Sensible Heat Thermal Energy Storage Research Articles

Influence of the air-cooled supercritical carbon dioxide recompression cycle design-point on molten salt power tower techno-economic performance

This paper investigates the techno-economic performance of a molten salt power tower integrated with an air-cooled supercritical carbon dioxide recompression cycle. Prior research into the cycle design point showed trade-offs between efficiency, cost, and temperature difference across the heat input, resulting in trade-offs between the design-point generation of the molten salt power tower system and the cost of sensible-heat thermal energy storage. Prior research into cycle off-design showed that colder ambient temperature designs have higher efficiencies on cold days but lower efficiency and capacity degradation on hot days. We present a framework to evaluate how cycle design, cost, and corresponding off-design performance affect the techno-economic performance of the molten salt power tower system. We use a steady-state off-design cycle model assuming fixed shaft speeds, inventory control, and air-cooler fan power control and integrate the cycle model with the molten salt power tower model from the National Renewable Energy Laboratory’s System Advisor Model. First, we present a surrogate model that uses a heuristic approach to correct the interpolation when the cycle reaches capacity limitations at ambient temperatures hotter than design. Next, we evaluate how the recompression cycle design-point ambient temperature, air-cooler approach temperature, air-cooler fan power, and recuperator conductance influence cycle and system design metrics. Finally, we complete annual simulations using an hourly “duck curve” pricing schedule and present annual performance metrics to evaluate the cumulative effects of the cycle design parameters and corresponding off-design performance on molten salt power tower techno-economics.

Numerical study on heat transfer augmentation techniques in concrete based thermal storage module for solar-thermal applications

• Thermal performance of sensible heat storage prototype is studied. • Heat transfer augmentation is investigated by varying the fin configuration. • The maximum reduction in charging time is 36.9%/. • Proposed optimized model increases the discharging rate by 75.6%. • Trapezoidal fin configuration is the best option with 50–75% cost reduction. In this study, the development and performance analysis of a concrete based thermal energy storage module with a capacity of 170 MJ operating in the temperature range of 523 K to 623 K is presented. To enhance the heat transfer rate in concrete based sensible heat thermal energy storage (SHTES) systems, the well-proven technique of fin incorporation is implemented. Longitudinal fins are attached on the outer side of the heat transfer fluid supply tube without compromising the thermal storage/discharge capacity of the storage module. Numerical simulations have been performed using COMSOL Multiphysics to study the thermal performance of the module by varying the design parameters such as the number of fins, fin dimension, and fin shape. The thermal performances of the models with fins, in terms of charging/discharging time and heat storage/retrieval rate, are compared with the model without fins for the same boundary condition. From the numerical study, it is observed that the maximum reduction in charging/discharging times of the storage module is 36.9%/48.1% and 36.9%/45.6% for rectangular and trapezoidal fin shaped models, respectively, in comparison with the model without fins. Whereas, the corresponding enhancement in heat storage/heat retrieval rate is 58.5%/92.7% and 58.5%/83.7% for rectangular and trapezoidal fin shaped models, respectively, in comparison with the model without fins. By adopting a trapezoidal shaped profile model, the fin material usage can be reduced by 50–75% without compromising on thermal performance. This numerical analysis would facilitate the design and development of efficient storage modules for solar thermal applications.

Study of eutectic organic phase change materials with enhanced thermal properties

Power shortage is a multifaceted problem of the developing nations. Due to the energy crisis, India, one of the Asia’s key economies is experiencing power shortages. During the recent years, electricity demand has gone up while there is a crunch in coal inventory at the thermal power plants. Therefore augmenting resources from solar energy to nuclear and fossil fuels helps to meet the energy demand. Thermal energy storage [TES] is an enabling technology which improves reliability, integrate generation sources and also help reduce environmental impacts. Phase change materials (PCMs) have been favourable in accumulation of energy in the form of latent heat. Latent heat thermal energy storage (LHTES) is preferred over sensible heat thermal energy storage (SHTES) due to thermal stability and higher storage density. This paper impart cognizance on methods to enhance thermal properties by introducing organic eutectic phase change materials (EO-PCMs) and nano-enhanced PCMs. Outcome of differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FT-IR), thermal reliability and thermal conductivity tests for various eutectic mixtures have been examined. Though practical application of PCMs is limited due to formidable challenges such as discharge during phase transformation and low thermal conductivity, eutectic PCMs & nano-enhanced PCMs address the aforementioned challenges due to congruent melting, stability under thermal cycling and significant sorption capacity. Finally, it deliberates some emerging research topics and challenges involved in developing EO-PCMs and nano-enhanced PCMs.

Fibre-Reinforced Geopolymer Concretes for Sensible Heat Thermal Energy Storage: Simulations and Environmental Impact

Power plants based on solar energy are spreading to accomplish the incoming green energy transition. Besides, affordable high-temperature sensible heat thermal energy storage (SHTES) is required. In this work, the temperature distribution and thermal performance of novel solid media for SHTES are investigated by finite element method (FEM) modelling. A geopolymer, with/without fibre reinforcement, is simulated during a transient charging/discharging cycle. A life cycle assessment (LCA) analysis is also carried out to investigate the environmental impact and sustainability of the proposed materials, analysing the embodied energy, the transport, and the production process. A Multi-Criteria Decision Making (MCDM) with the Analytical Hierarchy Process (AHP) approach, taking into account thermal/environmental performance, is used to select the most suitable material. The results show that the localized reinforcement with fibres increases thermal storage performance, depending on the type of fibre, creating curvatures in the temperature profile and accelerating the charge/discharge. High-strength, high-conductivity carbon fibres performed well, and the simulation approach can be applied to any fibre arrangement/material. On the contrary, the benefit of the fibres is not straightforward according to the three different scenarios developed for the LCA and MCDM analyses, due to the high impact of the fibre production processes. More investigations are needed to balance and optimize the coupling of the fibre material and the solid medium to obtain high thermal performance and low impacts.

Steady-state off-design modeling of the supercritical carbon dioxide recompression cycle for concentrating solar power applications with two-tank sensible-heat storage

Concentrating solar power researchers are evaluating the potential of the supercritical carbon dioxide recompression cycle to improve the thermal efficiency and decrease the capital costs of next-generation systems. This analysis investigates the steady-state off-design performance of a recompression cycle integrated with two-tank sensible-heat thermal energy storage as the ambient temperature and heat-transfer fluid (HTF) inlet conditions to the cycle change. This paper presents off-design component models and then cycle convergence and control models to maximize net cycle power output while constraining the high-side pressure and air-cooler fan power to their respective design values and fixing the cycle HTF outlet temperature to its design value. Results show that inventory control and air-cooler fan power are important control parameters that can be optimized to maximize off-design power output as the ambient temperature and HTF mass flow rate diverge from design. The high-side pressure and fan power constraints cause the cycle net power to degrade when the ambient temperature is warmer than the design value, and this study calculates a maximum mass flow rate for hot days above which the cycle cannot achieve the design HTF outlet temperature. Finally, the analysis shows that optimizing compressor shaft speeds can improve cold-day performance by around 1.5 percentage points and part-load performance by up to 2.5 percentage points versus a baseline case with no active compressor control.

Experimental characterization of a Sensible Heat Thermal Energy Storage using pebbles for charging

In today’s world, where reduction in the carbon footprints is emphasised, people are looking for alternative source of energies for power production and heat treatment of metals and alloys. One such alternative source is solar energy but due to intermittent nature a thermal energy storage (TES) is required in order to deal with heat flux that varies throughout the day so as to supply a constant power. In the present study, the characterization of the sensible heat thermal energy storage (SHTES) packed with sensible heat storage material are considered. The size of pebbles varies between 20-25mm with porosity of the SHTES as 40%. The flow rate is 40 LPM and TES was charged for 8 hours. It has been noticed that when the temperature of the inlet air is around 180°C, the temperature of the top surface of the TES is around 70°C which states that for TES high thermal conductivity materials are required so that charging and discharging can take place at faster rate. The azimuthal and axial variation of temperature is also shown and it is concluded that even after low thermal conductivity of the material azimuthal variation can be neglected for the sake of modeling the TES.

SWOT analyses of high-temperature phase change materials for thermal energy storage

High-Temperature Latent heat thermal energy storage (HTLHTES) is gaining importance to store thermal energy at high temperature. Large storage capacity, compact system and near-isothermal operating conditions are some of the added advantages of LHTES over sensible heat thermal energy storage (SHTES). HTLHTES system uses phase change material (PCM) to store thermal energy. This research identifies the possible integration of HTLHTES in Concentrated Solar power (CSP) plant at high-temperature. Energy storage improves the dispatchability of CSP plants. At high temperature, thermal reliability and corrosion behaviour of PCM are significant challenges. A detailed analysis of state-of-art technology and recent advancement in the field of high-temperature PCM are presented while focusing on problems and its solutions. The report is summarised in strength-Weakness-Opportunities-threats (SWOT) table on parameters like thermophysical properties, material response and corrosion behaviour of PCM. SWOT results highlight the strength, weakness of PCM and opportunities and threats for future research of high-temperature PCM. At present, the authors of this study are investigating the phase change behaviour of Al-Si alloys through modelling and simulation. SWOT analysis of this alloy, when compared to other PCMs, is done to understand the applicability of the alloy as LHTES. In this study, the authors also proposed a thermophysical property-based newer approach to compare PCMs.

Development of a Model for Performance Analysis of a Honeycomb Thermal Energy Storage for Solar Power Microturbine Applications

Solar power microturbines are required to produce steady power despite the fluctuating solar radiation, with concerns on the dispatchability of such plants where thermal energy storage may offer a solution to address the issue. This paper presents a mathematical model for performance prediction of a honeycomb sensible-heat thermal energy storage designed for application of concentrated solar power microturbine. The focus in the model is to consider the laminar developing boundary layers at the entry of the flow channels, which could have a profound effect on the heat-transfer coefficient due to large velocity and temperature gradients, an effect which has not been considered in the modelling of such storage systems. Analysing the thermal and hydrodynamic boundary layer development, the Nusselt number and the friction factor were evaluated using a validated conjugate heat-transfer method. The simulations results were used to develop accurate regression functions for Nusselt number and friction factor. These formulations have been adopted within a one-dimensional model to evaluate the performance of the storage under different operating conditions. The model was in good agreement with conjugate heat transfer results with maximum relative error below 2%. Two case studies are presented to demonstrate the applicability of the proposed methodology.

Where is Thermal Energy Storage (TES) research going? – A bibliometric analysis

Energy storage technologies can provide energy security, fight climate change, and improve the value of current or future energy systems. Thermal Energy Storage (TES) is a key enable technology, it allows to stock thermal energy that can be further used for heating and cooling applications and power generation. The methods and tools used to analyse all the literature about the evolution of TES systems research are described in this paper. Bibliometrics is the science that studies, in a statistical way, the written publications of a certain field of research, and it is considered one of the few interdisciplinary research fields that can be extended to almost all scientific areas. The bibliometric analysis of the database Web-of-science (core collection) shows highlighted information in order to figure out the scientific outputs. The importance of the bibliometrics is to analyse a knowledge development from a strategic point of view in order to detect its evolution regarding the research in such a field and to detect which are the opportunities within this area. This study presents the publication evolution in TES field over the last two decades, per year, per country, per authors, per journal, and per TES technology, taking into account sensible heat TES (SHTES), latent heat TES (LHTES), and thermochemical energy storage (TCS), and considering the connection between authorship communities and country interactions. The communities are obtained from the co/authorships, regardless of the country or affiliation; this permits to view the size of the communities, as well as to identify collaboration opportunities between communities with low or no interaction. Furthermore, studies are included regarding detailed analysis on each TES technology, as well as other factors (such as funding) that can influence the current and future research.

A General Model for Thermal Energy Storage in Combined Heat and Power Dispatch Considering Heat Transfer Constraints

Heat transfer (HT) is a major constraint in thermal system analysis. However, when discussing utilizing the flexibility provided by the heating sector, for example, using thermal energy storage (TES) to increase operational flexibility of combined heat and power (CHP), the HT process is often ignored. This may mean infeasibility of the resulting schedules. In response to this, this paper proposes a general TES model which takes detailed HT analysis into account. By setting the relevant parameters, this model can be used to describe the HT process for both sensible heat (SH) and latent heat (LH) TES devices. An iteration method is proposed to deal with the nonlinearity introduced by the HT constraints, and to solve the joint nonlinear dispatch problem for CHP with TES. The simulation results show that explicitly considering the HT process is essential to realistically assess and therefore make full use of the flexibility provided by TES. Moreover, the comparison between LH and SH TES shows that LH can provide more flexibility for the system, especially when the starting energy level in the TES device is low.

Parametric study of cascade latent heat thermal energy storage (CLHTES) system in Concentrated Solar Power (CSP) plants

Recently, Concentrated Solar Power (CSP) is attracting numerous research attentions, and thermal energy storage (TES) system filled with energy storage media is a critical component in all CSP plants. To realize a high energy storage efficiency (ξ) and exergy efficiency (η), a comprehensive study to the cascade latent heat thermal energy storage (CLHTES) system is necessary from the perspective of heat transfer. In this study, a dimensionless parametric study was presented using an enthalpy-based 1D transient model for energy storage/extraction in CLHTES system. A dimensionless parameter space (τr, HCR, Stf*) was constructed by considering ξ and η as the objective functions to explore the effects from dimensionless material properties (such as latent heat, specific heat at solid and liquid phases) and dimensionless operational parameters (such as charging/discharging time period, TES tank height and diameter). It is recommended that when HCR<0.5 and Πc/Πd<1.0, the system performance is very sensitive to HCR and Πc/Πd, furthermore for the same TES tank volume (H/D = D/H = 1.0), the sensitivity by varying its diameter alone is double than that from changing its height. The novelty of this study is to provide the design criteria for the CLHTES system, so that it can easily be designed and its efficiencies can be competitive to sensible heat thermal energy storage (SHTES) system. The results from this parametric study and sensitivity analysis are expected to benefit the solar thermal research and industry community to design the CLHTES system.

Storing energy for cooling demand management in tropical climates: A techno-economic comparison between different energy storage technologies

This paper addresses the role of energy storage in cooling applications. Cold energy storage technologies addressed are: Li-Ion batteries (Li-Ion EES), sensible heat thermal energy storage (SHTES); phase change material (PCM TES), compressed air energy storage (CAES) and liquid air energy storage (LAES). Batteries and CAES are electrical storage systems which run the cooling systems; SHTES and PCM TES are thermal storage systems which directly store cold energy; LAES is assessed as a hybrid storage system which provides both electricity (for cooling) and cold energy. A hybrid quantitative-qualitative comparison is presented. Quantitative comparison was investigated for different sizes of daily cooling energy demand and three different tariff scenarios. A techno-economic analysis was performed to show the suitability of the different storage systems at different scales. Three parameters were used (Pay-back period, Savings-per-energy-unit and levelized-cost-of-energy) to analyze and compare the different scenarios. The qualitative analysis was based on five comparison criteria (Complexity, Technology Readiness Level, Sustainability, Flexibility and Safety). Results showed the importance of weighing the pros and cons of each technology to select a suitable cold energy storage system. Techno-economic analysis highlighted the fundamental role of tariff scenario: a greater difference between peak and off-peak electricity tariff leads to a shorter payback period of each technology.

Thermal energy storage characteristics of sand as filler material for solar thermocline tank

The feasibility of sand at various grain sizes as filler material for solar sensible heat thermal energy storage(TES) was investigated. An indirect contact sensible heat TES experiment setup was built. The TES section is a cylindrical tank, which is embedded with 19 stainless tubes arranged like a hexagonal honeycomb. Air was chosen as the heat transfer fluid to flow inside the tubes and carry heat, while the sand in the tank contacts the outside of tubes. Four types of sand: silver sand, medium sand, filter sand and coarse sand, were selected. The results show that voidage is the determining factor for the TES performance rather than density or grain size. Coarse sand is the best among the four types. For materials such as sand whose basic thermal properties only vary a bit, the change of charge temperature can hardly affect the TES performance. When using air as the heat transfer fluid, the TES efficiency is relatively lower. To enhance heat transfer, a lower air velocity or longer tube length is needed. The simplified 2-D simulation results match well with the experimental results and can be used for the prediction of large scale TES tank performance.

Finite Element Method Modeling of Sensible Heat Thermal Energy Storage with Innovative Concretes and Comparative Analysis with Literature Benchmarks

Efficient systems for high performance buildings are required to improve the integration of renewable energy sources and to reduce primary energy consumption from fossil fuels. This paper is focused on sensible heat thermal energy storage (SHTES) systems using solid media and numerical simulation of their transient behavior using the finite element method (FEM). Unlike other papers in the literature, the numerical model and simulation approach has simultaneously taken into consideration various aspects: thermal properties at high temperature, the actual geometry of the repeated storage element and the actual storage cycle adopted. High-performance thermal storage materials from the literatures have been tested and used here as reference benchmarks. Other materials tested are lightweight concretes with recycled aggregates and a geopolymer concrete. Their thermal properties have been measured and used as inputs in the numerical model to preliminarily evaluate their application in thermal storage. The analysis carried out can also be used to optimize the storage system, in terms of thermal properties required to the storage material. The results showed a significant influence of the thermal properties on the performances of the storage elements. Simulation results have provided information for further scale-up from a single differential storage element to the entire module as a function of material thermal properties.

Thermodynamic Study of Advanced Supercritical Carbon Dioxide Power Cycles for Concentrating Solar Power Systems

Supercritical CO2 (s-CO2) operated in a closed-loop Brayton cycle offers the potential of higher cycle efficiency versus superheated or supercritical steam cycles at temperatures relevant for concentrating solar power (CSP) applications. Brayton-cycle systems using s-CO2 have a smaller weight and volume, lower thermal mass, and less complex power blocks versus Rankine cycles due to the higher density of the fluid and simpler cycle design. The simpler machinery and compact size of the s-CO2 process may also reduce the installation, maintenance, and operation cost of the system. In this work we explore s-CO2 Brayton cycle configurations that have attributes that are desirable from the perspective of a CSP application, such as the ability to accommodate dry cooling and achieve greater than 50% efficiency, as specified for the U.S. Department of Energy SunShot goal. Recompression cycles combined with intercooling and/or turbine reheat appear able to hit this efficiency target, even when combined with dry cooling. In addition, the intercooled cycles expand the temperature differential across the primary heat exchanger, which is favorable for CSP systems featuring sensible-heat thermal energy storage.

Thermoeconomic design and analysis of a sensible-heat thermal energy storage system with Joulean heating of the storage element : Zubair, S. M. et al. Exergy, An International Journal, 2002, 2, (4), 237–247

Thermoeconomic design and analysis of a sensible-heat thermal energy storage system with Joulean heating of the storage element : Zubair, S. M. et al. Exergy, An International Journal, 2002, 2, (4), 237–247

Thermoeconomic design and analysis of a sensible-heat thermal energy storage system with Joulean heating of the storage element

A second-law-based thermoeconomic model of a sensible heat-storage system with Joulean heating is derived and discussed in which the storage element is cooled by flowing stream of gases. In this analysis, unit cost values are attached to the irreversible losses caused by the finite-temperature difference heat transfer and pressure drop during the heat removal process. Important dimensionless parameters are identified and the results are presented in terms of the optimum number of heat transfer units (NTUopt) as a function of the dimensionless unit cost per unit heat conductance (γUA) and dimensionless temperature difference (τ) of the storage systems. The storage systems studied are optimized by introducing a new performance criterion described as the cost rate number(Γ∗). Performance results of low- and high-temperature storage systems are also examined and the results are compared with that obtained from Krane's analysis to illustrate the usefulness of the present approach. The influence of important unit cost parameters on NTUopt and Γopt∗ are also studied in somewhat more detail.

Study on combined latent- and sensible-heat thermal energy storage (Optimization of unit in relation with operating conditions).

In order to pursue the high performance of thermal energy storage, a combined type of latent-and sensible-heat thermal energy storage (TES) system is proposed, and its performance is investigated experimentally and theoretically. The theoretical treatment is made taking in account the recirculating flow in the capsule. In comparison with the theoretical answers and the experimental results given by preceding report, the optimum design of TES is determined in relation to the operating conditions and Phase Change Material (PCM).

Study on combined latent-and sensible-heat thermal energy storage. 2nd report Optimization of unit in relating with operating conditions.

A combined type of latent-and sensible-heat thermal energy storage (TES) is proposed, and it-s performance is investigated experimentally and theoretically. The theoretical treatment is made taking in account recirculating flow in the capsule. In comparison with the theoretical answers and the experimental results given by preceding report, the optimum design of TES is determined in relation with the operating conditions and Phase Change Material (PCM).

Study on combined latent-and sensible-heat thermal energy storage. 1st report Charging and discharging characteristics.

A combined type latent-and sensible-heat thermal energy storage is proposed, and its performance is investigated experimentally and theoretically. The dominant characteristics of this system are verified by comparison with proto-types, such as the sensible and the latent thermal energy storage types. The solidification and melting experiments are performed using a water-n-octerdencane and -CaCl2 6H2O systems. The charging and discharging characteristics and the basis of performance evaluation are clarified.