Evaluating energy and greenhouse gas emission footprints of thermal energy storage systems for concentrated solar power applications

Thermal energy storage is an indispensible technology for adjusting the instability and time discrepancy between supply and demand of energy. It is mainly utilized for intermittent occasion, such as solar energy, variable energy load, and excessive energy that would be wasted rather than effectively utilized if it cannot be stored. Due to their potential for efficiently improving the comprehensive utilization rate of energy, thermal energy storage systems are of growing importance within the energy awareness: solar thermal utilization, peak shaving, industrial energy saving and waste heat recovery, building energy conservation, energy internet construction and so on. Developing efficient and inexpensive thermal energy storage devices is as important as developing new sources of energy, thus, in the past several years the thermal energy storage techniques have attracted a great deal of attention from both fundamental research and technological applications. Usually, there are three different mechanisms for thermal energy storage techniques: the sensible heat storage, the latent heat storage and the themochemical heat storage. The scope of this review is to give an overview and further analysis on the research which has been done on these three kinds of thermal energy storage techniques, and this review will be beneficial for the researchers and engineers to develop more efficient and optimized thermal energy storage systems. On the one hand, the research trends of three kinds of thermal energy storage techniques from 2000 to 2015 are carefully analyzed in the present review by using the statistics functions within the Web of Science Platform managed by Thomson Reuters. The statistics results show that according to the trends on paper numbers of each thermal energy storage techniques within the whole statistics period, the latent heat storage currently can be concluded as the most popular thermal energy storage technique in terms of fundamental research, the sensible heat storage is classified as least concern because main sensible heat storage systems so far have been almost matured, and the thermochemical heat storage is attracting more and more attention from researchers. On the other hand, the main technical characteristics (such as, energy storage density, energy storage scale, energy storage period, energy storage cost, advantages of technology, disadvantages of technology, future research focus, technology maturity and so on) of three kinds of thermal energy storage techniques are systematically compared in the present review on the basis of summarizing the previous related research work, and the final compared results reveal that because the key features for each thermal energy storage technology are totally different, the selection and extension of application fields for one thermal energy storage technique cannot move forward without a full consideration of its own technical characteristics. Finally, the latest progress on the development of thermal energy storage technologies is further discussed. The technical principles of the recently developed novel thermal energy storage concepts, mainly including of new latent heat storage materials represented by heat-storage ceramics and ionic liquids, the calcium based high temperature thermochemical heat storage systems and hybrid thermal energy storage systems, are introduced in detail, moreover, the technical potential and future outlook of these new thermal energy storage concepts are also addressed.

Thermal energy storage plays an important role in energy conservation and reducing CO2 emissions. Thermal energy storage involves sensible heat storage, latent heat storage and thermochemical heat storage. Compared with sensible heat storage, latent heat storage and thermochemical heat storage benefits of their high energy storage densities, which helps to reduce the initial cost of the construction of heat storage systems. However, the thermal conductivities of the phase change and thermochemical reaction materials are usually lower than 1 W m - 1 K - 1, which impedes the development and further applications of the corresponding energy storage systems. Porous materials, e.g. metal foams and expanded graphite, combining with other materials to form composites is an effective method for heat transfer enhancement. In this paper, the feasibility of using metal foams to enhance the heat transfer characteristics of heat storage materials in thermal energy storage systems was assessed. Heat transfer in solid/liquid phase change and thermochemical reaction of porous materials (metal foams and expanded graphite) was investigated. Organic commercial paraffin wax and inorganic calcium chloride hydrate were employed as the low-temperature materials, whereas sodium nitrate was used as the high- temperature materials in the experiment. Heat transfer characteristics of these PCMs embedded with open-cell metal foams and expanded graphite were studied. Composites of paraffin and expanded graphite with a graphite mass ratio of 3%, 6%, and 9% were prepared. The heat transfer performances of these composites were tested and compared with the results using metal foams. It is shown that heat transfer can be enhanced by adding these porous materials. Metal foams have better heat transfer performance due to their continuous inter-connected structures than expanded graphite. However, porous materials can suppress the effects of natural convection in liquid zone, particularly for PCMs with low viscosities, thereby leading to different heat transfer performances at different regimes (solid, solid/liquid, and liquid regions). This implies that porous materials do not always enhance heat transfer in every regime; thereby an optimal metal foam structure or expanded graphite fraction can be developed using PCMs for the overal thermal energy storage performance. For thermochemical heat storage systems, the feasibility of using metal foams to enhance the heat transfer capability of heat storage materials was assessed. Reversible reaction MgH2↔Mg+H2 was used as thermochemical heat storage reaction. The effective thermal conductivities of metal foams with various porosities (0.88–0.98) were estimated with Boomsma & Poulikakos model. A two dimensional mathematical model for the Mg/MgH2 system was estabilished to study the transient heat and mass transfer process. Heat release characteristics of chemical reaction in fixed beds with/without metal foams were compared to illustrate the effects of metal foams. Various factors influencing the reaction time for fixed reaction beds with metal foams were analyzed. The results show that metal foams shorten the reaction time and increase the output power by decreasing the average temperatures of the fixed beds. After adding metal foams with a porosity of 0.92, a 40% reduction of the reaction time and 60% promotion of the exothermic power can be achieved. The parametric study shows that there exists an optimal porosity of metal foams for the highest output power under a certain reaction condition. The cooling fluid temperature and hydrogen pressure are confirmed to have a more significant impact on the reaction rate when metal foams are embeded in fixed beds. In general, as heat transfer is coupled to phase change and chemical reaction processes in latent heat storage and thermochemical heat storage, the effects of porous materials on these heat storage systems are complex. The porous materials need to be carefully selected in order to optimizing the performance of heat storage systems.

Techno-economic evaluation of solar-based thermal energy storage systems

In support of the DOE thermal and chemical energy storage program, the solar energy storage program (SERI) provides research on advanced technologies, systems analyses, and assessments of thermal energy storage for solar applications in support of the Thermal and Chemical Energy Storage Program of the DOE Division of Energy Storage Systems. Currently, research is in progress on direct contact latent heat storage and thermochemical energy storage and transport. Systems analyses are being performed of thermal energy storage for solar thermal applications, and surveys and assessments are being prepared of thermal energy storage in solar applications. A ranking methodology for comparing thermal storage systems (performance and cost) is presented. Research in latent heat storage and thermochemical storage and transport is reported.

Thermo-economic optimization of the thermal energy storage system extracting heat from the reheat steam for coal-fired power plants

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

Thermal energy storage: Recent developments and practical aspects

A Review on Chemisorption Heat Storage in Low-energy Buildings

Review on influence of nanomaterials on thermal energy storage methods

Modelling and simulation of a hybrid solar-electrical dryer of wood integrated with latent heat thermal energy storage system

Thermal performance study of a solar-coupled phase changes thermal energy storage system for ORC power generation

Thermal Energy Storage (TES) has emerged as a crucial innovation in solar cooking, addressing the major limitation of traditional solar cookers—their dependence on sunlight. This chapter explores the principles, technologies, and applications of TES in solar cookers, emphasizing its transformative role in enabling cooking during off-sunshine hours, such as evenings, nights, and cloudy days. By storing excess thermal energy collected during peak sunlight hours, TES systems extend the operational period of solar cookers, making them more practical, efficient, and reliable. While solar cookers offer an eco-friendly and cost-effective alternative to conventional cooking methods, their reliance on direct sunlight restricts their usability. TES bridges this gap by ensuring uninterrupted cooking and enhancing efficiency. The chapter categorizes TES systems into three main types: sensible heat storage, which utilizes materials like water, oil, or rocks that retain and release heat through temperature changes; latent heat storage, which leverages phase change materials (PCMs) such as paraffin wax or salt hydrates that store and release energy during phase transitions; and thermochemical storage, which employs reversible chemical reactions for long-term heat retention with minimal losses. A comparative analysis highlights their thermal properties, cost effective, and practicality for solar cooking. Effective TES integration requires high energy density, thermal stability, durability, and ease of use, and this chapter discusses how TES systems can be tailored to various solar cooker designs, from small household units to large-scale community systems. The discussion also covers key aspects such as thermal insulation, heat retention, and heat transfer mechanisms to maximize efficiency and minimize heat loss, while safety and user-friendliness are emphasized for adoption in resource-limited settings. TES significantly enhances solar cooking by extending cooking hours, reducing reliance on conventional fuels, and improving user convenience. However, challenges such as heat loss, material degradation, and inefficiencies, along with economic and accessibility barriers, must be addressed. The chapter underscores the need for continued research and innovation to improve TES-integrated solar cookers, making them more affordable, efficient, and accessible for widespread adoption.

Thermal energy storage (TES) is a promising technique that conserves accumulated thermal energy from heat and cold mediums, making it available for future use. This method allows energy to be stored under various conditions, presenting an attractive solution for harnessing solar radiation efficiently and in large quantities. TES is becoming increasingly important as renewable electricity integration grows and the demand for low-carbon energy rises. Concentrating solar power plants benefit from TES, enabling them to store excess solar energy during peak times and utilize it during periods of lower solar radiation, ensuring a continuous power supply. Additionally, standalone TES systems for grid applications are gaining popularity, especially with the declining costs of renewable energy. These systems facilitate energy integration and help meet the increasing energy demands sustainably. Phase change materials (PCMs) play a vital role in thermal energy storage systems, contributing to effective energy conservation. Their high thermal storage density and moderate temperature volatility make them ideal for storing and releasing significant amounts of thermal energy. As a result, PCMs have gained popularity in this field. This study examines various aspects of thermal energy storage systems, with a particular focus on research articles related to storage materials and methods. It explores sensible heat storage, which involves altering material temperatures to store energy, latent heat storage that capitalizes on phase change properties like those of PCMs, chemical storage utilizing chemical reactions for energy storage, and cascaded thermal storage systems that combine different methods for optimized energy storage. By exploring these areas, this research aims to advance the understanding of thermal energy storage and contribute to the ongoing efforts in achieving sustainable and low-carbon energy solutions for the future.

A review of solar collectors and thermal energy storage in solar thermal applications

A global transition towards more sustainable production and consumption systems has led to an increasing share of renewables in the energy market. Renewables, majorly solar PV and wind power are accounted for around 10 % of the global power production in 2020. In this context, concentrated solar power (CSP) technologies are seen to be one of the most promising ways to generate electric power in coming decades. However, because of the intermittent nature of solar energy, one of the key factors that determine the development of CSP technology is the integration of efficient and cost-effective thermal energy storage (TES) systems. TES system not only plays a crucial role in bridging the gap between energy supply and demand but also increases the performance and reliability of energy systems and plays a crucial role in energy conservation. Though there have been many reviews on TES system, however the existing literature is either over 5 years old or focus on thermal storage materials for low temperature applications. To bridge this gap, this work presents a comprehensive review on the actual state of all major components of cutting-edge TES technologies for CSP application and condenses all the available information and categorizes them considering the main functional parts and remarking the current research progress in each part as well as the future challenging issues. It intends to understand and explain the foundations of the innovative concepts, future research directions and strategies developed over the past 10 years to tune the engineering and thermal sciences of TES systems. Insight into classes of TES storage materials with details on geometrical configurations, design parameters, physical properties, operational issues, cost, technology readiness level, suitability to CSP application and comparative assessment of various TES systems is provided.