Research

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16 pages, 2912 KiB

Open AccessArticle

Solar Salt above 600 °C: Impact of Experimental Design on Thermodynamic Stability Results

by Julian Steinbrecher, Markus Braun, Thomas Bauer, Sebastian Kunkel and Alexander Bonk

Energies 2023, 16(14), 5241; https://doi.org/10.3390/en16145241 - 08 Jul 2023

Cited by 2 | Viewed by 1148

Thermal energy storage (TES) based on molten salts has been identified as a key player in the transition from fossil fuels to renewable energy sources. Solar Salt, a mixture of NaNO₃ (60 wt%) and KNO₃ (40 wt%), is currently the most [...] Read more.

Thermal energy storage (TES) based on molten salts has been identified as a key player in the transition from fossil fuels to renewable energy sources. Solar Salt, a mixture of NaNO₃ (60 wt%) and KNO₃ (40 wt%), is currently the most advanced heat transfer and storage material used in concentrating solar power (CSP) plants. Here, it is utilized to produce electricity via a Rankine cycle, with steam temperatures reaching 550 °C. The goal of this study is to increase the operating temperature of solar salt to over 600 °C, allowing it to be adapted for use in high-temperature Rankine cycles with steam temperatures greater than 600 °C. Yet, this goal is impaired by the lack of available thermodynamic data given the salt’s complex high-temperature decomposition and corrosion chemistry. The study explores the thermodynamics of the decomposition reactions in solar salt, with a focus on suppressing decomposition into corrosive oxide ions up to a temperature of 620 °C. The results provide a new understanding of the stabilization of solar salt at previously unexplored temperatures with effective utilization of gas management techniques. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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13 pages, 5046 KiB

Open AccessArticle

Thermal Management of Short-Range Distribution of Perishable Food Products Using Phase Change Materials in Packaging: Real-Time Field Data Acquisition

by Martim Aguiar, Pedro Dinis Gaspar and Pedro Dinho da Silva

Energies 2023, 16(13), 5191; https://doi.org/10.3390/en16135191 - 05 Jul 2023

Viewed by 970

Abstract

Maintaining a stable temperature is critical in ensuring the longevity of perishable foods, and frequent fluctuations due to short-range distribution conditions can negatively affect this stability. To mitigate these variations, an innovative modular packaging system utilizing phase change materials (PCMs) was employed in [...] Read more.

Maintaining a stable temperature is critical in ensuring the longevity of perishable foods, and frequent fluctuations due to short-range distribution conditions can negatively affect this stability. To mitigate these variations, an innovative modular packaging system utilizing phase change materials (PCMs) was employed in the transport and storage of horticultural products. This study’s real-time thermal condition data, collected using a wireless data acquisition system inserted in the packaging, demonstrated the efficacy of PCM in increasing temperature stability within the crates of horticultural products. The field tests conducted over 8 h showed that PCM-equipped packaging boxes exhibited a temperature variation of less than 1 °C, compared to non-PCM boxes, which saw variations up to 3 °C. This marked reduction in temperature fluctuation signifies the potential of PCM in improving thermal and logistics management in food conservation, thus reducing food waste. However, it is essential to implement a system for PCM alveoli reuse to avoid adverse environmental impacts. Future research should focus on the PCM alveoli autonomy and quantity requirements for specific conditions, and integrate sensors to monitor transport dynamics to enhance the understanding of temperature stability in perishable food transportation. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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18 pages, 7834 KiB

Open AccessArticle

Impact of Stearic Acid as Heat Storage Material on Energy Efficiency and Economic Feasibility of a Vacuum Tube Solar Water Heater

by K. Chopra, V. V. Tyagi, Sudhir Kumar Pathak, Apaar Khajuria, A. K. Pandey, Nazaruddin Abd Rahman, Muhamad Mansor and Ahmet Sari

Energies 2023, 16(11), 4291; https://doi.org/10.3390/en16114291 - 24 May 2023

Cited by 2 | Viewed by 1132

Abstract

The overheating of heat pipes, poor transfer of heat across the absorber and finned heat pipes, and inability to provide hot water in the late evening hours are major problems associated with conventional heat pipe vacuum collector systems. The amalgamation of highly conductive [...] Read more.

The overheating of heat pipes, poor transfer of heat across the absorber and finned heat pipes, and inability to provide hot water in the late evening hours are major problems associated with conventional heat pipe vacuum collector systems. The amalgamation of highly conductive storage material between the absorber tube (heat collecting surface) and the heat pipe is an effective way to overcome these problems. In this study, a stearic acid amalgamated vacuum tube solar collector system was designed and fabricated and its thermal output compared with a conventional vacuum tube system without storage material under the same environmental conditions. The experimental results showed that the amalgamation of stearic acid as storage material enhanced the thermal output of the solar system compared to the conventional one. The desired heat gain of the solar system with storage material increased by 31.30, 23.34, and 18.78% for Test 1_40 °C, Test 2_45 °C, and Test 3_50 °C, respectively. The technoeconomic analysis showed that almost 118.80 USD in revenue could be earned by the proposed solar system at the end of 15 years. The total running cost of ELG and the developed solar system was observed to be 202.62 and 86.70 USD, respectively. On average, the cost of hot water production using the solar system and ELG was found to be 0.0016 and 0.004 USD/L, respectively. The value of LEC was found to be 0.062 USD/electricity unit, which was much lower than the LEC value of ELG (0.116 USD/electricity unit). The value of NPW (73.73 USD) indicated high acceptability of the proposed system. The payback time is lower than the life of the system, indicating its suitability for use in the commercial sector. Therefore, the proposed solar system is highly recommended over conventional water heating systems in urban and rural areas. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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12 pages, 7130 KiB

Open AccessArticle

Development of Self-Passivating, High-Strength Ferritic Alloys for Concentrating Solar Power (CSP) and Thermal Energy Storage (TES) Applications

by Fadoua Aarab and Bernd Kuhn

Energies 2023, 16(10), 4084; https://doi.org/10.3390/en16104084 - 14 May 2023

Cited by 1 | Viewed by 1017

Abstract

Concentrating solar power (CSP) and thermal energy storage (TES) based on molten salts still lacks economic feasibility, with the material investment costs being a major drawback. Ferritic stainless steels are a comparatively cheap class of materials that could significantly contribute to cost reductions. [...] Read more.

Concentrating solar power (CSP) and thermal energy storage (TES) based on molten salts still lacks economic feasibility, with the material investment costs being a major drawback. Ferritic stainless steels are a comparatively cheap class of materials that could significantly contribute to cost reductions. The addition of aluminum to ferritic steel can result in self-passivation by forming a compact Al₂O₃ top layer, which exhibits significantly higher corrosion resistance to solar salt compared to the Cr₂O₃ surface layers typically formed on expensive structural alloys for CSP and TES, such as austenitic stainless steels and Ni-base super alloys. However, to date, no ferritic stainless steel combining Al₂O₃ formation and sufficient structural strength is available. For this reason, cyclic salt corrosion tests under flowing synthetic air were carried out on seven Laves phase-forming, ferritic model alloys (17Cr2-14Al0.6-1Nb2.6-4W0.25Si), using “solar salt” (60 wt. % NaNO₃ and 40 wt. % KNO₃). The Al content was varied to investigate the influence on the precipitation of the mechanically strengthening Laves phase, as well as the impact on the formation of the Al-oxide top layer. The W and Nb contents of the alloys were increased to examine their influence on the precipitation of the Laves phase. The salt corrosion experiments demonstrated that simultaneous self-passivation against a molten salt attack and mechanical strengthening by precipitation of fine Laves phase particles is possible in novel ferritic HiperFer^{SCR (salt corrosion-resistant)} steel. Microstructural examination unveiled the formation of a compact, continuous Al₂O₃ layer on the surface of the model alloys with Al contents of 5 wt. % and higher. Furthermore, a stable distribution of fine, strengthening Laves phase precipitates was achieved in the metal matrix, resulting in a combination of molten salt corrosion resistance and potentially high mechanical strength by a combination of solid solution and precipitation strengthening. These results show that high-strength ferritic alloys are suitable for use in CSP applications. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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17 pages, 13459 KiB

Open AccessArticle

Experimental Investigation of Graphene Nanoplatelets Enhanced Low Temperature Ternary Eutectic Salt Hydrate Phase Change Material

by B. Kalidasan, A. K. Pandey, Saidur Rahman, Kamal Sharma and V. V. Tyagi

Energies 2023, 16(4), 1574; https://doi.org/10.3390/en16041574 - 04 Feb 2023

Cited by 11 | Viewed by 1736

Abstract

A sustainable approach to ensuring the thermal regulation of space is reliable with phase change materials (PCMs) operating at 15–25 °C. Henceforth, there is a need of a search of binary and ternary eutectic PCMs operating at desirable phase transition temperatures of 15–25 [...] Read more.

A sustainable approach to ensuring the thermal regulation of space is reliable with phase change materials (PCMs) operating at 15–25 °C. Henceforth, there is a need of a search of binary and ternary eutectic PCMs operating at desirable phase transition temperatures of 15–25 °C, high energy storage enthalpy (180–220 J/g), improved thermal conductivity and better absorptivity of solar energy. In this current research, we developed a ternary eutectic inorganic salt hydrate PCM intended for a low-temperature thermal regulation system. Based on the eutectic melting point theory, the phase transition temperature and proportion of sodium carbonate decahydrate (SCD), sodium phosphate dibasic dodecahydrate (SPDD) and sodium sulphate decahydrate (SSD) were determined. As per the calculated proportion, ternary eutectic PCM was experimentally prepared. Furthermore, to enhance the thermal property, graphene nanoplatelets (GNP) were dispersed at weight concentrations of 0.4%, 0.7% and 1.0%. The prepared nanoparticle-dispersed PCMs were characterized using an optical microscope, Fourier transform infrared (FT-IR) spectroscopy and a thermal conductivity meter, and a differential scanning calorimeter (DSC) was used to evaluate the morphology, chemical stability and thermal properties. The results showed increases in thermal conductivity and optical absorbance by 71.5% and 106.5%, respectively, with GNP at 1.0% weight concentration. Similarly, the degree of supercooling and transmissibility was reduced by 43.5% and 76.2% correspondingly. The prepared composite PCM is expected to contribute towards cooling, with an intention to contribute towards sustainable development. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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19 pages, 1934 KiB

Open AccessArticle

Energy Performance Evaluation of a Solar PVT Thermal Energy Storage System Based on Small Size Borefield

by Evangelos I. Sakellariou, Petros J. Axaopoulos, Bill Vaneck Bot and Ioannis E. Sarris

Energies 2022, 15(21), 7906; https://doi.org/10.3390/en15217906 - 25 Oct 2022

Cited by 1 | Viewed by 932

Abstract

In this study, a PVT-based solar-assisted ground source heat pump (SAGSHP) system with a small size borefield as the long-term heat storage component was energetically evaluated. The mathematical model of the system was formulated in TRNSYS and three cities with distinctive climates were [...] Read more.

In this study, a PVT-based solar-assisted ground source heat pump (SAGSHP) system with a small size borefield as the long-term heat storage component was energetically evaluated. The mathematical model of the system was formulated in TRNSYS and three cities with distinctive climates were chosen: Athens (Greece); Melbourne (Australia); and Ottawa (Canada). The parametric analyses were carried out for 10 years by varying the number of the PVT collectors and the size of the earth energy bank (EEB). The evaluation of the systems was made via two energy indicators, and the heat flow across the EEB was analyzed. The under-consideration system was found capable of establishing self-sufficiency as regards the energy consumption (renewable power fraction RPF > 1) for all locations. Namely, for Athens, any system with more than four PVT collectors, and for Melbourne, any system with more than eight PVTs was found with an RPF higher than 1, regardless of the EEB size. For Ottawa, self-sufficiency can be achieved with PVT arrays larger than 12 collectors for small EEBs, and with eight collectors for larger EEBs. The storage capacity was found to be an important parameter for the energy performance of the system. In particular, it was determined that, as the storage capacity enlarges the RPF and the seasonal performance factor (SPF) of the system improves, mainly due to the reduction of the electricity consumed by the heat pump and the auxiliary heating. Moreover, a larger storage capacity facilitates solar heat production by enlarging the available heat storage volume and by maintaining the EEB at relatively low temperatures. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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13 pages, 3755 KiB

Open AccessFeature PaperArticle

Molecular Dynamics Simulation of Thermophysical Properties and the Microstructure of Na₂CO₃ Heat Storage Materials

by Haiming Long, Yunkun Lu, Liang Chang, Haifeng Zhang, Jingcen Zhang, Gaoqun Zhang and Junjie Hao

Energies 2022, 15(19), 7080; https://doi.org/10.3390/en15197080 - 27 Sep 2022

Viewed by 1494

Abstract

In recent years, heat storage technology has attracted wide attention in the fields of renewable energy storage for its relatively high melting point, high heat storage capacity and economy, Na₂CO₃ and eutectic salt mixtures containing Na₂CO₃ are [...] Read more.

In recent years, heat storage technology has attracted wide attention in the fields of renewable energy storage for its relatively high melting point, high heat storage capacity and economy, Na₂CO₃ and eutectic salt mixtures containing Na₂CO₃ are promising candidates in the field of solar energy storage. In this paper, a molecular dynamics (MD) simulation of Na₂CO₃ was conducted with the Born–Mayer potential function. The simulated solid–liquid phase change temperature is 1200 K, and the error is 5.4%. The heat capacity at constant pressure (C_p) is higher in liquid than in solid, the average C_p of solid is 1.45 J/g and that of liquid is 1.79 J/g, and the minimum error is 2.8%. The simulation results revealed the change rules of density and thermal expansion coefficient of Na₂CO₃ in the process of heating up, and these changes were analyzed by radial distribution functions (RDF) and angular distribution functions (ADF). Moreover, the RDF and ADF results show that the atomic spacing of Na₂CO₃ increases, the coordination number decreases, and the angle distribution between atoms becomes wider as the temperature rises. Finally, this paper examined the microscopic changes of ions during the phase transition of Na₂CO₃ from solid to liquid. It is concluded that the angle change of

{CO}_{3}^{2 -}

in the liquid state is more sharply. This study improves the understanding of the thermodynamic properties and local structure of Na₂CO₃ and provides theoretical support for Na₂CO₃ heat storage materials. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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16 pages, 8353 KiB

Open AccessArticle

Simulation Study of Solidification in the Shell-And-Tube Energy Storage System with a Novel Dual-PCM Configuration

by Moslem Mozafari, Ann Lee and Shaokoon Cheng

Energies 2022, 15(3), 832; https://doi.org/10.3390/en15030832 - 24 Jan 2022

Cited by 8 | Viewed by 2147

Abstract

This study proposes a novel dual-PCM configuration with outstanding solidification response in a horizontal shell-and-tube energy storage system. To demonstrate that the proposed PCM configuration is superior in its thermal responses, results from a range of numerical simulations are presented and compared between [...] Read more.

This study proposes a novel dual-PCM configuration with outstanding solidification response in a horizontal shell-and-tube energy storage system. To demonstrate that the proposed PCM configuration is superior in its thermal responses, results from a range of numerical simulations are presented and compared between different configurations of dual-PCM. As the melting/solidus point is a crucial factor for the solidification rate, dual PCMs are chosen such that the average of their melting point is equal to the melting point of the single-PCM in the reference case. Additionally, equal-area sectors are considered for all cases to ensure the same quantities of PCMs are compared. The temporal liquid fraction and temperature contours reveal that solidification is delayed in the upper half of the system due to strong natural convection motions. Therefore, a dual-PCM configuration is offered to improve the solidification rate in this region and accelerate the full solidification process. Results show that placing a PCM with a lower solidus point in the lower half or an annulus-shaped zone around the cold tube can save the full recovery time up to 8.51% and 9.36%, respectively. The integration of these two strategies results in a novel and optimum design that saves the solidification time up to 15.09%. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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Review

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46 pages, 5607 KiB

Open AccessReview

Combined “Renewable Energy–Thermal Energy Storage (RE–TES)” Systems: A Review

by Ahmed Elkhatat and Shaheen A. Al-Muhtaseb

Energies 2023, 16(11), 4471; https://doi.org/10.3390/en16114471 - 01 Jun 2023

Cited by 8 | Viewed by 3586

Abstract

Current industrial civilization relies on conventional energy sources and utilizes large and inefficient energy conversion systems. Increasing concerns regarding conventional fuel supplies and their environmental impacts (including greenhouse gas emissions, which contribute to climate change) have promoted the importance of renewable energy (RE) [...] Read more.

Current industrial civilization relies on conventional energy sources and utilizes large and inefficient energy conversion systems. Increasing concerns regarding conventional fuel supplies and their environmental impacts (including greenhouse gas emissions, which contribute to climate change) have promoted the importance of renewable energy (RE) sources for generating electricity and heat. This comprehensive review investigates integrating renewable energy sources (RES) with thermal energy storage (TES) systems, focusing on recent advancements and innovative approaches. Various RES (including solar, wind, geothermal, and ocean energy sources) are integrated with TES technologies such as sensible and latent TES systems. This review highlights the advantages and challenges of integrating RES and TES systems, emphasizing the importance of hybridizing multiple renewable energy sources to compensate for their deficiencies. Valuable outputs from these integrated systems (such as hydrogen production, electric power and freshwater) are discussed. The overall significance of RES–TES hybrid systems in addressing global energy demand and resource challenges is emphasized, demonstrating their potential to substitute fossil-fuel sources. This review provides a thorough understanding of the current state of RES–TES integration and offers insights into future developments in optimizing the utilization of renewable energy sources. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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28 pages, 4081 KiB

Open AccessReview

Modern Thermal Energy Storage Systems Dedicated to Autonomous Buildings

by Michał Musiał, Lech Lichołai and Dušan Katunský

Energies 2023, 16(11), 4442; https://doi.org/10.3390/en16114442 - 31 May 2023

Cited by 5 | Viewed by 2277

Abstract

This paper presents a detailed analysis of the research into modern thermal energy storage systems dedicated to autonomous buildings. The paper systematises the current state of knowledge concerning thermal energy storage systems and their use of either phase change materials or sorption systems; [...] Read more.

This paper presents a detailed analysis of the research into modern thermal energy storage systems dedicated to autonomous buildings. The paper systematises the current state of knowledge concerning thermal energy storage systems and their use of either phase change materials or sorption systems; it notes their benefits, drawbacks, application options, and potential directions for future development. The rapid proliferation of studies on installation systems, new composites, and phase change materials requires a systematisation of the subject related to short- and long-term thermal energy storage in building structures. This paper focuses on assessing the validity of the current improved thermal energy storage solutions for buildings with very high energy efficiency standards and buildings that are energy-independent. The paper presents the current results of the energy and economic analyses of the use of heat storage systems in buildings. This paper shows the optimal heat storage systems for autonomous buildings. Moreover, it also shows other potential ways to develop systems and composites capable of storing heat in autonomous buildings. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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14 pages, 4363 KiB

Open AccessReview

Nano-Enhanced Phase Change Materials for Thermal Energy Storage: A Bibliometric Analysis

by Javad Mohammadpour, Ann Lee, Victoria Timchenko and Robert Taylor

Energies 2022, 15(9), 3426; https://doi.org/10.3390/en15093426 - 07 May 2022

Cited by 17 | Viewed by 2431

Abstract

The high latent heat thermal energy storage (LHTES) potential of phase change materials (PCMs) has long promised a step-change in the energy density for thermal storage applications. However, the uptake of PCM systems has been limited due to their relatively slow charging response, [...] Read more.

The high latent heat thermal energy storage (LHTES) potential of phase change materials (PCMs) has long promised a step-change in the energy density for thermal storage applications. However, the uptake of PCM systems has been limited due to their relatively slow charging response, limited life, and economic considerations. Fortunately, a concerted global research effort is now underway to remove these remaining technical challenges. The bibliometric analysis of this review reveals that a major focus is now on the development of nano-enhanced phase change materials (NePCM), which have the potential to mitigate many of these technical challenges for PCM-based thermal energy storage systems. As such, our bibliometric analysis has zeroed in on research in the field of thermal energy storage using NePCMs since 1977. It was found that journal articles were the most frequently used document type, representing 79% of the records and that the pace of new work in this specific area has increased exponentially over these two decades, with China accounting for the highest number of citations and the most publications (168), followed by India and Iran. China has also played a central role in the collaboration network among the most productive countries, while Saudi Arabia and Vietnam show the highest international collaboration level. Full article

(This article belongs to the Special Issue Thermal Energy Storage and Energy Conversion Technologies)

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