Thermal energy storage characteristics of sand as filler material for solar thermocline tank

Thermal stratification significantly affects the performance of thermal energy storage (TES) systems, especially in domestic hot water (DHW) applications. While stratification in sensible heat storage is well studied, its optimization in phase change material (PCM)‐based systems has received less attention. This article examines the effects of heat transfer fluid (HTF) inlet temperature and flow rate on stratification and energy performance in a PCM‐based TES tank. Experiments are conducted at flow rates of 200, 300, and 400 LPH with inlet temperatures of 70 and 75 °C. Higher inlet temperatures reduce PCM charging time by 31.03%, 36.00%, and 36.84% for the respective flow rates. Stratification, measured by the MIX number, improves with higher flow rates and temperatures, as shown by lower values. Elevated HTF temperatures increase the temperature gradient, enhancing sensible heating and raising average storage temperature during PCM melting. The Richardson number rose initially but declined rapidly as melting reduced the thermal gradient. After melting, charging efficiency decreases due to weakened stratification. These findings emphasize the importance of controlling HTF operating conditions to enhance stratification and TES efficiency, supporting the development of advanced control strategies and designs for PCM‐based TES in DHW and renewable energy applications.

A very challenging issue about solar thermal power generation is the use of a high temperature heat transfer fluid (water, oils, or molten salts) for heat transfer and thermal storage material, which may freeze at night or cold weather. When choosing air as the heat transfer fluid, the problem of freezing is eliminated. In order to increase the performance of thermal storage system which uses air as the heat transfer fluid passing through a packed bed (by ceramic spheres of Al2O3), multiple small-diameter tanks are considered to replace a single large-diameter tank with the same packed-bed volume and airflow rate in this paper. Analysis about the thermal storage performance in a short big tank and in cascade thin tanks has been made for comparison. A long passage of airflow and faster flow speed of air in the cascade thin tanks has been found significantly beneficial to thermal storage. Results about the increased thermal storage performance and increased pressure loss will be presented. Longer passage of airflow made it possible to have a longer time of high temperature of outflow air during discharging period. And faster speed of the fluid enhanced the heat transfer between air and thermal storage material. The total effective energy and thermal storage efficiency of cascade thin-tank thermal energy storage (TES) are higher. The thermal storage efficiency in the two types of thermal storage arrangement was compared for optimal design. The obtained results are of great significance to the development of using air as heat transfer fluid and rocks or ceramic spheres as the thermal storage material for thermal storage system in concentrated solar thermal power plants.

The current chapter provides an overview about one of the most attractive topics related with energy i.e. thermal energy storage (TES) systems. Due to upsurge in the energy demand the usage of fossil fuel has increased dramatically. To find the substitute of fossil fuel is one of the vital issues throughout the world. The combustion of fossil fuel has severe effect not only on environment but also on human health. These issues can be properly addressed by using TES system. Different source of renewable energy, especially solar energy can be stored via TES and utilized for different household and industrial applications. The most common way of storing energy in the form of latent heat is carried out by using phase change materials (PCM). The common issues with traditional PCM are their poor thermal conductivity which can be enhanced by using nanoparticles. The charging rate and efficiency of TES can be boosted by using nanofluid. In the present chapter effect of a novel nanofluid i.e., hybrid nanofluid on performance of TES has been discussed. This chapter focuses on three aspects: charging of TES by different methods, enhancement in the performance of TES using nanofluid, and different applications of TES. Also, the detailed information about TES using nanofluids and different and thermo-physical properties of nanoparticles-based PCM are provided in this chapter.KeywordsHybrid nanofluidLatent heatPhase change materialThermal conductivityThermal energy storage

In today’s world, where reduction in the carbon footprints is emphasised, people are looking for alternative source of energies for power production and heat treatment of metals and alloys. One such alternative source is solar energy but due to intermittent nature a thermal energy storage (TES) is required in order to deal with heat flux that varies throughout the day so as to supply a constant power. In the present study, the characterization of the sensible heat thermal energy storage (SHTES) packed with sensible heat storage material are considered. The size of pebbles varies between 20-25mm with porosity of the SHTES as 40%. The flow rate is 40 LPM and TES was charged for 8 hours. It has been noticed that when the temperature of the inlet air is around 180°C, the temperature of the top surface of the TES is around 70°C which states that for TES high thermal conductivity materials are required so that charging and discharging can take place at faster rate. The azimuthal and axial variation of temperature is also shown and it is concluded that even after low thermal conductivity of the material azimuthal variation can be neglected for the sake of modeling the TES.

Compressed Air Energy Storage is a promising large-scale storage system in part because of its high power rating during discharge. But it is not the cleanest way of storing energy due to the necessity of an external heat source (typically the combustion of natural gas) to heat the air at the turbine inlet. This problem can be overcome with Thermal Energy Storage by storing the thermal energy of air at the compressor exhaust in order to be used for heating air before turbine. In this study, a numerical transient heat transfer model of Thermal Energy Storage is developed and the performance of Thermal Energy Storage is investigated based on heat storage capacity, required time to store unit amount of energy and air temperature profiles at the outlet of Thermal Energy Storage during discharge for the system. High heat storage per volume is necessary for more compact systems. Required time to store unit amount of energy is desired to be short for a fixed volume Thermal Energy Storage in order to maintain continuous operation; on the other hand, air at the outlet (turbine inlet) should be at a high temperature for the longest time possible to supply hot air to turbine. In order to investigate the effects of operating parameters, different volumes of Thermal Energy Storage tank filled with different storage mediums of various sizes are explored. Latent Heat and Sensible Heat Thermal Energy Storage systems are compared using magnesium chloride hexahydrate, paraffin, myristic acid and naphthalene as phase change materials and rock as sensible storage medium. Results show that Latent Heat Thermal Energy Storage gives a better performance than Sensible Heat Thermal Energy Storage. Among phase change materials, magnesium chloride hexahydrate provides the highest heat storage per volume. Required time to store unit amount of energy are comparable among the phase change materials. Magnesium chloride hexahydrate seems promising considering the discharge temperature profile at the Thermal Energy Storage outlet. Capsule size should be kept as small as possible which can be challenging in terms of manufacturing.

Efficient systems for high performance buildings are required to improve the integration of renewable energy sources and to reduce primary energy consumption from fossil fuels. This paper is focused on sensible heat thermal energy storage (SHTES) systems using solid media and numerical simulation of their transient behavior using the finite element method (FEM). Unlike other papers in the literature, the numerical model and simulation approach has simultaneously taken into consideration various aspects: thermal properties at high temperature, the actual geometry of the repeated storage element and the actual storage cycle adopted. High-performance thermal storage materials from the literatures have been tested and used here as reference benchmarks. Other materials tested are lightweight concretes with recycled aggregates and a geopolymer concrete. Their thermal properties have been measured and used as inputs in the numerical model to preliminarily evaluate their application in thermal storage. The analysis carried out can also be used to optimize the storage system, in terms of thermal properties required to the storage material. The results showed a significant influence of the thermal properties on the performances of the storage elements. Simulation results have provided information for further scale-up from a single differential storage element to the entire module as a function of material thermal properties.

Energy performance of seasonal thermal energy storage in underground backfilled stopes of coal mines

Optimizing the thermal energy storage performance of shallow aquifers based on gray correlation analysis and multi-objective optimization

Techno-economic planning and construction of cost-effective large-scale hot water thermal energy storage for Renewable District heating systems

Numerical investigation into the effects of geologic layering on energy performances of thermal energy storage in underground mines

The influence of reinjection and hydrogeological parameters on thermal energy storage in brine aquifer

Heat transfer (HT) is a major constraint in thermal system analysis. However, when discussing utilizing the flexibility provided by the heating sector, for example, using thermal energy storage (TES) to increase operational flexibility of combined heat and power (CHP), the HT process is often ignored. This may mean infeasibility of the resulting schedules. In response to this, this paper proposes a general TES model which takes detailed HT analysis into account. By setting the relevant parameters, this model can be used to describe the HT process for both sensible heat (SH) and latent heat (LH) TES devices. An iteration method is proposed to deal with the nonlinearity introduced by the HT constraints, and to solve the joint nonlinear dispatch problem for CHP with TES. The simulation results show that explicitly considering the HT process is essential to realistically assess and therefore make full use of the flexibility provided by TES. Moreover, the comparison between LH and SH TES shows that LH can provide more flexibility for the system, especially when the starting energy level in the TES device is low.

District energy (DE) and thermal energy storage (TES) are two energy technologies that can enhance the efficiency of energy systems. Also, DE and TES can help address global warming and other environmental problems. In this study, a stratified TES is assessed using exergy analysis, to improve understanding of the thermodynamic performance of the stratified TES, and to identify energy and exergy behavioural trends. The analysis is based on the Friedrichshafen DE system, which incorporates seasonal TES, and which uses solar energy and fossil fuel. The overall energy and exergy efficiencies for the Friedrichshafen TES are found to be 60 and 19 % respectively, when accounting for thermal stratification. It is also found that stratification does not improve the performance of the TES notably. Considering the TES as stratified and fully mixed does not significantly affect the overall performance of the Friedrichshafen TES because, for this particular case, temperatures are very close whether the TES is treated as stratified or fully mixed.

Investigation of boiling heat transfer for improved performance of metal hydride thermal energy storage

Power plants based on solar energy are spreading to accomplish the incoming green energy transition. Besides, affordable high-temperature sensible heat thermal energy storage (SHTES) is required. In this work, the temperature distribution and thermal performance of novel solid media for SHTES are investigated by finite element method (FEM) modelling. A geopolymer, with/without fibre reinforcement, is simulated during a transient charging/discharging cycle. A life cycle assessment (LCA) analysis is also carried out to investigate the environmental impact and sustainability of the proposed materials, analysing the embodied energy, the transport, and the production process. A Multi-Criteria Decision Making (MCDM) with the Analytical Hierarchy Process (AHP) approach, taking into account thermal/environmental performance, is used to select the most suitable material. The results show that the localized reinforcement with fibres increases thermal storage performance, depending on the type of fibre, creating curvatures in the temperature profile and accelerating the charge/discharge. High-strength, high-conductivity carbon fibres performed well, and the simulation approach can be applied to any fibre arrangement/material. On the contrary, the benefit of the fibres is not straightforward according to the three different scenarios developed for the LCA and MCDM analyses, due to the high impact of the fibre production processes. More investigations are needed to balance and optimize the coupling of the fibre material and the solid medium to obtain high thermal performance and low impacts.