Concentrated Solar Thermal Energy Research Articles

Methanol-based thermochemical energy storage (TCES) for district heating networks

With increasing volatility in natural gas markets and the need for residential heat, research for alternative thermal systems based on green hydrogen-based fuels is necessary. Massive implementation of hydrogen in the current fleet presents a challenge for the decarbonisation of conventional thermal processes. This paper presents the integration of green methanol from a seasonal thermochemical energy storage system (TCES) coupled with district heating networks (DHN). It allows for a solar-based storage and low-temperature heat generation from the exothermic discharge reaction. The system uses concentrated solar thermal energy to decompose methanol into syngas at moderate temperatures (<315 °C), reducing GHG emissions from combustion to meet residential heat. Its potential is assessed through an analysis of 458 rural municipalities in Spain, achieving a substitution of 3.1 % of the natural gas demand. The system allows the production of green fuels from syngas using an open-loop approach, offering new market pathways in primary sector. In a closed-loop configuration, roundtrip efficiencies exceeding 60 % and chemical conversion efficiencies exceeding 70 % are reached, resulting in a global efficiency of 12 % for the DHN and methanol-TCES. The results show a levelized cost of stored energy highly competitive with other storage systems (<200€/MWh), given its simplicity.

Heat Transfer Performance Tests of a Circular-Fin Sodium-to-Air Heat Exchanger for Sodium-Cooled Fast Reactors

Shell and tube-type crossflow heat exchangers with circular fins are widely used in various industries, including nuclear power plants. This study focuses on the sodium-to-air heat exchanger, which is one of the key safety features in sodium-cooled fast reactors. Tube alignment inside the heat exchanger is important because it directly determines the performance. Although heat exchangers are generally designed to have staggered tube alignment, inevitable inline-aligned zones exist. Therefore, this paper proposes a hybrid tube alignment modeling approach that considers both staggered and inline tube heat transfer phenomena. The results of the hybrid model calculations are verified and validated with liquid sodium experiments. The hybrid approach to the tube arrangement reduced the temperature deviation between experimental and calculated values to a difference of 4.55% and 7.38% for both sodium and air sides, respectively, while for the heat transfer, the difference was 15.12% and 9.06% for sodium and air sides, respectively. The results of this study can also be used as a basis for the safety evaluation of nuclear reactors and licensing processes for sodium-cooled fast reactors. In addition, this study is limited not only to sodium heat exchangers but also to any serpentine tube arrangement or crossflow heat exchanger under high-temperature systems, such as concentrated solar power and thermal energy storage industries.

Hydrogen Production via Off-Sun Solar-Thermal Supercritical Water Gasification and Membrane Reforming of Piggery Waste

Supercritical water gasification (SCWG) represents an emerging technology for liquid fuel synthesis, offering large potential in significantly improving the efficiency and environmental impact of clean fuel production. Compared to conventional gasification, SCWG proceeds at much lower temperatures, allowing char and tar-free gasification of biomass and for low-quality and high-moisture content biomass to be used. As the thermochemical processes involved in SCWG and steam methane reforming (SMR) are highly endothermic, combining them with concentrated solar power (CSP) and thermal energy storage (TES) could allow the process to be driven solely by renewable energy. As such, this work models an off-sun SCWG/SMR system using novel molten salt, proposed to reach up to 600°C [1], which overcomes the previously limiting molten salt temperature of 550°C. Using an off-sun configuration, it deals with the on-sun configuration’s issues of degraded lifetime and creep-fatigue, allowing for uniform heating and a reduced load on the reactors. The novel technology of an integrated Pd-based membrane reactor, highly selective to H₂, was chosen given its ability to carry out SMR at temperatures in the viable range of new molten salts. The system uses a waste feedstock, piggery waste, to provide the dual benefit of reducing the environmental cost associated with piggery waste’s release of CH4. From the model created in Aspen Plus, a plant output of 7.2 kmolH₂/h (1,135 Nm³/h of H₂), was obtained with a flow rate of 150 kg/h of dry piggery waste, a membrane area of 131.8 m², and a 73% CH4 conversion from the feed.

The techno-economics of transmitting heat at high temperatures in insulated pipes over large distances

This study reports a systematic techno-economic assessment of the cost-optimal transmission for air as the heat transfer fluid at temperatures of up to 1200 °C, at scales of 1 to 1000 MW and at distances of up to 10 km. It employs a steady state heat transfer analysis, with energy balances, to assess the effect of scale, temperature and insulation on the heat losses and efficiency of the thermal transmission system, following by a techno-economic assessment. The sensitivity of the Levelised Cost of Heat, LCOHtr, to variations in thermal scale, operating temperature, distance, refractory and insulation thickness, ratio of the thickness of refractory and insulation, cost of any supplementary heat and lifetime is reported. The results show that LCOHtr decreases with an increase in thermal scale, as expected. The role of insulation is much more complex, since increasing the thickness of thermal barrier increases both cost and efficiency of the transmission, requiring an economic optimum to be determined for each of the various conditions assessed. Parameters are also coupled because a higher cost of supplied energy/ heat justifies the use of more insulation material. For a large GW scale thermal system, we estimate that it is possible to achieve a minimum overall LCOHtr,min of 0.16–0.36 USD/GJ/km of the length of the thermal transmission system, excluding additional location-specific costs such as land-access and local construction costs. These estimated costs are sufficiently attractive to justify ongoing development of systems to transport renewable heat to industry from sources such as concentrated solar thermal energy.

Thermal stability and durability of solar salt-based nanofluids in concentrated solar power thermal energy storage: An approach from the effect of diverse metal alloys corrosion

Concentrated Solar Power (CSP) technology has witnessed substantial growth, with forecasts predicting an increase of 3.4 GW between 2019 and 2024. This expansion necessitates the installation of energy storage systems to meet the growing demand. Solar molten salts, specifically a mixture of 60 % NaNO3 and 40 % KNO3, have emerged as the primary thermal energy storage (TES) medium in commercial CSP plants. However, a significant challenge lies in the corrosive nature of molten salt at high temperatures, which poses limitations in TES applications. The literature has explored a promising solution: reducing corrosion rates by incorporating nanoparticles into molten salts, creating nanofluids. To assess the viability of nanofluids for CSP, it is essential to understand how they perform under working conditions, especially regarding their thermal stability and durability. This study presents further evidence of nanofluid interactions with component materials under static working conditions. Specifically, focus on the impact of corrosion products precipitated during corrosion tests on the physical and thermal properties of Solar Salt-based silica dioxide nanofluids. In this research, nanofluids in contact with stainless steel, nickel‑chromium alloy, and carbon steel were examined before and after subjecting them to a 90-day thermal exposure at 500 °C. These findings provide valuable data on key thermo-physical properties during service, contributing to the design of more precise TES systems and enhancing their overall efficiency and effectiveness.

Techno-environmental and economic analysis of a coal-based power plant integrated with solar field

Limited availability of conventional energy sources and the problems of environmental degradation associated with them compels the need for a supply of new sustainable energy options. Among renewable energy sources, solar thermal energy is the most abundantly available and feasible option for electricity generation. Solar-thermal-only plants have a very high initial investment and, due to the sporadic nature of solar energy, can be operated only during the daytime. This limitation of only solar-thermal plants leads to an innovative idea of combining solar energy with coal-based power plants. This study investigates the hybridization of an existing 660 MW power plant with concentrated solar thermal energy on technical, environmental, and economic criteria under three different replacement options. The results obtained using MATLAB Simulink (R2017a) showed that the cycle efficiency increases from base case cycle efficiency, that is, 41.74% to 44.36%, 47.41%, and 48.72%, respectively, for all three replacement options. The economic analysis showed that the levelized electricity cost (cents/kWh) for all three replacement options is 4.56, 4.69, and 4.82, respectively. The payback period (years) is found as 3.3, 3.7, and 3.9, respectively. The environmental factors such as annual reductions in coal usage and CO2 emissions, and solar contribution are also calculated. The outcomes of this research will help to reduce global warming and climate mitigation.

A preliminary evaluation of a molten metal helical coil solar receiver for heating pressurised air

Heating pressurised air to high temperatures with concentrated solar thermal energy is technically challenging mainly due to the heat transfer properties of the pressurised air and the intermittent nature of the solar energy. To address this challenge, a novel molten metal helical coil (M2HC) solar receiver for heating pressurised air or other gases is presented. This system comprises a cavity and a helical coil, both of which are submerged in a molten bath, e.g. a molten metal, which serves as a heat transfer fluid (HTF) between the submerged cavity and the helical coil. The absorbed concentrated solar thermal heat in the cavity is transferred to the molten bath via convection. Pressurised air is heated within the submerged helical coil, without any contact with the molten bath. The molten bath is agitated via the bubbles of an injected inert gas enabling a high rate of heat transfer between the submerged cavity and the helical coil. The purpose of this paper is to introduce the concept of the M2HC solar receiver and provide a preliminary evaluation to identify its potential benefits and challenges. In doing so, a one-dimensional model of the proposed M2HC solar receiver is developed, predicting the system performance considering gallium (Ga) and argon (Ar) as the HTF and dispersed inert gas into the molten Ga bath, respectively. The heat transfer model of the cavity, gallium bath, Ar bubbles and the helical coil is implemented with the consideration of convective and radiative losses in the cavity. The mixture of Ga and Ar bubbles is considered as one phase and modelled with a one-dimensional drift-flux correlations. A 1-D model has been also considered for the heating of the pressurised air within the coil. The reliability of the model was assessed through comparison with the available relevant experimental data in literature. The model is then employed to perform a sensitivity analysis to the variations in the temperature of the outlet air, length of helical coil and the ratio of the mass flow rates of the injected Ar into the molten bath and the inlet air. The predicted absorption and exergy efficiencies of the proposed M2HC solar receiver are ∼64% and 73%, respectively, at an output temperature of 900 °C and 5% Ar to air mass flow ratio. It has been also found that the variation of Ar to air mass ratio from 0% to 25% decreases the fraction of the absorbed energy that goes to air from 100% to ∼90%. Nonetheless, it increases the convective heat transfer between the molten bath, submerged cavity and the helical coil.

Thermodynamic analysis of a sorption-enhanced gasification process of municipal solid waste, integrated with concentrated solar power and thermal energy storage systems for co-generation of power and hydrogen

A system of coupled CO2 capture and gasification has led to a new concept entitled sorption-enhanced gasification (SEG) which can increase H2 concentration in the syngas composition. This study proposed a novel configuration of the SEG system comprising concentrated solar power and thermal energy storage systems. Calcium looping (CaL) is utilized as the CO2 capture process. Unlike conventional SEG systems in which calcination heat demand is supplied by an oxy-combustion process, this study considers a heliostat field to provide heat for sorbent regeneration. The solar and thermal energy storage systems are simulated dynamically to achieve accurate results. A steam Rankine cycle is also designed to recover the released heat sources through the SEG system. The overall system performance is explored through energy and exergy analyses. Based on the results, the proposed system managed to produce 0.58 kg/s pure hydrogen in addition to 13.96 MW of net electrical power. Meanwhile, CO2 is captured from syngas composition with capturing efficiency of 95%. The energy analysis shows cold gas efficiency and the annual total energy efficiency of 87.76 and 70.74%, respectively. Based on exergy analysis results, the carbonator reactor exhibits the highest permeance compared to the gasifier and calciner reactors, with an exergy efficiency of 88.74%. Parametric study results show an increase in the cold gas efficiency, hydrogen production rate, and electrical energy efficiency with enhancing steam-to-biomass ratio. An increase in CO2 capture efficiency also improves both the electrical energy efficiency and H2 concentration of the syngas composition. CO2 capture efficiency and S/B ratio are inversely related to the exergy efficiency of the system.

Low-cost crushed-rock heat storage with oil or salt heat transfer

The demand for variable electricity and heat is met by fossil-fuel power plants because the power plant capital costs and the cost of storing fossil fuels are low. A low-carbon economy requires replacement of the storage function of fossil fuels to provide variable heat and electricity as needed. The Crushed Rock Ultra-large Stored Heat (CRUSH) system is a new technology with the goal to provide heat storage at an incremental capital cost of $2–4/kWh at scales of 10 s to 100 s of GWhs that enables economic daily to multi-week storage. CRUSH can be coupled to nuclear power plants, concentrated solar power (CSP) plants and thermal energy batteries to provide variable electricity and heat on demand. Sensible heat is stored in crushed rock—the lowest-cost heat-storage material. Heat is transferred to and from the crushed rock using nitrate salt or heat-transfer oils but these fluids do not store heat. Heat from a nuclear reactor, CSP plant or conversion of low-price electricity into heat is used to heat the salt or oil. The hot fluid is poured over the crushed rock, trickles downward by gravity through the rock, heats the rock and is collected by the drain pans under the crushed rock. To recover heat cold salt or oil is poured over hot crushed rock, trickles down by gravity while being heated and is collected by the drain pans under the crushed rock. The system design and engineering trade-offs are described. The technology is in the early stages of development.

Numerical study and structural optimization of mid-and-low temperature solar absorber/reactor for methanol decomposition

• A multi-physics coupling numerical model of MLTSAR is established. • The circumferential non-uniform heat flux has a slight effect on the MCR and STE. • The MCR and STE of MSR is higher and lower than that of MD, respectively. • A novel structure can enhance the MCR and STE by 1.47% and 1.49%, respectively. Driving endothermic thermochemical reactions by employing concentrated solar thermal energy is a perspective method for efficient utilization of solar energy, and solar reactor is a key equipment for wider application. In this paper, a multi-physics coupling model of mid-and-low temperature solar absorber/reactor (MLTSAR) for methanol decomposition (MD) reaction is established. The thermochemical performance of MLTSAR and the influencing factors including solar radiation intensity and non-uniform solar heat flux in circumferential direction are studied. The non-uniform solar heat flux in circumferential direction has a slight effect on the methanol conversion rate (MCR) and solar thermochemical efficiency (STE) but it leads to the non-uniform temperature distribution of absorber/reactor. And then, the comparative study of the thermochemical characteristic between MD and methanol steam reforming (MSR) reaction indicates that the MCR of MSR is higher than that of MD, but the STE is lower than that of MD. The MLTSAR structure is optimized by changing the aperture width, to reduce the energy level difference between the concentrated solar heat and the chemical reaction. The results show that compared with the original MLTSAR, the MCR and STE of the novel MLTSAR can be enhanced by 1.47% and 1.49%, respectively, and the outlet temperature is reduced by 15.48 K under the typical working condition. This optimization scheme could guide the design of practical solar reactors.

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.

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.

A brief review of liquid heat transfer materials used in concentrated solar power systems and thermal energy storage devices of concentrated solar power systems

AbstractSolar power generation is an effective approach to promote the achievement of carbon neutrality. Heat transfer materials (HTMs) are important for concentrated solar power (CSP) systems and their accessary thermal energy storage (TES) devices. The performances of HTMs can influence the operation behaviors of CSP systems and TES devices. On the whole, the HTMs can be divided into three categories according to their physical states, which are the liquid, gaseous, and solid HTMs, respectively. This article presents a brief review of research works on liquid HTMs used in CSP systems and TES devices of CSP systems, mainly including different kinds of molten salts, heat transfer oils, nanofluids, liquid metals, and water. Some typical practical applications, experimental and simulation studies on different kinds of liquid HTMs used in CSP and TES systems are introduced, and the advantages, disadvantages, and further research and development work prospects of different kinds of HTMs are briefly summarized. This article aims to providing a reference for researchers in solar thermal power field.

A Case Study on Renewable Energy Sources, Power Demand, and Policies in the States of South India—Development of a Thermoelectric Model

This work aims to perform a holistic review regarding renewable energy mix, power production approaches, demand scenarios, power policies, and investments with respect to clean energy production in the southern states of India. Further, a thermoelectric-generator model is proposed to meet rural demands using a proposed solar dish collector technology. The proposed model is based on the idea of employing a parabolic concentrator and a thermoelectric (TE) module to generate electricity directly from the sun’s energy. A parabolic dish collector with an aperture of 1.11 m is used to collect sunlight and concentrate it onto a receiver plate with an area of 1.56 m in the proposed TE solar concentrator. The concentrated solar thermal energy is converted directly into electrical energy by using a bismuth telluride (BiTe)-based TE module mounted on the receiver plate. A rectangular fin heatsink, coupled with a fan, is employed to remove heat from the TE module’s cool side, and a tracking device is used to track the sun continuously. The experimental results show considerable agreement with the mathematical model as well as its potential applications. Solar thermal power generation plays a crucial part in bridging the demand–supply gap for electricity, and it can be achieved through rural electrification using the proposed solar dish collector technology, which typically has a 10 to 25 kW capacity per dish and uses a Stirling engine to generate power. Here the experimentation work generates a voltage of 11.6 V, a current of 0.7 A, and a power of 10.5 W that can be used for rural electrification, especially for domestic loads.

Current Advancement of Heliostats

Abstract This paper looks at the advancements made in Solar Power Towers and Heliostat Fields since 2017 and summarizes the current problems in various subsections. Heliostat fields capturing concentrated solar power (CSP) have been looked at for decades as a reliable renewable energy source that can balance out the variability of wind and photovoltaic cells. In recent years, many studies have researched possible improvements in CSP technology. Uniform methods have been developed to better estimate wind loads in various conditions. Gap size and hinge height to cord ratio have been studied to optimize structural strength. Coatings and cleaning schedules have been developed to increase the optical efficiency of plants. However, there are many studies that still need to be done to better understand wind and optics for solar power towers. While the levelized cost of electricity (LCOE) of power tower systems has decreased dramatically in recent years, more research and development need to be done to reach the Sunshot Initiative’s goal of 5 cents per kilowatt hour. A large area of improvement for future research comes from heliostat manufacturing costs which make up around 40% of energy plant costs. By lowering this cost from the current value of approximately $100/m2 to the Sunshot Initiative’s goal of $50/m2, the LCOE of concentrated solar thermal energy will be drastically reduced.

Semiconductor-dielectric-metal solar absorbers with high spectral selectivity

An ideal solar thermal absorber has a sharp transition between high and low absorptance at the wavelength where the blackbody emissive power begins to exceed the solar irradiance. However, most real selective absorbers have a fairly broad transition, leading to both solar absorption and thermal emission losses. Here, we model, fabricate, and characterize a highly selective semiconductor-dielectric-metal (Ga0.46In0.54As - MgF2 - Ag) solar absorber with an extremely sharp transition from high to low absorptance. The thin semiconductor serves as a selective filter, absorbing photons with wavelengths shorter than the bandgap and transmitting those with longer wavelengths. The highly reflective dielectric-metal rear mirror allows the structure to have very low emittance for longer wavelengths. These characteristics provide the absorber with a measured solar absorptance >91% below the bandgap wavelength and infrared emittance <5% at 100 C above the bandgap wavelength. This transition wavelength can be tuned by modifying the semiconductor composition, and modeling indicates that the absorber's optical properties should be stable at high temperatures, making the structure a good candidate for unconcentrated to highly concentrated solar thermal energy conversion.

Coupled parameters evaluation of three different finned structures for concentrated solar thermal energy storage

The main objective of this study is to improve the heat transfer of three cylindrical shell and tube exchangers including a novel honeycomb based finned structure, which is then compared to other finned structures (circular and longitudinal) for different thicknesses. This comparison is important in order to evaluate the honeycomb finned structure, however, to provide a reasonable comparison the PCM volume was kept constant for the three finned geometries compared at each thickness. For this reason, a 3D numerical model is performed using the COMSOL Multiphysics software, which is based on the FEM. Sodium Nitrite/Nitrate (NaNO2-NaNO3) is used as PCM and DelcoTerm is used as heat transfer fluid (HTF). The effect of thickness and number of fins for the three geometries was studied. However, most studies neglect the impact of the PCM volume, thus the methodology adopted in this work includes a coupled parametric combination of the number and thickness of the fins for three different fin structures. The results of this study have shown that the longitudinal finned geometry provided the shortest melting time for the configuration with a fin thickness of 1 mm. On the other hand, the evaluation of the fin thickness shows that even when keeping the same fins volume, the thickness still has a significant effect on the thermal performance of the units studied, where it can decrease the melting time around 3.6% for the circular geometry, 4.3% for the longitudinal geometry and 9.6% for hexagonal geometry.

The perspective of enhanced geothermal energy integration with concentrated solar power and thermal energy storage

AbstractA renewable energy‐only grid must couple mutable energy supplies such as wind and solar photovoltaic and affordable energy storage by lithium‐ion batteries to dispatchable energy supply such as Concentrated Solar Power (CSP) with thermal energy storage (TES) and Enhanced Geothermal Energy (EGS). EGS is centered on the exploitation of the substantial unconventional geothermal energy supplies in the crust of the Earth which is missing permeability and groundwater, with significant opportunities in western Saudi Arabia where the solar resource is also relevant. Regarding conventional geothermal energy, thermal efficiencies of the cycles can be increased to above 30% with EGS, and above 40% through the integration of EGS with CSP and TES, surpassing the 50% efficiency mark adopting advanced ultra‐supercritical (AUSC) technologies.

Experimental study on packed-bed thermal energy storage using recycled ceramic as filler materials

Thermal energy storage (TES) is used in renewable energy systems such as concentrated solar power (CSP) or electric thermal energy storage (ETES) plants to provide heat for dispatchable power production. This paper presents the experimental results of a new 100% recycled ceramic material, ReThink Seramic - Flora, for used in sensible heat packed-bed thermal energy storage. Results are compared to conventional α-alumina (alumina) materials. The study focuses on a full charge-discharge cycle and multiple repeated partial charge-discharge cycles. Air was used as the heat transfer fluid (HTF) with an inlet temperature of 150 °C. Three flow rates were considered in the study, 0.0034 m3/s, 0.0048 m3/s, and 0.0061 m3/s (5–9 SCFM). The thermal performance of ReThink Seramic - Flora was analyzed and compared to alumina in terms of energy stored/recovered, temperature distribution, thermal exergy efficiency, pressure drop, and net exergy efficiency (combined thermal and pressure drop losses). The results showed that alumina beads have higher performance in terms of thermal exergy efficiency than ReThink Seramic - Flora. The exergy efficiency increased from 46.8% to 55.4% for alumina and from 44.6% to 51.6% during full charge/discharge process at three flow rates. Pressure drop results indicate exergy losses over the flow rates from 3.6% to 7.9% for alumina and 2.5% to 5.1% for ReThink Seramic - Flora. This results in net exergy efficiencies at the three flow rates of 43.2%, 47.1%, and 47.5% for alumina compared to 42.1%, 45.4%, and 46.5% for ReThink Seramic - Flora.

A New Class of High Entropy Perovskite Oxides with Increased Reducibility and Stability for Solar Thermochemical Hydrogen Production

The growing demand for energy due to the increasing world population and industrialization of countries has caused pollution and climate change concerns. A global transition from fossil fuel energy to sustainable energy sources, in particular solar energy, calls for breakthroughs in energy storage and H2 fuel production. Two-step solar thermochemical hydrogen (STCH) production has emerged as an attractive route to produce clean H2 fuel from concentrated solar thermal energy. The two-step chemical looping is readily achieved using nonstoichiometric oxides such as ceria and perovskite oxides because those materials can retain their structural integrity throughout the cycling process. A new class of redox oxides, high-entropy perovskite oxides (HEPOs), are proposed to show great promises in the STCH application These novel HEPO materials have an unprecedented vast compositional space, large tunability, and unique thermodynamic and kinetic behaviors. Herein, we present that a HEPO family of La0.8Sr0.2(Mn[1-x]/3Fe[1-x]/3CoxAl[1-x]/3)O3- δ (x = 0.16, 0.2, 0.25, or 0.4) on the basis of an established STCH active material La0.6Sr0.4Mn0.6Al0.4O3- δ, was developed using high-energy ball milling (HEBM) and sintering. We comprehensively characterized the synthesized HEPOs in terms of phase purity, morphology, homogeneous elemental distribution, identification of redox active elements, reducibility extent (Δδ) and cycling structure stability and explored their STCH production performances. The optimal sample (La0.8Sr0.2(Mn0.2Fe0.2Co0.4Al0.2)O3- δ) showed a large Δδ ≥ 0.15 under the conditions of reduction at 1320 ℃ and oxidation at 870 ℃. All HEPO samples demonstrated R3-c phase stability during the cycling. Elemental mapping showed homogeneous distribution. Characterization of the electrical conductivity relaxation of the materials showed intrinsic material kinetic properties for oxygen surface exchange coefficient k ≥ 7.5 x 10-4 cm/s at 700 ℃, indicating the high kinetics for the HEPO reduction. The STCH production testing in our prototype setup showed that several promising samples had a high H2 yield of more than 300 μmol/g within less than 45 minutes upon exposure to 40 vol % steam and good cycling stability. This work opens up an avenue for the rational design of HEPOs for the solar thermochemical hydrogen production. Figure 1