Thermal Storage Research Articles

Trimodal thermal energy storage material for renewable energy applications.

The global aim to move away from fossil fuels requires efficient, inexpensive and sustainable energy storage to fully use renewable energy sources. Thermal energy storage materials1,2 in combination with a Carnot battery3-5 could revolutionize the energy storage sector. However, a lack of stable, inexpensive and energy-dense thermal energy storage materials impedes the advancement of this technology. Here we report the first, to our knowledge, 'trimodal' material that synergistically stores large amounts of thermal energy by integrating three distinct energy storage modes-latent, thermochemical and sensible. The eutectic mixture of boric and succinic acids undergoes a transition at around 150 °C, with a record high reversible thermal energy uptake of 394 ± 5% J g-1. We show that the transition involves melting of the boric acid component, which simultaneously undergoes dehydration into metaboric acid and water that dissolve into the liquid. Being retained in the liquid state allows the metaboric acid to readily rehydrate to re-form boric acid on cooling. Thermal stability is demonstrated over 1,000 heating-cooling cycles. The material is very low cost, environmentally friendly and sustainable. This combination of a solid-liquid phase transition and a chemical reaction demonstrated here opens new pathways in the development of high energy capacity materials.

Integrating a phase change material based thermal energy storage system with a solar vacuum timber dryer

ABSTRACT This study focused on the development of a solar-heated vacuum dryer with a thermal-energy storage system. The timbers layers were stacked between specially fabricated aluminum platens, integrated with sealed tubes filled with phase-change material (PCM) for thermal storage. Each platen had openings in both the ends to allow hot water enter from one end and exit through another end. An evacuated tube collector (ETC)-based solar hot-water system was used to heat the water, and the hot water was flown through the platens for melting and charging of the PCM inside the tubes. The platens, along with the wood layers, were placed in a vacuum tank. During the day, the heating of wood and the melting of PCM were done simultaneously, while in night time, wood layers got heated through conduction using stored heat in the platens. Two 38 mm thick hardwoods (Populus deltoides and Mangifera indica) were dried in January, the coldest month in India. Moisture content of Populus deltoides (initial moisture content of 110%) and Mangifera indica (initial moisture content of 95%) dropped to the final moisture content of 14% in nine days of the drying with an average moisture content drop of of 10.7%/day and 8.9% perday, respectively.

Collaborative Control Strategy of Electric–Thermal–Hydrogen-Integrated Energy System Based on Variable-Frequency Division Coefficient

To address the issues of diverse energy supply demands and power fluctuations in integrated energy systems (IESs), this study takes an IES composed of power-generation units, such as wind and photovoltaic units, along with various energy-storage systems, including electrical, thermal, and hydrogen storage, as the research subject. A collaborative control strategy is proposed for the IES, which comprehensively considers the status of diverse energy-storage systems like battery packs, thermal tanks, and hydrogen tanks. First, a mathematical model of the IES is constructed. Then, a dual-layer collaborative control strategy is designed, considering different operating modes of the IES, which includes a multi-energy-storage power allocation control layer based on second-order power-frequency processing and distribution and an adaptive adjustment layer for adjusting power-frequency coefficients based on adaptive fuzzy control. Finally, MATLAB is used to simulate and validate the proposed strategy. The results indicate that the collaborative control strategy based on variable-frequency coefficients optimizes the allocation of fluctuating power among multiple energy-storage systems, enhances the stability of bus voltage, reduces the deep charge and discharge time of battery packs, and extends the service life of battery packs.

Physics-based numerical evaluation of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) in the Upper Jurassic reservoir of the German Molasse Basin

Abstract. Concepts of High-Temperature Aquifer Thermal Energy Storage (HT-ATES) (> 50 °C) are investigated in this study for system application in the Upper Jurassic reservoir (Malm aquifer) of the German Molasse Basin (North Alpine Foreland Basin). The karstified and fractured carbonate rocks exhibit favourable conditions for conventional geothermal exploitation of the hydrothermal resource. Here, we perform a physics-based numerical analysis to further assess the sustainability of HT-ATES development in the Upper Jurassic reservoir. With an estimated heating capacity of approx. 19.5 MW over half a year, our approach aims at determining numerically the efficiency of heat storage under the in situ Upper Jurassic reservoir conditions and projected operation parameters. In addition, the hydraulic performance of the HT-ATES system is further evaluated in terms of productivity and injectivity index. The numerical models build upon datasets from three operating geothermal sites at depths of approx. 2000–3000 m TVD, located in a subset of the reservoir dominated by karst-controlled fluid fluxes. Commonly considered as a single homogeneous unit, the 500 m thick reservoir is subdivided into three discrete layers based on field tests and borehole logs from the three considered sites. The introduced vertical heterogeneity with associated layer-specific enhanced permeabilities allows to examine potentially arising favourable heat transfer, and in combination with the facilitated high operation flow rates (100 kg s−1) to evaluate thermal recoveries in the multilayered reservoir. All simulations account for fluid density and viscosity variation based on thermodynamically consistent equations of state (EOS). Computation results reveal that the reservoir layering induces preferential fluid and heat migration primarily into the high-permeability zone, while thermal front propagation into the lower permeable rock matrix is inhibited. The simulations further display a gradual temperature increase in the warm wellbore and its surrounding host rock, and a consequent progressive improvement in the heat recovery efficiency. Despite the elevated permeability that may trigger advective heat losses, heat recovery factor values range from approx. 0.7 over the first year of operation to over 0.85 after 10 years of operation. An additional scenario is examined with fluid injection solely in the high permeable zone, in order to quantify potential enhancement in the recovery efficiency by omitting fluid injection in the lower-permeability layers where heat propagation is diminished. This is due to the geometrical shape of the thermally perturbed rock volume as heat losses occur during thermal equilibration between injected fluid and reservoir rock, as well as at the contact-surface area between propagating thermal front and adjacent rock matrix. Results suggest that under the stratified reservoir configuration, additionally constrained by the selected spatial distribution of rock properties, heat storage performed only into the upper high-permeability zone corresponds to an improved thermal performance. Simulation results further indicate that density-induced buoyant fluxes, which would considerably decrease thermal efficiencies are inhibited in the system, and the prevailing heat transport mechanism is forced convection.

Evaluation of a micro-particle-enhanced phase-change material integrated heat pipe evacuated tube solar collector system using lanthanum oxide/water nanofluid

ABSTRACT In this study, the thermal performance of a microparticle-enhanced form-stable phase change material (PCM) integrated heat pipe evacuated tube solar collector (ETSC) system is evaluated through outdoor experimentation. The study examines the thermal performance of PCM-enhanced ETSC using acetamide with varying percentages of expanded graphite (EG) at 10, 15, and 20 wt% and aluminum microparticles at 1, 2, and 5 wt%, focusing on the use of EG at different concentrations and microparticles. The microparticle-enhanced form-stable PCM is integrated into the tube only. The system was tested under open environmental conditions, comparing outcomes with a normal ETSC system, considering water outlet temperature, charging-discharging behaviors, collector efficiency, and energy analysis. The study revealed that the micro-particle enhanced PCM integrated heat pipe ETSC system significantly improved thermal performance, energy storage and release capabilities, and efficiency in generating heat at lower solar irradiance, compared to conventional ETC systems. The maximum collector efficiency of 47.4% is achieved when utilizing acetamide with 10% EG and 2% Al, which is 10.9% more than conventional ETSC. The study explores the use of lanthanum oxide/water nanofluid in solar collectors, revealing that increasing nanoparticle concentrations enhances water outlet temperature, heat gain, and solar thermal collector efficiency up to 64.14%.

Latent Thermal Energy Storage for Cooling Demands in Battery Electric Vehicles: Development of a Dimensionless Model for the Identification of Effective Heat-Transferring Structures

Thermal energy storage (TES) systems open up alternative paths for air conditioning to increase the range of battery electric vehicles (BEVs) by reducing power consumption. The central prerequisites for this purpose are high storage densities: high-temperature TES systems are being focused on for heat demands, while effective solutions for cooling are missing. Due to their lower temperature potentials, concepts with high storage capacities and heat transports between the storage and cold transferring medium are needed. Latent TES systems based on water enable these capacities but require adequate internal structures for effective heat transfer. Due to the large number of geometric options, high simulation efforts must be conducted to identify favored structures, or the possible design space must be limited for investigations. For this purpose and for the first time, an alternative way is presented using newly developed dimensionless models in a top-down methodology for time-efficient design studies and evaluations. These models were successfully validated and used as a design tool to identify effective structures in latent TES systems for cooling demands in BEVs. A wide array of variation studies on tube, finned plate and novel Triply Periodic Minimal Surface (TPMS) structures were performed and uniformly evaluated with regard to storage densities, cooling efficiencies and geometry. The results show high storage densities for novel TPMS structures, including the enclosure of 100 Wh/kg or 102.2 kWh/m3 with average cooling capacities of 1 kW over 30 min, confirming the usability of latent TES systems in terms of compactness and efficiency for cooling demands in BEVs.

Nuclear Cogeneration to Support a Net-Zero, High-Renewable Electricity Grid

UK Government projections anticipate increasing electricity use, provided by variable renewables (i.e., wind and solar PV). A side effect of increasing the proportion of variable renewable generation is increased support costs, including curtailment, energy storage, and (most significantly) the cost of supplying electricity for periods of high demand when variable renewable generation is low. As the proportion of variable renewable capacity increases, demand for supporting capacity increases but the capacity factor of the support generation decreases, raising the support costs. Using nuclear power for dedicated baseload supply makes the situation worse. This paper explores in the UK context an original low-cost solution using nuclear cogeneration with hydrogen production as the main application. Electricity is diverted at low cost to the grid at times of high demand when renewables are not available. This ensures nuclear maintains a high capacity factor. When higher temperature advanced systems become available, using thermal energy storage will increase the nuclear electrical capacity. This “Flexible Nuclear” scenario substantially reduces support costs for accommodating variable renewables, saving GBP 14 bn/yr and leading to an 80% reduction in CO2 equivalent emissions, compared to a recent UK Government scenario utilising a large capacity of hydrogen and unabated gas generation at very low capacity factors.

Development of a simplified model of a water thermal storage tank for district heating network modeling tool

Development of a simplified model of a water thermal storage tank for district heating network modeling tool

Innovative Approaches to Bridging Energy Supply and Demand Gaps Through Thermal Energy Storage: A Case Study

This study investigates innovative solutions for balancing energy supply and demand using long-term thermal energy storage (TES) systems, with a focus on tank thermal energy storage (TTES) for European buildings, which account for approximately 40% of energy consumption in the European Union. Research conducted at the Technical University of Košice explores the potential of TTES systems for efficient and long-term energy storage. The accumulation is carried out in three existing underground tanks of different volumes. Among various outputs, we present the cooling process resulting from covering the water surface and the effect of tank size on cooling. The findings indicate that covering the water surface in the tanks can effectively double the energy retention time, thereby extending the cooling period. A tank with a larger volume cools slower and better ensures the formation of temperature layers. Temperature layering allows for better utilization of the tanks’ potential in terms of energy. The overall result is a significant reduction in heat losses and CO₂ emissions. These results demonstrate the critical role of TTES in stabilizing renewable energy sources, especially solar energy, to support sustainable energy solutions in buildings by providing reliable and long-term energy storage.

Explore the operational performance of phase change radiation terminal heating system in different heating zones of China

IntroductionHeating is one of the main factors leading to high energy consumption and serious carbon emissions in buildings. The clean heating system formed by the coupling of phase change building maintenance structure and solar heating system can improve the thermal storage density of the building maintenance structure, while reducing energy consumption in winter while maintaining a comfortable room temperature through stable energy security.MethodsTherefore, a phase change radiation terminal heating (PCRTH) system with the phase change radiation module as the terminal and the solar energy and air energy as the clean heat source is established in this study. Nanjing, Tianjin and Shenyang in China were selected as the study zones which correspond to the hot summer and cold winter zone, the cold zone and the severe cold zone respectively. The operational effect of the PCRTH system in different climate zones was studied, and the parameters of the PCRTH system were optimized by the GenOpt program combined with Hooke-Jeeves optimization algorithm.ResultsThe analysis results show that the cascade phase change radiation terminals in the three zones reduced room temperature fluctuation, energy consumption and carbon dioxide emissions, but the heating cost was higher. After the Hooke-Jeeves optimization algorithm was used to optimize the PCRTH system parameters in three zones, the PCRTH system heating cost was reduced, and the PCRTH system energy consumption and PCRTH system carbon dioxide emissions were further reduced.DiscussionTherefore, the building heating system composed of PCM maintenance structure and renewable energy has great application advantages in maintaining a comfortable room temperature and improving heating system energy conservation and environmental protection.

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.

Improvement of Heat Conduction in Triply Periodic Minimal Surface Heat Sinks Filled with Phase Change Materials

Recently phase change materials (PCMs) have received significant attention in the field of thermal management and energy storage systems. However, the thermal performance of PCMs is restricted by their low thermal conductivity. Triply periodic minimal surface (TPMS) is a novel surface with high strength, high specific surface area, and high connectivity, which can be applied in PCM heat sinks to enhance the local heat transfer rate. In this study, a topology optimization method for TPMS structures applied in PCM heat sinks with the objective of least dissipation of heat transport potential capacity is proposed. The optimized structure has a higher volume fraction of metal material near the heating surface while lower in the region away from the heating surface. Furthermore, the optimized structure accelerates the advancement of the melting interface. With a constant heat flux on the heating surface, the average temperature of the heating surface can be reduced by about 30 K compared to the uniform TPMS structure.

Thermodynamics analyses on a novel CHP system integrated with multi-grade thermal energy storage

The high penetration level of intermittent renewable power necessitates the crucial requirement for combined heat and power systems to possess both high efficiency and flexibility. However, the heat-controlled operation modes of traditional combined heat and power systems impose limitations on their efficiency and flexibility. Therefore, it is of great significance to develop a heat-power decoupling technology that exhibits exceptional efficiency and flexibility. A novel combined heat and power system integrated with multi-grade thermal energy storage is proposed in this study. Thermodynamic analysis models of all operational conditions are developed, and the comprehensive characteristics of efficiency and operational flexibility for the proposed system are assessed by taking a 330 MW system as an example. Results show that the proposed system can decrease/increase 16.05 MW/30.96 MW power loads comparing with the reference system during the charging/discharging periods under the design condition. Energy efficiency of the proposed system can reach 49.40 %, which is improved by 1.66 percentage points. Exergy analysis reveals the exergy destruction order for the proposed system, and shows that the combustion and heat transfer in the boiler are the major process of exergy dissipation. Moreover, operation strategies of the proposed system during charging-discharging cycle are explored and formulated under off-design condition, suggesting that thermodynamic performances of the novel system under various conditions even extreme conditions exhibits exceptional properties. The maximum heat load of the proposed system can be improved by 46.78 % comparing with the reference system, and the maximum improvement of power load capacity during charging-discharging cycle is 14.58 percentage points. This study provides a promising approach for multi-grade thermal energy storage to improve the comprehensive characteristics of combined heat and power systems.

The Integration of Thermal Energy Storage Within Metal Hydride Systems: A Comprehensive Review

Hydrogen storage technologies are key enablers for the development of low-emission, sustainable energy supply chains, primarily due to the versatility of hydrogen as a clean energy carrier. Hydrogen can be utilized in both stationary and mobile power applications, and as a low-environmental-impact energy source for various industrial sectors, provided it is produced from renewable resources. However, efficient hydrogen storage remains a significant technical challenge. Conventional storage methods, such as compressed and liquefied hydrogen, suffer from energy losses and limited gravimetric and volumetric energy densities, highlighting the need for innovative storage solutions. One promising approach is hydrogen storage in metal hydrides, which offers advantages such as high storage capacities and flexibility in the temperature and pressure conditions required for hydrogen uptake and release, depending on the chosen material. However, these systems necessitate the careful management of the heat generated and absorbed during hydrogen absorption and desorption processes. Thermal energy storage (TES) systems provide a means to enhance the energy efficiency and cost-effectiveness of metal hydride-based storage by effectively coupling thermal management with hydrogen storage processes. This review introduces metal hydride materials for hydrogen storage, focusing on their thermophysical, thermodynamic, and kinetic properties. Additionally, it explores TES materials, including sensible, latent, and thermochemical energy storage options, with emphasis on those that operate at temperatures compatible with widely studied hydride systems. A detailed analysis of notable metal hydride–TES coupled systems from the literature is provided. Finally, the review assesses potential future developments in the field, offering guidance for researchers and engineers in advancing innovative and efficient hydrogen energy systems.

Grooved single-channel dual media tank thermal energy storage systems to improve overall thermal performance: Numerical analysis

In this study, a numerical analysis of a single-channel structured dual media tank (DMT) thermal energy storage (TES) system is done to investigate the effect of grooves on thermo-hydraulic performance. Due to computational complexity, a single channel is considered, and results are validated by the numerical results of other studies. The study encompasses the analysis of unsteady temperature distribution, heat transfer coefficient, and friction factor by varying the groove size ratio with the diameter of the pebbles. The φ ratio (grooves diameter/pebbles diameter) is varied from 3.15 to 4.73, and the effect of the Re for different widths of the channel is studied. The numerical result reveals a 50 % increase in heat transfer coefficient when φ is varied from 3.15 to 4.73 at a Reynolds number of 22.4. Similarly, a small variation in the frictional factor can be observed. amounts to 22 % while keeping a Reynolds number of 22.4 and a diameter ratio (φ) ranging from 3.15 to 4.73. Furthermore, research is done on how Reynolds number affects volumetric heat transfer (ℎv). The results indicate a 31 % decrease in ℎv at φ = 3.15. on the other hand, a larger value of φ is observed to result in a lesser drop in ℎv. Additionally, the computation performance improvement factor (PEF) shows greater values for φ = 3.15, indicating that the ideal groove diameter to achieve maximum heat transfer rate and minimum pressure drop is smaller.

Developing energy-efficient cool roof coatings using microencapsulated eutectic phase-change material and poly(methyl methacrylate-co-methacrylic acid) copolymer shell emulsion

ABSTRACT The rise in the construction of modern structures of buildings has increased the demand for energy sources to cool indoor and outdoor temperatures. Cool coating is a highly effective roofing technology for absorbing less heat and reflecting more sunlight than conventional coating. These coatings are made from a special type of material with high solar reflectance, allowing them to reflect more sunlight. The cool coating is applied over the building roofs, which gives an efficient way to cool the building inside passively and the surrounding environment. In this context, incorporating phase-change material (PCM) into cool coating enhances its capacity for regulating temperature by storing and releasing heat as required. Combining these two would improve the coating’s overall cooling capabilities, increasing its efficacy in maintaining a lower surface temperature and lowering the cooling energy consumption in buildings. There is a lack of research studies incorporating PCM into a cool roof coating. The present work fills this gap. In this study, we have developed an easy-to-maintain thermal storage cool roof coating using microencapsulated phase-change material (MPCM) latex and white cement. This coating integrates a cooling effect, making it ideal for building applications. Lauric acid (LA), palmitic acid (PA), and stearic acid (SA) eutectic PCM as core were microencapsulated with polymethyl methacrylate-co-methacrylic acid (PMMA-co-MAA) shell using oil-in-water emulsion polymerization. The microcapsule was prepared by altering the core-to-shell ratio. The microcapsules were characterized using various techniques such as thermogravimetric analysis (TGA), polarized optical microscopy (POM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The melting temperature of LA-PA-SA eutectic PCM, MPCM 1, and MPCM 2 was 32.66°C, 31.47°C, and 32.73°C, respectively. The TGA analysis indicates that the prepared microcapsules have good thermal stability and degrade in two steps. Microcapsules’ average particle size diameter was observed in the 3–9 µm range. The cool roof coating was fabricated by partially replacing the acrylic copolymer latex with prepared MPCM 1 latex. This study evaluates the influence of MPCM 1 latex loading on the coating’s mechanical and thermal properties. The temperature changes from the building’s exterior to the interior have been recorded using thermal energy transfer analysis. General coating properties such as water resistance, stain resistance, alkali resistance, and gloss were investigated. DSC result shows that the thermal storage enthalpy of the coating has been improved from 17.85 J/g to 37.45 J/g by partially replacing MPCM 1 latex with acrylic copolymer from 50 to 70 wt.%. Coating with 70 wt.% MPCM 1 latex reduced the rise in the room’s temperature, showing it to be a promising candidate for utilizing thermal energy within building technologies.

Integrated Energy Management in Small-Scale Smart Grids Considering the Emergency Load Conditions: A Combined Battery Energy Storage, Solar PV, and Power-to-Hydrogen System

This study introduces an advanced Mixed-Integer Linear Programming model tailored for comprehensive electrical and thermal energy management in small-scale smart grids, addressing emergency load shedding and overload situations. The model integrates combined heat and power sources, capable of simultaneous electricity and heat generation, alongside a mobile photovoltaic battery storage system, a wind resource, a thermal storage tank, and demand response programs (DRPs) for both electrical and thermal demands. Power-to-hydrogen systems are also incorporated to efficiently convert electrical energy into heat, enhancing network synergies. Utilizing the robust Gurobi solver, the model aims to minimize operating, fuel, and maintenance costs while mitigating environmental impact. Simulation results under various scenarios demonstrate the model’s superior performance. Compared to conventional evolutionary methods like particle swarm optimization, non-dominated sorting genetic algorithm III, and biogeography-based optimization, the proposed model exhibits remarkable improvements, outperforming them by 11.4%, 5.6%, and 11.6%, respectively. This study emphasizes the advantages of employing DRP and heat tank equations to balance electrical and thermal energy relationships, reduce heat losses, and enable the integration of larger photovoltaic systems to meet thermal constraints, thus broadening the problem’s feasible solution space.

Sustainable and Self-Sufficient Fresh Water Through MED Desalination Powered by a CPV-T Solar Hybrid Collector: A Numerical and Experimental Study

The effects of global warming are severely recognizable and, according to the OECD, 47% of the world’s population will soon live in regions with insufficient drinking water. Already, many countries depend on desalination for fresh water supply, but such facilities are often powered by fossil fuels. This paper presents an energy self-sufficient desalination system that runs entirely on solar power. Sunlight is harvested using parabolic trough collectors with an effective aperture area of 1.5 m × 0.98 m and a theoretical concentration ratio of 150 suns, in which a concentrator photovoltaic thermal (CPV-T) hybrid-absorber converts the radiation to electricity and heat. This co-generated energy runs a multi-effect distillation (MED) plant, whereby the waste heat of multi-junction concentrator solar cells is used in the desalination process. This concept also takes advantage of synergy effects of optical elements (i.e., mirrors), resulting in a cost reduction of solar co-generation compared to the state of the art, while at the same time increasing the overall efficiency to ~75% (consisting of an electrical efficiency of 26.8% with a concurrent thermal efficiency of 48.8%). Key components such as the parabolic trough hybrid absorber were built and characterized by real-world tests. Finally, results of system simulations, including fresh water output depending on different weather conditions, degree of autonomy, required energy storage for off-grid operation etc. are presented. Simulation results revealed that it is possible to desalinate around 2,000,000 L of seawater per year with a 260 m2 plant and 75 m3 of thermal storage.

Optimal Scheduling of Virtual Power Plants Under a Multiple Energy Sharing Framework Considering Joint Electricity and Carbon Trading

The virtual power plant (VPP) is an excellent approach for mitigating the intermittency and fluctuation of renewable energy sources. The present work proposes an optimal scheduling model for VPPs to leverage the benefits of joint electricity and carbon trading from the perspective of multiple energy-sharing mechanisms. First, the optimal sharing scheduling model of the electric, thermal, and hydrogen energy was established. The model integrates various components, including wind turbines, photovoltaic units, electrolytic cells, combined heat and power units, hydrogen-doped gas boilers, electric energy storage, thermal storage tanks, and hydrogen storage tanks. Then, the model incorporates a tiered carbon trading mechanism to minimize operating and trading costs. Finally, numerical results indicate that, compared with the independent operation of virtual power plants and the lack of joint electricity and carbon trading, the optimal scheduling scheme proposed in this paper reduces the total cost and carbon emissions of the three VPPs by 3.3% and 49.7%, respectively. This demonstrates that the proposed model can effectively reduce the total operating expenses of VPPs by facilitating the allocation of electric, thermal, and hydrogen energy and achieving low-carbon emission operations.

Flexibility enhancement of combined heat and power unit integrated with source and grid-side thermal energy storage

The potential of improvement of both overall energy efficiency and penetration of renewable energy for the combined heat and power (CHP) unit was investigated by integrating the source-side and grid-side thermal energy storage (TES) systems simultaneously. The mathematical model of the proposed thermal system was established, with which the flexibility-enhancing features across diverse operating conditions were analyzed. The flexibility improvement rate, heat consumption rate, TES cycle efficiency and energy efficiency were revealed. Moreover, the wind power consumption, coal-savings and net annual revenue of CHP unit integrated with different TES were presented. The results indicated that the flexibility improvement rate of source-side TES, grid-side TES and dual TES is 2.4 %, 21.2 % and 26.2 %, respectively. The heat consumption rate of a CHP unit integrated with source-side TES system is lower compared to that of a traditional CHP unit when power load ratio is below 50 %. The CHP unit integrated with a dual TES system exhibited a maximum increase in wind power accommodation rate of 37.7 % and a maximum reduction in standard coal consumption of 7.7 %. The proposed systems offer a promising approach for enhancing the flexibility of CHP units to accommodate more renewable energy.