Energy Storage Cycle Research Articles

Excellent energy storage performance of multi-alternating-layer structured PMMA/PVDF dielectric composite at high-temperature

Polymer dielectric capacitors have high power density and are an integral component of electronic and power device. Currently, the limited energy density restricts their further application. In this research, a novel method was designed to optimize performance of PMMA/PVDF composite via an alternating stacked multi-layer structure. And, the five-alternating-layer of PVDF-PMMA-PVDF-PMMA-PVDF (F-A-F-A-F) composite has excellent dielectric properties, for instance, a better dielectric constant (4.52@1 kHz) and a low dielectric loss (0.034@1 kHz). The discharge energy density (Ue) of it is significantly larger than that of PMMA and PVDF. Particularly, the Ue of F-A-F-A-F composite is increased by 83.0 % (from 4.71 J/cm3 to 8.62 J/cm3) with charging-discharging efficiency of 60 % at 80 °C. Moreover, the F-A-F-A-F composite achieves an excellent stability after 40,000 cycles. This composite has a wide range of potential applications in the field of traditional dielectric capacitor due to its good energy storage performance and cycle stability.

In-Situ Preparation of Iron(II)-phthalocyanine@multi-Walled-CNTs Nanocomposite for Quasi-Solid-State Flexible Symmetric Supercapacitors with Long Cycling Life.

The construction of supercapacitor electrode materials with exceptional performance is crucial to the commercialisation of flexible supercapacitors. Here, a novel in-situ precipitation technique was applied for constructing iron(II)-phthalocyanine (FePc) based nanocomposite as the electrode material in quasi-solid-state flexible supercapacitors. The highly redox-active FePc nanostructures were grown in the multi-walled-CNTs (MWCNTs) networks, which shows convenient electron/electrolyte ion transport pathways along with outstanding structural stability, leading to high energy storage and long cycling life. The electrode of FePc@MWCNTs delivered a higher specific capacity than that of individual MWCNTs and FePc. The quasi-solid-state symmetric flexible device that was constructed using FePc@MWCNTs electrode demonstrated impressive performance with a maximum energy density of 29.7 Wh kg-1 and a maximum power density of 4000 W kg-1. Moreover, the device demonstrated superior durability and flexibility, as evidenced by its exceptional cyclic stability (111.3 %) even after 30000 cycles at 8 A g-1. These results reveal that the FePc@MWCNTs nanocomposite prepared by this simple in-situ precipitation method is promising as electrode material for next-generation flexible wearable power sources.

Recent Research Advancements in Carbon Fiber‐Based Anode Materials for Lithium‐Ion Batteries

Energy consumption is a critical element in human evolution, and rapid advances in science and technology necessitate adequate energy. As human society evades, the advancement of energy storage components has become critical in addressing societal challenges. Lithium‐ion batteries (LIBs) are promising candidates for future extensive use as optimal energy storage devices. However, the current limitations of LIBs pose a challenge to their continued dominance. Researchers are constantly exploring new materials to enhance the performance of LIBs, and carbon fiber (CF) is a dominant contender in this pursuit. The high electrical conductivity of carbon‐based materials benefits the battery system by facilitating efficient electron transfer and improving overall performance. CF‐based materials provide enhanced energy storage capacity and cycling stability in LIBs. Progress in carbon‐based materials has resulted in electrodes with increased surface areas, enabling greater rates of charging and discharging. In addition, the exceptional corrosion resistance of CF ensures the durability and robustness of LIBs. A comprehensive review is carried out on the correlation between the material's structure and its electrochemical performance, with a special emphasis on the uses of pure carbon fibers, transition metal oxides, sulfides, and MXene carbon‐based transition metal compounds in LIBs.

Techno-economic analysis of power-to-heat-to-power plants: Mapping optimal combinations of thermal energy storage and power cycles

To enable the widespread exploitation of intermittent, low-cost, and non-dispatchable renewable energy technologies, energy storage plays a key role in providing the required flexibility. This study introduces maps of optimal combination of Thermal Energy Storage (TES) and power cycles, supporting decision-making in power-to-heat-to-power applications. These maps span a wide temperature range from 200 to 1200 °C and are proposed for different charging costs, installed capacities, and storage durations. For thermal-to-electricity reconversion, this study explores power blocks including steam Rankine cycle, supercritical CO2 (sCO2) Brayton cycle, Organic Rankine Cycle (ORC), and combined gas turbine with Rankine and sCO2. Results highlight that, in a grid-based plant with a 50 EUR/MWh charging cost, the most cost-effective pairing involves sCO2 cycles with recompression and intercooling, with particle TES at 600–800 °C. Air packed-bed suits scenarios where TES contributes significantly to capital costs or involves low charging costs. Molten salt TES is the optimal choice when the design temperatures align with salt temperature limitations. Particle TES proves cost-effective across a broad temperature range and scales (10–200 MW). For solar-based systems, the integration of molten salt TES with simple sCO2 recuperated cycles demonstrates market potential for southern European locations.

Significantly Enhanced Oxidation Resistance and Electrochemical Performance of Hydrothermal Ti3C2Tx MXene and Tannic Acid Composite for High-Performance Flexible Supercapacitors.

The electrochemical performances of Ti3C2Tx MXene are severely restricted by the easy oxidation and restacking. Herein, tannic acid (TA) is introduced into Ti3C2Tx dispersion, and the mixed dispersion is further subjected to a simple hydrothermal treatment to prepare the hydrothermal Ti3C2Tx and TA composite (h-Ti3C2Tx@h-TA). Due to the decomposition of TA into gallic acid (GA), hydrothermal TA (h-TA) is a mixture of TA and GA. The strong interaction between h-TA and MXene mainly involves chemical interaction between the hydroxyl groups in h-TA and the surface/edge Ti atoms, along with numerous hydrogen bonds. The h-TA intercalation weakens MXene restacking and increases interlayer spacing, thereby improving ion transport pathways and accessibility. The chemical interaction between the hydroxyl groups of GA and the Ti atoms significantly enhances oxidation resistance and pseudocapacitive active sites. Therefore, the h-Ti3C2Tx@h-TA film electrode shows significantly enhanced capacitance (848 F·g-1 at 1 A g-1) and cycling stability (100% retention after 20 000 cycles). Moreover, flexible sandwiched supercapacitors with symmetrical h-Ti3C2Tx@h-TA electrodes exhibit a high energy density of 30.1 Wh kg-1 at a high power density of 300 W kg-1, outperforming those of Ti3C2Tx-based film electrodes and sandwiched supercapacitors reported so far. The extrusion-printed microsupercapacitors with h-Ti3C2Tx@h-TA electrodes demonstrate high areal capacitance (135 mF cm-2 at 5 mV s-1) along with energy storage performance (6.74 μWh cm-2 at 506 μW cm-2) and cycling stability (98.8% retention after 41 460 cycles), all while maintaining excellent flexibility. These impressive results indicate the great application potential of the hydrothermal Ti3C2Tx MXene and tannic acid composite in flexible energy storage devices.

Analysis of various system designs for adsorption cycle in building heating applications

Buildings are major energy consumers, highlighting the need for efficient thermal energy storage to reduce reliance on non-renewable sources. Adsorption-based systems offer significant energy savings for heating applications. This research compares four critical adsorption-based cycles: adsorption thermal energy storage, adsorption heat transformer, adsorption mass recovery with heating and cooling, and a novel combined cycle. The study uncovers new insights into temperature and pressure control challenges through lumped parameter modeling. These dynamic modeling results advance our understanding and optimization of adsorption systems, enhancing their feasibility and efficiency for building heating. The adsorption mass recovery cycle demonstrates superior energy storage density (289 kW h/m³) compared to the adsorption heat transformer cycle (240 kW h/m³) and the adsorption thermal energy storage cycle (157 kW h/m³). It also has the highest water uptake (0.56 kg/kg), surpassing the other two cycles. Despite its pressure fluctuations and temperature instability challenges, the adsorption mass recovery cycle outperforms the adsorption heat transformer and adsorption thermal energy storage cycles in energy storage density. The novel combined cycle optimizes heat storage and release, achieves the highest energy storage density (302 kW h/m³), and outperforms the individual cycles. The combined cycle's performance was evaluated in a home in South Korea, revealing significant energy savings and proving an effective solution for enhancing energy efficiency in building heating systems. This research addresses a crucial gap and provides a foundation for future advancements in thermal energy storage.

Probing the layer-dependent behavior of electronic properties and quantum capacitance in 2H MoS2: A computational analysis with emphasis on mechanical stability

The quest for clean, sustainable energy sources was prompted by the fast depletion of fossil fuels and the world's expanding energy requirements. To store renewable energy, it is important that effective energy storage devices such as supercapacitor (SCs) be manufactured. SCs offer a promising avenue for fast-charging, energy storage, and long-life cycles but maximizing their energy density remains a problem. This study theoretically explores the intrinsic Quantum capacitance (Cq) of MoS2 in the 2H phase with a few number of layers and how factors like electronic structure and density of states influence its capacitance behavior. In the present work, the first principles analysis utilizing computational modelling with Density Functional Theory (DFT) has been employed to investigate the Cq and surface charge density (σ) of MoS2. By explaining the connection between MoS2's electrical and structural properties with its Cq, valuable insights for optimizing it's SC performance were obtained. Both the density of states (DOS) and the Cq increase with the number of layers. Among the observed structures the highest value of Cq is observed for the three layered structure of 2H–MoS2 (2H3L-MoS2) at +1 V which is 1615.14 μF cm−2. Investigating the mechanical stability of optimized structure (2H3L-MoS2), a high Young's modulus of 180.46 GPa is observed for 2H3L structure. Hence, 2H-phase of MoS2 can be used as an excellent anode material for asymmetric SCs and flexible electronic devices.

Dynamic characteristics and performance analysis of a double-stage energy storage heat transformer with a large temperature lift

Intermittence and low grade are significant barriers for the widespread application of renewable/waste energy. An absorption energy storage heat transformer with adequate energy storage and temperature lift characteristics effectively addresses this challenge. An advancement in this technology is the double-stage energy storage heat transformer (DESHT), which further enhances the range of temperature upgrade through twice temperature lifts. This paper proposes a time-dependent approach for a comprehensive study of the DESHT cycle with a working pair of LiBr/H2O. Firstly, the dynamic characteristics of the DESHT cycle are shown. Subsequently, the effects of discharging temperatures, charging temperatures, and solution mass ratio on cycle performance are analyzed. Results show that the DESHT cycle can achieve a temperature lift from 35 °C to 55 °C. 90 % of the total storage capacity can be reached in 60–70 % of the total charging time. The maximum discharging time per unit of charging time is achieved at a temperature lift of 45 °C. Besides, compared to the conventional double-stage absorption energy storage cycle, the DESHT cycle shows a higher exergy efficiency. Optimizing the solution mass ratio can enhance the cycle performance. These findings can serve as a valuable reference in exploring the DESHT cycle.

Fe/LiNO3/TiN co–modified MgO for enhanced thermochemical energy storage performance in MgO/Mg(OH)2 cycles

MgO/Mg(OH)2 thermochemical energy storage can convert solar energy and industrial waste heat into forms that are easier to store and transport by cyclic hydration/dehydration reactions. To achieve excellent energy storage performance, cyclic stability and optical absorption capability of MgO/Mg(OH)2, Fe/LiNO3/TiN co–modified MgO were synthesized for energy storage cycles by wet-mixing method. The energy storage performance, cyclic stability and dehydration kinetics of Fe/LiNO3/TiN co–modified MgO were studied in dual fixed–bed system and simultaneous thermal analyzer. The experimental results show that the Fe and LiNO3 in the composite not only increase the hydration conversion of MgO by 6.3 times at 30 min, but also reduce the dehydration temperature and dehydration activation energy of Mg(OH)2 by 99.4 °C and 64 %, respectively. TiN overcomes aggregation of MgO and sustains the excellent porous structure, which results in only a 9 % decrease in energy storage performance of Fe/LiNO3/TiN co–modified MgO after 15 energy storage cycles. Subsequently, TiN significantly strengthens the optical absorption performance of Mg(OH)2 and photothermal temperature under xenon-lamp simulated sunlight radiation. Furthermore, density functional theory calculation reveals that Fe and Li enhance the adsorption of H2O on MgO model and reduce energy barrier for hydration reactions by 62.76 %, while TiN effectively inhibits MgO clusters migration within the material and enhances the optical absorption coefficient. Hence, Fe/LiNO3/TiN co–modified MgO shows significant research value in MgO/Mg(OH)2 energy storage process.

Lithium and water: Hydrosocial impacts across the life cycle of energy storage

AbstractAs a key ingredient of batteries for electric vehicles (EVs), lithium plays a significant role in climate change mitigation, but lithium has considerable impacts on water and society across its life cycle. Upstream extraction methods—including open‐pit mining, brine evaporation, and novel direct lithium extraction (DLE)—and downstream processes present different impacts on both the quantity and quality of water resources, leading to water depletion and contamination. Regarding upstream extraction, it is critical for a comprehensive assessment of lithium's life cycle to include cumulative impacts related not only to freshwater, but also mineralized or saline groundwater, also known as brine. Legal frameworks have obscured social and ecological impacts by treating brine as a mineral rather than water in regulation of lithium extraction through brine evaporation. Analysis of cumulative impacts across the lifespan of lithium reveals not only water impacts in conventional open‐pit mining and brine evaporation, but also significant freshwater needs for DLE technologies, as well as burdens on fenceline communities related to wastewater in processing, chemical contaminants in battery manufacturing, water use for cooling in energy storage, and water quality hazards in recycling. Water analysis in lithium life cycle assessments (LCAs) tends to exclude brine and lack hydrosocial context on the environmental justice implications of water use by life cycle stage. New research directions might benefit from taking a more community‐engaged and cradle‐to‐cradle approach to lithium LCAs, including regionalized impact analysis of freshwater use in DLE, as well as wastewater pollution, cooling water, and recycling hazards from downstream processes.This article is categorized under: Human Water > Human Water Human Water > Water Governance Human Water > Water as Imagined and Represented Science of Water > Water and Environmental Change

Economic and exergy transmission analysis of the gas-liquid type compressed CO2 energy storage system

Exergy transmission characteristic of the compressed CO2 energy storage system is significant to evaluate the system performance while little attention has been paid to this analytical method in the literature. A CO2 energy storage cycle configured with a gas holder as a low-pressure gas reservoir and a liquid tank as a high-pressure gas reservoir is studied comprehensively. The exergy transmission characteristics and the cost uncertain analysis are considered. Results demonstrated that the round trip efficiency and levelized cost of storage are 71.2 % and 0.1286 $/kWh under optimal design parameters, respectively. Keeping the charge/discharge duration ratio close to 1 has a positive effect on optimizing the economic performance of the system. With the general exergy model of the whole system configured for the charge and discharge process, the study uncovers the fluctuations in the pertinent proportional ratios and exergy transfer efficiency in relation to important parameters. Except for the turbomachinery isentropic efficiency, which impacts nearly all efficiencies, the variation of each parameter only governs the modification of the exergy transfer efficiency for a specific term or a pair of terms. Furthermore, the thermal exergy efficiency of the discharge process and intercooler has a maximum value as the cold-side temperature difference of the high-temperature cooler changes to 27 °C.

Operation strategy and optimization configuration of hybrid energy storage system for enhancing cycle life

Hybrid energy storage system (HESS) can take advantage of complementarity between different types of storage devices, while complementary strategies applied to configuration or operation have a significant impact on the battery cycle life. Therefore, in order to enhance the battery cycle life, this paper proposes an operation strategy and configuration technique for HESS and verifies it by a scenario of HESS tracking scheduling plan. Firstly, a linear rainflow counting method, which can be embedded in the optimization process, is proposed to quantitatively evaluate the cycle life of energy storage based on the half cycle identification model. Secondly, an operation strategy with the integration of the constraint of state-of-charge (SOC) recovery capability considering the dynamic degradation of energy storage cycle life during operation is proposed to ensure a certain charging and discharging margin for storages, thereby enhancing the cycle life of HESS. Thirdly, an optimization configuration model considering the operation strategy of HESS is established based on the minimum annualized investment cost. And the linearization techniques are used to transform the original problem into a mixed-integer linear programming problem, and the mathematical programming technique is adopted to solve the problem. Finally, the effectiveness of the proposed method is validated through case studies. The results of the case studies show that the use of the HESS operation strategy proposed in this paper can manage the VRB's SOC more efficiently, and the control effect of VRB's SOC is improved by 71.5 %. Meanwhile, by controlling the VRB's SOC, the cycle life of the energy storage in the HESS can be effectively improved, which reduces the annualized cost of the HESS by 53 %.

Comprehensive Dataset on Electrical Load Profiles for Energy Community in Ireland

This paper describes a comprehensive energy-related dataset, collected from residential electricity households within an energy community in Ireland, as part of StoreNet project. The data includes local weather parameters and per household power (W) and energy (Wh) components for various aspects such as active power consumption, PV generation, grid import and export, charging and discharging, and the state of charge of energy storage. Additionally, it provides weather data for the location at a 1-minute temporal resolution for the year 2020. The dataset has been validated by comparing measurements that should yield identical results to standard load profiles, with no significant inconsistencies discovered. Validation examples have also been given through the published articles where this dataset has been used to analyse peer-to-peer energy trading benefits for the energy community and decision-making support for aggregators. The dataset aids in understanding patterns in electrical load curves and the duty cycle of energy storage within an energy community. Furthermore, it can assist in comprehending the impact on distribution networks caused by distributed energy storage.

Experimental investigation of two-stage NH3–H2O resorption heat storage system with solution concentration difference

Widespread application of solar energy is severely restricted to its instability in time and space. Heat storage system is considered to be one of the most effective pathways to achieve long-term heat supply. Among all the heat storage technologies, solution concentration difference storage technologies stand out for low heat loss and high energy density. By substituting condenser and evaporator in conventional absorption cycle with a high-pressure absorber and low-pressure generator, a resorption cycle could be established. Compared with absorption heat storage cycle, working pressure of resorption heat cycle is lower, making it possible to utilize low-pressure heat source. Two-stage heat source cycle is further proposed to lower working pressure and upgrading supply water temperature. Resorption energy storage cycle with solution concentration difference is established and studied. A prototype based on two-stage ammonia-water resorption heat storage cycle was set up and tested. The result shows that the constraint relation between ambient temperature and heat source temperature of the proposed system. In single-stage mode, the lowest working ambient temperature is 5 °C when heat source temperature is 90 °C. The lowest working ambient temperature could be declined to 0 °C when heat source temperature rises to 120 °C. In two-stage mode, the lowest working ambient temperature is 0 °C when heat source temperature is only 110 °C, which proves the adaptability of two-stage cycle. The highest ESCOP appears in the 15 °C–120 °C single-stage mode, which is 0.742. The highest COP is 1.324 under the same condition. The highest energy density occurs in two-stage mode, which is 467.07 kJ/kg when ambient and heat source is set as 15 °C, 120 °C. The advantage that two-stage mode could enlarge solution concentration difference is verified.

Thermo-economic optimization of an innovative integration of thermal energy storage and supercritical CO2 cycle using artificial intelligence techniques

This research delves into the integration of Thermal Energy Storage (TES) and Supercritical Carbon Dioxide (s-CO2) in an innovative Energy Recycling System (ERS) that aims to improve overall system efficiency. The combination of TES and s-CO2 is a promising solution to address modern energy challenges and promote a sustainable and efficient energy future. For this research, the TES system is based on a packed bed of stones (PBS). This approach has several benefits, such as the use of inexpensive and readily available materials for storage, a broad range of operating temperatures, allowing for direct heat transfer, and the ability to achieve high maximum temperatures. The simulation methodology for TES is based on Schumann's approach, and energy and exergy analysis are used for thermodynamic modeling. Additionally, levelized costs are employed for the economic modeling of the system. Through rigorous thermos-economic modeling and simulation, operational parameters are optimized using genetic algorithms and neural network techniques to balance thermodynamic efficiency, energy storage, and economic feasibility. The findings reveal exceptional energy and exergy efficiencies, exceeding expectations, and suggest the ERS, with grid-scale energy storage, as a cost-effective solution. The simulations demonstrate remarkable energy and exergy efficiencies of 92.15% and 49.66%, respectively, with levelized costs of 104.69 €/MWh for heat, 135.20 €/MWh for electricity, and 65.7€/MWh for storage.

Synthesis of Organopolysilazane Nanoparticles as Lithium-Ion Battery Anodes with Superior Electrochemical Performance via the Two-Step Stöber Method.

The Stöber method, a widely utilized sol-gel technique, stands as a green and reliable approach for preparing nanostructures on a large scale. In this study, we employed an enhanced Stöber method to synthesize organopolysilazane nanoparticles (OPSZ NPs), utilizing polysilazane oligomers as the primary precursor material and ammonia as the catalytic agent. By implementing a two-step addition process, control over crucial parameters facilitated the regulation of the nanoparticle size. Generally, maintaining relatively low concentrations of organopolysilazane and catalyst while adjusting the water/acetonitrile ratio can effectively enhance the surface energy of the organopolysilazane, resulting in the uniform formation of small spherical particles. The average particle size of the synthesized OPSZ NPs is about 140 nm, which were monodispersed and characterized by scanning electron microscopy, transmission electron microscopy, and dynamic light scattering. Furthermore, the composition of OPSZ NPs after pyrolysis was confirmed as SiC2.054N0.206O1.631 with 5.44 wt % free carbon structure by X-ray diffraction and energy-dispersive X-ray spectroscopy. Notably, the electrochemical performance assessment of SiCNO NPs as potential electrode materials for lithium-ion batteries exhibited promising outcomes. Specifically, at 1 A g-1 current density, the specific capacity is 585.45 mA h g-1 after 400 cycles, and the minimum capacity attenuation per cycle is only 0.1076 mA h g-1 (0.0172% of the original capacity), which indicates excellent energy storage capacity and cycle stability. In summary, this research contributes to the development of advanced anode materials for next-generation energy storage systems, marking a stride toward sustainable energy solutions.

A multi-scale modeling of Ca-based material for solar-driven calcium-looping energy storage process: From calcination reactor to energy carrier

The calcium looping (CaL) for thermochemical energy storage possesses a great potential to promote solar thermal utilization. However, the performance of CaL, especially for the Ca-based energy carrier, cannot satisfy the expectations of industrial application, requiring enhancement between multiple length scales. Hence, a model for solar-driven CaL energy storage process, coupled by three-dimensional reactor, two-dimensional light field and one-dimensional particle models, is proposed to study the multiprocess behavior on particle flow, photothermal conversion, calcination reaction, heat-mass transfer and stress response. It is found that moving-bed reactor contributes to achieving continuous calcination and reducing particle waste, while the rapid bouncing particles inhibit the performance of single particle, with up to 45.7 % reduction in conversion. Additionally, energy carrier with stable and continuous flow normally yields high energy storage efficiency and cycle stability when the conversion of outlet particle is closed to 1 and thermal stress is less than 50 MPa.

TiO2/MnFe2O4 co-modified alkaline papermaking waste for CaO-CaCO3 thermochemical energy storage

CaO-CaCO3 thermochemical energy storage is a promising technology for solar energy utilization and storage. Alkaline papermaking waste (APW) from paper mills, which is mainly composed of CaCO3. Herein, TiO2/MnFe2O4 co-modified APW was synthesized. The energy storage capacity of TiO2/MnFe2O4 co-modified APW was studied during CaO-CaCO3 thermochemical energy storage cycles in a duel fixed bed reactor. TiO2/MnFe2O4 co-modified APW mainly consists of CaO, MgO, CaTiO3, CaMnO3, and Ca2Fe2O5. The introductions of TiO2 and MnFe2O4 significantly improve the cyclic stability and optical absorption property of APW in 30 cycles. The co-modified APW (the mass ratio for CaO:TiO2:MnFe2O4 = 100:5:5) possesses high sintering resistance, energy storage, and optical absorption capacities in 30 cycles. The energy storage conversion and capacity of the co-modified APW are 0.72 and 2288.57 kJ/kg after 30 cycles, respectively. The optical absorptance of the co-modified APW reaches 49%, which is 9.25 times as high as that of APW. CaTiO3 and CaMnO3 effectively mitigate the sintering of CaO grains. CaMnO3 and Ca2Fe2O5 significantly increase the optical absorptance of APW. The co-modified APW possesses stronger basicity and more oxygen vacancies, which is favourable for the carbonation reaction. Thus, TiO2/MnFe2O4 co-modified APW is a good energy storage material.

Enhancement of the Power-to-Heat Energy Conversion Process of a Thermal Energy Storage Cycle through the use of a Thermoelectric Heat Pump

The principal strategy for achieving a neutral climate entails enhancing the share of renewable energies in the energy mix, in conjunction with promoting innovation in efficient technologies. Thermal energy storage systems have the potential to efficiently handle the intermittent nature of renewable energy sources. Furthermore, these systems can effectively handle shifts in both heat and electrical demand. Thus, efficient power-to-heat technologies are needed to boost thermal energy storage. This manuscript explores the potential of utilising a thermoelectric heat pump system in conjunction with electric resistances for charging a thermal energy storage. In order to achieve elevated temperatures, the thermoelectric system integrates thermoelectric heat pump blocks in a two-stage configuration. Air has been employed as a heat transfer medium for sensible heat storage. Higher airflow rates improve the performance of thermoelectric heat pump system. Moreover, its impact on the optimal voltage supply of the thermoelectric system is observed when it is combined with an electric resistance to achieve elevated temperatures. In comparison to the basic charging process that solely relies on the electric resistance of a thermal energy storage at 120 °C, a significant 30 % increase in power-to-heat energy conversion has been achieved by including the thermoelectric heat pump system. In fact, it efficiently elevates the temperature from the initial ambient temperature of 25 °C to a remarkable 113.1 °C, achieving a coefficient of performance of 1.35 with an airflow rate of 23 m3/h. Therefore, the use of this technology to enhance a complete process of storing excess renewable energy in the form of heat for subsequent use in both heat and electricity through a combined heat and power cycle is demonstrated.

The Norbornadiene/Quadricyclane Pair as Molecular Solar Thermal Energy Storage System: Surface Science Investigations.

For the transition to renewable energy sources, novel energy storage materials are more important than ever. This review addresses so-called molecular solar thermal (MOST) systems, which appear very promising since they combine light harvesting and energy storing in one-photon one-molecule processes. The focus is on norbornadiene (NBD), a particularly interesting candidate, which is converted to the strained valence isomer quadricyclane (QC) upon irradiation. The stored energy can be released on demand. The energy-releasing cycloreversion from QC to NBD can be initiated by a thermal, catalytic, or electrochemical trigger. The reversibility of the energy storage and release cycles determines the general practicality of a MOST system. In the search for derivatives, which enable large-scale applications, fundamental surface science studies help to assess the feasibility of potential substituted NBD/QC couples. We include investigations under well-defined ultra-high vacuum (UHV) conditions as well as experiments in liquid phase. Next to the influence of the catalytically active surfaces on the isomerization between the two valence isomers, information on adsorption geometries, thermal stability limits, and reaction pathways of the respective molecules are discussed. Moreover, laboratory-scaled test devices demonstrate the proof of concept in various areas of application.