Thermal Energy Storage Subsystem Research Articles

Economic impact of thermal energy storage on natural gas power with carbon capture in future electricity markets

As policies evolve to reflect climate change goals, the use of fossil fuel power plants is expected to change. Many fossil fuel power plants may opt to incorporate carbon capture and storage (CCS) technologies in response to evolving emissions policies. Additionally, fossil plants may need to be operated flexibly to accommodate the growing concentration of renewable energy systems. Unfortunately, most CCS technologies are very expensive, and they impose a parasitic load on the power plant, thereby decreasing net power output and the ability to operate flexibly. This investigation evaluated the economic potential of using hot and cold thermal energy storage (TES) to supplement the peak power output and flexibility of a natural gas combined cycle (NGCC) power plant with CCS capabilities. The two TES subsystems (hot and cold) were charged during periods of relatively low electricity prices and discharged during NGCC operation: resistively heated hot TES to offset the CCS parasitic heat load and vapor compression cooled cold TES to chill the inlet air to the power plant. Thermodynamic models were created for the base NGCC + CCS power plant, the hot TES equipment, and the cold TES equipment, to determine key performance and cost parameters such as net power output, fuel consumption, emissions captured, capital costs, and operational costs. These parameters were then used to simulate the operation of the power plant with and without the TES technologies in accordance with fourteen electricity pricing structures predicted for different future electricity market scenarios. The difference in net present value (NPV) between the base NGCC + CCS power plant and power plant with the TES technologies was used as the primary economic metric in this analysis. The NPV benefit from increased revenue due to TES utilization was found to outweigh the NPV penalty from the additional capital costs. This economic result was attributed to the low cost of the TES equipment and the ability to charge the storages using cheap electricity from high levels of renewable output. The results have shown that hot TES increased NPV in 12 of 14 market scenarios while the cold TES increased NPV in 14 of 14 market scenarios. A combination of both hot and cold TES yielded the largest increases in NPV.

Performance investigation of standalone multi-effect mechanical vapor compression desalination system powered by cascade photovoltaic/thermal-photovoltaic solar field-assisted heat pump system

A new stand-alone system of modified multi-effect mechanical vapor compression (ME-MVC) desalination unit powered by photovoltaic/thermal-photovoltaic (PVT-PV) collectors is studied The system incorporates solar-assisted heat pumps (HPs), an external preheater, and electrical and thermal energy storage subsystems. The system is investigated under different seawater feed configurations, effects number, and HP evaporator temperatures. It is compared with the conventional PV-powered single-effect mechanical vapor compression (SE-MVC) desalination system. The designed system is modeled and solved using MATLAB under weather conditions of Alexandria, Egypt, in terms of energy and economics impacts. Results indicate that the combined subsystem of the solar-assisted HPs and ME-MVC of parallel/cross feed and four effects has the lowest electricity consumption of 6.39 kWh/m3 while the value for SE-MVC is 7.58 kWh/m3. The average daily freshwater production of the proposed system is 86.4 m3 in summer and 72.89 m3 in winter with a freshwater cost of 5.11 $/m3. Yearly PVT-PV electrical efficiencies are 20.51 % and 19.35 %, respectively, whereas PVT thermal efficiency is 46.65 % and the overall solar system combined efficiency is 20.31 %. The proposed system's electricity consumption is 15.7 % lower, its solar system's efficiency is 23.54 % larger, and its freshwater cost is 3 % lower than that of the PV-powered SE-MVC.

Performance analysis and optimization study of a new supercritical CO2 solar tower power generation system integrated with steam Rankine cycle

Currently, the supercritical CO2 solar tower power generation (S-CO2 STPG) has become a research hotspot, but due to S-CO2 Brayton cycle characteristics, the solar energy utilization rate of the system is low. Therefore, a new S-CO2 STPG system integrated with steam Rankine (SR) cycle is first proposed. The SR cycle absorbs the waste heat of the S-CO2 Brayton cycle, and the introduction of the SR cycle can increase the solar energy utilization rate. The research is based on the simulation results, the system model is developed by Ebsilon, and system operation calculation is developed by MATLAB. The daily and monthly performances of the new S-CO2 STPG system integrated with SR cycle are compared with those of conventional S-CO2 STPG system in detail. The system location is Bakersfield. The comparative analysis results show that compared with the conventional system, the monthly power output for the new system rises significantly, especially in summer. The new system can effectively improve the solar energy utilization rate. The effect of SR cycle power output on new system performance is studied. Increasing SR cycle power output can improve the thermal energy storage subsystem and solar field subsystem performances. The optimal SR cycle power output is related to the solar radiation level. The Fargo, Bakersfield and Phoenix are selected as three places representing low-direct normal irradiance (DNI), medium-DNI and high-DNI districts, respectively. For the medium-DNI and high-DNI districts, the SR cycle power outputs corresponding to the optimal thermal performance and optimal economic performance are 20 MW and 15 MW, respectively; for the low-DNI district, those are 15 MW and 5 MW, respectively.

Evaluation of discharging performance of molten salt/ceramic foam composite phase change material in a shell-and-tube latent heat thermal energy storage unit

Molten salts are widely used energy storage media in integrated solar power systems, however, due to their high corrosivity and the extreme high-temperature environment, many current methods of heat transfer enhancement do not apply. Herein, we proposed to use ceramic foam to enhance the discharging performance of molten salt to efficiently supply heat for power generation. The ceramic foam was prepared and its corrosion resistance was confirmed experimentally. The discharging performance in a shell-and-tube latent heat thermal energy storage unit was numerically studied. It is found that compared to the configuration without enhancement, the solidification time of the ceramic foam-enhanced unit is shortened by up to 52.0%. The unit with the upper foam insert shows better discharging performance than the one with the lower foam insert. Different foam filling height is also considered and results indicate that the thermal energy release rate always increases with the foam filling height and that of the fully foam-inserted unit is 118.1% higher than that of the none foam-inserted unit. For the first time, the discharging performance of ceramic foam-enhanced molten salt is quantitatively evaluated. This study provides guidance on designing thermal energy storage sub-system with excellent heat supply performance for solar power generation.

An efficient hydrogen production process using solar thermo-electrochemical water-splitting cycle and its techno-economic analyses and multi-objective optimization

A conceptual solar thermo-electrochemical water-splitting system is developed for producing green hydrogen and electricity. The system consists of a solar power tower and thermal energy storage subsystem, a four-step Cu-Cl thermo-electrochemical water-splitting cycle, supercritical CO2 Brayton cycle, and waste heat recovery unit with an organic Rankine cycle. The system is simulated in Aspen Plus with the mathematical models of the heliostat fields and electrolyzer written in the Fortran language and embedded. The performance of the proposed system is evaluated and optimized based on energy, exergy, techno-economic analysis, and sustainability assessment. The tradeoff between maximum exergy efficiency, minimum total annual cost (TAC), and minimum levelized cost of hydrogen (LCOH) is conducted by multi-objective optimization, which is implemented based on the non-dominated sorting genetic algorithm-II and the interaction between Aspen Plus and MATLAB software. The Pareto solutions indicate that the optimal exergy efficiency, TAC, and LCOH are 48.72 %, 50.96 M$/year, and 1.28 $/kg, respectively, and the LCOH is 36 % lower than that reported in the literature.

Heat storage design and performance analysis of a parabolic trough thermal power generation system based on sectional heating collection

The integration of solar thermal utilization and energy cascade utilization can bring the possibility to increase the overall plant efficiency by decreasing the exergy loss while maintain a firm supply. This paper takes SEGS VI Plant and its improved plant using sectional heating as research object, two novel thermal energy storage subsystem structures were proposed and designed for the improved plant, to explore the enhancing effect of energy cascade utilization on commercial solar thermal power plants. Calculation models of the energy storage efficiency and collector field multiples of the thermal energy storage tank were established. This paper used the software Ebsilon to establish the simulation model of the commercial 30 MW solar thermal power plant with traditional thermal energy storage structure, the improved plants with two different thermal energy storage structures, and conducted the performance analysis of the plants under design and operating conditions. The results show that, compared with the system using traditional thermal energy storage structure, the overall plant efficiency of the improved plant adopt the novel thermal energy storage structure increased by 0.71% and 0.95% under design conditions day, the overall plant efficiency increased by 0.60% and 0.81% under operating conditions, which can realize the better use of energy. Simultaneously, the total capital investment cost and levelized cost of electricity also can be reduced by 6.77 M$ and 4c$/kWh, which has good application prospects.

Transient thermodynamic modeling and economic analysis of an adiabatic compressed air energy storage (A-CAES) based on cascade packed bed thermal energy storage with encapsulated phase change materials

With the penetration of solar and wind plants into the energy markets, power production is becoming more erratic; therefore, a promising energy storage system is required for a reliable grid. Adiabatic compressed air energy storage, as a large-scale energy storage technology, has great promise to mitigate the challenges of managing the variability and intermittency of renewable energy generation. The Thermal Energy Storage subsystem is a key component that improves the efficiency of adiabatic compressed air energy storage, making it a feasible option as a large-scale energy storage system for scalability. In this article, a comprehensive investigation of a novel, efficient, and green adiabatic compressed air energy storage system based on a cascade packed bed thermal energy storage filled with encapsulated phase-change materials is employed, encompassing thermodynamic and economic aspects of the cycle, and transient modeling of the TES tanks. The objective of the proposed concept is to recover the waste heat generated in the compression process as much as possible to improve system performance. In this regard, the influence of the introduced thermal energy storage configuration on the efficiency and exergy destruction of the system is studied and compared with basic designs. The findings show that round trip energy and exergy efficiencies of 61.5% and 68.2% with a payback period is 3.5 years, resulting from the consumption of low-price off-peak electricity for charging and generating power at the peak demand hours.

Concurrent optimization and 4E analysis of organic Rankine cycle power plant driven by parabolic trough collector for low-solar radiation zone

TheOrganic Rankine Cycle driven by parabolic trough collectors for the low-solar radiation zone was investigated in this study. Six environment-friendly refrigerants namely R152a, R600a, R601a, cyclopentane, cyclohexane, toluene were evaluated.In addition, the conventional Rankine cyclewas evaluated. The dynamic energy and exergy analysis based on the daily average solar data was conducted. The system was designed in a combination solar field, thermal energy storage subsystem, and power block for 24 h of working time without any external energy source. The designed system was concurrently optimized through the economic indicator namely net present value since all the parameters depend on each other. The best design was obtained for conventional cycle with a net present value of 9.012 million US$. The optimum pressure and temperature of the turbine inlet were determined as 3250 kPa and 380oC, respectively. The optimal ratio of the heat transfer fluid was found around 34.1%. The maximum energy and exergy efficiencies were respectively obtained as 11.05% and 11.86%. These values were respectively conducted as 10.19% and 10.94% at the design point. It was also conducted that the reductions in the emissions of CO2, SO2,and NOxwere 108,046.4 ktones, 2,457.6 ktones, and 249.7 ktones, respectively.

Design and development of an innovative integrated structure for the production and storage of energy and hydrogen utilizing renewable energy

Herein, solar dish collector, phase change material energy storage, solid oxide electrolysis cell, and thermoelectric generator sub-systems for synchronous supply of hydrogen and electricity in Farakhi village was introduced for the first time and comprehensively investigated. A hybrid renewable energy system was integrated into the integrated structure to generate and store the direct current electrical energy required by the solid oxide electrolysis cell sub-system and other consumers. Modeling of solar dish collector, phase change material energy storage, and thermoelectric generator sub-systems were performed in MATLAB engineering software, while solid oxide electrolysis cell sub-system modeling was carried out both in ASPEN HYSYS and MATLAB software. In addition, the modeling of hybrid renewable energy system was conducted by HOMER Pro software. It is worth noting that this is the first study presented on the use of hybrid renewable energy system to generate and store electrical energy required by process facilities. The influence of influential parameters on the proficiency of each sub-system was examined comprehensively through sensitivity analysis. The results obtained revealed that the amount of utilizable heat absorbed by the heat transfer fluid as well as the outlet temperature of the collector in summer was considerable than the amount of heat required. Therefore, most of the heat stored in the thermal energy storage sub-system occurred in this season. During charging process of the thermal energy storage sub-system 60.56 kWh of energy was stored. The output power of the thermoelectric generators increased with the molar flow rates of oxygen and hydrogen streams. PV/WT/BG/Bat hybrid system was selected as the best option to supply the required electricity. The share of photovoltaic panels, wind turbines, and biogas generators to supply the required electricity in the first scenario were 53.3%, 35.0%, and 11.6%, respectively. The efficiency of the hybrid system without and considering the thermoelectric generator sub-system was achieved 79.72% and 80.69%, respectively.

Operation Strategy Analysis and Configuration Optimization of Solar CCHP System

This paper proposed a new type of combined cooling heating and power (CCHP) system, including the parabolic trough solar thermal (PTST) power generation and gas turbine power generation. The thermal energy storage subsystem in the PTST unit provides both thermal energy and electrical energy. Based on the life cycle method, the configuration optimization under eight operation strategies is studied with the economy, energy, and environment indicators. The eight operation strategies include FEL, FEL-EC, FEL-TES, FEL-TES&EC, FTL, FTL-EC, FTL-TES, and FTL-TES&EC. The feasibility of each strategy is verified by taking a residential building cluster as an example. The indicators under the optimal configuration of each strategy are compared with that of the separate production (SP) system. The results showed that the PTST-CCHP system improves the environment and energy performance by changing the ratio of thermal energy and electric energy. The environment and energy indicators of FEL-TES&EC are superior to those of FTL-TES&EC in summer, and the results are just the opposite in winter. The initial annual investment of the PTST-CCHP system is higher than that of the SP system, but its economic performance is better than that of the SP system with the increase of life-cycle.

Development of a new integrated energy system with compressed air and heat storage options

The present study investigates a biomass driven power plant integrated with compressed air and thermal energy storage subsystems. Compressed air energy storage system exploits the pressurized air at non-peak periods to be used in peak times when there is a need for extra energy. Thermal energy storage systems including phase change material, allow the solar subsystem to operate independently in order to produce hot air when solar irradiation is insufficient. The energy stored in the present system is then supplied to both the gasifier and combustion chamber in order to achieve a higher combustion efficiency. Three different phase change materials (PCMs) are investigated and their efficiencies are comparatively evaluated. Among the considered PCMs, LiNO3 is the most suitable material for the considered system with 82% energy efficiency and 84% exergy efficiency. The current study also aims at designing a renewable energy based power plant which operates continuously through using storage subsystems and is more environmental benign compared to fossil fuel based conventional systems. In this regard, wet wood (CH1.46O0.64N0.002) with 15% moisture content is selected as a fuel instead of fossil-based fuels in order to reduce the greenhouse gas emissions and eliminate the dependency on fossil fuels. A comprehensive thermodynamic analysis is conducted to evaluate the entropy generations, exergy destructions, and energy and exergy efficiencies. The highest overall energy and exergy efficiencies are obtained as 28.58% and 24.08% in the discharging period, respectively.

Dynamic modeling and behavior of parabolic trough concentrated solar power system under cloudy conditions

As a promising application of solar energy, parabolic trough concentrating solar power with indirect thermal energy storage has been widely used in concentrating solar power plants constructed in China. The dynamic modeling and behavior of the power plants were important for achieving fast start-up and shut down and to overcome weather disturbances. This study investigated the dynamic characteristics of a 50 MW parabolic trough concentrating solar power plant with indirect thermal energy storage. Simplified cloud disturbances were simulated to obtain the dynamic characteristics of a power block coupled with solar field and thermal energy storage. Simulation results indicated that the thermal inertia of solar field is an order of magnitude larger than that of power block and thermal energy storage subsystems, and the heat transfer fluid temperature at the solar field outlet fluctuates within a narrow range at rated value under the control scheme of solar field. The disturbances caused by heat transfer fluid temperature fluctuation were reduced by thermal energy storage operation. To minimize the generation load fluctuation under thick-cloud condition, the thermal energy stored in solar field could be used to moderate the fluctuation caused by the start-up of thermal energy storage discharging exchanger.

Design and analysis of a solar tower power plant integrated with thermal energy storage system for cogeneration

In the current study, a solar tower–based energy system integrated with a thermal energy storage option is offered to supply both the electricity and freshwater through distillation and reverse osmosis technologies. A high-temperature thermal energy storage subsystem using molten salt is considered for the effective and efficient operation of the integrated system. The molten salt is heated up to 565°C through passing the solar tower. The thermal energy storage tanks are designed to store heat up to 12 hours. The temperature variations in the storage tanks are studied and compared accordingly for evaluation. The effect of operating temperatures on the freshwater production and overall system efficiency is determined. About 24.46 MW electricity is generated in the steam turbine under sunny conditions. Furthermore, the storage subsystem stores heat during sunny hours to utilize later in cloudy hours and night time. The produced power decreases to 20.17 MW in discharging hours due to temperature decrease in the tank. The electricity generated by the system is then used to produce freshwater through the reverse osmosis units and also to supply electricity for the residential use. A total flowrate of 240.02 kg/s freshwater is obtained by distillation and reverse osmosis subsystems.

Progress in thermochemical energy storage for concentrated solar power: A review

Energy plays an important role in a fast-paced modern society. With the depletion of fossil energy, effective utilization of solar energy is getting increasingly urgent. Thermal energy storage is an inevitable choice for effective utilization of renewable energy sources. As one of the most promising renewable energy sources, solar energy is inexhaustible. But it has some shortcomings such as instability and intermittency, affected by time, climate, and geographical location. Thermal energy storage technology, which can effectively reduce the cost of concentrated solar power generation, plays a crucial role in bridging the gap between energy supply and demand. In addition, thermal energy storage subsystem can improve performance and reliability of the whole energy system. According to different principles, thermal storage technology is generally classified as sensible heat storage, latent heat storage, and thermochemical energy storage. Most solar thermal power generation systems, currently demonstrated and operated in the world, adopt the method of sensible thermal energy storage. In contrast, thermochemical energy storage is a relatively new concept, which is still in the stage of basic test and verification. Thermochemical energy storage technology stores and releases energy through endothermic and exothermic reversible reactions. A closed system with separated reactants and products, in theory, can store energy indefinitely. The main thermochemical energy storage systems include redox system, metal hydride system, carbonate decomposition system, ammonia decomposition system, methane reforming system, and inorganic hydroxide system.

Performance assessment of a solar hydrogen and electricity production plant using high temperature PEM electrolyzer and energy storage

This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants.

On numerical model of one-dimensional time-dependent gas flows through bed of encapsulated phase change material

Mathematical model and numerical method are proposed for investigating the one-dimensional time-dependent gas flows through a packed bed of encapsulated Phase Change Material (PCM). The model is based on the assumption of interacting interpenetrating continua and includes equations of state, continuity, momentum conservation and energy for PCM and gas. The advantage of the method is that it does not require predicting the location of phase transition zone and can define it automatically as in a usual shock-capturing method. One of the applications of the developed numerical model is the simulation of novel Adiabatic Compressed Air Energy Storage system (A-CAES) with Thermal Energy Storage subsystem (TES) based on using the encapsulated PCM in packed bed. Preliminary test calculations give hope that the method can be effectively applied in the future for modelling the charge and discharge processes in such TES with PCM.

Heat recovery and storage installation in large-scale battery systems for effective integration of renewable energy sources into power systems

The large-scale battery is a promising solution to reduce the wind and solar curtailments, while some electricity will be dissipated to heat and wasted inevitably. In this contribution, a heat recovery and thermal energy storage (TES) subsystem are introduced to the battery system to recover heat generated by the battery and satisfy a part of heat load concurrently. By applying the newly proposed power flow method in heat transfer system analysis together with the traditional power system analysis method, the power flow mode of the integrated electric and thermal energy system is established, and the system is then optimized to reduce wind curtailment. The optimized results present that the introduction of the heat recovery and TES subsystem could supply a certain percentage of heat to residents by recovering the generated heat from the battery and decrease the coal consumption of the thermal power plant and the combined heat and power plant simultaneously. Meanwhile, the mass flow rate of the heat conducting oil keeps high in most time and drops to near zero when the battery switches between charge and discharge. Furthermore, the alternation frequency of the mass flow rate of the heat conducting oil has a lower bound for normal operation.

Solar Thermal Energy with Molten-salt Storage for Residential Heating Application

Abstract Heating application is one of the areas in residential building where residents pay a significant part of energy bill. Thermal energy from solar irradiance can be collected by solar thermal collector (STC) and absorbed by heat transfer fluid (HTF) to transport heat to the heat-exchanger and to the load. This paper investigated various solar collectors and considered parabolic trough collector (PTC) to develop a residential heating application. The system structure mainly consists three subsystems: solar thermal absorption subsystem, thermal energy storage subsystem and underfloor heating subsystem. Because of temperature range and specific heat capacity Nitrate salt (0.54KNO3+0.46NaNO3) was considered in the model. A typical house in Melbourne with heating area of approximately 240m 2 is considered as thermal load. Model was evaluated for summer, winter and yearly load demand and result showed that molten-salt storage helped the system to operate consistently even at night-time (19:00 – 05:00) without solar radiation.

Design and analysis of a solar tower based integrated system using high temperature electrolyzer for hydrogen production

This paper studies the integration of solar tower technology and thermal energy storage (TES) with a power plant and a high temperature Solid Oxide Steam Electrolyzer (SOSE) to produce hydrogen from solar energy. The different subsystems are integrated and optimized to achieve high overall energy efficiency, maintain continuous operation, and reduce exergy destruction. In this regard, energy and exergy analyses are conducted to investigate the requirements and performance of the SOSE while powered by a solar tower subsystem. Therefore, the SOSE cell performance is modeled and the hydrogen production is measured based on different cell and solar field operating conditions. The SOSE is modeled as an integral part of a concentrated solar power plant where the power produced is used for hydrogen production as a final product. In order to maintain continuous plant operation, a TES subsystem is integrated. Furthermore, a supercritical carbon dioxide (s-CO2) Brayton cycle is adapted for the power plant for high efficiency energy conversion from thermal to electric energy. The overall integrated system solar-to-hydrogen conversion efficiency is found to be about 12.7% while charging the TES, and 39.5% while discharging (TES-to-hydrogen). These high efficiencies rank this technology as competitive with other renewable hydrogen production technologies. The integrated high temperature TES achieved energy and exergy efficiencies of more than 96%. The main implementation challenges are discussed in addition to the comprehensive energy and exergy analyses which provide deeper insight into the performance of the system components, potential improvements and limitations.

Dynamic Behavior of a Sensible-heat based Thermal Energy Storage

In this paper, a mathematical model is developed to study the behavior of thermal energy storage (TES) under operation in the particular case of Adiabatic Compressed Air Energy Storage (A CAES). The A CAES consists of storing the available extra electrical energy of the electricity network in a form of compressed air (in a cavern) to discharge it during peak periods. The TES sub-system is used to charge and discharge the corresponding heat of compression, leading to a quasi adiabatic mode and an increase in the overall electricity storage efficiency (roughly from 50 to 70%) compared to diabatic CAES. The mathematical model has been converted into a computer simulation program with all the effective parameters of heat transfer in the storage reservoir. This model used to define a geometry reservoir able of storing a given power and restore it while maintaining a required temperature level at the output of unit. The influence of the input and output parameters on the storage efficiency is studied. The results illustrate the behavior of the storage reservoir under dynamic mode.