Solar Thermochemical Process Research Articles

Assessing the Viability of GeO2/GeO Redox Thermochemical Cycle for Converting CO2 into Solar Fuels

The solar thermochemical process of splitting CO2, known as CDS, is studied here using a redox cycle involving GeO2/GeO. The required thermodynamic data for a second-law-efficiency analysis is obtained from the HSC Chemistry software. The goal of this study is to investigate how different parameters, such as the operating temperatures and molar flow rate of the inert sweep gas, as well as the inclusion of separation units, heat exchangers, heaters, and coolers, can affect the solar-to-fuel energy conversion efficiency of the GeO2/GeO cycle. All calculations assume a constant gas-to-gas heat recovery effectiveness of 0.5. The analysis shows that the solar-to-fuel energy conversion efficiency is lower at a thermal reduction temperature of 1600 K (11.9%) compared to 2000 K. This is because high energy duties are required for heater-2, heater-3, and separator-1 due to the need for a higher inert gas flow rate. After conducting a comparative analysis of the three CDS cycles, it can be inferred that the GeO2/GeO cycle exhibits a significantly higher solar-to-fuel energy conversion efficiency in comparison to the ZnO/Zn and SnO2/SnO cycles across all thermal reduction temperatures. According to the comparison, it is confirmed that the GeO2/GeO CDS cycle can achieve a reasonably high solar-to-fuel energy conversion efficiency of 10% at less than 1600 K. On the other hand, ZnO/Zn and SnO2/SnO CDS cycles require a thermal reduction temperature of more than 1850 K to achieve a solar-to-fuel energy conversion efficiency of 10%.

Hybrid Biomass Fast Pyrolysis Process and Solar Thermochemical Energy Storage System, Investigation and Process Development

Hybrid Biomass Fast Pyrolysis Process and Solar Thermochemical Energy Storage System, Investigation and Process Development

Multi-field coupling and collaborative optimization design of the solar thermochemical cycle process based on ceria

Most solar reactors commonly encounter challenges such as high-temperature gradients, suboptimal photo-thermal efficiency, and limited catalyst utilization. This lack of coordination in the design of solar reactors stems from the inadequate integration of the photothermal-chemical coupling synergistic relationship within the reactor. We developed a comprehensive multi-physics coupling mathematical model that incorporates optics, heat transfer, and chemical reactions to facilitate the cooperative optimization design of solar reactors. This study unveils the multi-field coordination mechanism within solar reactors. The optimization design of the secondary concentrator, reactor structure, fluid flow layout, and porous media catalyst structure was systematically carried out. A two-step thermochemical cycle of methane reducing cerium oxide decomposing water vapor to produce hydrogen was used as the reaction system to analyze the performance of the prototype reactor. The influences of ray power, reaction flow rate, and oxygen carrier mass on the solar-to-chemical efficiency were analyzed. The optimization results demonstrate that, by considering factors such as light power, mass transfer flow, and oxygen carrier mass within the optimization framework, the solar chemical energy conversion efficiency can reach a maximum of 38.75%.

4E Analysis of a novel combined cooling, heating and power system coupled with solar thermochemical process and energy storage

4E Analysis of a novel combined cooling, heating and power system coupled with solar thermochemical process and energy storage

Experimental Performance of a Nonlinear Control Strategy to Regulate Temperature of a High-Temperature Solar Reactor

Abstract Despite the significant potential of solar thermochemical process technology for storing solar energy as solid-state solar fuel, several challenges have made its industrial application difficult. It is important to note that solar energy has a transient nature that causes instability and reduces process efficiency. Therefore, it is crucial to implement a robust control system to regulate the process temperature and tackle the shortage of incoming solar energy during cloudy weather. In our previous works, different model-based control strategies were developed namely a proportional integral derivative controller (PID) with gain scheduling and adaptive model predictive control (MPC). These methods were tested numerically to regulate the temperature inside a high-temperature tubular solar reactor. In this work, the proposed control strategies were experimentally tested under various operation conditions. The controllers were challenged to track different setpoints (500 °C, 1000 °C, and 1450 °C) with different amounts of gas/particle flowrates. Additionally, the flow controller was tested to regulate the reactor temperature under a cloudy weather scenario. The ultimate goal was to produce 5 kg of reduced solar fuel magnesium manganese oxide (MgMn2O4) successfully, and the controllers were able to track the required process temperature and reject disturbances despite the system's strong nonlinearity. The experimental results showed a maximum error in the temperature setpoint of less than 0.5% (6 °C), and the MPC controller demonstrated superior performance in reducing the control effort and rejecting disturbances.

Remarkable solar thermochemical CO2 splitting performances based on Ce- and Al-doped SrMnO3 perovskites

In the solar thermochemical CO2 splitting process, a remarkable CO yield (799.34 μmol g−1) at 1350/1100 °C is reported based on proposed Sr0.6Ce0.4Mn0.8Al0.2O3.

Investigation of an integrated thermochemical hydrogen production and high temperature solar thermochemical energy storage and CO2 capture process

Depletion of fossil fuels and their environmental impacts are significant issues of today. While the increasing energy demands have led researchers to explore new areas. Hydrogen is one of the most promising alternatives that could provide clean energy from renewable sources. Hydrogen production using solar energy has been investigated; however, hydrogen storage and novel processes that rely less on external energy are still a literature gap. For the first time, a novel integration of the zinc-sulfur-iodine hydrogen production system with heliostat solar collector and thermochemical energy storage is proposed in this study. The proposed system allows for the production of clean hydrogen, reduced need of external energy, and improved process efficiency. Three scenarios for the H2 production are discussed where exergy efficiency, solar fraction, storage tank dimensions, auxiliary heater load, and thermal efficiency are evaluated. Simulations are performed with System Advisor model/ Aspen Plus, and results show a solar fraction of 75.46% as 0.5 mol/s H2 is produced and 2.3 mol/s CO2 is captured. Further, employing the storage system decreases required heat of the ZnSI system by half to 4710 kW and increases efficiency to 17.54%. The exergy and thermal efficiency of the system are obtained as 65.87% and 28.90%, respectively.

Copper ferrite and cobalt oxide two-layer coated macroporous SiC substrate for efficient CO2-splitting and thermochemical energy conversion

CO2-splitting and thermochemical energy conversion effectiveness are still challenged by the selectivity of metal/metal oxide-based redox materials and associated chemical reaction constraints. This study proposed an interface/substrate engineering approach for improving CO2-splitting and thermochemical energy conversion through CuFe2O4 and Co3O4 two-layer coating SiC. The newly prepared material reactive surface area available for gas–solid reactions is characterized by micro-pores CuFe2O4 alloy easing inter-layer oxygen micro mass exchanges across a highly stable SiC-Co3O4 layer. Through a thermogravimetry analysis, oxidation of the thermally activated oxygen carriers exhibited remarkably CO2-splitting capacities with a total CO yield of 1919.33 µmol/g at 1300 °C. The further analysis of the material CO2-splitting performance at the reactor scale resulted in 919.04 mL (788.94 µmol/g) of CO yield with an instantaneous CO production rate of 22.52 mL/min and chemical energy density of 223.37 kJ/kg at 1000 °C isothermal redox cycles. The reaction kinetic behavior indicated activation energy of 30.65 kJ/mol, which suggested faster CO2 activation and oxidation kinetic on SiC-Co3O4-CuFe2O4 O-deficit surfaces. The underlying mechanism for the remarkable thermochemical performances was analyzed by combining experiment and density functional theory (DFT) calculations. The significance of exploiting the synergy between CuFe2O4 and Co3O4 layers and stoichiometric reaction characteristics provided fundamental insights useful for the theoretical modeling and practical application of the solar thermochemical process.

Thermodynamic and economic analysis of the solar carbothermal and hydrometallurgy routes for zinc production

This paper assesses the viability of the solar carbothermal reduction process for zinc production by comparing the thermodynamic efficiencies and levelized cost of zinc (LCOZ) with the solar hydrometallurgy routes. Four configurations of the hydrometallurgy route - concentrated solar power (CSP), photovoltaics (PV), solar-tariff, and grid-tariff based processes have been considered. The analysis is reported for the pilot (300 kWth), demonstration (5 MWth) and commercial (30 MWth) size systems. It is seen that the solar carbothermal process is thermodynamically more efficient than the hydrometallurgy route. The technology, however, is not viable at the pilot and demonstration scales and is likely to become cost-effective only at the commercial scale. For the commercial-scale plant, the LCOZ from the solar carbothermal process (172–204 $/ton) is lower than the solar (403 $/ton) and grid (281 $/ton) based hydrometallurgy processes. The cost of zinc obtained from solar thermochemical process is expected to further reduce by 7% in 2030. The bottom-up assessment shows the possibility of an 8–10% reduction. The solar carbothermal process appears to be promising at a commercial (30 MWth) scale. Therefore, the concept should now be demonstrated on a pilot scale for all sunshine hours in a year to boost confidence in the technology.

Techno-economic analysis of a solar thermochemical cycle-based direct coal liquefaction system for low-carbon oil production

Direct coal liquefaction turns solid coal into transportable liquid fuel with a high energy conversion efficiency of nearly 60%. However, the hydrogen used in the direct coal liquefaction process mainly comes from coal gasification units, and gasification coal consumption accounts for about 30% of the total coal consumption. The authors of this article have proposed a solar thermochemical cycle-based direct coal liquefaction system and conducted a corresponding thermodynamic analysis. In this work, the economic feasibility, environmental impact, and the influence of key factors (coal price, oil price, carbon tax) for the industrial-scale low-carbon oil production system are analyzed. Compared with the traditional direct coal liquefaction system, the total coal consumption of the new system is reduced by ∼40%. Under low carbon constraints, the economics of the new system is comparable to that of the traditional one with a lower solar thermochemical hydrogen production cost (<13–16 yuan/kg H2). With the help of the solar thermochemical hydrogen production process, CO2 emissions of the new system can be reduced by 63%. Moreover, the solar thermochemical cycle could generate additional pure oxygen and profits. The methodology and results can provide important references for coal-to-liquid technology with high efficiency and low carbon emissions.

Solar thermo-chemical process assisting a pressure oxidation process for co-production of electricity and metal

The mining industry is looking at the use of solar energy to address issues related to highly variable energy prices, falling ore grades, and increasing concern about the industry’s carbon footprint. The pressure oxidation of ore sulfides is an economic alternative to the smelting process because it has the potential to reduce energy consumption and treat low-grade ores. In the pressure oxidation of ore sulfides, the purity and utilization of oxygen are key factors. Indeed, oxygen production and consumption constitute the major operating cost of the pressure oxidation process. Solar thermo-chemical looping processes have been identified as one of the most efficient pathways for the production and storage of oxygen. This study investigates the integration of a solar thermo-chemical looping process with a pressure oxidation process to treat ore sulfide and produce electricity. The analysis shows that the temperature of the cold storage tank has a strong influence on the performance of the complete system. The increase in the cold tank temperature results in a sharp decrease in the size of the receiver. This reduces the investment costs for both the solar receiver and the heliostat field. For the considered case, the useful heat of the solar receiver is 3.7 MWth when the cold tank temperature is set at 100°C. If the cold tank temperature is set at 400°C, the required useful solar heat is about 3.1 MWth and the nominal output of the gas turbine is 0.56 MWe. The analysis showed that about 80% of the useful solar heat can be used to generate oxygen when the temperature of the cold tank is as high as that of the reduction reaction

Solar-Driven Chemical Looping Methane Reforming Using ZnO Oxygen Carrier for Syngas and Zn Production in a Cavity-Type Solar Reactor

Converting sunlight into chemical fuels and metal commodities, via solar thermochemical conversion processes, is an attractive prospect for the long-term storage of renewable energy. In this study, the combined methane reforming and ZnO reduction in a single reaction for co-production of hydrogen-rich syngas and metallic Zn was demonstrated in a flexible solar thermochemical reactor prototype, driven by highly concentrated sunlight. Using solar energy as the process heat source in chemical-looping methane reforming with the ZnO/Zn oxygen carrier is a means to reduce the dependence on conventional energy resources and to reduce emissions of CO2 and other pollutants, while upgrading the calorific value of the feedstock for the production of energy-intensive and high-value chemical fuels and materials. On-sun experiments were carried out with different operating parameters including operating temperatures (800–1000 °C), inlet methane flow-rates (0.1–0.4 NL/min), and inlet ZnO feeding-rates (0.5–1.0 g/min) both in batch and continuous modes under reduced (0.15 and 0.45 bar) and atmospheric pressures (0.90 bar), thereby demonstrating solar reactor flexibility and reliability. As a result, increasing the temperature promoted net ZnO conversion at the expense of favored methane cracking reaction, which can be lowered by decreasing pressure to vacuum conditions. Diminishing total pressure improved the net ZnO conversion but favored CO2 yield due to insufficient gas residence time. Rising ZnO feeding rate under a constant over-stoichiometric CH4/ZnO molar ratio of 1.5 enhanced ZnO and methane consumption rates, which promoted Zn and syngas yields. However, an excessively high ZnO feeding rate may be detrimental, as ZnO could accumulate when the ZnO feeding rate is higher than the ZnO consumption rate. In comparison, continuous operation demonstrated greater performance regarding higher ZnO conversion (XZnO) and lower methane cracking than batch operation. High-purity metallic Zn with a well-crystallized structure and of micrometric size was produced from both batch and continuous tests under vacuum and atmospheric pressures, demonstrating suitable reactor performance for the solar thermochemical methane-driven ZnO reduction process. The produced Zn metal can be further re-oxidized with H2O or CO2 in an exothermic reaction to produce pure H2 or CO by chemical-looping.

Heat transfer analysis of solar-driven high-temperature thermochemical reactor using NiFe-Aluminate RPCs

Converting solar energy efficiently into hydrogen is a promising way for renewable fuels technology. However, high-temperature heat transfer enhancement of solar thermochemical process is still a pertinent challenge for solar energy conversion into fuels. In this paper, high-temperature heat transfer enhancement accounting for radiation, conduction, and convection heat transfer in porous-medium reactor filled with application in hydrogen generation has been investigated. NiFe-Aluminate porous media is synthesized and used as solar radiant absorber and redox material. Experiments combined with numerical models are performed for analyzing thermal characteristics and chemical changes in solar receiver. The reacting medium is most heated by radiation heat transfer and higher temperature distribution is observed in the region exposed to high radiation heat flux. Heat distribution, O2 and H2 yield in the reacting medium are facilitated by convective reactive gas moving through the medium's pores. The temperature gradient caused by thermal transition at fluid-solid interface could be more decreased as much as the reaction chamber can store the transferred high-temperature heat flux. However, thermal losses due to radiation flux lost at the quartz glass are obviously inevitable.

A concentrating solar power system integrated photovoltaic and mid-temperature solar thermochemical processes

The approach of cascading solar energy utilization provides access to reliable and ample supplies of energy and has thus attracted widespread attention. Currently, the hybridization of a concentrating solar photovoltaic process and a solar thermochemical process is a promising approach. This paper describes and investigates a concentrating solar power system to harvest solar energy. Co-producing photovoltaic electricity and solar thermal fuel is its attractive distinction. The visible spectrum is cast onto concentrating photovoltaics to generate electricity, and the ultraviolet and infrared spectra are used to drive methanol decomposition at approximately 250 °C. A spectral splitting parabolic trough concentrator is developed in which incident solar radiation is first split and then concentrated. Based on the measured optical data of concentrators, photovoltaics and reactor, the solar-to-electricity performance is evaluated in the proposed system. The results show that a satisfied solar-to-electricity efficiency of approximately 31.8% would be realized if monocrystalline silicon photovoltaics is adopted. In comparison to individual systems, the efficiency enhancements of about 15.3% and 6.3% are obtained. The solar-to-electricity efficiency can reach approximately 35.1% by adopting gallium arsenide. Meanwhile, the improved optical performance proves that the approach of first splitting and then concentrating sunlight is feasible and promising. Finally, the results are anticipated to lead to a new approach for improving full-spectrum solar energy utilization and guiding the establishment of a prototype in the near future.

Ammonia Synthesis through Hydrolysis of a Trianionic Pincer Ligand‐Supported Molybdenum–Nitride Complex

Reported is the hydrolysis of a homogeneous Mo-nitride complex bearing a trianionic pincer-type ligand to produce ammonia. Treating the anionic [(ONO)]Mo≡N(OtBu)]Ph3 PCH3 with two equivalents of water produces ammonia and the dioxo complex [(ONO)]MoO2 ]Ph3 PCH3 . X-Ray crystal structures of the starting nitrido complex and product dioxo complex are presented. Evidence for ammonia release comes from GC-MS and deuterium-labelling studies. The reaction is presented in the context of a two-stage solar thermochemical dinitrogen fixation process as the solid-state nitride hydrolysis step.

Performance investigation of a hybrid photovoltaics and mid-temperature methanol thermochemistry system

This work theoretically and experimentally presents a high-efficiency solar system which integrates photovoltaic cells and methanol thermal decomposition to make full use of the full-spectrum solar energy. In this optimized system, spectral beam splitting technology is used to split the solar spectrum into several wavebands. The spectrum suitable for photovoltaic conversion is directly converted to electricity using photovoltaic cells. The rest of the spectrum is converted into chemical energy of syngas (to be stored and converted to electricity on demand) via a mid-temperature solar-thermochemical process of methanol vapor decomposition reaction. A theoretical model is established and predicts that the electrical efficiency of the hybrid system could surpass 35%. The best system electrical efficiency, that we have experimentally demonstrated, was as high as 31.18% for a concentration ratio as low as 56 and a solar thermal temperature as low as 265 °C. The comparison to existing solar systems indicates that this proposed solar system has a great potential for efficient utilization of solar energy in large scale. This work paves the way to high-efficiency and full-spectrum utilization of solar energy.

100 kWe power generation pilot plant with a solar thermochemical process: design, modeling, construction, and testing

Using concentrated solar thermal energy to drive endothermic thermochemical reactions offers promising prospects for the efficient utilization of solar energy by upgrading solar energy to high-quality chemical energy. A 100 kWe power generation pilot plant with mid-and-low temperature solar thermochemistry is designed, modeled, constructed, and tested in this work. The mid-and-low temperature solar thermochemistry and power generation are investigated experimentally, and successfully integrated operation is achieved for the first time. In the pilot plant, solar energy is upgraded into the chemical energy of solar fuel (H2 and CO) through the solar thermochemical process of the methanol decomposition reaction. The solar fuel is then fed to an internal combustion engine to generate power, achieving efficient and stable conversion of solar energy to electricity. The solar generation pilot plant is constructed, including four solar thermochemistry units (with a solar field area of 198 m2), power generation unit (100 kWe), syngas storage unit (with a volume of 19.2 m3), preheating unit, and measurement instrumentation. The thermodynamic performance of the pilot plant is tested under varying solar irradiation levels and power loads. The catalyst bed temperature distribution, methanol decomposition rate, and solar-to-chemical energy efficiency are experimentally investigated. The solar thermochemistry generates with catalyst bed temperatures of 70–290 °C, and a methanol conversion rate exceeding 80% is achieved. The solar-to-chemical energy efficiency is in the range of 37.12–45.51% for solar fluxes of 404–761 W/m2. The system achieves an electrical efficiency of 24.73%, and it can provide a fuel saving of 16.71% compared with direct methanol combustion systems.

An experimental study on temperature control of a solar receiver under transient solar load

Solar thermochemical process technology has great potential to store solar energy as chemical fuels, however, there remain several challenges that have hindered its industrial commercialization. One of the main challenges is the transient nature of solar energy which causes instability and reduces the efficiency of the process. A promising solution to cope with this problem is to use a variable aperture mechanism to regulate the light entry into solar receiver. A robust control algorithm is required to automatically adjust the aperture size and keep the temperature semi-constant under various transient conditions including short or long cloud coverage and natural variation of solar radiation from sunrise to sunset. In our previous work, an adaptive predictive controller was developed for aperture size adjustment and its performance was evaluated by computer simulations. The present work takes our previous study to the next level by experimental evaluation of the proposed controller on a solar receiver radiated by a 7 kW solar simulator. Two different variable aperture mechanisms, namely as iris mechanism and rotary aperture, are used for adjustment of the light entry into the receiver. Experimental results indicate that both of the mechanisms have reasonable performance in response to changes to a setpoint and disturbance in incoming solar radiation. However, the iris mechanism exhibits superior performance due to its capability of continuously changing the aperture size. For an elaborated evaluation of the iris mechanism, a real day of solar irradiation was simulated in the lab by changing the power level of the solar simulator based on a normal irradiance profile of a sunny day. According to the experimental results, the required temperature control was achieved with a maximum error in the temperature setpoint less than 1.95 °C.

100 kWe solar thermochemical pilot power plant: design, construction and testing

Abstract The engineering design, construction and testing of a 100 kWe solar-hybrid power generation pilot plant are conducted in this work. In the pilot plant, solar energy is upgraded to chemical energy of solar fuel (H2 and CO) by the solar thermochemical process of methanol decomposition reaction, and steadily stored and effectively utilized as the forms of chemical energy of solar fuel. The solar fuel is fed to the internal combustion engine to generate power. The solar generation pilot plant, including four solar thermochemistry units (with solar field area of 198 m2), power generation unit (100 kWe), syngas storage unit (with the volume of 19.2 m3), preheating unit and measurement instrumentation, is built. The thermodynamic performances of the pilot plant are experimentally investigated, and the solar-to-chemical energy efficiency ranges from 37.12% to 45.51% when the solar flux is 404-761 W/m2.

Moving Brick Receiver–Reactor: A Solar Thermochemical Reactor and Process Design With a Solid–Solid Heat Exchanger and On-Demand Production of Hydrogen and/or Carbon Monoxide

Three crucial aspects still to be overcome to achieve commercial competitiveness of the solar thermochemical production of hydrogen and carbon monoxide are recuperating the heat from the solid phase, achieving continuous or on-demand production beyond the hours of sunshine, and scaling to commercial plant sizes. To tackle all three aspects, we propose a moving brick receiver–reactor (MBR2) design with a solid–solid heat exchanger. The MBR2 consists of porous bricks that are reversibly mounted on a high temperature transport mechanism, a receiver–reactor where the bricks are reduced by passing through the concentrated solar radiation, a solid–solid heat exchanger under partial vacuum in which the reduced bricks transfer heat to the oxidized bricks, a first storage for the reduced bricks, an oxidation reactor, and a second storage for the oxidized bricks. The bricks may be made of any nonvolatile redox material suitable for a thermochemical two-step (TS) water splitting (WS) or carbon dioxide splitting (CDS) cycle. A first thermodynamic analysis shows that the MBR2 may be able to achieve solar-to-chemical conversion efficiencies of approximately 0.25. Additionally, we identify the desired operating conditions and show that the heat exchanger efficiency has to be higher than the fraction of recombination in order to increase the conversion efficiency.