Showing papers on "Thermal energy published in 2020"

Coupling of Solar Energy and Thermal Energy for Carbon Dioxide Reduction: Status and Prospects

Abstract: Enormous efforts have been devoted to the reduction of carbon dioxide (CO2 ) by utilizing various driving forces, such as heat, electricity, and radiation. However, the efficient reduction of CO2 is still challenging because of sluggish kinetics. Recent pioneering studies from several groups, including us, have demonstrated that the coupling of solar energy and thermal energy offers a novel and promising strategy to promote the activity and/or manipulate selectivity in CO2 reduction. Herein, we clarify the definition and principles of coupling solar energy and thermal energy, and comprehensively review the status and prospects of CO2 reduction by coupling solar energy and thermal energy. Catalyst design, reactor configuration, photo-mediated activity/selectivity, and mechanism studies in photo-thermo CO2 reduction will be emphasized. The aim of this Review is to promote understanding towards CO2 activation and provide guidelines for the design of new catalysts for the efficient reduction of CO2 .

Latent thermal energy storage technologies and applications: A review

Abstract: The achievement of European climate energy objectives which are contained in the European Union's (EU) “20–20–20″ targets and in the European Commission's (EC) Energy Roadmap 2050 is possible, among other things, through the use of energy storage technologies. The use of thermal energy storage (TES) in the energy system allows to conserving energy, increase the overall efficiency of the systems by eliminating differences between supply and demand for energy. The article presents different methods of thermal energy storage including sensible heat storage, latent heat storage and thermochemical energy storage, focusing mainly on phase change materials (PCMs) as a form of suitable solution for energy utilisation to fill the gap between demand and supply to improve the energy efficiency of a system. PCMs allow the storage of latent thermal energy during phase change at almost stable temperature. The article presents a classification of PCMs according to their chemical nature as organic, inorganic and eutectic and by the phase transition with their advantages and disadvantages. In addition, different methods of improving the effectiveness of the PCM materials such as employing cascaded latent heat thermal energy storage system, encapsulation of PCMs and shape-stabilisation are presented in the paper. Furthermore, the use of PCM materials in buildings, power generation, food industry and automotive applications are presented and the modelling tools for analysing the functionality of PCMs materials are compared and classified.

Fiber-Based Energy Conversion Devices for Human-Body Energy Harvesting

Abstract: Following the rapid development of lightweight and flexible smart electronic products, providing energy for these electronics has become a hot research topic. The human body produces considerable mechanical and thermal energy during daily activities, which could be used to power most wearable electronics. In this context, fiber-based energy conversion devices (FBECD) are proposed as candidates for effective conversion of human-body energy into electricity for powering wearable electronics. Herein, functional materials, fiber fabrication techniques, and device design strategies for different classes of FBECD based on piezoelectricity, triboelectricity, electrostaticity, and thermoelectricity are comprehensively reviewed. An overview of fiber-based self-powered systems and sensors according to their superior flexibility and cost-effectiveness is also presented. Finally, the challenges and opportunities in the field of fiber-based energy conversion are discussed.

Optimization strategies of composite phase change materials for thermal energy storage, transfer, conversion and utilization

Abstract: Thermal energy harvesting technologies based on composite phase change materials (PCMs) are capable of harvesting tremendous amounts of thermal energy via isothermal phase transitions, thus showing enormous potential in the design of state-of-the-art renewable energy infrastructure. Great progress has been recently made in terms of enhancing the thermal energy storage capability, transfer rate, conversion efficiency and utilization of composite PCMs. Although there are some recent reviews on composite PCMs, they are mainly concentrated on the thermal transfer enhancement and conventional utilization of PCMs. There are few systematic reviews concerning optimization strategies of PCM for thermal energy conversion. In particular, advanced multifunctional utilization of PCMs is still in its infancy. Herein, we systematically summarize the optimization strategies and mechanisms of recently reported composite PCMs for thermal energy storage, thermal transfer, energy conversion (solar-to-thermal, electro-to-thermal and magnetic-to-thermal conversion) and advanced utilization (fluorescence emission, infrared stealth technologies, drug release systems, thermotherapy and thermal protection), including some novel supporting materials (BN nanosheets and metal organic frameworks (MOFs)). Simultaneously, we provide in-depth and constructive insights into the correlations between the structural optimization strategies and thermal performances of composite PCMs. Finally, future research trends, alternative strategies and prospects are also highlighted according to up-to-date optimization strategies.

Five thermal energy grand challenges for decarbonization

Abstract: Roughly 90% of the world’s energy use today involves generation or manipulation of heat over a wide range of temperatures. Here, we note five key applications of research in thermal energy that could help make significant progress towards mitigating climate change at the necessary scale and urgency.

Carnot battery technology: A state-of-the-art review

Abstract: The growth of renewable energy requires flexible, low-cost and efficient electrical storage to balance the mismatch between energy supply and demand. The Carnot battery buffers electrical energy by storing thermal energy (charging cycle mode) from a resistive heater or a heat pump system when the electricity production is higher than the demand. When electricity demand is higher than the production, the Carnot battery generates power from the stored thermal energy (power cycle mode). This paper is a review of this emerging and innovative technology, including a market analysis. First, the different possible technologies and configurations of Carnot batteries are described. This includes charging cycles, power cycles and thermal energy storage systems. Furthermore, a state-of-the-art of the existing prototypes in the world is given. The performance indicators for this technology are unclear, and this paper tries to define objective performance indicators. Finally, all the described technologies are compared, and conclusions are drawn to help engineers select the optimal technology for a given case.

Near-perfect photon utilization in an air-bridge thermophotovoltaic cell.

Abstract: Thermophotovoltaic cells are similar to solar cells, but instead of converting solar radiation to electricity, they are designed to utilize locally radiated heat. Development of high-efficiency thermophotovoltaic cells has the potential to enable widespread applications in grid-scale thermal energy storage1,2, direct solar energy conversion3–8, distributed co-generation9–11 and waste heat scavenging12. To reach high efficiencies, thermophotovoltaic cells must utilize the broad spectrum of a radiative thermal source. However, most thermal radiation is in a low-energy wavelength range that cannot be used to excite electronic transitions and generate electricity. One promising way to overcome this challenge is to have low-energy photons reflected and re-absorbed by the thermal emitter, where their energy can have another chance at contributing towards photogeneration in the cell. However, current methods for photon recuperation are limited by insufficient bandwidth or parasitic absorption, resulting in large efficiency losses relative to theoretical limits. Here we demonstrate near-perfect reflection of low-energy photons by embedding a layer of air (an air bridge) within a thin-film In0.53Ga0.47As cell. This result represents a fourfold reduction in parasitic absorption relative to existing thermophotovoltaic cells. The resulting gain in absolute efficiency exceeds 6 per cent, leading to a very high power conversion efficiency of more than 30 per cent, as measured with an approximately 1,455-kelvin silicon carbide emitter. As the out-of-band reflectance approaches unity, the thermophotovoltaic efficiency becomes nearly insensitive to increasing cell bandgap or decreasing emitter temperature. Accessing this regime may unlock a range of possible materials and heat sources that were previously inaccessible to thermophotovoltaic energy conversion. An air gap embedded within the structure of a thermophotovoltaic device acts as a near-perfect reflector of low-energy photons, resulting in their recovery and recycling by the thermal source, enabling excellent power-conversion efficiency.

Arylazopyrazoles for Long-Term Thermal Energy Storage and Optically Triggered Heat Release below 0 °C.

Abstract: Arylazopyrazole derivatives based on four core structures (4pzMe, 3pzH, 4pzH, and 4pzH-F2) and functionalized with a dodecanoate group were demonstrated to store thermal energy in their metastable Z isomer liquid phase and release the energy by optically triggered crystallization at -30 °C for the first time. Three heat storage-release schemes were discovered involving different activation methods (optical, thermal, or combined) for generating liquid-state Z isomers capable of storing thermal energy. Visible light irradiation induced the selective crystallization of the liquid phase via Z-to-E isomerization, and the latent heat stored in the liquid Z isomers was preserved for longer than 2 weeks unless optically triggered. Up to 92 kJ/mol of thermal energy was stored in the compounds, demonstrating remarkable thermal stability of Z isomers at high temperatures and liquid-phase stability at temperatures below 0 °C.

Photochemical Phase Transitions Enable Coharvesting of Photon Energy and Ambient Heat for Energetic Molecular Solar Thermal Batteries That Upgrade Thermal Energy.

Abstract: Discovering physicochemical principles for simultaneous harvesting of multiform energy from the environment will advance current sustainable energy technologies Here we explore photochemical phase transitions-a photochemistry-thermophysics coupled regime-for coharvesting of solar and thermal energy In particular, we show that photon energy and ambient heat can be stored together and released on demand as high-temperature heat, enabled by room-temperature photochemical crystal↔liquid transitions of engineered molecular photoswitches Integrating the two forms of energy in single-component molecular materials is capable of providing energy capacity beyond that of traditional solar or thermal energy storage systems based solely on molecular photoisomerization or phase change, respectively Significantly, the ambient heat that is harvested during photochemical melting into liquid of the low-melting-point, metastable isomer can be released as high-temperature heat by recrystallization of the high-melting-point, parent isomer This reveals that photon energy drives the upgrading of thermal energy in such a hybrid energy system Rationally designed small-molecule azo switches achieve high gravimetric energy densities of 03-04 MJ/kg with long-term storage stability Rechargeable solar thermal battery devices are fabricated, which upon light triggering provide gravimetric power density of about 27 kW/kg and temperature increases of >20 °C in ambient environment We further show their use as deicing coatings Our work demonstrates a new concept of energy utilization-combining solar energy and low-grade heat into higher-grade heat-which unlocks the possibility of developing sustainable energy systems powered by a combination of natural sunlight and ambient heat

Thermal runaway hazards investigation on 18650 lithium-ion battery using extended volume accelerating rate calorimeter

Abstract: With the increase of lithium-ion batteries energy density and capacity, the thermal runaway (TR) is becoming a significant issue that can't be ignored In this work, one kind of commercial 18650 lithium-ion battery with different states of charge (SOCs) and cycling times is used to evaluate the TR hazards by a ramp heating method in an extended volume accelerating rate calorimeter Some thermal characteristic parameters are selected and analyzed from the experiment trails, such as the cell surface temperature, temperature rise rate, canister internal pressure and average canister surface temperature The experiment results show that the maximum surface temperature of the battery and the maximum canister internal pressure increase with the increase of SOC when the TR occurs The thermal energy released from the battery during TR is calculated using the initial and the maximum temperature on the battery and the canister surface A fully charged fresh battery can release 6172 kJ energy when it gets into TR, which could be converted to an explosion equivalent of 557 g TNT-equivalent Compared with fresh batteries, aged batteries are more prone to get into TR and the TR hazards increase

Thermal Energy Storage for Grid Applications: Current Status and Emerging Trends

Abstract: Thermal energy systems (TES) contribute to the on-going process that leads to higher integration among different energy systems, with the aim of reaching a cleaner, more flexible and sustainable use of the energy resources. This paper reviews the current literature that refers to the development and exploitation of TES-based solutions in systems connected to the electrical grid. These solutions facilitate the energy system integration to get additional flexibility for energy management, enable better use of variable renewable energy sources (RES), and contribute to the modernisation of the energy system infrastructures, the enhancement of the grid operation practices that include energy shifting, and the provision of cost-effective grid services. This paper offers a complementary view with respect to other reviews that deal with energy storage technologies, materials for TES applications, TES for buildings, and contributions of electrical energy storage for grid applications. The main aspects addressed are the characteristics, parameters and models of the TES systems, the deployment of TES in systems with variable RES, microgrids, and multi-energy networks, and the emerging trends for TES applications.