simplicity of the prediction model compared to the use of the classical activation functions. The proposed activation functions do not require high-performance features according to their execution times. Therefore, it could be a good alternative for engineers to apply in other thermal energy systems to make their prediction models more accessible and practical in the control and optimization process.

Load Frequency Control With Renewable Energy Sources Using Practical Swarm Optimization Based On PID

Future competitive solutions for the production of electricity may be provided by emerging renewable energy sources (RESs) technologies as wind, solar photovoltaic, and solar thermal power systems. In this study, simulation tests have been conducted on autonomous hybrid generating systems(HGSs) made up of diesel engine generators (Degs), fuel cells (FCs), wind turbine generators (Wpg), solar photovoltaic generators (Pvpg), battery energy storage systems (Bess), and flywheels (Fess). The abrupt fluctuations in load, generation, or both cause the power system's frequency to vary. PID controller tuning using particle swarm optimization (PSO) is used for the optimization of controllers’ gains of the proposed hybrid systems. The proposed method is compared with a genetic algorithm (GA) and a traditional PID controller. To test the proposed controller, three different scenarios were used: first, changing the load's value with a fixed value over a set period of time; second, changing the load's value with variable values; and third, changing the load's value with a variable value while changing the system parameters. The simulation results reveal that the suggested controller performs better and is more resilient against load and generational disruptions by reducing the maximum overshoot value and settling time by 70% and 65%, respectively, and by 14.2% and 5% when compared to a GA-PID control.

Performance comparison of three supercritical CO2 solar thermal power systems with compressed fluid and molten salt energy storage

In recent years, the supercritical carbon dioxide (sCO2) Brayton cycle power generation system has gradually attracted the attention of academics as a solar thermal power generation technology. To achieve the stable and effective use of solar energy, three sCO2 solar power generation systems were studied in this paper. These systems included a molten salt thermal storage system, a compressed CO2 energy storage system, and a combined molten salt thermal storage and compressed CO2 energy storage system. The thermodynamic analysis model of the sCO2 power generation system is constructed, and a mathematical model of the solar power tower system is produced. The operating conditions, thermal efficiency, exergy efficiency, and economics of these three systems on typical days are investigated and compared. The results indicate that the power generation system coupled with compressed CO2 storage has higher thermal and exergy efficiencies than the other two systems with the same daily heliostat field. The thermal efficiencies can be as high as 6.56% and 5.91% respectively, and the exergy efficiencies as high as 5.76% and 6.22% respectively. The system coupled with compressed CO2 energy storage is more cost-effective and has a shorter payback period than the system coupled with molten salt thermal storage system and the system with both forms of energy storage.

A novel solar-driven Organic Rankine Cycle system based on the two-stage solar thermal collection and accumulation

Solar thermal power has attracted much attention because it is instrumental to solar energy storage and power grid peak shaving. Among the various solar thermal power technologies, the Organic Rankine Cycle stands out as a prevalent choice for low and intermediate-temperature (80 – 200 °C) solar thermal power generation applications. However, it is required of the concentrating solar collectors for medium temperature supply and its performance is greatly affected by the off-design operation owing to variable solar irradiance. In this paper, a novel solar-driven Organic Rankine Cycle system that consists of a two-stage solar thermal collection and accumulation design is proposed to solve the above issues. Two-stage non-concentrating solar plants are adopted to harvest global solar irradiance and regulate system operation. Two-stage energy accumulators can not only mitigate the influence of the solar irradiance fluctuation on the Organic Rankine Cycle off-design running but also enhance the temperature drop of thermal energy storage. Through the experimental test and numerical simulation, the results indicate that the influence of solar irradiance on the Organic Rankine Cycle steady operation has been weakened (reducing power output fluctuation range by approximately 70%), and the overall system efficiency has also been improved by 43.85%. Consequently, the solar Organic Rankine Cycle system proposed in this paper exhibits superior thermal performance compared to the conventional systems and is conducive to the advancement of the non-concentrating solar thermal power system.

Performance Improvement of AGC Using Novel Controllers in a Multi-Area Solar Thermal System under Deregulated Environment

The performance improvement of Automatic Generation Control (AGC) in a Multi Area Solar Thermal Power System (MASTPS) under a deregulated environment is considered as MIPS and their performance is compared using various controllers to improve the performance of AGC in the proposed MIPS. This study takes into account a three-area conventional thermal power system in conjunction with a solar thermal power plant in each area, along with the proper generation rate constraints (GRC). The performance of the different controllers, including the Adaptive Neuro Fuzzy Inference System (ANFIS) controller and the Droop Controller (DC), Fuzzy Logic Controller (FLC), Artificial Neural Network (ANN), and Fractional Order PID (FOPID) controllers, is compared in the proposed AGC deregulated power system. The proposed MIPS is designed and implemented to make the system as realistic as possible with real world scenarios. The recommended MIPS is being simulated in MALTAB Simulink environment and simulated for multiple times to investigate the performance improvement in AGC using the adopted controllers with 0.1 per unit of step load perturbation to verify its dynamic characteristics. According to the investigation, the suggested ANFIS controller improves the AGC performance in proposed MIPS and offers better dynamic performance than other controllers.

Optimal dynamic frequency regulation of renewable energy based hybrid power system utilizing a novel TDF-TIDF controller

ABSTRACT Insertion of intermittent natured renewable energy resources in the microgrid to decline global warming and due to highly inconsistent propulsion load, frequency control of the isolated hybrid micro-grid system (HMGs) is the key point of attraction and necessitates a highly competent and robust control strategy. Hence, in this paper, an efficient frequency control mechanism for HMGs is proposed by utilizing an efficient tilt derivative filter-tilt integral derivative filter (TDF-TIDF) controller. HMGs are composed of solar, wind, fuel cell, freezer, diesel engines, heat pumps, and loads. A recently appeared dragonfly algorithm (DFA) is employed to optimize the suggested controllers’ design variables. The dynamic analysis is exhibited with different types of energy storage units under various conditions. The conditions incorporate perturbations in demanded load and power generation through renewable energy sources. In this study, solar thermal and wind power systems are not contributing to frequency control owing to the plan of their maximum power tracking approach. The dynamic performance of different controllers such as PIDF, TIDF, PDF-PIDF, and TDF-TIDF controllers are evaluated with their design variables tuned by employing genetic algorithm, particle swarm optimization, gravitational search algorithm, quasi harmony search algorithm, grasshopper algorithm and dragonfly algorithm. The output graphs of transient responses and collected statistical data corroborate that the suggested DFA-based TDF-TIDF scheme provides least objective function value (8.1e‒ 07) compared to PDF-PIDF (4.011e‒ 06), TIDF (3.14e‒ 05) and PIDF (5.03e‒ 05), hence, more capable in reducing the oscillations quickly for the system with non-linearities. Moreover, statistical data yielded by DFA is observed superior when evaluated with other existing optimization methods.

Comparison study of thermoclinic heat storage tanks using different liquid metals for concentrated solar power

Liquid metals are good potential heat transfer materials for thermoclinic heat storage (THS) systems and will play an important role in the next generation solar thermal power system with higher operating temperature. This paper presents a comparative research work on the charging, discharging and mechanical performances of THS tanks based on four different liquid metal materials, which are lead (Pb), lead-bismuth alloy (PbBi), sodium (Na) and sodium-potassium alloy (NaK). The analysis results indicate that for both the charging and discharging processes, the lead-based THS tank can have the shortest operating duration, largest charging and discharging quantities (9.78 × 109 J and 9.21 × 109 J) as well as the highest discharging efficiency (94.17%), revealing its best operating performance. Relatively acceptable operating performances of lead-bismuth-based and sodium-based THS tanks are also demonstrated. Furthermore, in contrast with other three liquid metals, the lead-based THS tank also has the best mechanical performance. It has the smallest peak maximum mechanical stress of the steel wall (58.6 MPa). In summary, the lead-based THS tank has both the best heat storage and mechanical performances.

Performance analysis of a dish solar thermal power system with lunar regolith heat storage for continuous energy supply of lunar base

Sustainable energy supply is a major challenge for the lunar base because of the lengthy night of the Moon. In-situ resource utilization based on lunar regolith heat storage is a promising solution to this challenge. Herein, a dish solar thermal power system with lunar regolith heat storage is proposed to supply energy to a lunar base. A theoretical model is established using finite-time thermodynamics to investigate system performance in a lunar circadian cycle. A case study shows that the output power and efficiency of the system gradually decrease whether in lunar day or lunar night. The average output power during the lunar day and night is 10.8 kW and 7.0 kW, respectively. The system can achieve a high energy efficiency of 48.0%, which is mainly owing to the full utilization of lunar resources. In addition, the effects of several key parameters on the system performance are discussed and the results show that the energy supply of the system requires a tradeoff between lunar day and night. This work reveals that the proposed system has the potential to supply energy to the lunar base continuously and efficiently, providing a scheme for the energy supply system of the future lunar base.