Concentrated Solar Power Systems Research Articles

Experimental research on heat transfer characteristic of HITEC molten salt in evacuated tube solar collector

HITEC molten salt (7% NaNO3, 53% KNO3, 40% NaNO2) has been identified as a suitable heat transfer fluid for concentrated solar power (CSP) systems, such as parabolic trough collectors (PTC) and evacuated tube solar collectors (ETSC). In order to optimize the flow and heat transfer performance of HITEC in ETSC, a molten salt heat transfer test rig was built to conduct an experimental study, varying inlet and outlet temperatures and mass flow rates of HITEC. Results show that the heat loss of HITEC in ETSC is lower than the other tubes. The convective heat transfer coefficient of HITEC is much lower than that of HITEC in round tube. Because the experimental data of HITEC in ETSC largely differed from the classical correlation equations, a new empirical heat transfer correlation equation was set for HITEC in ETSC, and the deviation between the experiment data and new correlation was within ±19.2%. Finally, by comparing the inlet and outlet temperatures of ETSC under different irradiation intensities, it is concluded that the ETSC can work stably when the temperature exceeds 700 W/m2.

Thermodynamic assessment of binary chloride salt material for heat transfer and storage applications in CSP system

Molten chloride salt is recognized as a promising heat transfer fluid and thermal energy storage material (TES) in concentrating solar power (CSP) in recent years, and its phase diagram as key data for material design still need further research. In this work, the phase equilibrium characteristics of solid-liquid equilibrium and vapor-liquid equilibrium for binary chloride salt system (Na/K–Ca/Mg) are investigated respectively. Based on Wilson model, the activity coefficient and non-ideal behavior of liquid salts are predicted effectively, and then the solid-liquid phase diagrams of binary salts are calculated, and the predicted eutectic temperature and component agree well with experimental data. Vapor-liquid phase diagrams of binary salts are also calculated, and azeotropic temperature can only be found in the MgCl2 based mixed salts. As the system pressure rises, the azeotropic temperature increases, while azeotropic component slightly changes. According to the variation of vapor pressure for eutectic salts, the correlations for vapor pressure with temperature and composition are developed. Thermal stability of eutectic salts is experimentally studied by Thermo-gravimetric analyzer (TGA) and operating temperature ranges of these mixed salts are revealed. It can be found that the mass loss rate at different temperature is directly proportional to the vapor pressure. In general, present binary chloride salts show wide operating temperature range and high heat storage density, and eutectic NaCl–MgCl2 with advantage of heat storage density and azeotropic point existence is recommended as TES in the CSP plant.

Novel integration between propane pre-cooled mixed refrigerant LNG process and concentrated solar power system based on supercritical CO2 power cycle

Liquefaction of natural gas (LNG) is an energy-intensive process with large CO2 emissions. This study addresses these problems by introducing a novel hybrid integration between the propane pre-cooled mixed-refrigerant (C3MR) liquefaction process and concentrated solar power (CSP), utilizing an intercooled supercritical CO2 power block. The proposed system is designed to minimize or eliminate the need for thermal energy storage (TES) and reduce CO2 emissions while providing economic benefits. These benefits are obtained mainly by recovering the cold energy of the flash-gas of the C3MR process through the precooling process of the sCO2 cycle. Then, the flash-gas is stored and combusted (using an auxiliary heater (AH)) at nighttime or when CSP is insufficient to meet the power demand. Five integration cases are evaluated from energetic, exergetic, economic, and environmental points of view: the sCO2 cycle is driven by CSP and its thermal energy storage (TES) without AH in Case-1, by CSP+TES+AH in Case-2 to Case-4 with different contribution from TES and AH, and by CSP+AH without TES in Case-5. In addition, this study optimizes the operating parameters of the hybrid system to further enhance its economic and environmental benefits. The proposed system reduces the CSP field size, minimizes or eliminates the need for TES, and reduces or eliminates CO2 emissions. The optimized results show that Case-2 and Case-5 reduced the levelized cost of electricity from 14.16¢/kWh to 10.35¢/kWh and 8.19¢/kWh, respectively, and reduced the CO2 emissions by 86% and 36%. This study contributes to the field by introducing a novel hybrid integration between the C3MR process and CSP system, providing thorough evaluations of its performance and benefits, and providing significant benefits to the decarbonization strategies of LNG and other industrial processes.

Macro encapsulated Cu-based phase change material for high temperature heat storage with characteristic of self-sealing and high durability

The objective of this research is to develop encapsulated phase change materials with applications exceeding 1000 °C that can be applied to concentrated solar power systems and industrial waste heat recovery. In this study, a macro-encapsulation phase change storage material with a copper-based core and an alumina-based shell was developed by slip-casting method and filling mixture of copper beads and Cu-40 %Al powder. The capsule was able to achieve self-sealing by local oxidation reaction at the entrance without leakage. After aging tests at 1100 °C for up to 1000 h, no leakage or damage was found and mass increase of the encapsulate phase change material was only 4.5 %, confirming the superior durability and oxidation resistance of the encapsulated phase change material. The heat storage density of the copper-based phase change material was evaluated as high as 147 J/g. The heat storage capacity did not decrease after 1000 h and ten cycles of aging. The mechanism of its high durability was explored by morphological observations and Raman spectroscopy. In the original material, a small amount of aluminum was oxidized with priority to alumina which significantly enhanced the durability of the capsules. This macro-encapsulated phase change material exhibits excellent thermal storage performance, as well as self-sealing and durability properties, which are of great significance for improving the efficiency of thermal energy recovery above 1000 °C.

Techno-economic and GHG mitigation assessment of concentrated solar thermal and PV systems for different climate zones

In this study, energy production by two solar energy technologies, namely concentrated solar power (CSP) and photovoltaic (PV) power, is compared from a technical, economic and environmental perspective. Initially, a 50 MW CSP plant is modeled and simulated at four selected sites in Pakistan. Then, the most feasible location of the CSP plant is compared with the solar PV plant of the same capacity. The effect of the solar thermal storage size and cooling system of the CSP system is investigated, while the photovoltaic tracking system is investigated to evaluate the technical and economic performance of the power plants. Technical performance is evaluated based on energy generation and capacity factors metrics, while economic performance is evaluated with respect to levelized cost, payback period and net present value. In addition, environmental criteria such as reducing greenhouse gas emissions (GHG), saving fossil fuels, and life-cycle water consumption are evaluated. From the results, it was concluded that the CSP plant located in Quetta is technically and economically viable. The capacity factor of the CSP plant is 36.6% compared to 19.8% for the PV plant, while the solar-to-electrical efficiency of the CSP plant is 14.2% compared to 20.8% for the PV plant. The required land area is 2.77 acres/GWh for the CSP plant and 2.33 acres/GWh for the PV plant, while the net capital cost of the CSP plant is five times higher than that of the PV plant. Various design parameters are optimized to obtain the minimum levelized cost of energy (LCOE) for both CSP and PV plants. The results of CSP and PV plants indicate that the LCOE can be reduced to 11.57 cents/kWh and 4.69 cents/kWh, respectively. Thus, the CSP plant performs better from the technical point of view while the PV plant performs better from the economic perspective.

Enhanced corrosion resistance of alloy in molten chloride salts by adding nanoparticles for thermal energy storage applications

Because of the exceptional heat transfer characteristics, thermal-chemical stability, and thermal energy storage potential, molten salts are widely used in concentrating solar power (CSP) plants. However, corrosion induced by molten salt is a major factor affecting the safety of the system under long-term energy storage operation conditions, especially at high temperatures. In this work, chloride salt (NaCl-KCl-MgCl2) was considered as base salt for the preparation of nanocomposite salt using Al2O3 nanoparticles. The gravimetric method and other in-situ characterization technics were employed for the analysis of corrosion behavior, mass loss, surface microstructure, and chemical composition of Inconel 625 alloy in base salt and nanocomposite salt at 500 to 700 °C temperature range. This study demonstrated the nanocomposite salt could slow down the corrosion of the Inconel 625 alloy in the high-temperature molten salt. The experimental results disclosed the mass loss and corrosion rate behavior of the Inconel 625 alloy immersed in nanocomposite salt which is lower than those of the Inconel 625 alloy immersed in base salt. The presence of Al2O3 nanoparticles results in a thinner corrosion layer of Inconel 625 alloy in nanocomposite salt. Through the corrosion mechanism analysis of Inconel 625 alloy in molten salt, it was found that the surface of corroded Inconel 625 alloy is characterized by a dense oxide layer mainly composed of MgCr2O4. The corrosion resistance mechanism of Inconel 625 alloy in nanocomposite salt was also analyzed, and the results showed that Al2O3 nanoparticles played an important role in the corrosion resistance of Inconel 625 alloy. This study provided innovative approaches to enduring the heat storage capacity of molten salt in concentrated solar power and other related thermal energy storage systems.

Coordinated control of concentrated solar power systems with indirect molten salt storage considering operation mode switching: Using switching model predictive control

Coordinated control of concentrated solar power systems with indirect molten salt storage considering operation mode switching: Using switching model predictive control

New insights into the heat capacity enhancement of nano-SiO2 doped alkali metal chloride molten salt for thermal energy storage: A molecular dynamics study

Molten salts and their based nanofluids are important media for heat transfer and thermal energy storage in concentrated solar power (CSP) system. To improve the overall efficiency of the CSP plants, it is important to increase the specific heat capacity of molten salt to the extent possible. Nanomaterials have been doped in molten salt to enhance the specific heat capacity of molten salt; however, the mechanism of enhancement in specific heat capacity caused by doping of nanoparticles in molten salt is still unclear. In this work, the Buckingham force field parameters for alkali metal chloride molten salts (KCl, NaCl, LiCl) were first derived and carefully validated. The specific heat capacities, viscosities, and self-diffusion coefficients of pure molten salts and the specific heat capacities of molten-salt-based nanofluids with SiO2 nanoparticles were investigated by molecular dynamics (MD) simulations. The calculated thermophysical properties of the chloride molten salts using the derived Buckingham potential parameters are in good agreement with the experimental data, and the overall prediction performance is better than that of the BMH potential. Results show that the specific heat capacity of molten salt first increases and then decreases with increasing SiO2 doping ratio, reaching a maximum value at 1 wt%. The specific heat capacities of KCl, NaCl and LiCl nanofluids with 1 wt% SiO2 nanoparticle are increased by 6.2 %, 8.6 % and 19.8 % compared to the base salts, respectively. Number density, radial distribution function, coordination number curves, and energy of the nanofluid system were systematically analyzed. It is found that the increase of the specific heat capacities of the molten salt-based nanofluids can be explained by the energy and coordination number change caused by the number density mismatch of cations and anions. Interestingly, the local delamination of cations around SiO2 nanoparticle surfaces in LiCl-SiO2 nanofluids is clearly observed and visualized for the first time; it is a phenomenon well explained by the analysis of number density and contributes to the further enhancement of the heat capacity. The findings of this work could provide important fundamentals in understanding and designing more efficient molten salt nanocomposites for thermal energy storage in future studies.

Hybrid solar-driven hydrogen generation by sorption enhanced–chemical looping and hydrocarbon reforming coupled with carbon capture and Rankine cycle

Hydrogen (H2) production from fossil fuels using Hydrocarbon Reforming Methods (HRM) accounts for nearly 95% of Global H2 production. Unlike hybrid Chemical Looping Steam Reforming (CL-SR) systems, the Integrated Solar-Driven Sorption Enhanced–Chemical Looping of Hydrocarbon Reforming (SE-CL-HR) utilises solar thermal energy from the Concentrating Solar Power (CSP) system to drive the endothermic decomposition of feedstocks. Furthermore, the simulated hybrid systems utilise recovered heat to generate electricity, reuse of by-product CO2 for more syngas production and finaly, CO2 capture by reaction of CaO to form CaCO3. This work focused on simulating hybrid CSP systems and SE-CL-HR plants with Heat Transfer Fluid (HTF) output temperatures between 750 and 1050 °C. In this study, System Advisor Model (SAM) and MATLAB software are used to develop the CSP system. While the CSP result saved in the MATLAB workspace gets exported to Simulink to feed SE-CL-SMR, SE-CL-POX and SE-CL-ATR Aspen plus models. The integrated system was fed with CH4 as the working fluid of the solar furnace. Stoichiometric and Gibbs free-energy minimisation were employed to investigate the effect of operating parameters. The output of the integrated system shows ≥9.5% exergy efficiency in comparison to conventional HRM. In addition, CO2 capture by CaO and high-pH water (Ca, Mg, Na+, O2, OH− and Cl−) to produce CaCO3, MgCO3 and other valuable products was also investigated in a process simulation. The research results revealed that for 8.1 tons/hr of CH4 and 277.1 tons/hrH2O (steam) flowrates, 62 tons/hr of H2 can be generated and 338.5 tons/hr of CO2 emission can be reused and captured by the adoption of these new innovative technologies.

Cost of Using Laser Powder Bed Fusion to Fabricate a Molten Salt-to-Supercritial Carbon Dioxide Heat Exchanger for Concentrating Solar Power.

Advances in manufacturing technologies and materials are crucial to the commercial deployment of energy technologies. We present the case of concentrating solar power (CSP) with molten salt (MS) thermal storage, where low-cost, high-efficiency heat exchangers (HXs) are needed to achieve cost competitiveness. The materials required to tolerate the extreme operating conditions in CSP systems make it difficult or infeasible to produce them using conventional manufacturing processes. Although it is technically possible to produce HXs with adequate performance using additive manufacturing, specifically laser powder bed fusion (LPBF), here we assess whether doing so is cost-effective. We describe a process-based cost model (PBCM) to estimate the cost of fabricating a MS-to-supercritical carbon dioxide HX using LPBF. The PBCM is designed to identify modifications to designs, process choices, and manufacturing innovations that have the greatest effect on manufacturing cost. Our PBCM identified HX design and LPBF process modifications that reduced projected HX cost from $750 per kilo-Watt thermal (kW-th) ($8/cm3) to $350/kW-th ($6/cm3) using currently available LPBF technology, and down to $220/kW-th ($4/cm3) with improvements in LPBF technology that are likely to be achieved in the near term. The PBCM also informed a redesign of the HX design that reduced projected costs to $140-160/kW-th ($3/cm3).

Enhanced thermal and mechanical performance of 3D architected micro-channel heat exchangers

Many crystals in nature have simple interatomic microstructures, such as simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC) lattice symmetries, making these structures extremely stable. Inspired by these arrangements, a series of architected micro-channel heat exchangers with rationally designed 3D microstructures were established. A multi-physics mathematical model using thermal-fluid-structure interaction (TFSI) was employed to investigate the coupled heat transfer performance and mechanical properties of these architected heat exchangers. When compared with the corrugated straight plate (CSP) microchannel heat exchanger, the thermal-hydraulic performance factors (TPC) of FCC and BCC microchannel heat transfer were 2.20 and 1.70 times that of SC microchannel heat exchanger, respectively. The micro-channel heat exchanger with FCC architectures could enhance the convective heat transfer performance by 201.0%, while the micro-channel heat exchanger with SC architectures reduced the Von-Mises equivalent (VME) stress by 20.0% when compared with the conventional 2D CSP heat exchanger. The proposed architected micro-channel heat exchangers could find a wide range of potential applications ranging from power electronics in electric vehicles to concentrated solar power systems, where both good convective heat transfer performance and high mechanical strength are simultaneously pursued.

Influence of different thermal degradation processes on the optical property of Pyromark-2500

Concentrating solar power (CSP) is emerging as an increasingly important component of renewable energy. CSP systems are being widely adopted in the establishment of large-scale thermal power plants, with an increase in the number of successfully operating demonstration systems.Special coatings are generally used in various types of receivers for solar collector systems. Selective coatings are used for receivers intended to be operated at low or medium temperatures. Similar selective coatings are not currently available for application under high temperatures. In such cases, high-temperature absorbing coatings are generally used to improve the thermal efficiency of the receiver and protect their tubes from oxidation. It is worthwhile to observe the behaviour of such coatings when exposed to high fluxes for extended periods, in order to develop more efficient technologies.Currently, the essential properties for characterizing the paint are absorptivity, emissivity, and structural integrity of the coating (adhesion and cohesion). Good understanding of the behaviour of this paint under representative operating conditions would help to improve the design of the plant, maintain its performance and maintain the thermal efficiency of the receiver. The principal objective of this study was to provide extensive knowledge of the durability and variation of the optical properties of Pyromark when it is consolidated with improved methods. No degradation or loss of optical performance was observed at temperatures under 700 °C. The substrate affected the crystalline structure of an initial coating at high temperatures owing to the diffusion of metal ions. Concentrated solar radiation was the main factor that affected the integrity of the coating. At concentrations higher than 550× suns, a significant area of the irradiated samples was found to be uncoated. These results can be used to design more accurate latest generation receivers to improve the performance of this technology.

Sensitivity analysis and exergoeconomic optimization of an improved He-CO2 cascade Brayton cycle for concentrated solar power

Nowadays, solar energy is one of the most promising renewable energy sources that can effectively mitigate the current serious energy crisis and environmental pollution. To efficiently utilize solar energy and positively comply with the carbon neutrality policy, this research developed an efficient and environmentally-friendly improved He-CO2 cascade Brayton cycle for concentrated solar power, and then implemented a series of studies, including performance prediction, sensitivity analysis, and exergoeconomic optimization. After optimization, the most suitable condition was determined via a decision-making method, and the exergoeconomic performances of each subsystem and component were thoroughly investigated. Finally, the concentrated solar power system was comprehensively evaluated from the perspectives of thermodynamic and exergoeconomic performance. The numerical results imply that the system provides excellent thermodynamic and exergoeconomic performance with power, investment cost rate, and exergoeconomic factor of 697.75 kW, 33.09 $/h, and 77.48%, respectively, representing an exergy efficiency improvement of 3.51%–6.35% compared to similar concentrated solar power configurations. This research complies with the carbon neutrality policy, meets energy conservation and emission reduction requirements, and offers meaningful guidance for scientists who are committed to improving solar energy conversion and implementing exergoeconomic analysis.

Integration design and control strategy of sCO 2 Brayton cycle for concentrated solar power system

The concentrated solar power (CSP) system integrated with supercritical carbon dioxide (sCO 2) Brayton cycle is considered as the major development trend of clean energy technology in mitigating climate change and promoting sustainable energy owing to its more compact structure, higher efficiency and lower cost. While the system integration and control are more complex because the thermal energy storage and heat exchange units are obliged to be provided with capacity and property matching with sCO 2 compression and expansion units. Therefore, there is an urgent need for the whole system modeling and dynamic simulation of sCO 2-CSP plants. In the paper, running logic of the integrated system is determined and novel system dynamic simulation platform is built. Moreover, for the sake of optimizing the system design, different control strategies are further studied. When the extremum-seeking control strategy is used, the average daily generating capacity of the system is 2.06% higher than that of the traditional fixed inventory control strategy; and when iterative learning control strategy is used, the average daily generating capacity of the system is 2.15% higher than that of the traditional fixed inventory control strategy. The progress of the technology will promote the development of new power systems and early realization of carbon neutrality.

Parametric analysis on optimized design of hybrid solar power plants

There is increasing interest in utility-scale solar power plants with storage which can flexibly dispatch renewable energy to the grid. However, plant design possesses many degrees of freedom and non-obvious trade-offs in performance. Software tools can estimate or optimize the performance of a specific plant configuration under market and weather conditions of interest; the associated cost parameters and operating assumptions strongly influence estimates of plant performance and decisions regarding optimal sizing. We employ the National Renewable Energy Laboratory’s Hybrid Optimization and Performance Platform, which incorporates optimal dispatch when evaluating plant performance, and investigate the sensitivity to weather and market conditions, operating limitations, and the presence of a capacity-based incentive. We demonstrate changes in plant performance and optimal sizing with respect to these inputs and discuss implications. Results show that PV-with-battery designs are more profitable under our assumptions, but that designs including a concentrated solar power (CSP) system produce significantly greater annual energy; and that CSP-with-thermal energy storage designs maximizing the benefit-to-cost ratio have an input-dependent linear relationship between the CSP field solar multiple and the hours of storage as the project budget varies.

Analysis on the Effects of Different Receiver Structures and Porous Parameters on the Volumetric Effects and Heat Transfer Performance of Porous Volumetric Solar Receiver

The volumetric solar receiver is an important heat transfer component of the concentrated solar power (CSP) system. Moreover, in order to improve the absorption of concentrated solar radiation, the porous media are widely used in volumetric solar receiver. In recent years, many studies were concerned with the effects of porosity, pore number density and size, Reynolds number, and Darcy number on heat and flow performance in volumetric solar receiver. However, there are few studies on the effects of structure type and geometric parameters on the volumetric effects and the radiation characteristics of a porous volumetric solar receiver with nonuniform heat flux boundary condition. In this contribution, in order to analyze the effects of structures on the volumetric effects and heat transfer performance, we design six types of porous volumetric receiver structures, whereas the volume of different structures keeps consistent. Then, we apply the local non-thermal-equilibrium model and also consider the effect of structure shape on the concentrating solar radiation transport characteristic. Furthermore, we apply the Gaussian distribution model (GDM) to simulate the actual nonuniform heat flux boundary condition. The result shows that drum-type structure (RT-III) has the best heat transfer performance among the six structures; e.g., the outlet average temperature of fluid is up to 851 K when the pore size and porosity of porous media are 2 mm and 0.7, respectively, which is 41 K increased than the scaled cone-type structure. In addition, the pore diameter has less influence on the outlet temperature of fluid, but it has greater influence on the pressure drop. The contribution can provide a reference for this type of solar receiver design and reconstruction.

Solar lighting systems applied in photocatalysis to treat pollutants – A review

Abstract This work summarizes the different natural lighting systems applied for pollutant treatment systems using photocatalysis. The principles and fundamentals of the technologies used are revisited and examples of technologies most used for treatment either at the laboratory or at the pilot plant level are disclosed. This unveils a general panorama of treatment technologies via photocatalysis, using natural sunlight as an illumination source. Aside from these concentrated solar power systems that are inviable for photocatalytic aqueous treatments, reported scientific works are shown about heliostats, parabolic troughs, Fresnel lenses, and direct illuminated systems. As a valuable result of this review, the power used in photocatalytic systems requires higher attention not only in these systems but in laboratories and prototypes. Photocatalysts and their countless configuration variants are limited due to the potential barriers in particle borders, interfaces, and surfaces to cause redox reactions in water and pollutant target molecules. These factors reduce photocatalyst efficiencies for converting light energy to useful electron pair charge carriers for water treatments. The use of solar concentration systems applied to photocatalytic treatment systems can generate enough charge carriers, improving the efficiency of the systems, and making it feasible to scale up various configurations of this treatment pathway. Subsequently, the photocatalyst material and light are both important.

Hierarchically doping calcium carbonate pellets for directly solar-driven high-temperature thermochemical energy storage

Ca-based thermochemical energy storage (TCES) system is one of the most promising energy storage techniques for the next generation concentrated solar power systems (CSP). However, it still suffers from low optical absorption, poor cycle stability, and limited energy storage density. Here, a hierarchically doping strategy is proposed to overcome above challenges and achieve high-performance energy storage under direct solar irradiation. Hierarchically doped calcium carbonate pellets, which are suitable for scalable applications, are successfully fabricated with Al-doped internal cores and Mn-rich external shells. The average solar absorptance achieves 87.15% with a 7.4% increase compared with traditionally homogeneous doping approaches. The energy storage density is still as high as 1143 kJ/kg after 20 cycles, which is enhanced by 16.6% over homogeneous counterparts. The underlying mechanism is that hierarchically doping increases contents of active CaCO3 inside pellets and absorption-enhanced substances on the outer surface simultaneously. This work presents a novel approach for the design of high-performance pellets for achieving scalable and efficient thermochemical energy storage under direct solar irradiation.

Special issue on “Optimal design and operation of energy systems”

Special issue on “Optimal design and operation of energy systems”

Neurofuzzy Defocusing strategy for a Fresnel collector

Concentrating Solar Power systems are widely applied as a means to utilize the sun's abundant renewable energy, but the design of these processes facilitates the occurrence of overheating. This work presents two approaches for calculating the mirror angles of a fresnel collector in order to limit the amount of solar energy collected. The proposed structures are designed to receive a desired focus value from a controller and generate references for the mirror inclination controllers of the collector. The first strategy consists of the use of an optimization problem coupled with a simplified model of the collector. Whereas, the second approach consists of an ANFIS network that is trained with data from a reliable collector model made in SolTrace®. Both approaches are compared with simulations in SolTrace® the results show that the ANFIS solution presented overall better results, taking into account error and computational time.