Solar Thermal Power Applications Research Articles

Feasibility of solar-powered air-conditioning system using natural refrigerants

This research focuses on low carbon dioxide alternatives to air-conditioning systems that use sustainable and low-power drives. This detailed research takes into account a 1 t capacity air-conditioning system using several refrigerants based on vapor compression. Natural refrigerants should be used instead of all-synthetic ones due to their environmentally favorable properties. Using the CoolPack software platform, a comparative analysis was conducted, and it was found out that the natural refrigerants R290 and R600a exhibited promising results in terms of heat removal from the evaporator (Q e (kW)), heat removal from the condenser (Q c (kW)), work done by the compressor (W (kW)) and coefficient of performance when fixed temperatures of 10°C for the evaporator and 50°C for the condenser were maintained. For the refrigerant R600a, superheating at the compressor (inlet) suction by 5°C was necessary to maintain the running cycle within a practical working zone. Given that a 1 t vapor compression cycle air-conditioning system based on R290 has a compressor work consumption of 640 W, the motor power input for a single-phase induction motor will be roughly 1000 W. In contrast, direct-current (DC) motors require about 30% less power (770 W) and can be readily driven by solar photovoltaic systems (DC). Thus, by presenting solar thermal (required for R600a) and solar photovoltaic power (DC) applications for the natural refrigerants R290 and R600a, the present work will contribute to a sustainable environment and demonstrate the capabilities of dependable operation with optimal power usage.

Volumetric solar carbon dioxide receiver designs with geometric parameters optimized in combination

Porous volumetric solar receivers with carbon dioxide as the working fluid can simultaneously harvest solar energy and utilize carbon dioxide. This means they hold promise for next-generation solar thermal power applications. The optimization of porous receivers has been performed in many works with their geometric parameters optimized using an exhaustive method. Such methods are computationally intensive and their deduced design guidelines are not consistent. This work presents a distinct design method where geometric parameters (porosity, pore size, and length) are combined into three heat transfer parameters (volumetric convection coefficient, effective solid-phase thermal conductivity and optical thickness), so that they are optimized in combination. The optimization objective is the combination of a large volumetric convection coefficient, a large effective solid-phase thermal conductivity and an optimal optical thickness. The corresponding combination of parameters is a small pore size, a small length and a moderate porosity. Guided by this criterion, the best combination is 0.4 mm pore size, 4 mm length and 0.85 porosity, which result in a corresponding thermal efficiency of 71.5%. This combination is consistent with that from the exhaustive method and the optimization complexity for the developed method is reduced by two dimensions.

On the compatibility of liquid sodium as heat transfer fluid for advanced concentrated solar thermal energy systems

The use of liquid sodium as a heat transfer fluid has shown great promise and application in nuclear power generation and it is now being utilized in concentrated solar thermal power (CSP) applications, owing to its favorable thermodynamic properties. Its implementation, however, comes with a unique array of technical issues in CSP applications, primarily the incompatibility of structural materials with liquid sodium in these operational environments. In this review, major damage mechanisms will be discussed, with a focus on their relevance to advanced CSP plants. Such mechanisms include corrosion, liquid metal embrittlement, carburization/de-carburization, erosion, creep, and thermal fatigue. The degradation factors such as impurities in the sodium (e.g. oxygen) and the dissolution of the structural material's alloying elements (Cr, Mn, Ni and Si, etc.) are also discussed. This review presents a holistic overview of these inter-connected mechanisms, and most importantly explores potential solutions to mitigate these issues, including better structural material candidates, robust plant operational parameters/design, better service life predictions, and improved purification and monitoring methods for stringent control of impurities. The future directions of research are also discussed to ensure the successful use of liquid sodium in the next generation of CSP technology.

An overview on thermal energy storage for solar thermal power plant

In the current situation of high energy consumption, exclusive reliance on fossil fuels would almost definitely result in a future catastrophe, particularly for emerging countries. Although renewable energy sources such as solar energy are now widely used, the issue lies in the law and economics, namely social and acceptable. The main causes of these problems are the low density of solar radiation on the earth's surface, and if it is accessible, its fluctuation in nature with time of day and year. Solar energy storage units must be used in solar thermal power applications to overcome these challenges. The literature on thermal energy storage units using phase change materials has been thoroughly examined in this article in order to choose the appropriate PCMs and materials for the construction of a thermal energy storage unit test bench.

ADVANCEMENT OF SOLAR SELECTIVE DLC COATING USING CAPVD FOR SOLAR THERMAL APPLICATIONS

Metal nitride multilayer films display a unique combination of exceptional properties with respect to optical absorption, thermal emission, corrosion resistance, adhesion between coating and surface and high temperature withstand. Most considerable aspects of nitride coatings were economical, environmentally friendly and easy to develop. Similar to nitride thin films, to achieve a considerable absorption (α) -0.92 and low emission (Є) -0.08 along with chemical and radiation stable solar selective coatings, Diamond Like Carbon (DLC) thin films exhibit the desirable properties for Concentrated Solar thermal Power(CSP)applications. The main advantages of DLC films were high hardness, chemical and radiation stability and good control over the optical properties. To achieve above-mentioned properties, optimization of each layer of the DLC coating has needed. The main aim of this research is optimization of Cr-base layer using Cr-Target current 175A to get 125 nm thicknesses, optimise the AlSiN absorber layer by controlling the AlSi- target current 175A to maintain 35nm thickness. The sequence of the DLC coating layers was selected based on their relative thickness, which was optimize to get good solar selectivity (α/Є). Individual layers of the DLC solar coatings have unique properties to get overall required high absorbance and low emission along with chemical and radiation stability. These solar selective multi-layers (Cr/DLC/AlSiN) have deposited by using available Cathodic targets (Cr , AlSi & Ti) in Cathodic Arc Physical Vapor Deposition (CAPVD) and optimized parameters were mainly depend on the target currents to control over the thickness of the each layer, base pressure 1*10-5 mbar and deposition temperature 400°C. The DLC multilayer solar selective coatings were characterized using Ultraviolet Visible Near infrared (UV- Vis- NIR) spectrophotometer, Scanning Electronic Microscopy (SEM), Transmission Electron Microscopy (TEM) and Raman spectroscopy etc. Scratch test and corrosion tests have conducted for these absorber coatings testing.

Experimental study on forced convection heat transfer of KNO3–Ca(NO3)2 + SiO2 molten salt nanofluid in circular tube

Molten salt is a major heat storage medium for medium–high temperature solar thermal power applications. The heat storage density and heat transfer efficiency of molten salt are important factors of solar thermal power efficiency. Recently, many studies have reported that molten salt nanofluid, which is formed by adding nanoparticles in molten salt, can remarkably enhance the specific heat capacity of molten salt. However, research on the forced convection heat transfer of molten salt nanofluid is inadequate. In this study, the forced convection heat transfer experiments were carried out in a circular tube of a previously reported promising molten salt nanofluid composed of KNO3–Ca(NO3)2 + 1 wt% of 20 nm SiO2 nanoparticles (K-C-Snm). Results showed that compared with its base pure molten salt, the K-C-Snm molten salt nanofluid exhibited substantially better forced convection heat transfer performance under the same working condition. The Nusselt number and the convective heat transfer coefficient of K-C-Snm molten salt nanofluid were 16.3% and 39.9% higher than its base pure molten salt, respectively. The experimental data of K-C-Snm molten salt nanofluid largely differed from the classical correlation equations. Hence, a new empirical heat transfer correlation equation was set for K-C-Snm molten salt nanofluid, and the deviation between the experiment data and new correlation was within ±7%.

Cr-(CrN/TiAlN)m-AlSiN-AlSiO open-air stable solar selective coating for concentrated solar thermal power applications

A novel spectrally selective multilayer coating: Cr-(CrN/TiAlN)m-AlSiN-AlSiO on SS316 substrate/tube was deposited via Cathodic Arc Physical Vapor Deposition (CAPVD) technique. The coating exhibited state-of-the-art absorptivity (α = 0.95–0.96) and emissivity (ε = 0.09–0.11). In view of open-air solar thermal application requirements, the coating has been systematically analysed for its thermal, environmental (corrosion) and mechanical stability. The thermal cycling studies carried out at 500 °C in open-air conditions have shown no change in optical properties for about 150 cycles. Further, accelerated thermal aging tests have shown an extrapolated service life of 25 years at 411 °C. In the case of corrosion studies, up to 520 h of exposure to 5% NaCl medium, no considerable change in optical properties was observed. Further, the coatings were well adherent to the substrates/tubes (6 N of critical load) with a considerable hydrophobicity (104° contact angle). The observed results indicate that, Cr-(CrN/TiAlN)2–AlSiN–AlSiO coating may be a good choice for developing receiver tubes used in Concentrated Solar Power (CSP) systems with best solar selective properties and the capability to withstand harsh environments like solar flux variations, thermal shocks in the presence of open-air pollutants, dust and humidity.

Mirror Surface Assessment in Solar Power Applications by 2-D Coded Light

Concentrative mirrors are typically used to provide the reliable thermal source in solar thermal power applications. Their geometrical optical characteristics are of essential importance to the sun-to-electricity conversion efficiency. However, there is a lack of cost-effective approach for measuring these characteristics in field applications. In this article, we propose a color-coded grid pattern-based method to extract optical properties of paraboloidal mirrors. Comparing with the existing techniques, our assessment system only consists of a digital camera, a color-coded grid plane, and a flat mirror with chess-board pattern, and no additional equipments are required. In our system, the image of the grid pattern is captured by the camera through the reflection of the test mirror. Benefiting from the representation of grid positions with colors, the image points can be easily paired with their source points on the grid plane. Applying ray-tracing and reflection principle, the normal vectors of the reflecting points on the test mirror surface can be determined. These normals facilitate to construct the surface model in the form of a second-order polynomial. The gradient descent algorithm is used to minimize the discrepancy between the measured normals and those calculated from a guess model, by which we improve the accuracy of the model parameters and, finally, obtain the optical properties of the test mirror. The accuracy and efficiency of the proposed method are verified by a set of numerical simulations with respect to mirrors with known parameters. Also, for a real concentrative mirror, the proposed method helps to retrieve quantities of interest and show little dependence on mirror position.

Intensive Flux Analysis in Concentrative Solar Power Applications Using Commercial Camera

Solar thermal power application is one of the most promising directions for renewable clean energy development. Typically, a large area of sun radiation needs to be collected, providing an extremely high temperature (intensive energy flux) source. Flux distribution analysis, as a way of verifying the quality of the thermal source and identifying potential hot spots that would potentially damage the attached thermal engine, is of crucial importance. In this paper, we propose an image processing-based method applied via commercial cameras to analyze the intensive flux distribution, targeting especially the difficulties in accurate measurement of flux profile in solar thermal power applications. Rather than linearly mapping the absorbed energy to pixel value, we extract realistic camera responding function with simple steps and use it to build an accurate flux distribution map. We then formulate quantitative parameters, such as peak flux intensity, quadrant balance, and compression ratio, to describe thermal source quality. An on-sun test with a 25-kW dish-Stirling solar system shows good consistency with the obtained parameters. The proposed method can be directly applied to other concentrative solar power industries, such as tower solar power and trough solar power.

Blended morphologies of plasmonic nanofluids for direct absorption applications

Direct absorption solar collectors were introduced to overcome the limitations of conventional surface absorber collectors. The advances in nanotechnology accompanied with phenomenological discoveries at the nanoscale have allowed the appearance of plasmonic nanofluids, which utilize localized surface plasmon resonance phenomenon that multiplies the extinction efficiency of the plasmonic nanoparticle several times at the resonance wavelength. Silver nanoparticles exhibit a high intensity of the localized surface plasmon, which can be fine-tuned within the broadband 350–1200 nm by tailoring their shape, size and aspect ratio. In this paper, we have numerically investigated the effects of silver nanoparticles' morphology on the localized surface plasmon resonance and on the extinction peaks. Numerical results allow determining the effective morphologies at every band of the solar spectrum. Thus, nanofluids composed of blended Ag nano-morphologies were designed, which can expand the absorbance over the entire solar spectrum. By means of the radiative transfer equation, we found that blended plasmonic nanofluids have the potential to raise the efficiency of the direct solar collector to more than 85% at a very low concentration below 0.001 wt%. Utilization of the blended plasmonic nanofluids are not limited to solar thermal and concentrated solar power applications, but also can be extended into the optical filters in PV/thermal applications.

Assembly and attachment methods for extended aluminum fins onto steel tubes for high temperature latent heat storage units

High temperature latent heat storages are being developed for both concentrating solar thermal power applications as well as integration in industrial processes. One of the concepts being developed is an extended finned-tube in a shell-and-tube assembly. This concept can be used at high pressures for steam applications and be built at a large scale. The design of the extended fins allowing for independent thermal expansion of the steel tubes and the aluminum fins with a physically possible assembly has not thus far been optimized. Due to the large fin surfaces necessary for storing large amounts of heat, conventional finned-tube assemblies have to date not been applicable for thermal energy storage systems.Designs using spring steel clips on axial fins have been proven, using conservatively high numbers of clips. In this paper, various fin and tube diameters with spring steel clips as well as other mounting methods are compared. Experiments were conducted to analyze the mechanical strength of the assembly; these are described and the results discussed. In addition, two assembly methods were tested using the same fin geometry and testing environment, allowing for a thermodynamic comparison of the assemblies. The tests have shown that while the steel clips allow for the best heat transfer, the crimping method has a higher bond strength. These results can be used for reducing costs and optimizing design of high temperature latent heat storages.

Techno-economic assessment of solid–gas thermochemical energy storage systems for solar thermal power applications

Thermochemical energy storage (TCES) systems are a promising alternative to conventional molten salt systems for integration with solar thermal power plants. TCES systems can offer high storage densities and high storage temperatures. Thus, they have the potential to increase the efficiency and reduce the levelized cost of electricity of solar thermal power plants. The present study investigates reacting systems with alkaline carbonates and hydroxides and metal oxides performing redox and chemical looping combustion reactions for their near-term deployment potential. 17 solid–gas TCES systems are identified from the initial set of 21 systems for techno-economic assessment. A quantitative assessment methodology based on techno-economic performance indicators (TPIs) is proposed for the comparative analysis. The techno-economic analysis indicates that energy consumption by auxiliary equipment and the cost of the feedstock are the most important factors affecting the system capital cost. Eight TCES systems are identified as competitive with molten salts in the near term, with an estimated capital cost lower than $25 MJ−1: hydroxide looping with Ca(OH)2/CaO, Sr(OH)2/SrO and Ba(OH)2/BaO; carbonate looping with CaCO3/CaO and SrCO3/SrO; redox with BaO2/BaO and chemical looping combustion with Fe3O4/FeO and NiO/Ni.

Zirconia nanoparticles embedded spinel selective absorber coating for high performance in open atmospheric condition

Spectrally selective absorber coatings which have high thermal stable at temperatures ≥ 500°C in open air atmosphere are more beneficial for all types of concentrated solar thermal power (CSP) applications. In order to achieve this, high crystalline zirconia nanoparticles are synthesized via Lyothermal process were embedded into a spinel matrix to form a novel composite solar selective absorber layer (Mn-Cu-Co-Ox-ZrO2). To enhance the absorption substantially, an ink-bottle type mesoporous MgF2 nanoparticles are synthesized via novel route have been deposited further. As a result, a novel tandem absorber system (Mn-Cu-Co-Ox-ZrO2/MgF2) has been developed with α/ε = 0.97/0.17 @500°C. The composite layer comprises of tetragonal phase Zirconia particles which were uniformly distributed in the spinel matrix responsible for high optical performance and high thermal stability. These properties are thoroughly investigated by micro X-ray diffraction (µXRD), X-ray photoelectron spectrometer (XPS) and Elemental mapping by Energy filtered transmission electron microscope (EF-TEM) technique. This novel composite absorber layer developed by a facile route exhibits superior stability up to 700°C ideally in the air makes a promising advancement for the cost-effective power generation by CSP systems.

Techno-economic assessment of thermal energy storage solutions for a 1 MWe CSP-ORC power plant

Organic Rankine Cycle (ORC) have principally been used in the past couple of decades to recover medium grade heat from sources such as geothermal, biomass and the exhaust of a realm of different industrial processes (waste heat recovery). In the past few years, this power generation technology has also been proposed in concentrating solar thermal power applications, aiming to exploit its features in intermediate temperature systems (low water consumption, water-free operation, scalability). These inherent features are best exploited if coupled with thermal energy storage systems to enable good performance in spite of the intermittent energy supply and also to increase the average load factor. To achieve these objectives though, a proper storage system tailored to the heat profile captured by the solar collector and to the characteristics of the power cycle must be identified.This paper discusses the cited design criteria and presents an analysis aimed at identifying the potential storage solutions to be implemented into a Concentrated Solar Power (CSP) plant for electricity generation operating at temperatures between (170°C) and (300°C). The system so developed will be integrated in the 1MWe CSP-ORC facility based on Fresnel technology that is currently under construction at Iresen’s premises in Benguerir, Morocco. Detailed transient models of performance of two-tank and thermocline storage systems are presented. The annual simulations carried out reveal that thermocline solutions are globally more attractive, since they exhibit similar thermal performance but at a much lower (30% lower) cost.

LIQUID LEAD-BISMUTH EUTECTIC AS A COOLANT IN GENERATION IV NUCLEAR REACTORS AND IN HIGH TEMPERATURE SOLAR CONCENTRATOR APPLICATIONS: CHARACTERISTICS, CHALLENGES, ISSUES

Heavy liquid metals have found a wide range of application in energy conversion systems, due to their beneficial thermal properties, especially their low melting points and their capability of operating at higher temperatures without boiling. In addition, the neutronic properties of various liquid metals make them attractive for fusion as well as in Generation IV nuclear reactors. Lately, concentrated solar power (CSP) systems have developed an interest in this technology, calling for temperatures up to 800 o C. The main challenge in realizing engineering scale units is to find proper structural materials that can withstand the corrosion and provide mechanical strength at operation conditions. Lead-Bismuth Eutectic (LBE) is one of the main candidate coolants for liquid metal cooled reactors and solar thermal power applications due to its physical properties such as good thermal conduction, low thermal expansion and melting point, non-violent reactivity to water and low neutron absorption. However, the key limiting factor for LBE usage is the fact of its high corrosiveness to steels and other structural materials. In this work, the results of our systematic materials study in liquid LBE and its alternatives are presented. Various potential structural materials were exposed to LBE, Rose’s metal (Pb-Bi-Sn) and Pb-Bi-Zn eutectic, in static corrosion tests. Post corrosion characterization was conducted by micro-structural analysis (SEM/EDS, X-ray diffraction, Raman spectroscopy) and preferential corrosion mechanisms were evaluated.

Design and fabrication of spectrally selective TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber for high-temperature solar thermal power applications

A new nanostructured TiAlC/TiAlCN/TiAlSiCN/TiAlSiCO/TiAlSiO tandem absorber has been designed for high-temperature solar thermal power applications. The first three layers in this tandem act as an absorbing layer, whereas, TiAlSiCO and TiAlSiO act as semi-transparent and anti-reflecting layers. The tandem absorber was deposited on stainless steel substrates using a four-cathode reactive direct current unbalanced magnetron sputtering system. The composition and thicknesses of the individual component layers have been optimized by adjusting the reactive flow rate of C2H2, N2, O2, and also Al, Ti and Si target power densities to achieve high absorptance (0.961) and low emittance (0.07 at 82°C). The reflectance data showed that the absorptance increases gradually with shift of reflectance minimum to higher wavelengths from first layer to last layer (i.e., TiAlC to TiAlSiO). The thickness of optimized tandem absorber was calculated from the cross-sectional field-emission scanning electron microscopy images and confirmed using transmission electron microscopy. The performance evaluation of the tandem absorber has been evaluated by heating it in air and vacuum under cycling conditions at different temperatures. These results showed that the tandem absorber was stable up to 325°C in air for 400h and up to 650°C in vacuum for 100h, thus demonstrating its suitability for high-temperature solar thermal power generation applications.

LIQUID LEAD-BISMUTH EUTECTIC AS A COOLANT IN GENERATION IV NUCLEAR REACTORS AND IN HIGH TEMPERATURE SOLAR CONCENTRATOR APPLICATIONS: CHARACTERISTICS, CHALLENGES, ISSUES

Heavy liquid metals have found a wide range of application in energy conversion systems, due to their beneficial thermal properties, especially their low melting points and their capability of operating at higher temperatures without boiling. In addition, the neutronic properties of various liquid metals make them attractive for fusion as well as in Generation IV nuclear reactors. Lately, concentrated solar power (CSP) systems have developed an interest in this technology, calling for temperatures up to 800 oC. The main challenge in realizing engineering scale units is to find proper structural materials that can withstand the corrosion and provide mechanical strength at operation conditions. Lead-Bismuth Eutectic (LBE) is one of the main candidate coolants for liquid metal cooled reactors and solar thermal power applications due to its physical properties such as good thermal conduction, low thermal expansion and melting point, non-violent reactivity to water and low neutron absorption. However, the key limiting factor for LBE usage is the fact of its high corrosiveness to steels and other structural materials. In this work, the results of our systematic materials study in liquid LBE and its alternatives are presented. Various potential structural materials were exposed to LBE, Rose’s metal (Pb-Bi-Sn) and Pb-Bi-Zn eutectic, in static corrosion tests. Post corrosion characterization was conducted by micro-structural analysis (SEM/EDS, X-ray diffraction, Raman spectroscopy) and preferential corrosion mechanisms were evaluated.

Growth, characterization and performance evaluation of Ti/AlTiN/AlTiON/AlTiO high temperature spectrally selective coatings for solar thermal power applications

We describe the growth, characterization and performance evaluation of a multilayer solar selective coating useful for solar thermal power generation. The solar selective coating of the present work consists of Ti/chrome interlayer, two absorber layers of AlTiN and AlTiON, and an anti-reflection layer of AlTiO. All the layers have been deposited using reactive pulsed direct current sputtering of Ti and Al targets in Ar+N2, Ar+N2+O2 and Ar+O2 plasmas, respectively. A large number of analytical tools have been used to characterize the structural and optical properties of the absorber coating. The optimized coating exhibited an absorptance of 0.930 and an emittance of 0.16–0.17 on stainless steel substrates and an absorptance of 0.933 and an emittance of 0.07 on copper substrates. The absorber coating displayed improved adhesion, UV stability, corrosion resistance and thermal stability in air and vacuum up to 350 and 450°C, respectively under cyclic heating condition for more than 1000h.

Potential of Concentrating Solar Power in Canada

In this paper, results of an analysis to assess the potential of concentrating solar thermal power applications in Canada are presented. First, a direct normal solar resource (DNI) resource map for Canada is introduced. This map indicates the locations where the DNI is the highest in Canada and is derived from the most recent Perez's SUNY satellite-based solar resource model Version number 3. Second, the methodology and results of a GIS analysis to identify the locations of the most suitable lands for concentrating solar thermal power (CSP) applications in Canada are discussed. The total areas of the CSP-suitable lands are presented in a tabulated and a map formats for each of the Canadian provinces where there is a maximum DNI solar resource. Third and finally, results of a technical economical analysis for two CSP system designs are discussed. The two CSP systems considered include parabolic trough with synthetic oil heat transfer fluid with and without storage, molten salt power tower with and without storage.

Performance and Thermal Stability of a Polyaromatic Hydrocarbon in a Simulated Concentrating Solar Power Loop

Because polyaromatic hydrocarbons show high thermal stability, an example of these compounds, phenylnaphthalene, was tested for solar thermal-power applications. Although static thermal tests showed promising results for 1-phenylnaphthalene, loop testing at temperatures to 450 ℃ indicated that the fluid isomerized and degraded at a slow rate. In a loop with a temperature high enough to drive the isomerization, the higher melting point byproducts tended to condense onto cooler surfaces. This would indicate that the internal channels of cooler components of trough solar electric generating systems, such as the waste heat rejection exchanger, may become coated or clogged affecting loop performance. Thus, pure 1-phenylnaphthalene, without addition of stabilizers, does not appear to be a fluid that would have a sufficiently long lifetime (years to decades) to be used in a loop at temperatures significantly greater than the current 400 ℃ maximum for organic fluids. Similar degradation pathways may occur with other organic materials. The performance of a concentrating solar loop using high temperature fluids was modeled based on the National Renewable Laboratory Solar Advisory Model. It was determined that a solar-to-electricity efficiency of up to 30% and a capacity factor of 60% could be achieved using a high efficiency collector and 12 h thermal energy storage when run at a field outlet temperature of 550 ℃.