Thermochemical Energy Storage System Research Articles

Development and characterization of mesoporous silica-MgSO4-MgCl2 binary salt composites for low-grade heat storage in fluidized bed systems

Achieving nearly zero-energy buildings requires the efficient utilization and storage of renewable energy. Salt-hydrate-based thermochemical energy storage (TCES) systems are promising due to their high heat storage capacity and minimal seasonal heat loss. However, challenges remain in their commercialization and large-scale application. For instance, TCES systems using magnesium sulphate (MgSO4) provide low temperature lifts due to slow reaction kinetics. Incorporating deliquescent salts like magnesium chloride (MgCl2) can enhance sorption performance but may introduce stability issues such as agglomeration and decomposition. This study presents a novel binary-salt composite combining MgSO4 and MgCl2 within commercial mesoporous silica (CMS) to address these challenges and enhance overall performance. The binary-salt composite powder, with a particle size range of 150–300 μm, is well-suited for use in fluidized-bed reactors, where fast mass and heat transfer promote efficient moisture adsorption, prevent uneven temperature distribution, and reduce agglomeration. Thermogravimetric analysis (TGA) was employed to evaluate the water sorption and desorption behaviour of MgCl2-MgSO4@CMS binary-salt composites with a total salt content of 50 wt% and salt mixing ratios of 3:1, 1:1, and 1:3. The corresponding water sorption capacities were 0.95, 0.68, and 0.57 g/g, respectively. In comparison, the MgSO4@CMS single-salt composite showed a lower water adsorption capacity of 0.47 g/g and required temperatures exceeding 150 °C for complete regeneration. Reactor-scale experiments demonstrated that the MgCl2-MgSO4@CMS composite with a 1:1 salt mixing ratio could be fluidized at low gas velocities on the order of 10−2 m/s, achieving a maximum temperature lift of 24.7 °C and an energy density of 1018 kJ/kg during hydration at 80% relative humidity and 30 °C. Additionally, the binary-salt composite showed good cyclic stability with less particle agglomeration compared to the MgCl2@CMS single-salt composite.

Integration of energy storage and determination of optimal solar system size for biomass fast-pyrolysis

This study presents a model and analysis of a heliostat field collector (HFC) system integration with fast-pyrolysis of biomass and determination of the optimal solar system size for this integrated system. Given the intermittent nature of solar energy, an auxiliary heater and a thermochemical energy storage system (TCES) are included. Four cases of HFC integration with the fast-pyrolysis process have been studied: 1) low solar radiation, 2) sufficient solar radiation, 3) high solar radiation, and 4) no solar radiation with available stored energy in TCES. The solar energy system was modeled and calculated using the Engineering Equation Solver (EES) software, while the fast-pyrolysis process and the TCES were simulated using the Aspen Plus software. A thermodynamic and economic analysis has been conducted to estimate the share of solar energy for different process configurations. Economic calculations have been conducted for three different heliostat filed areas: 4000, 8000, and 12000 m2. Solar fraction, investment and operational costs, as well as total cost were calculated for these three heliostat field areas. The results indicate that the optimum heliostat field area for the studied biomass pyrolysis plant is 8000 m2 and the average solar fraction of the required energy in summer is 0.39 and while it is 0.34 for the whole year. Simulation results considering this optimized heliostat filed area indicate that 6.27 t/h of bio-oil is produced from 10 t/h of hybrid poplar biomass. Implementing this solar-assisted system reduces CO2 emissions, increases efficiency of the system and lowers thermal energy requirement for the fast-pyrolysis process from 6MW to 3.99MW.

Calcium Manganite Based Materials for Thermochemical Energy Storage in High Temperature Solar Thermal Plants: Materials Screening

The urgent need for sustainable energy supply requires maximum exploitation of renewable energy sources. The latter, being of intermittent nature, need to be coupled with efficient energy storage. Solar-thermal power-plants are inherently compatible with thermal storage, which is a cost-efficient method of storing energy for later use but the field is currently dominated by sensible heat molten salts used as heat storage media but with a maximum operating temperature of about 560oC. Certain ceramic materials, able to induce reversible reduction-oxidation reactions under air flow, are promising alternatives to molten salts because they can withstand much higher temperatures (>1000oC) and thus can be integrated with high-efficiency air-Brayton thermodynamic cycles. At the same time the chemical energy stored/released during such reduction-oxidation reactions can boost energy storage density by up to 10 times cf. sensible only concepts. In this framework, Ca-Mn-based perovskite compositions were demonstrated to function effectively as energy storage materials. The current work offers insights on material synthesis parameters to achieve relatively high purity Ca-Mn-based compositions and subsequently optimize their redox performance in the course of a preliminary 5-cycle campaign. Moreover, the occurring structural transitions and their corresponding heat effects are also discussed and elaborated upon. This study is the first step towards the, currently in progress, process of synthesising – at multi kg scale – and shaping these compositions into extruded honeycomb-like monolithic structures for subsequent future application in lab- and pilot-scale high temperature thermochemical energy storage systems.

Investigation of a model predictive control (MPC) strategy for seasonal thermochemical energy storage systems in district heating networks

This research investigates the integration of model predictive control (MPC) with seasonal thermochemical energy storage systems (STES) within district heating networks, focusing on the Nottingham district heating as a case study. The primary aim is to develop an MPC strategy that utilizes machine learning models for accurate heat load forecasting. This strategy optimizes the charging and discharging cycles of thermochemical energy storage systems to mitigate the mismatch between heating energy supply and demand by storing surplus heat during summer and utilizing it during winter. We employed and validated machine learning models, including support vector regression (SVR), regression trees, and long short-term memory (LSTM) networks, using historical heat load and meteorological data. A validated numerical model of the thermochemical energy storage system (TCES) was integrated into the MPC framework, formulated as a mixed-integer linear program to optimize the STES's operations. The performance of the MPC strategy was benchmarked against a rule-based control approach under varying supply capacities to evaluate scalability and robustness. Our findings reveal that each machine learning model achieved comparable performance, with CVRMSE values within the 9–11% range. The LSTM model, in particular, provided accurate multi-step forecasts essential for the MPC framework. Incorporating these models into the MPC strategy allowed for precise heat demand predictions, enhancing the management of energy storage and distribution. Results confirmed that MPC effectively shifts energy seasonally, reduces reliance on auxiliary heating during winter, and minimizes waste heat. The MPC strategy outperformed the rule-based control by storing a significantly higher percentage of waste heat and meeting a greater portion of the additional heat demand that was not covered by the auxiliary heat supply. The system demonstrated effective performance under varying supply capacities, with the MPC strategy efficiently utilizing stored heat to meet demand at 80% supply capacity, achieving a waste heat reduction to 4% and meeting most of the heat demand. However, performance declined at 60% capacity, indicating the need for careful consideration of supply capacities in system design. This study highlights the potential of integrating machine learning models with MPC to enhance the performance and adaptability of district heating systems with STES, minimizing waste heat and efficiently meeting energy demands.

Continuously stirred tank reactor for oil-suspended thermochemical energy storage systems for CuSO4·5H2O

Thermochemical energy storage can be used for heating applications, thereby helping to cut down on greenhouse gases from burning non-renewable fuels by offering a solution for seasonal heat storage. In the scope of the EU project RESTORE, a thermochemical energy storage is used to store low temperature waste heat and use it for district heating. This study presents the thermochemical energy storage as a new continuously stirred tank three-phase suspension reactor for storing heat from renewable sources or waste heat with almost no losses, in reaction. Therefore, the reactor was built of glass, where process parameters, such as the mean residence time, have been varied to obtain optimized results for thermochemical energy storage operating at the fixed temperature of 125 °C chosen due to project restrictions. The heat is used to dehydrate CuSO4·5H2O in the charging step and recovered by rehydrating CuSO4·3H2O or CuSO4·H2O, respectively, while generating heat in the discharging step. Using a mixture of silicone and mineral oil to prevent foaming, conversion rates of over 94 % to CuSO4·H2O were reached in the charging step with the continuously stirred tank reactor, with 1 kW thermal power, 150 mm diameter and 900 mm height in continuous operation. In discharging operation, 100 % conversion from CuSO4·H2O to CuSO4·5H2O was measured. This paper lays the groundwork for a new technology for thermochemical heat storage in low temperature application.

A Review of Thermochemical Energy Storage Systems for District Heating in the UK

Thermochemical energy storage (TCES) presents a promising method for energy storage due to its high storage density and capacity for long-term storage. A combination of TCES and district heating networks exhibits an appealing alternative to natural gas boilers, particularly through the utilisation of industrial waste heat to achieve the UK government’s target of Net Zero by 2050. The most pivotal aspects of TCES design are the selected materials, reactor configuration, and heat transfer efficiency. Among the array of potential reactors, the fluidised bed emerges as a novel solution due to its ability to bypass traditional design limitations; the fluidised nature of these reactors provides high heat transfer coefficients, improved mixing and uniformity, and greater fluid-particle contact. This research endeavours to assess the enhancement of thermochemical fluidised bed systems through material characterisation and development techniques, alongside the optimisation of heat transfer. The analysis underscores the appeal of calcium and magnesium hydroxides for TCES, particularly when providing a buffer between medium-grade waste heat supply and district heat demand. Enhancement techniques such as doping and nanomaterial/composite coating are also explored, which are found to improve agglomeration, flowability, and operating conditions of the hydroxide systems. Furthermore, the optimisation of heat transfer prompted an evaluation of heat exchanger configurations and heat transfer fluids. Helical coil heat exchangers are predominantly favoured over alternative configurations, while various heat transfer fluids are considered advantageous depending on TCES material selection. In particular, water and synthetic liquids are compared according to their thermal efficiencies and performances at elevated operating temperatures.

Design and evaluation of a geothermal power plant integrated with Mg(OH)₂/MgO thermochemical energy storage system: A dynamic simulation for assessing flexibility in power generation, energy, and economics

This study proposes a Carnot battery system that integrates MgO/Mg(OH)2-thermochemical energy storage (TCES) in a fluidized bed reactor (FBR) with Kalina cycle of a geothermal power plant. In the charge mode, surplus electricity from variable renewable energy is converted into heat and stored through the dehydration of Mg(OH)2. In the discharge mode, the hydration of MgO occurs in the FBR, and the reaction heat is converted into electricity through the Kalina cycle. Dynamic simulations of the charge and discharge modes were conducted using a non-steady state fluidized bed model. Results show the energy storage efficiency and capital cost were 76.4% and 68 USD/MJth for the base case, respectively. Round-trip efficiency and levelized cost of storage were 8.62% and 0.291–0.769 USD/kWhe, respectively, when the charging electricity cost was 0–0.042 USD/kWhe. A cost-competitive Carnot battery system using MgO/Mg(OH)2-TCES with high energy storage density and an easy-to-operate FBR has been developed.

Performance Analysis of Vermiculite–Potassium Carbonate Composite Materials for Efficient Thermochemical Energy Storage

In this study, the preparation of the composite material consisting of expanded vermiculite (EV) and potassium carbonate (K2CO3) was conducted using a solution impregnation method. Sorption and desorption experiments were undertaken to investigate the dynamic and thermodynamic properties of the EV/K2CO3 composites with varying salt contents. The findings suggest that the EV/K2CO3 composites effectively address the issues of solution leakage resulting from the deliquescence and excessive hydration of pure K2CO3 salt, thereby substantially improving the water sorption capacity and overall stability of the composite materials. The salt content plays a vital role in the sorption and desorption processes of EV/K2CO3 composites. As the salt content rises, the resistance to sorption mass transfer increases, resulting in a decline in the average sorption rate. Concurrently, as the salt content increases, there is a corresponding increase in the average desorption rate, water uptake, and heat storage density. Specifically, at a temperature of 30 °C and a relative humidity of 60%, the EVPC40 composite with a salt content of 67.4% demonstrates water uptake, mass energy density, and volumetric energy density values of 0.68 g/g, 1633.6 kJ/kg, and 160 kWh/m3, respectively. In comparison to pure K2CO3 salt, the utilization of EV/K2CO3 composites under identical heat demand conditions results in a 57% reduction in the required reaction material. This study offers essential empirical evidence and theoretical backing for the utilization and development of EV/K2CO3 composites within thermochemical energy storage systems.

Acceleration mechanisms of Fe and Mn doping on CO2 separation of CaCO3 in calcium looping thermochemical heat storage

The doping strategy with dark metallic oxide has proven effective in improving optical absorptions and heat storage performances of calcium-based materials for the direct solar-driven thermochemical energy storage system, but the microscopic mechanisms of accelerated decomposition of CaCO3 during heat storage process are still unclear. Carbide slag as an industrial waste with low cost and high CaO content is considered as a potential calcium-based precursor for large-scale thermochemical energy storage. Herein, the novel Fe-doped and Mn-doped calcium-based materials were synthesized from carbide slag and their optical absorption properties and heat storage performances were determined in the experiment. The optimum decomposition temperatures of CaCO3 during heat storage process decreased 10.5 °C and 18.6 °C due to Fe doping and Mn doping, respectively. The acceleration mechanisms by Fe doping and Mn doping for enhancing the CO2 separation of CaCO3 in the calcination stage of the heat storage process were investigated by density functional theory (DFT) calculations. The structural parameters, partial density of states, electron differential densities and energy barriers during CO32– dissociation in heat storage process on the doped CaCO3 and undoped CaCO3 surfaces were compared to clarify the effects of Fe doping and Mn doping on the CaCO3 decomposition. The energy barriers of Fe-doped material and Mn-doped material are 1.68 eV and 1.42 eV, respectively, which are 29.4% and 40.3% lower than that of undoped material. This work helps to understand the microscopic mechanisms of accelerated CaCO3 decomposition by Fe and Mn during heat storage process.

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.

Modeling CO2 Adsorption in a Thin Discrete Packing.

Local dynamics of CO2 adsorption in a discrete packing contained in a thin tube was assessed by 3D modeling. Thin tube packed bed adsorbers are currently used over tube structures in thermochemical energy storage systems and atmospheric revitalization of confined spaces. Driven by the interplay between key factors such as the exothermicity and the fluid flow, the advective transport was found less effective than the diffusive one on the breakthrough trends of CO2 which displayed significant concentration gradients at both inter- and intraparticle scales. The lack of angular symmetry inside the particles by the reduction in resistance to mass transfer in the area of solid particles exposed to high velocities led to greater convective transports from the bulk of the gaseous phase to the pores. The result of the modeling agreed with the experimental data obtained at the exit of the adsorber, helping reduction in reliance on the empirical dispersion models used in the one-dimensional modeling.

Heat storage and release characteristics of a prototype CaCO3/CaO thermochemical energy storage system based on a novel fluidized bed solar reactor

CaCO3/CaO thermochemical energy storage (TCES) system has a high heat storage density (1780 kJ/kg) along with high heat storage and release temperature (650–850 °C), which can be applied to concentrated solar power (CSP) technology utilizing CO2 Brayton cycles to improve power generation efficiency. There are several problems to be urgently resolved in current CaCO3/CaO solar calciners, such as poor heat and mass transfer and low thermochemical efficiency. This paper proposed a prototype CaCO3/CaO TCES system based on a novel fluidized bed solar reactor, which has a serrated arc surface in alignment with the direction of the incident solar rays to receive concentrated solar energy. The natural limestone particles were used as the reactive particles. The effects of operating modes (intermittent/continuous), initial mass of reactive particles, and initial carbonation temperature Tcar,initial on the heat storage and release characteristics of the TCES system were experimentally explored. During the carbonation reaction stage, the effective carbonation degrees in the continuous mode were generally higher than in the intermittent mode under the experimental conditions and declined at a slower rate. The reactive particles were recovered from the reactor for microstructural characterization after completing the experiments, high-temperature particle agglomeration and pore structure clogging were directly responsible for the decrease of the effective carbonation degree. In the continuous mode, the average thermochemical and total thermal efficiencies of 24.7 % and 53.5 % were obtained in the 1st calcination reaction, respectively, which represents significant advantages over other CaCO3/CaO solar calciners. The novel fluidized bed reactor demonstrated excellent fluidization in the experiments and did not exhibit mechanical deformation after multiple experiments under non-uniform concentrated radiation provided by an 84 kWe high-flux solar simulator. Overall, this paper provides a successful gas-solid reactor design to be coupled with CSP technology.

Development of a Two‐Stage Hydrogen‐Based Thermochemical Energy Storage System

Both energy conservation and the use of renewable resources are necessary due to the global increase in energy demand. A useful technique for energy storage, when renewable energy sources are available, is a thermochemical energy storage system that relies on the interaction of gases with solids. From this vantage point, hydrogen offers a sustainable and regenerative response to this pressing issue. In line with that, herein, the operation of a novel two‐stage hydrogen‐based thermochemical energy storage system (TS‐H‐TCES) is proposed to attain a higher energy density and is analyzed with the help of the thermodynamic cycle. The proposed system operates at 298, 373, 403, and 423 K as atmospheric temperature (Tatm), waste heat input temperature (Tm), storage temperature (Ts), and upgraded/enhanced heat output temperature (Th), respectively. For the given operating temperature, the thermodynamic performance of TS‐H‐TCES is evaluated using experimentally measured pressure–concentration isotherms of LaNi4.7Al0.3, LaNi4.6Al0.4, and MmNi4.6Al0.4. The maximum coefficient of performance, second law efficiency (ηII), and thermal energy storage density are found to be 0.67, 0.70, and 220.98 kJ kg−1, respectively. The impact of operating temperatures on system performance is also investigated, which is important in choosing the best temperature range for a certain application.

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

Impacts, Barriers, and Future Prospective of Metal Hydride‐Based Thermochemical Energy Storage System for High‐Temperature Applications: A Comprehensive Review

This article summarizes various thermochemical energy storage (TCES) systems based on their thermochemical properties, operating temperature, and storage density. Metal hydride (MH)‐based TCES is a potential energy storage system due to its higher energy storage density (&gt;100 kWh m−3), higher operating temperature (&gt;500 °C), relatively better reaction kinetics, and minimal or no energy losses (theoretically). MHs operate at various temperature ranges, and based on temperature, they are classified as low‐temperature MH and high‐temperature MH. This article highlights potential metal alloys operating above 300 °C, with an energy storage density of more than 100 kWh m−3, suitable for concentrated solar thermal power generation and industrial process heating applications. Magnesium (Mg) alloy‐based hydrides have shown good cyclic stability (up to 1500 cycles) at a temperature above 400 °C. The lower cost of material, higher energy storage capacity, better reversibility, and higher thermal stability of Mg‐based alloys have been explored in several small‐scale experimental investigations. The thermal energy storage (TES) efficiency of MH‐based TCES systems is reported ≈ 90%, which is significantly higher than sensible and latent TES systems. Challenges associated with MH‐based TES systems, such as heat transfer enhancement, cost reduction, and chemical and thermal stability, have been discussed in detail.

Investigation of water adsorption characteristics of MgCl2 salt hydrates for thermal energy storage: Roles of hydrogen bond networks and hydration degrees

Thermochemical energy storage holds great promise in solar energy applications, and MgCl2 hydrate salt is considered a promising material for medium and low-temperature thermochemical energy storage. Understanding the adsorption behavior of water molecules in MgCl2 hydrate salts and uncovering the underlying mechanisms are crucial for designing efficient thermochemical energy storage systems. This paper investigated the water adsorption characteristics of MgCl2 hydrate salt utilizing the Grand Canonical Monte Carlo (GCMC) method and captured the adsorption isotherm and concentration distributions of water molecules in MgCl2 hydrate salts pores at various temperatures. The results demonstrate that at low temperatures, particularly when the pore size is small (D < 0.8 nm), the interconnected hydrogen bond network plays a crucial role in enhancing the water adsorption capacity of pure MgCl2. As the temperature increases, the influence of hydrogen bond networks diminishes, and their impact on the water adsorption capacity becomes negligible. Moreover, the hydration degrees of MgCl2 salt significantly influence their water adsorption capacity. MgCl2·6H2O exhibits the best water-uptake performance, followed by MgCl2·4H2O, while MgCl2·2H2O displays the worst water-uptake performance. These findings shed light on the adsorption behavior of water molecules in MgCl2 hydrate salt and offer valuable insights into the design and optimization of efficient thermochemical energy storage systems. Such knowledge is essential for advancing the utilization of thermochemical energy storage in solar energy applications.

Incorporation of CaZrO3 into calcium-based heat carriers for efficient solar thermochemical energy storage

Calcium-based materials (CaCO3/CaO) have shown significant potential for use in thermochemical energy storage systems for concentrated solar power generation due to their low-cost, high-energy storage efficiency, and operational temperature range. However, the energy storage performance of calcium-based heat carriers degrades rapidly over cycles due to high-temperature sintering, limiting practical applications. In this study, we incorporated Zr into CaO using both heat-drying and freeze-drying methods, forming CaZrO3 as a physical barrier to prevent agglomeration and sintering of calcium particles at elevated temperatures. Experimental results demonstrated that Zr incorporation markedly improved cyclic energy storage stability, particularly for heat carriers derived from freeze-drying. Cao incorporated with 10 % CaZrO3 (FD-Zr10) showed a high energy storage density of 2161.75 kJ/kg over ten storage/release cycles, which was 25.89 % higher than that of pure CaO sample. Even over an extended operation of 30 cycles, FD-Zr10 still possessed the high energy storage density of 1939.76 kJ/kg. CO2-containing harsh storage conditions caused more sintering for the heat carriers, thus resulting in the performance reduction, but FD-Zr10 performed much better than other samples in resisting sintering. Various characterization analyses were conducted to investigate the reasons for the samples' cyclic stability. It was discovered that freeze-drying incorporation generated a dendritic surface with a more abundant pore structure, and the incorporated CaZrO3 functioned as a metal skeleton to mitigate high-temperature sintering.

Experimental investigation of a thermochemical energy storage system based on MgSO4-silica gel for building heating: adsorption/desorption performance testing and system optimization

To address the gap between the thermochemical energy storage (TCES) performance of MgSO4-porous matrix composites in small-scale prototypes and their practical application, a TCES system with an output power of 50 kW was designed and constructed to investigate the feasibility of using MgSO4-silica gel composites in large-scale storage systems for long-term heating applications. Thirty consecutive sets of experiments were performed on both the reactor and the system. Aiming at energy storage system for space heating and hot water supply, four parameters (energy consumption, energy storage density, energy storage efficiency, and specific energy storage capacity) were investigated as the key performance evaluation indicators. The experiment results indicated the energy consumption of the heater and humidifier account for approximately 80 % of total energy consumption. The findings also demonstrated the potential to increase the ESD from 0.47 GJ/m3 to 0.76 GJ/m3 by exploiting the heat generated from the additional circulation water in the reactor’s shell. The optimized system achieved an efficiency increase of ∼ 11 %, reaching over 60 %, and the specific energy storage capacity can reach up to 198.15 Wh/kg. In addition, the supply water temperature can stay above 50 °C for roughly 4 h, with a maximum value from 70.1 °C to 82.4 °C, and the water temperature lift was found to as high as 57.4 °C. Additionally, the adsorption heat accounted for approximately 44 % of the total energy storage.

Performance study of a thermochemical energy storage reactor embedded with a microchannel tube heat exchanger for water heating

Thermochemical energy storage (TCES) provides a promising solution to addressing the mismatch between solar thermal production and heating demands in buildings. However, existing air-based open TCES systems face practical challenges in integrating with central water heating systems and controlling the supply temperature. To overcome these limitations, a novel water-based TCES-HEX-HRU system is proposed in this study, which integrates a water-to-air microchannel tube heat exchanger (HEX) and an air-to-air heat recovery unit (HRU). A comprehensive evaluation of the TCES-HEX-HRU system is conducted numerically using a COMSOL model, including a comparative assessment for different TCES system configurations. The results demonstrate that the TCES-HEX-HRU system achieves an overall thermal efficiency of 82.35 %, marking a substantial 69 percentage points improvement over the TCES-HEX system. Although slightly lower than the typical air-based TCES system without HEX and HRU by 15.44 percentage points, the TCES-HEX-HRU system can be a practically promising and viable choice for applications in central heating systems. Numerical investigations indicate that the thermal performance of the system is influenced by the inlet conditions of airflow and waterflow. Moreover, increasing the number of water channels in the HEX of the TCES-HEX-HRU system enhances heat transfer but reduces the amount of heat released by TCES composite materials, resulting in a maximum overall thermal efficiency of 92.09 % with 35 channels and a peak outlet water temperature of 33.67 °C at with 30 channels. However, further increases in the number of channels lead to a decline in overall thermal efficiency and outlet water temperature. Changes in the width of water channels in the HEX have a minor impact on the highest outlet water temperature and overall thermal efficiency, while affecting the volume of the TCES composite materials.

A flexible methanol-to-methane thermochemical energy storage system (TCES) for gas turbine (GT) power production

This study introduces an innovative solution to address the challenges arising from the volatile natural gas market and the growing integration of renewable energy sources within the industrial sector. The research strives to confront this challenge by including renewable methanol (CH3OH) and converting it into methane (CH4), with an intermediate step involving synthesis gas (CO/H2) by using concentrating solar power. This approach provides a sustainable and adaptable solution to reduce dependence on natural gas. The process entails a methanol decomposition reaction at moderate temperatures (<350 °C). Subsequently, the synthesis gas is compressed to 40 bar, stored, and discharged through a methanation process that can be conducted at high temperatures (>500 °C). The resulting methane is used as fuel for gas turbines and can also serve as feedstock in the chemical industry. The simulations were conducted in ASPEN HYSYS and yielded overall system efficiencies exceeding 29% and roundtrip efficiencies of 44%. Through techno-economic optimisation of the reaction conditions, competitive levelized fuel costs (LCOF) of €172/MWh and future LCOE values of €145/MWh were achieved. These findings present an innovative strategy for integrating gas turbine cycles and additional conversion pathways for green methanol.