Concentrated Solar Thermal Power Plants Research Articles

Modelling of Solar Thermal Electricity Plants in the POSYTYF Research Project for an Extensive Integration of Renewable Energy Sources

This article presents a simplified simulation model of a concentrated solar thermal power plant developed in the framework of the European research project POSYTYF (POwering SYstem flexibiliTY in the Future through RES). Increasing the share of Renewable Energy Sources (RES) in modern power grids is of critical importance for the transformation of the energy markets worldwide. However, the stability of the grid and the limited participation in ancillary services of RES limit their use, especially when high penetration is expected from them. A solution to overcome these issues is to increase the share of so-called dispatchable RES (hydropower, biomass, concentrating solar thermal power). The main objective of the POSYTYF project is to group several renewable and non-renewable energy sources into a Dynamic Virtual Power Plant (DVPP). The simplified simulation model of a parabolic-trough solar thermal power plant developed consists of sub-models for the solar field, thermal energy storage system and power block and it has been validated with real DNI profiles and production data of a commercial STE plant in Spain. The differences between the simulation and real data of daily net production for the days analysed are lower than 1%. Parts of this paper were published as journal article “Using time-windowed solar radiation profiles to assess the daily uncertainty of solar thermal electricity production forecasts”, Journal of Cleaner Production, Volume 379, Part 2, 2022. Mario Biencinto, Lourdes González, Loreto Valenzuela (https://doi.org/10.1016/j.jclepro.2022.134821).

Effect of Morphological Characteristics of Aggregates on Thermal Properties of Molten Salt Nanofluids

Molten salt-based nanofluid is a thermal storage and heat transfer medium for concentrated solar thermal power plants formed by adding nanoparticles to molten salt, which can enhance the thermal performance of molten salt. However, the nanoparticles tend to aggregate in nanofluids, causing changes in thermal properties. In this work, molecular dynamics simulations were used to study the effect of morphological characteristics of aggregates on the thermal conductivity and specific heat capacity of molten salt-based nanofluids. The results show that the aggregated nanoparticles cause a greater increase in thermal conductivity and specific heat capacity than dispersed nanoparticles. Additionally, the increase in fractal dimension leads to thermal conductivity reduction, while there is no clear correlation between the fractal dimension and specific heat capacity. New insights into the thermal properties of aggregated nanofluids are provided by analyzing the contribution of material components, heat flux fluctuation modes, and energy compositions. It is found that the thermal conductivity of aggregated nanofluids is mainly dominated by the base liquid and collision term. However, the specific heat is not related to the variation in the contribution of different energy compositions. Moreover, compared to the dispersed nanofluid, the increased specific heat capacity of aggregated nanofluids is attributed to the thicker semi-solid layer. This study provides guidance for the design and control of the thermal properties of molten salt-based nanofluids.

Produced-Water Desalination Approach Uses Renewable Thermal Energy

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 211175, “An Innovative Method of Water Management by Desalinating Produced Water Using Thermal Renewable Energy,” by Sharifa M. Al-Ruheili, Felix Tiefenbacher, and Khansaa H. Almahrami, ARA Petroleum Exploration and Production, et al. The paper has not been peer reviewed. _ The operator is adopting a method to manage high-salinity produced water in an environmentally sustainable way by extracting potable water from produced water and reducing discharge water volume by at least 50%. For desalination of the produced water, a combination of forward and direct osmosis technology is used. This process is driven mostly by thermal energy, which is provided to thermal collectors that are 100% solar. This technology uses renewable energy and will have no carbon footprint. Technology Description The technology involves concentrated solar thermal (CST) power plants that provide 100% renewable water desalination. Forward osmosis (FO) and direct osmosis (DO) can desalinate highly saline and polluted water, such as produced water, mainly with solar thermal energy. A pneumatic solar thermal plant consisting of two HELIOtube collectors, each 121 m long, provides the thermal energy for the desalination process. The plant includes a mirror technology based on CST, a cost-effective heat-transfer system using pressurized water as heat transfer fluid (HTF), and a low-maintenance thermal energy storage (TES) system allowing nighttime operations of 35 m3 volume with an operating temperature of 180°C using a pressurized water tank at 10-bar operating pressure. The desalination system will contain a pretreatment unit for the produced water and a desalination (FO) and brine-concentration (DO) unit. The unit will be integrated with thermal power to operate the desalination plant. In addition, a fully automated control system with a live backup will be installed. The system is classified as having low maintenance and cleaning costs because of its encapsulation features, rotatability of 300°, and convex shape. Fig. 1 of the complete paper shows the planned plant layout. The desalination plant will feature two outputs: fresh water of potable quality and brine. The fresh water will be used to serve the company’s freshwater demand, with excess water used for agricultural purposes or mixed with water in an injector well to improve injectivity. The other output, the highly concentrated brine (20% salt), will be collected in the existing evaporation pond where two main research and development studies are ongoing, one related to mineral extractions and the second related to salt monetization (using salt as a drilling additive).

A Novel Dual Receiver–Storage Design for Concentrating Solar Thermal Plants Using Beam-Down Optics

Advanced power cycles—such as the supercritical carbon dioxide (sCO2) cycle—have the potential to reduce the levelized cost of energy (LCOE) of concentrated solar thermal power (CST) plants by significantly boosting their overall solar-to-electric efficiency. To successfully integrate these cycles into CST plants, the industry may need to transition away from liquid working fluids (e.g., synthetic oils and molten salts) to solid and/or gaseous heat transfer media, which are more stable at high temperatures. To address this challenge, this study investigates a novel rotating receiver–storage unit that could enable high-temperature CST plants. A validated numerical model is presented for the charging and discharging processes of the proposed design. It was found that with cast steel as the storage medium in the proposed design, it is possible to achieve >70% receiver efficiency for operation temperatures of 850–1000 K. The overall plant model shows this design is best for relatively small CST systems as modularized units of 10 m diameter (reaching an energy density around 80 kWh/m3), which can be used to drive a 5 MWe sCO2 CST plant. These findings suggest that such a design would have up to 9 h of storage and could be effectively employed as an efficient peaking plant.

Development and characterization of a quaternary nitrate based molten salt heat transfer fluid for concentrated solar power plant

Over the past few years, there has been growing interest in using inorganic quaternary nitrate-based molten salt mixtures as a highly effective heat transfer fluid (HTF) for concentrated power plants, primarily because they can achieve low melting temperatures. However, the high viscosity of these salt mixtures is still a significant challenge that hinders their widespread adoption. The high viscosity leads to high pumping power requirements, which increases operational costs, and reduces the efficiency of the Rankine cycle. To address this challenge, this study developed and characterized a novel quaternary molten salt, focusing on the effect of LiNO3 additions on the salt's viscosity, thermal conductivity, melting point temperature, heat capacity, and thermal stability. The quaternary mixture comprised KNO3, LiNO3, Ca(NO3)2, and NaNO2, with varying percentages of each salt. The study utilized various standard techniques to examine the characteristics of the developed mixture. Results showed that increasing LiNO3 content led to a decrease in melting temperature, higher heat capacity, improved thermal stability, conductivity, and reduced viscosity at solidification temperature. The lowest endothermic peak for the new mixture emerged at 73.5 °C, which is significantly lower than that of commercial Hitec and Hitec XL, indicating better potential for use as a heat transfer fluid for concentrated solar thermal power plant applications. Furthermore, the thermal stability results showed high stability up to 590 °C for all the samples examined. Overall, the new quaternary molten salt shows promise as a potential replacement for current organic synthetic oil, offering a more efficient solution.

A comparative study of sensible energy storage and hydrogen energy storage apropos to a concentrated solar thermal power plant

To achieve dispatchable and reliable power generation through renewable sources, energy storage is often indispensable. This paper attempts a quantitative investigation and comparison between two different energy storage technologies, Thermal Energy Storage System (TESS), which is already mature, and Hydrogen Energy Storage System (HESS), applied to a common concentrated solar thermal power (CSP) plant. A solar field (SF) comprising parabolic troughs and molten salt as a heat transfer fluid is conceived with a power block running on the Rankine cycle. An integrated TESS system is first considered, and the SF size is iteratively determined, so that plant with TESS has a capacity factor of 100 % for a typical summer day, thereby standardizing the TESS performance. The TESS is then replaced with the HESS, keeping the same SF capacity. The plant capacity and storage performances are then compared with simplistic assumptions. The results show superior TESS performance, while HESS delivers only 58 % capacity factor. TESS also delivers superior energy and power density (68 kWh/m3 and 4.5 kW/m3 for TESS, as opposed to 26 kWh/m3 and 1.8 kWh/m3 for HESS, respectively). However, the specific energy and power for both are comparable (approx. 93 Wh/kg and 6 W/kg, respectively). Although electrolyzer and fuel cell efficiencies individually outperform Rankine efficiency, HESS lags in performance with CSP configuration due to multiple steps of energy conversion.

CONCENTRATING SOLAR POWERED TRANSCRITICAL CO2 POWER GENERATION CYCLE FOR THE UNION TERRITORY OF LADAKH, INDIA

High solar irradiation, cloud-free dry climate, abundant barren land, and low ambient temperature make the Union Territory of Ladakh, India, suitable for concentrating solar thermal power (CSP) plants. The present study comprehensively analyzes a 5 MW transcritical CO<sub>2</sub> Rankine cycle power tower CSP plant. Low ambient temperature of the region allows transcritical operation, which provides high cycle efficiency. The study focuses on five aspects: solar field and thermal energy storage (TES), thermodynamic cycle simulation, turbomachines, and off-design performance analysis. Modeling and optimization of the solar field are undertaken to capture the diurnal and annual variations of direct normal irradiation levels using System Advisor Model open source software. Molten salt TES is integrated to overcome the dynamic variations of solar energy by providing stable operations and additional hours. The effect of storage sizes, starting from no storage to 12 hours, on the solar field size and specifications is also assessed. An in-house algorithm is developed for thermodynamic cycle optimization, exergy analysis, and off-design operations. The turbomachines of the cycle are designed using in-house meanline codes, and 3D CFD simulations are conducted for efficiency estimations. The effects of ambient temperature variations on the low side saturation pressure, cycle efficiency, and power output are evaluated. The proposed plant offers annual optical efficiency of 54.1%, thermal efficiency of 36.5%, and overall efficiency of 19.7%.

On the compatibility of liquid sodium as heat transfer fluid for advanced concentrated solar thermal energy systems

The use of liquid sodium as a heat transfer fluid has shown great promise and application in nuclear power generation and it is now being utilized in concentrated solar thermal power (CSP) applications, owing to its favorable thermodynamic properties. Its implementation, however, comes with a unique array of technical issues in CSP applications, primarily the incompatibility of structural materials with liquid sodium in these operational environments. In this review, major damage mechanisms will be discussed, with a focus on their relevance to advanced CSP plants. Such mechanisms include corrosion, liquid metal embrittlement, carburization/de-carburization, erosion, creep, and thermal fatigue. The degradation factors such as impurities in the sodium (e.g. oxygen) and the dissolution of the structural material's alloying elements (Cr, Mn, Ni and Si, etc.) are also discussed. This review presents a holistic overview of these inter-connected mechanisms, and most importantly explores potential solutions to mitigate these issues, including better structural material candidates, robust plant operational parameters/design, better service life predictions, and improved purification and monitoring methods for stringent control of impurities. The future directions of research are also discussed to ensure the successful use of liquid sodium in the next generation of CSP technology.

Heat transfer modelling of an isolated bubble in sodium pool boiling

Sodium tubular boiler receivers in concentrated solar thermal power plants are a viable option to provide near-isothermal heat for industrial applications. Accurately predicting the boiling behaviour in the receivers is imperative to improve the performance of these plants. A physics-based reduced-order bubble growth model is developed in this work to gain a fundamental understanding of the boiling process in the receiver. The model predicts the growth rate of an isolated bubble in a sodium pool based on heat transferred from the microlayer, the macrolayer, the thermal boundary layer and the bulk liquid surrounding the bubble. A transient 2D conduction equation is solved to model the cooling of the wall below the bubble due to evaporation of the microlayer and the macrolayer. The model is used to study the growth of a sodium bubble in a liquid pool and analyse the relative contribution of different heat transfer mechanisms to the growth process. It is found that the microlayer heat transfer is the dominant mechanism controlling bubble growth in sodium. Furthermore, a parametric study of the effect of wall superheat, contact angle and temperature of the bulk liquid on the bubble growth process in sodium shows that the bubble size increases with increasing superheat, contact angle and bulk liquid temperature.

Investigation of the corrosion of electro-less nickel-plated alloys in molten salt and its effect on phase change properties for energy storage applications

Interactions between electroless nickel plated Inconel 601, Monel 400, and stainless steel 316L alloys with two eutectic salts used as phase change materials, K2CO3 + Na2CO3 and NaCl + Na2CO3, were investigated at 720 °C (isothermal). The results of this study show that at these high temperatures, which is the target temperatures of the next generation of concentrated solar thermal power plants, these salt phase change materials are highly corrosive to stainless steel, whereas the Inconel 601, a high temperature nickel alloy, was resistant. Monel 400 experienced the most corrosion damage (500 µm thick corrosion layer) and resulted in the salts experiencing the greatest latent heat decrease by 18.1%, as confirmed by Differential Scanning Calorimetry (DSC). IN601 performed the best with an observed corrosion layer thickness of 107 µm, and resulted in one of the salts only decreasing in latent heat by 5.9%. IN601 with the nickel plating has shown improved corrosion resistance over uncoated samples. The thermophysical properties of the salt was measured before and after the exposure tests to demonstrate the significant effect corrosion has on the performance of the salts as a phase change material. Scanning Electron Microscopy (SEM) analysis showed that constituent elements have diffused from the alloy specimens, through the nickel plated layer and leached into the molten sat, which was characterized by Inductively Coupled Plasma- Optical Emission Spectroscopy (ICP-OES). A correlation was found between the corrosion of the specimens, the solubility of the alloying elements and a large decrease in the salt’s latent heat properties.

Outdoor exposure approach in a harsh environment toward the study of corrosion aspects of primary solar reflectors

Corrosion is among the most observed phenomena that threaten the profitability of concentrated solar thermal power plants and constitutes a real risk factor for metallic materials. Solar reflectors are between the impacted materials by corrosion because they are composed of metallic reflective layers that can easily be oxidized in air. To avoid this, paint systems could be applied in the back of the reflective layers as a barrier, that prevents the diffusion of corrosive elements to the metal layer. Metallic structures that support those reflectors can also be easily corroded and are replaced with composite structures that are not affected by corrosion. However, the durability of the paint protection systems and the composite structures must be inspected to ensure their effectiveness in protecting solar mirrors against corrosion, since they are found in sites that are often characterized by arid conditions, which affects corrosion protection solutions. This work is devoted to study the corrosion aspects and the parameters that affect the resistance of the protection systems of glass solar mirrors and solar mirrors fixed on composite structures by the use of a real outdoor exposure facility on a coastal site. The results show the important role of the paint coating layers number on the protection against corrosion. Also, the role of edge protection and shape were highlighted. Solar mirrors fixed on composite structures show a weak resistance because of the degradation of the fixing glue which creates areas of retention of salts and moisture that cause an aggressive corrosion of the metal layers.

Simulation of Performance for 140 MW Thermal Power Station at Alkuraymat Using Solar Parabolic Trough Concentrators with Thermal Storage

Solar power is a primary source of renewable energy and one of the most effective strategies for reducing emissions by reducing the consumption of fossil fuels. Alkuraymat power station produces about 140 MWe divided into 120 MWe produced from a combined cycle and 20 MWe from a solar field with Therminol VP-1 as a heat transfer fluid. For environmental considerations, the present work aims to evaluate the design parameters and thermal performance of the Alkuraymat power plant operated with parabolic trough solar field with thermal energy storage simulated by using System Advisor Model (SAM) software. Alkuraymat location is suitable for using a concentrated solar thermal power plant due to receiving an annual direct normal irradiance of about 2,522.15 kWh/m²/year. The results indicated that the concentrated solar thermal power plant consists of 514 solar collector loops, with each loop comprising of 4 parabolic trough collectors. As well, the proposed plant can produce annual electricity of efficiency of the power plant the 893.82 GWh andost Cevelized LRelated to the optimization of the system configuration, the is 19.4%. thermal energy storage and the full load hours of ,of energy equal to 4.79 Cents/kWhparabolic Additionally, the suggested design of thereduces from 16 to 12.5 hrs. motivates further trough concentrated power plant and the study of its performance . solar t thermal power plants in the Egyp of improvement innovation and

Thermo-economic analysis of an integrated solar thermal cycle (ISTC) using thermal storage

Solar integrated power plants are a combination of the concentrated solar power plant and thermal power plant. The thermal energy storage systems, when integrated with concentrated solar power based solar cycle, can address issues related to energy availability during non-solar hours.This study presents an integration of concentrated solar power technology based solar energy capture and storage with the 210 MW conventional Rankine cycle based thermal power plant in Dadri (India). The mathematical model of Integrated Solar Thermal Cycle (ISTC) has been developed which includes the modelling of the Linear Fresenel reflector solar system, steam power cycle, and two tank thermal storage method. Here, water and molten salt are chosen as heat transfer fiuid in the collector loops as a medium to transfer and store the solar thermal energy. A MATLAB code is used as a simulation tool to analyse the ISTC performance for different parametric variations such as temperature difference in the solar receiver, solar output, the mass flow rate of heat transfer fluids, fuel-saving ratio by varying direct normal irradiation. Based on the simulation, it is discussed that the integration of solar field with power cycle offers enhanced efficiency along with the reduction of emission of carbon dioxide. Integration of solar field with Thermal Energy Storage (TES) using two tank method with molten salt further improves the efficiency of the power cycle up to 40%. Based on results of simulations, it is discussed that ISTC using two tank method with molten salt results into the saving of large amount of fuel by replacement of one and two feed water heater(s) which ensures the recovery of the capital expenditure within approximately 10 years. Further, this improvisation contributes to environment and society by curtailing the emission of carbon dioxide drastically.

Optimization of water management plans for CSP plants through simulation of water consumption and cost of treatment based on operational data

Considering the importance of water in local communities and the development of Concentrated Solar Thermal Power (CSP) projects in arid regions, water footprint analysis and finding water-saving solutions towards optimized use of raw water resources in CSP plants are essential. Within this study, we present an integrated simulation tool for a comprehensive simulation of CSP plants including the water and wastewater streams, treatment units, and the cost of treatment. The models are compared to a set of measured water consumption data from a commercial CSP plant. Furthermore, strategies to reduce raw water consumption are identified and then investigated through the detailed simulation of alternative water management plans. The results show that with optimized solutions, raw water consumption can be reduced by 14% while the cost of electricity remains the same or is even slightly reduced.

A novel hybrid geo-solar thermal design for power generation in Australia

This paper proposes a novel hybrid geo-solar thermal design for power generation in Australia. The low-grade geothermal heat, from shallow resources already flowing to the surface, will be used to off-load the recuperator duty in a supercritical carbon dioxide Brayton cycle for a concentrated solar thermal power plant. Hence, our design is limited to locations with reasonably high DNI at the vicinity of hot flowing wells. Winton in Queensland has been a case of interest where about 80 kg/s of water flows to the surface at a temperature of approximately 80 °C. Accordingly, a case study, pertinent to Winton, has been presented here. Our simulation of a geo-solar thermal power plant with this configuration has showed significant benefits compared to either solar thermal or geothermal plants in isolation. It is shown that the recuperator can be replaced by a less expensive shell and tube heat exchanger and a smaller, and hence less costly, recuperator while the overall efficiency gain is just under 5% compared to that of a solar thermal plant.

Designing a Concentrated Solar Thermal Power Plant Using Energy–Exergy–Economic–Environment Analysis

The paper deals with the design aspects of a 5-megawatt electrical (5-MWe) parabolic trough based concentrated solar thermal power plant located in the city of Jaipur, India using energy, exergy, economic, and environment cost analysis. As a novelty in the study, quantification of the energetic and exergetic potential of heat transfer fluid has also been carried out. Based on the energetic heat of the heat transfer fluid (HTF) going into the boiler, the solar field design is then carried out. The energy–exergy analysis shows that the energetic efficiency of parabolic trough based concentrated solar power plant (PTCSTPP) was 29.38% and exergetic efficiency was 31.86%. The gross thermal efficiency of the power plant was 31.47% and net thermal efficiency is 25.07%. Methodology for arriving at a solar-alone operating power plant has also been enumerated and shown that at a levelized cost of energy (LCOE) of US cent 5.6, the total cost of the plant comes out to be US $ 53 million payback of 19 years, with an annual coal saving worth US $ 0.96 million and CO2 savings of US $ 0.29 million. Analysis has also been carried out to assess the per-hour increment in the design cost owing to additional operating hours of the solar plant.

Analytical assessment of a concentrated solar sub-critical thermal power plant using low temperature heat transfer fluid

The paper presents energy–exergy–economic–environment–ethics analysis of a concentrated solar thermal power plant. Design basis of a concentrated solar power for 24 h operation on parabolic trough collector technology in best suited direct normal irradiation location and least capital cost analysis has been presented. An unconventional approach of reducing the capital cost is analyzed by intentionally designing the power plant for sub-critical conditions using a low-cost mineral oil with permissible operating temperature of 320°C in place of the conventional synthetic solar grade oil of 400°C. Using low pressure and temperature steam in the plant, it has been shown that while there is a reduction of 0.1% in energetic efficiency, there is a gain of 0.28% in the exergetic efficiency of the solar power plant conditions, gross thermal efficiency decreases by 1.18% and the net thermal efficiency decreases by 2.91%. However, the energetic and exergetic utilization factor for heat transfer fluid is increased by 0.84 and 5.58%, respectively. By suitably adjusting the solar field configuration and inlet oil temperature, energy savings to the tune of 45% is possible apart from 2.5 times of cost saving. An attempt has been made to quantifiably assess the ethics of switching to renewable electricity through shared responsibility as a novelty in the study. The payback period for the investment has also been shown to reduce from 20 years to 5 years assuming that the carbon price increases, concentrated solar power cost comes down by 25%, and cost at which electricity can be sold increases to US $0.14 (Rs. 10) per unit.

A review of numerical modelling of high-temperature phase change material composites for solar thermal energy storage

High-temperature phase change materials (PCMs), due to their high energy density and capability of maintaining nearly constant temperature, have been widely investigated to replace the current molten salt sensible storage system in concentrated solar thermal power plants. However, the performance of the PCM storage system is severely restricted by the low thermal conductivity and high corrosion of molten salt PCMs. Fabrication of PCM into PCM composite is a promising and effective method to improve the usability and handleability of high-temperature PCMs. The feasibility of fabrication process and material characterisation has been conducted through laboratory-scale experiments. This work reviews mathematical models used to describe the heat transfer process in high-temperature PCM composites, and hence to simulate the thermal performance of the storage system. It is critical to design a high efficiency storage system via numerical modelling. In order to include the natural convection in liquid PCM, the fundamental governing equations of continuity, momentum and energy need to be applied in the numerical model, together with the heat conduction equation in the solid structure material and the heat convection equation between the PCM and structure material. This detailed model is usually applied in metal and ceramic composites where the pore size is large, and the equations are usually solved by using commercial computational fluid dynamics software. For graphite-based composites, the model can be simplified into the energy equation with thermal equilibrium between the PCM and graphite.

Generalized distributed state space model of a CSP plant for simulation and control applications: Single-phase flow validation

Concentrating solar thermal power plants, also known as CSP plants, can be of different configurations depending on type of collectors, temperatures, heat transfer fluid, working fluid, and the thermodynamic cycle used in the plant. This leads to complex behavior with nonlinear dynamics, potential instability and parameters that vary in both space and time. In this work, a distributed state space model is proposed to ensure computational flexibility and facilitate industrial applications, such as optimization, control and automation. The format used allows the model to represent the thermal dynamics at different operation points including phase changes (liquid or gas) along the spatial dimension. To validate the model, some experimental tests have been made on an operating solar thermal plant located at the University of South Florida, in United States, where real input disturbances were applied to compare measurements with model predictions. Preliminary results show good agreement with experimental observations. Literature data of water and steam properties were used in the model, that can be easily extended to direct steam generation (DSG) plants.

Simulation of Triplex Tube Thermal Energy Storage System Using High Temperature Phase Change Material

To increase the capacity factor of a concentrated solar thermal power plant (CSTPP) beyond the hours of sunlight, the use of thermal energy storage systems (TES) can be a promising solution. Phase change materials (PCMs) can store latent thermal energy in the course of the melting process and release it when solar energy is not available. Generally, PCMs have low thermal conductivity. One of the most commercially promising solutions is the application of an extended heat transfer surface inside the PCM container. Moreover, the distance of the heat transfer fluid (HTF) to the core of the PCM in a TES system can affect the storage performance. Accordingly, a triplex tube heat exchanger with eight fins is considered in this paper, to investigate the impact of the different velocity of HTF and different entrance pattern in a vertical PCM container. Notably, the middle enclosure of the triplex tube is filled with PCM. Numerical analysis using an enthalpy porosity technique revealed that increasing HTF velocity reduces the charging time. Also, when the HTF enters from the bottom of the container, the storage time will diminish owing to a natural convection side-effect, but if the HTF flows downward, the amount of sensible thermal energy storage is higher than in the other cases.