Concentrating Solar Thermal Technologies Research Articles

Socio‐economic impact of solar cooking technologies on community kitchens under different climate conditions: A review

AbstractResidential cooking with non‐renewable energy sources, such as firewood, charcoal, natural gas, participate in the emission of more than a gigaton of CO2 per year, which represents 2% of the global CO2 emissions. Additionally, toxic particles including sulfur dioxide, carbon monoxide, and mercury are released leading to elevated levels of indoor air pollution, and adversely affecting the health of the inhabitants. The residential sector's non‐renewable energy cooking devices also pose significant problems, consuming approximately 30%–40% of global energy usage, with over 80% dedicated to cooking applications. To mitigate the negative impacts of traditional cooking on health and the environment, various renewable energy‐based cooking technologies have been developed recently. The primary contributions of our paper are to: (a) present a comprehensive review of concentrated solar thermal cooking technologies, assessing their social, economic, and environmental impact across different climatic zones in developing countries like India; (b) classify and compare different solar cooking technologies, highlighting their advantages and limitations in various scenarios; (c) evaluate the energy efficiency of diverse solar cooking technologies; (d) analyze the impact of solar cookers on communities in developing countries; and (e) identify the challenges and future directions for solar cooker technologies, particularly in solar community kitchens. Our novel findings demonstrate that using solar cooking devices can reduce energy consumption by up to 56% in Indian schools. Moreover, the payback period ranges from 3 to 6 years, contingent on the technology's cost, climatic conditions, and available subsidies. Consequently, significant positive impacts on society, the economy, and the environment are observed when traditional cooking devices are replaced by solar cooking devices. This study provides a unique and thorough analysis, contributing to the growing body of knowledge on sustainable cooking solutions and their potential to transform energy consumption patterns in developing regions.

Recent Advancements in High-Temperature Solar Particle Receivers for Industrial Decarbonization

Concentrated solar thermal (CST) systems are pivotal in the pursuit of renewable energy solutions to meet emissions reduction targets. They play a vital role in addressing the negative impacts of energy-intensive industrial processes, such as the high-temperature calcination step in the alumina Bayer process, requiring temperatures of approximately 1000 °C. However, achieving such high temperatures poses challenges, as radiative losses increase significantly with temperature. Current commercially available CST technologies, employing heat transfer mediums like molten salts, are constrained to temperatures below 600 °C. The emerging focus on sand-like ceramic particles, either as standalone materials or in suspension within an air stream, as heat transfer mediums signifies a promising avenue in the development of high-temperature receiver-based CST technologies. These particle-laden suspension flow receiver systems have the potential to reach operating temperatures exceeding 1000 °C. This review paper provides a comprehensive overview of CST technologies, with a primary focus on high-temperature particle receivers. It sheds light on the existing challenges within the CST state-of-the-art technologies and introduces the concept of refractory-lined particle receivers. This paper also underscores the significance of transient-based thermal analysis for high-temperature particle receivers and highlights the necessity of such analyses to guide their practical implementation. By addressing these critical aspects, this review paper contributes to the advancement of CST technologies, emphasizing their role in achieving sustainable, high-temperature heat for emission reduction objectives.

Effect of geometric variation and solar flux distribution on performance enhancement of absorber tube thermal characteristics for compound parabolic collectors

A compound parabolic collector (CPC) is a concentrated solar thermal technology widely used for thermal energy storage and electricity generation. Usage of proficient absorber tube configuration improves its thermal efficiency and the present study is an attempt to numerically evaluate the feasibility of employing elliptical absorber tube design in CPCs. Initially, the thermal characteristics of the conventional circular and proposed elliptical absorber tube configurations were evaluated for an ideal condition, taking into account the solar radiation effect from Monte-Carlo ray-tracing analysis. The effect of governing factors that include fluid flow rate (0.015–0.05 kg/min), heat flux (1175–1200 W/m2), and inclination angle (3°) were analyzed for optimum condition identification delivering maximum efficiency. Further analysis was focused on evaluating the thermal loss influence with face-split and top-wall insulation conditions. Results indicated that the elliptical configuration outperformed the circular tube with an increment in the maximum temperature rise by 42.2%, 33.4%, and 27.7% for simple, face-split, and face-split top-wall insulated conditions along with better stability over the local hydrodynamic changes. Face-split analysis contributed to better realistic results over constant heat flux and it was inferred that the inclined face-split elliptical configuration exhibited maximum thermal efficiency with higher temperature rise and nominal pressure drop characteristics.

Photothermal conversion potential of full-band solar spectrum based on beam splitting technology in concentrated solar thermal utilization

It is still a great challenge for the concentrated solar thermal (CST) technology to promote the utmost out of solar energy further because the CST's receiver generally discards the longer wavelength spectra to prevent radiative heat loss due to high temperatures. Spectrum splitting is a well-known technology generally used in multi-energy cogeneration devices, such as Photovoltaic/thermal (PV/T) systems, aiming to improve photoelectrical efficiency. In this study, the solar spectrum splitting technology is employed in the CST system to take full advantage of solar radiation through enhanced absorptions and conversions of piecewise solar radiation. The exergy efficiency of a beam-splitting photothermal (BSPT) system is used to evaluate its effectiveness. Here, the mechanisms of beam splitting under different splitting wavelengths (λsp) and concentration ratios (Cr) are investigated. Furthermore, the influence of the split number is evaluated, and the performance of the dual-segment BSPT system is compared with traditional photothermal systems with real and assumed coatings. It shows that beam splitting can play an excellent role in improving exergy performance. The exergy efficiency improvement ratio of the BSPT stabilizes at around 9% when λsp is 1300 nm, and the proposed dual-segment BSPT system can maintain an excellent performance even under off-design working conditions.

Hydrothermal liquefaction of wood wastes in a concentrating solar plant: A techno-economic analysis

This paper reports the simulation and techno-economic analysis of a hydrothermal liquefaction (HTL) solar plant for bio-oil production from forestry residues. The HTL solar plant is designed to process 1 ton of biomass daily. The heat required by the HTL process is provided by a parabolic trough solar collector field and a natural gas boiler to allow continuous operation. The annual simulation of the thermal performance of the plant is carried out using the TRNSYS software. The considered location is Temixco, México, and a Typical Meteorological year is used to characterize the site's climate. The bio-oil yield is calculated by a kinetic model that considers the biomass's composition and the slurry's temperature. An economic model is implemented that includes the costs involved and helps determine the bio-oils minimum selling price for the system's financial viability. The obtained yields of biogas, bio-oil, biochar, and organic aqueous phase are 13.3, 29.4, 13.6, and 42.9 wt%, respectively. The minimum fuel sale price (MFSP) for the annual production obtained is estimated between $1.27 and USD 1.55/kg. Eliminating transportation costs, the value of MFSP was assessed in a range of $0.89 to USD 1.09/kg. The results show that integrating concentrated solar thermal technology for processing lignocellulosic waste from the sawmill industry may be an attractive, viable, and sustainable option for producing biofuels, with potential application in countries with high availability of forest biomass, such as Mexico.

Cavity-shaped direct solar steam generator employing conical helical tube for high-temperature application: Model development, experimental testing and numerical analysis

Concentrating solar thermal technologies are drawing more attention since it can substantially contribute to a carbon-neutral society. The solar receivers are essential in this technology to convert solar energy efficiently into thermal energy. Moreover, high-temperature steam generation is the promising application for concentrated solar power plants or industirial processes. Therefore, the direct solar steam generator has been gaining more attention due to its advantages of low operation and maintenance costs. Most solar steam generator designs consist of a tube with helical configuration because of its high heat exchange performance and compactness. However, only few studies address solar steam generators with conical helical tubes. Thus, both experimental and simulation data of this design are scarce. This paper shows the successful development and experimental testing of a solar steam generator with a conical helical tube. The experimental results proved that the developed solar steam generator can produce high-temperature steam of 600 °C at an inlet pressure and mass flow rate of 150–200 kPa and 2.5 kg/h, respectively. The overall calculated energy efficiency (thermal and optical efficiency) was 60–62%. In addition, a coupled 1D-3D numerical model was implemented to analyze the solar steam generator’s performance. The model consists of a 3D cavity heat transfer model and a 1D two-phase fluid flow model. The numerical analysis demonstrated the ideal generator’s performance (energy efficiency of 68–69%) and the great impact of convection in the heat losses (50% of the total energy losses). Although more research of the convection is required, the presented results provide a basis for designing further, upscaled solar steam generators employing conical helical tubes.

Techno-economic and exergo-economic evaluation of a novel solar integrated waste-to-energy power plant

The content of municipal solid waste generation is increasing due to the industrial and population growth. Energy generation from municipal solid waste is one of the efficient and promising method to dispose waste in a sustainable manner, while reducing the fossil fuel energy limitations. However, conventional waste-to-energy plants have less thermal efficiency due to the higher moisture content that lowers its heating value. The solar thermal integration is one of the proposed solutions to enhance the steam inlet temperature in the power generation system that will further increase the plant performance. In this study, an innovative solar integrated municipal solid waste incineration plant is proposed to advance the waste-to-energy and concentrated solar power thermal energy technologies. The system integration is carried out utilizing the useful solar heat harvested in the heliostat tower receiver system by transferring heat to the working steam of the incineration plant in the heat exchanger and enhance the turbine inlet temperature and the system’s performance considerably. Based on 300 t/d incineration facility, proposed system is investigated exergo-economically by varying certain influential parameters using engineering equation solver and performance has been compared with the conventional reference plant. The system is integrated with high-temperature Phase Change Materials, which able to store thermal energy enough for the light-time system operation. The results attribute that the network output of the proposed integrated facility has substantial improved (almost 12.61 %) but with the penalty of increase in the exergy destruction cost rate. In addition, levelized cost of electricity of the proposed plant is 13.9 % less than the conventional one and it decreases with the rise of steam temperature. Energy efficiency of the proposed plant improves to approximately 36.34 % as direct normal irradiation increases from 650 W/m2 to 900 W/m2. In addition, Incineration boiler is the major source of exergy destruction (almost 50 %) with 175.2 $/hr exergy destruction cost.

Microstructure and optical properties of W/W‐WxN/WOx multilayer metal‐dielectric solar selective absorbing coating

The solar spectrum selective absorption coating (SSAC), as a core component of the concentrated solar power (CSP) system, faces increasingly stringent performance criteria as concentrated solar thermal power production technology advances and becomes more industrialized. Due to atom interdiffusion at the layer border, the current traditional composition and structure of progressive absorption coatings suffer from coating property loss at high temperatures. In this work, W/W‐WxN/WOx SSACs were prepared utilizing a medium frequency reactive magnetron sputtering approach with transition metal nitride as the absorption layer and WOx film with superior intrinsic absorption as the antireflection layer. The optical properties, structural composition, and thermal stability of the coatings were evaluated and characterized using field emission scanning electron microscopy (FE‐SEM), X‐ray diffractometer (XRD), ultraviolet–visible spectrophotometer (UV‐vis), X‐ray photoelectron spectrometer (XPS), and thermal emission meter, and the coatings' failure model and failure mechanism were established and explained. The experimental results demonstrated that the coating had outstanding spectrally selective absorption performance with an absorbance of 0.90 and thermal emissivity of 0.08 under air circumstances, as well as high thermal stability at 250°C and 20 h.

Multi-criteria decision making for different concentrated solar thermal power technologies

Solar thermal power technologies are promising renewable energy sources that could replace the conventional fossil fuel power plants. Parabolic trough collector (PTC), linear Fresnel reflector (LFR), solar power tower (SPT), and Solar power dish (SPD) are the commercial concentrated solar thermal power technologies. Technical, economical, and environmental aspects are varied from one technology to another. Deciding the best solar thermal power technology is quite important for the commercial applications. In order to decide the best technology, based on 22 criterions including the technical (9), economical (2), and environmental (11) aspects, different multi-criteria decision making (MCDM) models were applied. The main parameters of the MCDM model that determine the rating of alternatives include the choice of the method of normalization of the matrix of decisions, the choice of the method for evaluating the weights of the criteria and the choice of the method of aggregation of attributes when determining the indicator of the effectiveness of alternatives. Three different groups of MCDM methods are defined as a method for aggregating attributes in determining the performance indicator of alternatives: based on a weighted sum approach (WSM, WPM, WAPRAS), based on the concept of distance or distance from the desired object (TOPSIS, GRA, VIKOR), and based on the approach of aggregating local ratings based on setting the preference function (PROMETHEE-II). According to the results of all models, alternative A4 that represents the solar power dish technology is the best selection among the different solar technologies. A4 is winner (first rank I) for about 65% of considered cases followed by A3 that represents solar power tower technology. A3 is winner (first rank I) for about 35% of considered cases.

Evaluating the Market Potential of Concentrated Solar Thermal Technology for Different Applications in the MENA Region

Abstract Missing financial and regulatory frameworks lead to low development and stagnating costs of concentrated solar thermal technology. Nevertheless, in locations with high direct normal irradiance (DNI) such as the Middle East and Northern Africa (MENA) region, the technology could become competitive, being promised a learning rate of 10–20%, and boost local economies. This study aims to identify potential business cases and evaluate the increased technology's investment likelihood in the region, focusing on Egypt. A thorough market assessment on the structure, regulatory framework, demand, and potential revenues was conducted for the power and process heating sector. A SWOT analysis was performed considering the local context and competing technologies. Egypt was shown to offer local manufacturing potential, regulatory framework, and renewable energy (RE) strategies, facilitating the technology's deployment. Moreover, the market is already open for private investment and selected international funds are directed toward CSP development. High initial technology cost, subsidized fuel and electricity prices for industry, alongside lack of long-term financial incentives and awareness of potential long-term benefits for the economy were identified as the most significant threats. High solar heat demand for industrial processes and large potential for concentrated solar heat (CSH) application were identified. Yet, the market is decentralized and the processes are very diverse, moreover retrofitting may pose risks alongside the high upfront investment and additional land costs, which makes concentrated solar heat applications less attractive for the Egyptian industrial sector. Hence, for concentrated solar technology deployment, financial incentives and a regulatory framework specifically directed toward the technology would be necessary.

Techno‐economic analysis of a hybrid solar‐geothermal power plant integrated with a desalination system

This paper proposes the use of a hybrid 5 MW power generation system combining concentrated solar thermal and solar photovoltaic technology where the efficiency of the power block is increased by taking advantage of hot water from a low-temperature geothermal source. Aiming at a case study for Winton in Queensland the pertinent meteorological data are used for our simulations. In addition, the paper analyzes the feasibility of including a thermal desalination technology that uses the waste heat from the power block for producing clean water from wastewater. Our design replaces the traditional dry cooling system with a water-cooled heat exchanger to remove the waste heat from the power block. Finally, this work explores the ratio of concentrated solar thermal and photovoltaic electricity production that optimizes the levelized cost of electricity and water production. the results indicate that the incorporation of the desalination system does not produce a significant increase in this value, and the optimal ratio of electricity production is obtained when the photovoltaic system contributes to 27.5% of the total electricity generation. Our water production cost can be as low as 40 ₵/m3 while for the combined system our minimum levelized cost of electricity figures out at 12.4 ₵/kWh to generate the base load with thermal storage.

Improving the performance of calcium looping for solar thermochemical energy storage and CO2 capture

Concentrating solar thermal (CST) technologies for power production can play a major role in the future portfolio of renewable energies. Limestone calcination/carbonation (Calcium Looping (CaL)), is an appealing reaction whose integration with CST is widely investigated for thermochemical energy storage (TCES) and carbon capture and storage/utilization (CCSU). Experimental data under realistic CST conditions/reactors currently lacks, since most of the experimental activities have been performed in thermogravimetric analyzers. In this study, CaL-CST integration was investigated in a lab-scale directly irradiated fluidized bed reactor, able to mimic the operating conditions required for industrial implementation of the technology. Three different techniques to improve the performance of CaL-CST for TCES and CCSU were investigated: i) lowering of calcination temperature; ii) precalcination; iii) use of dolomite instead of limestone. Experimental results revealed that all the strategies moderately improve system performance. After 20 cycles, depending on the technique applied, the mean carbonation degree ranges within 28.1–37.1% (TCES) and 15.3–18.7% (CCSU) with limestone, and values 61.5% (TCES) and 36.7% (CCSU) with dolomite. Figures of energy storage density are less sensitive to the different techniques, as pay for the lower calcination temperature (limestone), or for the presence of an inert MgO fraction (dolomite). Corresponding values range within 941–1065 MJ m−3 (TCES) and 777–872 MJ m−3 (CCSU), for loose-packed conditions. N2-physisorption analyses revealed that the increased reactivity arises from better microstructural properties in terms of specific surface. Optimal choice among the different strategies should consider the intrinsic peculiarities of each investigated technique.

A novel fluidized bed “thermochemical battery” for energy storage in concentrated solar thermal technologies

Thermochemical energy storage is gaining widespread consideration to increase energy dispatchability in concentrating solar thermal power plants. Accordingly, excess solar energy input drives an endothermic reaction, accomplishing high energy densities and virtually unlimited storage times. As gas–solid reactions are usually involved, multiphase reactor design is essential for the success of this technology. A novel concept of directly-irradiated fluidized bed autothermal reactor is investigated for applications in concentrated solar thermal technologies. The device can be operated as a rechargeable battery, alternating a charge phase, during which solar energy is collected and stored by an endothermal gas–solid reaction, and a discharge phase, during which the stored chemical energy is released by the reverse exothermic reaction. The autothermal operation, during the charge process, consists in the recovery of the sensible heat of the reaction products to preheat the reactants by means of an internal double-pipe countercurrent heat exchanger. This operation allows to increase the overall efficiency, reducing the required solar energy input. A compartmental model to simulate the operation of the thermochemical battery is developed and closed with constitutive equations and parameters obtained by previous experimental studies on lab-scale test facilities. Limestone calcination/carbonation has been considered as model reversible reaction. Both the charge and the discharge steps were assessed investigating the effect of the design and operational variables. For the charge operation, an optimal temperature was found around 900 °C with thermal efficiencies close to 90%. For the discharge operation, thermal efficiency was found to depend almost solely on the reactor temperature, reaching values as high as 80%, whereas the gas flowrate can be set independently. The upper limit for reaction temperature is set to the reaction equilibrium condition corresponding to the inlet concentration of carbon dioxide. The obtained results represent the basis for the realization of a new prototype, that will serve for the complete proof-of-concept of the directly-irradiated fluidized bed autothermal reactor.

Techno-economic assessment of concentrated solar thermal power generation and potential barriers in its deployment in Pakistan.

In this study, the current situation and future prospects of cleaner energy production through concentrated solar power (CSP) plants in Pakistan are analyzed. The assessment of required resources, evaluation of techno-economic feasibility, analysis of existing policy framework, and potential barriers in adopting the concentrated solar thermal technologies in Pakistan are presented. Six potential sites for installing solar thermal power plants are selected on the basis of solar resource assessment, land availability, and feasible infrastructure. A case study of a 100 MW parabolic trough collector (PTC) solar thermal power plant is simulated for these potential sites by using the System Advisor Model (SAM) software. The optimization of solar field size and thermal energy storage is performed to obtain the minimum Levelized cost of electricity (LCOE) for each potential site. Results indicate that the LCOE under the optimized configuration of the PTC solar thermal power plant in Pishin and Quetta can be minimized to 14.7 cents/kWh and 15.3 cents/kWh, respectively. Although the LCOE is the lowest in Pishin, the better availability of the desired infrastructure including transmission lines, water facility, and grid stations in Quetta makes it a more favorable site for installing the PTC solar thermal power plant.Furthermore, a discussion of government policies, along with major barriers (financial, political, infrastructural, technical, and social) that hinder the development of concentrated solar thermal technologies in Pakistan, is presented in detail. In order to overcome these barriers, several recommendations, including the introduction of financial incentives to investors, promoting private stakeholders, the establishment of research facilities in the country, and educating the general population regarding the benefits of clean energy are also outlined.

Comprehensive Review of Line-Focus Concentrating Solar Thermal Technologies: Parabolic Trough Collector (PTC) vs Linear Fresnel Reflector (LFR)

In the present review, parabolic trough collector (PTC) and linear Fresnel reflector (LFR) are comprehensively and comparatively reviewed in terms of historical background, technological features, recent advancement, economic analysis and application areas. It is found that although PTC and LFR are both classified as mainstream line-focus concentrating solar thermal (CST) technologies, they are now standing at different stages of development and facing their individual opportunities and challenges. For PTC, the development is commercially mature with steady and reliable performance; therefore, extension of application is the main future demand. For LFR, the development is still in rapid progress to commercial maturity, yet indicating very promising potentials with high flexibility in novel designs and remarkable reduction in capital and operational costs. The question, which has to be answered in order to estimate the future perspectives of these two line-focus CST technologies, becomes which of these characteristics carries more weight or how to reach an optimal trade-off between them.

Directly irradiated fluidized bed reactor for thermochemical energy storage and solar fuels production

The path toward a greener economy is leading the world energy scenario to an ever-increasing use of renewable energy sources. Concentrating Solar Thermal (CST) systems are typically based on technologies in which solar energy, concentrated by means of optical sun tracking mirrors, is exploited to drive power cycles or sustain chemical processes. Integration of CST technologies with relatively inexpensive energy storage systems decouples the collection of solar radiation from its use, and thus greatly increases the dispatchability of thermal energy production. Huge research efforts are currently devoted to the study of ThermoChemical Energy Storage (TCES) systems, in which solar energy is used to perform endothermal chemical reactions featuring large latent heat, so as to store solar energy in the noble and stable form of chemical bonds and/or produce solar fuels. Since most TCES processes involve gas/solid chemical reactions, multiphase chemical reactors own a key role for the success of the TCES technology. In this study, a novel batch lab-scale fluidized bed reactor for TCES of concentrated solar power and solar fuels production was designed. The reactor targets at maximizing the collection of solar energy, withstanding the highly-concentrated flux typical of high-temperature CST applications and ensuring uniform temperature distribution of the reactive materials. An experimental campaign consisting in hydrodynamical and thermal characterization of the system under inert conditions was performed. Moreover, reactive tests aimed at TCES of solar energy were performed using limestone calcination/carbonation as model reversible reaction. Heating of the system was performed by means of a simulator of concentrated solar energy made of a 7 kWe short-arc Xe lamp coupled with an elliptical reflector. The hydrodynamical characterization disclosed the main features of the reactor and the possibility of establishing different regimes of operation. Thermal characterization revealed that reactor can be safely operated at temperature of over 1000 °C. Reactive tests proved the feasibility and reliability of the designed reactor toward chemical reactions aimed at TCES of concentrated solar energy and encourage future studies toward solar fuels production.

Review on the development of high temperature phase change material composites for solar thermal energy storage

The development of cost-effective and reliable high temperature phase change materials (HTPCMs) for solar thermal energy storage is an important step in the future application of concentrated solar thermal technologies. Inorganic eutectic salts relying on their advantages such as low cost, high melting temperatures and latent heats of fusion, are promising candidates for HTPCMs. However, both the thermal conductivity and thermal stability of the inorganic salts are relatively low. In addition, they have corrosion issues with containment materials at high temperatures. All of these issues have been problematic for their use in this application. A potential solution to these issues is the development of HTPCM composites, where high temperature molten salts as PCMs are encapsulated by supporting materials to achieve improved corrosion resistance with containment materials and enhanced thermal conductivity and thermal stability. This paper reviews current trends and recent developments in the preparation and classification of high temperature (>300 °C) PCM composites. The effect of developed HTPCM composites on their melting point, latent heat of fusion, thermal stability and heat transfer performance are also discussed in the context of this review.

Influence of gaseous pollutants and their synergistic effects on the aging of reflector materials for concentrating solar thermal technologies

Concentrating solar thermal technologies have experienced an important boost in the last few years. Besides the production of electricity, they are particularly useful for the supply of industrial process heat. The industrial atmospheres affecting these solar plants typically contain gaseous pollutants that are likely to promote corrosion on the components of the solar facility, specifically solar reflectors, thereby compromising their optimal performance and the overall system efficiency. Seven accelerated aging tests were designed to study the effects of three air pollutants (H2S, SO2 and NO2) on the durability of two commercially available reflector types (silvered-glass and aluminum), both in single-gas tests and in multicomponent gas mixtures. Additionally, the same material types were exposed outdoors at five representative polluted sites, including industrial, urban and coastal environments. Reflectance and optical microscope monitoring corroborated which degree of corrosion was developed on a specific type of reflector in the different tests with gaseous pollutants, as well as the synergistic effects of gas combinations. For example, tests with sulfur were harmful for silvered-glass reflectors (up to a total of 16 corrosion spots), whereas aluminum was particularly affected by tests with NO2 (numerous micro spots of around 50 μm size). Moreover, comparisons of the corrosion patterns found in accelerated-aging and outdoor exposures revealed which laboratory test reproduced the different real polluted atmospheres in the most realistic way, which is the main goal of this work. For instance, the degradation found at Site 2 was reproduced by Test NO2+SO2, with an acceleration factor of 27.

Novel solid–solid phase-change cascade systems for high-temperature thermal energy storage

In this work, we investigate novel solid–solid phase-change cascade systems based on mixtures of lithium and sodium sulfates. Solid–solid phase-change materials (PCMs) can be coupled with concentrated solar power technologies. They present several advantages over solid–liquid PCMs including lower thermal expansion, lower or no corrosiveness, and no need for encapsulation. In solid–solid PCMs, the energy is stored during crystal structure transitions. Specifically, lithium sulfate undergoes a crystal structure transition (monoclinic to cubic) at 576 °C, which is a suitable temperature for concentrated solar thermal technologies. Due to the high cost of lithium sulfate, we evaluated the potential of mixing lithium with sodium sulfate to create solid–solid cascaded PCM systems to provide higher thermal storage densities. We used differential scanning calorimetry, high-temperature in situ X-ray diffraction and thermogravimetric analysis to evaluate the phase-transition temperature, phase-change enthalpy, specific heat capacity, crystalline phase composition and thermal expansion. The obtained values for heat capacity and enthalpies of phase transitions showed good agreement with available thermodynamic databases. Therefore, further calculations of thermodynamic properties of each mixture in the system were performed for designing cascaded latent thermal energy storage system. From the PCM mixtures studied, NaLiSO4 shows the greatest stability under ambient conditions. A mixture of 59.17% NaLiSO4 and 40.83% Li2SO4 allows an optimum charge of both PCMs for power cycles such as supercritical CO2. Economic assessment revealed that this cascade system has an estimated cost of $50.2 kWhth−1.

Durability Studies of Solar Reflectors Used in Concentrating Solar Thermal Technologies under Corrosive Sulfurous Atmospheres

Concentrating solar thermal (CST) technologies are a feasible and promising option to tackle worldwide energy problems. These solar facilities are sometimes located near industrial sites, where their main components—including concentrating solar reflectors—are prone to significant degradation caused by corrosive agents, especially in the presence of sulfurous atmospheres such as H2S and SO2. This paper focuses on analyzing the influence of sulfurous atmospheres on the durability of reflector materials used in CST technologies. To this end, accelerated aging tests were performed on the most commonly used materials found in solar reflectors (i.e., thick silvered glass and aluminum-based reflectors) by applying the same concentrations of H2S and SO2 under the same conditions of temperature and relative humidity. The results showed that the solar reflectors based on a silver reflective layer are significantly corroded by H2S atmospheres—several corrosion defects were found in the samples tested. However, those based on aluminum were barely affected by sulfurous environments in the conditions tested. Nonetheless, the study suggests that both reflector types are suitable candidates, depending on the purpose of the CST technology in question and the specific environmental conditions.