Sensible Heat Storage Research Articles

Comparative Study of the Performance of Packed Beds Using Different Types of Thermal Storage Materials

In packed bed thermal energy storage (PBTES) systems, the selection of a suitable storage material as packing material depends on several factors, including specific heat capacity, desired temperature range, heat transfer properties, thermal stability, cost-effectiveness, and availability. This work offers a comparative analysis of various thermal storage materials, providing valuable insights into their performance and suitability for energy storage applications. A numerical method, subsequently confirmed by experimental results, was used to analyze the performance of the studied packed beds, taking into account the thermo-physical characteristics of the different storage materials. Numerical simulations were carried out over the charging and discharging periods. The findings indicate that the thermal properties of the materials under investigation have a significant impact on the stratification and efficiency of the system. Among the materials evaluated, quartzite emerges as the most promising Sensible Heat Storage (SHS) material for PBTES systems, offering an optimal balance of thermal performance and cost-effectiveness, making it a highly suitable choice for large-scale thermal energy storage applications.

Assessment of heat storage integration for water vapour compression heat pumps: thermodynamic and techno-economic perspectives

ABSTRACT The integrated system, consisting of a two-stage high-temperature heat pump (HTHP) and thermal energy storage (TES), has been proposed as an effective solution to reduce CO2 emissions in industrial processes effectively. The water vapour HTHP, which can supply heat at 200°C, demonstrated a coefficient of performance (COP) between 4.4 and 7.5. Two different TES systems were introduced: concrete sensible heat storage (SHS) and strontium bromide/water (SrBr2/H2O) thermochemical energy storage (TCES). While the concrete SHS is limited to temperature below 200°C, the SrBr2/H2O TCES can deliver heat between 196°C and 228°C with higher cycle efficiency. The integrated system of HTHP and SrBr2/H2O TCES achieved a net present value (NPV) of €464,559 and €182,374 over a 20-years lifespan, with internal rates of return (IRR) ranging from 15.8% to 23.6%. This HTHP and TCES system has sufficient potential to replace fossil-fuel industrial boilers, leading to significant reduction in CO2 emissions in industrial processes.

Experimental analysis of a solar air heater using waste mild steel chips as a sensible heat storage material.

Heat storage materials improve the utility of solar air heaters (SAHs) after sunset. This study investigates an improved solar air heater (SAH) performance with baffles and waste mild steel chips as sensible heat storage (SHS) materials. Comparative experimental natural convection heat transfer studies were performed with four different improved air heater setups under similar solar radiation conditions. These setups consist of a flat collector plate (I), a baffled plate collector (II), a flat plate collector with SHS (III) and a baffled plate collector with SHS (IV) respectively. Setups I, II, III and IV were obtained by modifying the same air heater enclosure and each experiment was replicated for three similar sunny days. During the periods, the solar radiation varied in the range of 556-934 W/m2. The maximum thermal efficiencies found for setups I, II, III and IV were 18.76%, 22.40%, 27.21% and 28.22% respectively under natural convection. The highest average useful energy rate was produced by setup IV, followed by setups III, II and I. After sunset, setups III and IV were able to deliver warm air for an extended period of 1h, 18min and 1h, 42min, respectively. It was found that setups III and IV had sensible thermal energy storage reserves of 0.38kJ and 0.53kJ, respectively. The storage efficiencies found for setups III and IV were 60.25% and 70.89%, respectively. Among the four setups, setup IV boasts the most economical energy cost at 1.39 ₹/kWh and having the least payback period of 1year 4months. As a result, the employment of baffles and waste mild steel chips as SHS in a flat plate SAH not only presents a method for harvesting waste for efficient heat retention, but it also effectively uses solar energy for beneficial uses.

Unlocking the power of LiOH: Key to next-generation ultra-compact thermal energy storage systems

This study explores the potential of untapped lithium hydroxide (LiOH) as a phase change material for thermal energy storage. By overcoming the challenges associated with the liquid LiOH leakage, we successfully thermal-cycled LiOH in a laboratory scale experimentation, and observed its stability (>500 thermal cycles), without chemical decomposition. This step has never been performed to date. Its solid-to-liquid reversible transitions temperatures and related solidification/melting enthalpies values have been verified. Then, the first experimental characterization of LiOH's thermal properties shows unexpected values for its heat capacity, thermal conductivity and diffusivity, in contradiction with the few ones available in literature. This opens avenues for LiOH's applications for the storage of sensible and latent heat, as shown through the increased cycle efficiency potential of a thermal energy storage system if based on its energy storage capacity; up to six times more volumetric energy density compared to traditional Solar Salt-based systems used in the solar tower plant (4.5 GJ/m3 vs. 0.76 GJ/m3 over 1000 thermal cycles). Additionally, we observed a softening phenomenon that occurs inconsistently during heating, but which may account for its excellent melting properties and the interplay with other raw chemicals. This new insight contributes certainly to the underlying mechanisms in the synthesis of another promising heat storage material in development: the peritectic compound Li4Br(OH)3. This pioneering work suggests LiOH as a promising ultra-compact thermal energy storage material for filling the intermediary gap from current to next-generation solar power plants, although its large-scale application requires further investigation to achieve economic viability.

Development of sensible heat storage based solar hybrid dryer with evacuated tube collector and biomass gasifier for shrimp drying

The work was aimed at developing an energy-efficient solar hybrid dryer with a biomass-based gasifier heat backup suitable for drying shrimps even during off-sunshine hours. In this dryer, water was utilized as a sensible heat storage (SHS) material as well as heat transfer fluid and biomass gasifier as an indirect backup heat source. The performance of the solar-gasifier hybrid dryer was assessed by drying shrimp (Metapenaeus dobsoni) samples and compared it with solar, and gasifier modes. Shrimp obtained the desired moisture content of 15.09 %, 13.46%, and 14.77% (w.b.) in 9 h, 6 h, and 6 h of drying in solar mode, gasifier mode, and solar-gasifier hybrid drying mode, respectively. The average drying rate of the solar, gasifier and hybrid modes of drying were 0.33 g/g dm.h, 0.46 g/g dm.h, and 0.47 g/g dm.h, respectively. Results revealed that the evacuated tube solar water collector harnessed 193104 kJ and 160185 kJ of heat energy during sunshine hours under the solar and hybrid mode of operation. The maximum drying efficiency of 34.97%, 35.62%, and 41.66% was obtained for gasifier mode, solar mode, and hybrid mode of shrimp drying. The economic evaluation revealed that the hybrid mode of operation is highly economical with the annual savings of $10983.06 and the lowest payback period of 0.62 years.

Thermal performance study of a PV-driven innovative solar dryer with and without sensible heat storage for drying of Garcinia Pedunculata.

Uneven drying is the key drawback of a conventional multi-tray dryer. Therefore, an improved active solar dryer with and without integrated sensible heat storage (SHS) was proposed. A unique feature of this dryer is its movable walls from the sides of the dryer to transform it to an indirect or mixed-mode as and when necessary. Garcinia Pedunculata (GP) is a local seasonal medicinal fruit in Northeast India. Drying kinetics of GP, the dryer performance and economic analysis of dryer were evaluated in the indirect solar dryer without SHS (Exp. I), mixed-mode solar dryer without SHS (Exp. II), indirect solar dryer with SHS (Exp. III), mixed-mode solar dryer with SHS (Exp. IV), and open sun drying (OSD). The dryer's average efficiencies were 18.12%, 22.37%, 21.74%, and 24.46% for Exp. I, Exp. II, Exp. III, and Exp. IV, respectively. The moisture content of GP was reduced to 12.09% in wet basis (w.b.) from 87.99% (w.b.). The overall drying time for Exp. I, Exp. II, OSD, Exp. III and Exp. IV were 31, 26, 53, 28, and 10h, respectively. From the eleven drying models, the Two-Term model was the best-fitted model for Exp. I, Exp. II, OSD and Exp. III, and Midilli and Kucuk model was for Exp. IV. The final product's fragrance and colour are better for Exp. IV. Developing this dryer for Exp. I, Exp. II, Exp. III and Exp. IV, the price required was around 25,000, 27,000, 26,000, and 28,000 INR (1 US$ = 74.57 INR), respectively, while the economic payback periods are 1.6years, 0.9year, 1.4years, and 0.59year, respectively.

A medium-temperature, tubeless heat exchanger based on alloy microencapsulated phase change material (MEPCM)/ceramic composites

High-performance heat storage materials and devices are urgently needed to meet the demand for efficient heat storage. Herein, a novel SnBi58 alloy microencapsulated phase change material (MEPCM)/ceramic composite with flow channels inside is fabricated for medium-temperature heat storage, which combines the characteristics of sensible heat storage (SHS) and latent heat storage (LHS). Then a tubeless heat exchanger based on the composite is constructed, and its heat storage performance is experimentally studied. The results show that the thermal conductivity of the composite-based heat exchanger is doubled (up to 3.09 W/(m·K)) and the heat storage density is increased by 30.4% to 559.1 MJ/m3 compared with the ceramic-based heat exchanger. Meanwhile, the heat storage performance of the heat exchanger can be improved with the increase of inlet temperature and mass flow rate, and it is more sensitive to the response of the inlet temperature. Furthermore, the average heat storage duty of the heat exchanger reaches 1183 W/(m3·°C), which is 3.56 times the mean value of other heat storage devices. Finally, test results confirm the high thermal reliability of the composite, which can meet the tubeless heat exchange requirements.

Analysis of energy storage materials for developments in solar cookers.

Solar energy is accessible freely and can be utilized for many household and industrial applications. The consumption of solar energy for cooking applications has found significant success. Various innovations have been employed in facilitating cooking during off-sunshine hours. Thermal energy storage helps in overcoming the fluctuations in the supply of energy required for cooking during different time periods of the day. This study focuses on the different types of thermal energy storage mediums that are currently utilized in solar cooking. Primarily, oils and pebbles are most commonly used as sensible heat storage (SHS) while organic phase change materials (PCMs) are used as latent heat thermal energy storage materials (LHTES). The properties and performances of various SHS and latent heat storage (LHS) mediums have been compared for their suitable utilization. SHS materials are cost-effective but have lower thermal gradient compared to LHTES materials. The energy storage capability of LHTES is high while degradation with the increasing number of charging and discharging cycles is also considerable. The melting point should be close to the utilization temperature for being used as LHTES as thermal diffusivity of the materials greatly influences the performance of solar cookers. The cooking time is lower for solar cooking systems equipped with energy storage compared to non-equipped cooking systems. It is recognized that the use of energy storage has been proved as a huge advantage to solar cooking systems, however, the design, and heat transfer characteristics of the cooking vessel along with the storage material type and volume must be optimized in order to make this technology more influential.

Thermo-economic optimization of a novel confined thermal energy storage system based on granular material

Concentrated solar power is a suitable technology for production of green electricity. However, to attain a uniform electricity production, concentrated solar power should be coupled with large Thermal Energy Storage (TES) systems. Among the different technologies of TES systems, storage of sensible heat in granular material is widely used due to its simple operation. These TES systems store energy as an increase of temperature of a large mass of small solid particles, through which a fluid circulates exchanging heat. TES systems are typically operated in a fixed bed regime, maximizing their exergy output, thus limiting the maximum allowable velocity of the fluid flow. In this work, a novel confined bed is proposed to mechanically prevent the motion of the solid particles conforming the TES system even for high fluid velocities, to guarantee that the exhaust temperature of the fluid is maximum during a discharge process. In this novel confined bed, a thermocline evolves from bottom to top of the system, separating the low and high temperature of the bed during the discharge process. An analytical model was applied to describe the evolution of the thermocline and the effect of the different operating parameters on the thermocline thickness.The effect of the thermocline thickness was combined with a thermo-economic analysis of a confined bed TES system proposed for a case of study. The new confined bed here proposed was optimized considering thermodynamics aspects, namely the fluid exergy increment in the bed, and economic factors, specifically the total investment cost of the TES system. The optimization resulted in low values of the fluid velocity, between 0.2 and 0.4 m/s, but still higher than the minimum fluidization velocity of sand particles of 750 μm, justifying the requirement of a confined bed, and low bed aspect ratios, between 0.25 and 0.9, to prevent excessively high fluid pressure drops. However, the bed aspect ratio increases significantly for higher granular material particle sizes, up to a ratio of bed height to diameter of 3 for a particle size of 10 mm and a TES demand time of 6 h.

Thermal Energy Storage in Concentrating Solar Power Plants: A Review of European and North American R&D Projects

Thermal energy storage (TES) is the most suitable solution found to improve the concentrating solar power (CSP) plant’s dispatchability. Molten salts used as sensible heat storage (SHS) are the most widespread TES medium. However, novel and promising TES materials can be implemented into CSP plants within different configurations, minimizing the TES costs and increasing the working temperature to improve the thermal performance of the associated power block. The first objective of this review is to provide an overview of the most widespread CSP technologies, TES technologies and TES-CSP configurations within the currently operational facilities. Once this information has been compiled, the second aim is to collect and present the existing European and North American TES-CSP Research and Development (R&D) projects within the last decade (2011–2021). Data related to these projects such as TES-CSP configuration path, TES and CSP technologies applied, storage capacity, power block associated and the levelized cost of electricity (LCOE) of the commercial up-scaling project are presented. In addition, project information such as location, research period, project leader and budget granted are also extracted. A timeline of the R&D projects launched from 2011 is built, showing the technology readiness level (TRL) achieved by the end of the project.

Thermo-economic analysis of steam accumulation and solid thermal energy storage in direct steam generation concentrated solar power plants

In direct steam generation (DSG) concentrated solar power (CSP) plants, a common thermal energy storage (TES) option relies on steam accumulation. This conventional option is constrained by temperature and pressure limits, and delivers saturated or slightly superheated steam at reduced pressure during discharge, which is undesirable for part-load turbine operation. However, steam accumulation can be integrated with sensible-heat storage in concrete to provide higher-temperature superheated steam at higher pressure. In this paper, this conventional steam accumulation option (existing) and an integrated concrete-steam TES option (extended) are described and analysed, and their thermo-economic performance are compared taking the 50-MW Khi Solar One DSG CSP plant in South Africa as a case study. The results show that the extended option with five 10-m long, square cross-section concrete blocks, each with 3600 equally spaced tubes, provides an additional TES capacity of 177 MWh compared to the existing configuration as a result of utilising most of the available thermal power in the solar receivers. Moreover, the extended option delivers 58 % more electricity with a 13 % enhancement in thermal efficiency during TES discharging mode. With an estimated additional investment of $4.2M, the levelised costs of storage and electricity for Khi Solar One with the extended TES option are, respectively, 29 % and 6 % lower than those obtained with the existing TES option. With the extended TES option, the projected net present value of Khi Solar One increases by 73 %, from $41M to $71M, at an average electricity price of 280 $/MWh.

Analysis of energy storage materials for developments in solar cookers

Solar energy is accessible freely and can be utilized for many household and industrial applications. The consumption of solar energy for cooking applications has found significant success. Various innovations have been employed in facilitating cooking during off-sunshine hours. Thermal energy storage helps in overcoming the fluctuations in the supply of energy required for cooking during different time periods of the day. This study focuses on the different types of thermal energy storage mediums that are currently utilized in solar cooking. Primarily, oils and pebbles are most commonly used as sensible heat storage (SHS) while organic phase change materials (PCMs) are used as latent heat thermal energy storage materials (LHTES). The properties and performances of various SHS and latent heat storage (LHS) mediums have been compared for their suitable utilization. SHS materials are cost-effective but have lower thermal gradient compared to LHTES materials. The energy storage capability of LHTES is high while degradation with the increasing number of charging and discharging cycles is also considerable. The melting point should be close to the utilization temperature for being used as LHTES as thermal diffusivity of the materials greatly influences the performance of solar cookers. The cooking time is lower for solar cooking systems equipped with energy storage compared to non-equipped cooking systems. It is recognized that the use of energy storage has been proved as a huge advantage to solar cooking systems, however, the design, and heat transfer characteristics of the cooking vessel along with the storage material type and volume must be optimized in order to make this technology more influential.

Life Cycle Assessment of Sensible, Latent and Thermochemical Thermal Energy Storage Systems for Climate Change Mitigation – A Systematic Review

Renewable energy sources coupled with thermal energy storage (TES) systems offer a better hope in mitigating climate change. But, in order to integrate TES systems into the grid, it is important to understand their environmental performances. Life cycle assessment (LCA) serves as a leading methodological tool for environmental decision-making processes that allows one to identify the critical areas of improvement in a product life cycle, and hence can be used effectively in climate change mitigation strategies. Due to the scarcity of review articles that provide useful information on the LCAs of TES systems, a total of 23 papers were reviewed in this study. These were reviewed under three categories: sensible heat storage (SHS) systems, latent heat storage (LHS) systems, and thermochemical heat storage (THS) systems. Further, the greenhouse gas (GHG) emissions arising from TES systems were evaluated, giving special attention on the global warming potential impact category. The production stage was found to be the major contributor to GWP in all three TES systems. Following this review study, it can be concluded that the environmental performance can be greatly enhanced through TES systems, due to significant reductions in GHG emissions. Keywords: LCA, thermal energy storage, sensible heat, latent heat, thermochemical heat, PCMs DOI: 10.7176/JETP/12-5-02 Publication date: November 30 th 2022

Development of core-shell type microencapsulated phase change material with Zn-30 mass% Al alloy and its shell formation mechanism

Latent heat storage (LHS) technology is promising because it can store and release heat at a constant temperature utilizing phase change material (PCM) and is a superior alternative for sensible heat storage (SHS) technology. In this study, we report an improved preparation method for microencapsulated PCM (MEPCM) with Zn–30 mass% Al (melting temperature: 440–512 °C) as the PCM. Conventional MEPCM preparation involves boehmite treatment for 3 h in boiling water to form AlOOH shells on Zn–30 mass% Al alloy particles (average diameter: 35.7 μm) and heat-oxidation treatment to form an oxide shell in oxygen atmosphere at 800 °C. In this study, Al(OH)3 is added to the treatment solution before boehmite treatment; furthermore, precipitation treatment at 75 °C for 16 h is investigated. After heat-oxidation treatment, different Al and Zn oxide shells are formed on the surface of the alloy particles depending on the Al(OH)3 quantity added before boehmite treatment and precipitation treatment. The prepared MEPCM has a heat storage density of 0.48 GJ m−3 and excellent cyclic durability of >100 melting and solidification cycles. In addition to this, investigations related to the fabrication of composite PCM by mixing it with a glass frit was carried out for improving the durability of the MEPCM. Therefore, this material can be utilized in future medium-to-high temperature heat applications such as transportation, chemical processes, and renewable energy.

Thermo-economic evaluation of PCM layer thickness change on the performance of the hybrid heat storage tank for concentrating solar power plants

The current research examines how increasing the thickness of the phase change material (PCM) layer impacts the thermal and economic behavior of the hybrid sensible-latent heat storage reservoir utilized in solar power plants in order to prevent temperature fluctuations at the end of discharge cycles. On the basis of two-phase dispersion-concentric equations, a detailed transient numerical analysis is developed. The mathematical model equations are computed using the MATLAB program, and the present numerical findings are validated. Numerical investigations are used to compare the proposed storage system to the sensible heat storage (SHS) system in the context of cost and efficiency. The impact of various performance evaluation indexes, including axial temperature allocation, thermocline layer degradation, charging time, discharging time, and overall efficiency, are investigated. The results showed that the (35% PCM-30% SHS-35% PCM) configuration possesses the most considerable thermocline thickness of 7.94 m at the charge period of 360 min, while the SHS case has 3.2 m thermocline thickness at the charge period of 420 min. Due to its optimized efficiency, reduced thermocline area, and comparatively low cost, the (15% PCM-70% SHS-15% PCM) configuration demonstrates a more viable choice among the considered cases.

Design, Fabrication, and Thermal Evaluation of a Solar Cooking System Integrated With Tracking Device and Sensible Heat Storage Materials

Energy need for cooking in both the rural and urban areas all over the world is increasing every day as a result of an increase in population. The consequence of global warming due to the usage of fuels such as fossil fuel, firewood, and other biomass products for cooking necessitates innovative techniques that will improve the standard of living of people. In this study, the design, fabrication, and thermal evaluation of a solar cooking system integrated with an Arduino-based tracking device and sensible heat storage (SHS) materials was investigated. During the water boiling trials with black oil sensible material (BOSHSM), the obtained maximum temperatures for water, cooking box, and sensible heat storage material at 14:00 h when the solar radiation attained its peak value of 881.2 W/m2 were 64,52, and 54°C, respectively, while at 14:00 h with Black coated granite sensible heat storage material (BCGSHSM) at the solar radiation peak value of 890.4 W/m2, the maximum temperatures for water, cooking box, and sensible heat storage material were 73.5, 76, and 59°C, respectively. The maximum cooking power and thermal efficiency obtained from the water boiling trials were 48.4 and 56.4 W, and 31.6 and 35.8% respectively. Also, the results from the cooking of edibles revealed that the cooking power values ranged between 42.5 and 58.2, while that of efficiency ranged between 34.5 and 40.3% respectively. The maximum solar radiation during the cooking trial period was 986, 975, 956, and 953 W/m2. In general, from the results, the developed solar cooking system is a viable alternative to cooking with traditional/open burning of wood or other biomass products that pose a serious environmental and health-related threat to the people living in developing countries.

Parametric analysis of a sensible heat storage unit in an indirect solar dryer using computational fluid dynamics

The non-continuity of the drying process after sunset is one of the most significant limitations with solar dryers that has an impact on product quality and drying time. To overcome this problem, we installed a Thermal Energy Storage (TES) unit in an indirect solar dryer. Given the economic advantages offered by Sensible Heat Storage (SHS) systems and their availability, they are the best option to consider in a drying application. In this paper, we investigated a SHS unit integrated within a solar dryer under real meteorological conditions in eastern Morocco. The solar dryer with a storage system was simulated using the Computational Fluid Dynamics (CFD) approach, which was validated using experimental data from the literature. The research is mainly focused on the amount of material required, the proper porosity of the packed bed, and the overall performance of the solar dryer for various types of SHS materials. The obtained results proved that when compared to the case without storage, the efficiency of the solar dryer with sensible heat storage increased by about 2.47% at night. Regarding the study of different materials, granite stones showed better performance with a porosity of 40% and a packed bed thickness of 15 cm, where the temperature differences between the two cases with and without storage reached almost 5° at night.

Experimental investigations of high-temperature shell and multi-tube latent heat storage system

High-temperature thermal energy storage (TES) systems improve the reliability and performance of solar-thermal utilization systems due to their ability to levelize the gap between the energy supply and demand. The present work focuses on conducting extensive experimental investigations to study the performance characteristics of a latent heat storage (LHS) system. A customized experimental facility was designed and developed with air as the heat transfer fluid operating at a maximum temperature of 400 °C. Sodium nitrate used as the phase change material (PCM) was filled in the shell side of a multi-tube heat exchanger and performance parameters such as charging/discharging time, energy stored/discharged, and output power were estimated by varying the flow rate and inlet temperature of air. The axial and radial temperature distributions reveal that the heat transfer occurs predominantly due to natural convection during the charging process, whereas, discharging takes place primarily due to conduction heat transfer in the axial direction. The energy storage of ~ 19.5 MJ was achieved with maximum PCM temperature reaching up to 365 °C. A comparison with cast steel and concrete based sensible heat storage (SHS) mediums operating at similar experimental conditions indicates that the LHS medium possesses high energy storage density and low storage cost, however, a combination of SHS and LHS mediums can meet the diverse load requirements in the end-user applications.

Thermochemical heat recuperation for compressed air energy storage

Compressed Air Energy Storage (CAES) suffers from low energy and exergy conversion efficiencies (ca. 50% or less) inherent in compression, heat loss during storage, and the commonly employed natural gas-fired reheat prior to expansion. Previously, isothermal, and adiabatic (or ‘advanced’ adiabatic) compressed air energy storage have been proposed to enhance the efficiency of the process. Among the adiabatic schemes, thermal storage can be used to store heat from compression process. Prior to expansion, the air can recuperate the stored thermal energy, which could reduce or even eliminate the need for natural gas-fired reheat. Although sensible heat storage (SHS) and latent heat storage (LHS) have been previously investigated for this purpose, there are very few published studies looking at the use of thermochemical energy storage (TCES) for the CAES application. Here, a direct heat transfer scheme with combined thermochemical and sensible energy storage is proposed. The present study develops a mathematical model to address the conceptual design of the proposed idea. A detailed model and analysis are performed for TCES-rock-filled PBTES (packed bed filled with both barium oxides and rocks) and rock-filled PBTES. Results showed that similar round-trip efficiency (RTE) is achieved between rock-filled and TCES-rock-filled PBTES due to the relatively low heat capacity and heat of reaction for the barium oxides materials used in the current study. A 60% RTE is achieved for both systems with 20 h storage time after charge. However, with TCES material placed on top of the packed bed, a more stable turbine air inlet temperature (less than 200 K temperature variation) is obtained compared with all rock-filled packed bed (more than 300 K temperature difference) if idle time after charge is less than 20 h. In addition, with future advanced materials, the proposed idea could potentially improve the roundtrip efficiency of the process, have longer duration of storage and stable turbine air inlet temperature under suitable operating conditions. To better illustrate the potential of the concept, a hypothetical material with same heat capacity with rocks but a thermochemical storage capacity equal to three times that of barium oxides is investigated using the developed mode. Results showed that a potential of more than 5% RTE improvement could be obtained using the hypothetical material. Longer storage durations will increase the added value of the TCES. Additionally, 45% less volume is needed for the hypothetical-TCES-filled PBTES to achieve similar energy storage capacity as rock-filled PBTES with the case of 40 h idle time after charge. The concept could also be applied to Liquid Air Energy Storage.

Influence estimate of liquid lead–bismuth eutectic temperatures on operation and mechanical behaviors of sensible heat storage tank

Thermocline sensible heat storage (SHS) systems are usually utilized in parabolic trough solar power systems. Liquid lead–bismuth eutectic (LBE) is a potential heat transfer medium for SHS systems, but its influences on the performances of SHS systems are rarely studied. In this study, a simulation model of thermocline SHS tank using liquid LBE as the heat transfer fluid is established, and the influences of initial cold and hot LBE temperatures on the operation and mechanical performances of the tank are estimated. The results reveal that when the liquid LBE is used as the heat transfer fluid, the SHS tank can operate stably. The initial cold LEB temperature has almost no influence on both the total heat storage and heat release durations of the tank, while the initial hot LBE temperature has proportional relationships with the total heat storage and heat release durations. The heat storage performance as well as the heat release behavior of the tank can be improved by increasing the initial cold LBE temperature, or by decreasing the initial hot LBE temperature. The peak maximum mechanical stress of the tank can be decreased by increasing the initial cold LBE temperature, or by decreasing the initial hot LBE temperature.