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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "A2: Solar Energy and Photovoltaic Systems".

Deadline for manuscript submissions: 30 May 2025 | Viewed by 9016

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Special Issue Editors

Dr. Marco Francesconi

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Guest Editor

Department of Energy, Systems, Territory and Constructions Engineering (D.E.S.T.eC), University of Pisa, 56126 Pisa, Italy
Interests: fluid machinery; internal combustion engine; solar energy
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Dr. Elisa Sani

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Guest Editor

Istituto Nazionale di Ottica (INO) nel CNR, 50125 Florence, Italy
Interests: materials for solar energy; optical properties of materials; solar receivers; ceramics; nanofluids; nanoparticles; coatings; photon management
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Dr. Mario Petrollese

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Guest Editor

Department of Mechanical, Chemical and Materials Engineering, University of Cagliari, 09124 Cagliari, CA, Italy
Interests: energy system modeling; energy storage system integration; system optimization; renewable energy source integration; thermal energy storage system; ORC power system; concentrating solar power plants; combined heat and power plant
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Special Issue Information

Dear Colleagues,

As widely recognized in the literature, solar energy is a renewable, abundant, widely distributed, and sustainable renewable source. For these reasons, solar technologies represent a potential strategy for decarbonization to ensure greener energy production. Nonetheless, the main drawback of solar energy is its intermittent behavior that changes with the alternation of day and night, weather conditions, and seasons, thus requiring heat storage to alleviate this limit.

This special issue, "Advanced Solar Technologies and Thermal Energy Storage", focuses on studies of different uses of solar energy, possibly coupled with heat storage systems, to improve the spread of solar technologies and define their state of the art in different research fields. For this reason, original papers, reviews, and perspective papers that discuss solar technologies and their uses are welcome.

Dr. Marco Francesconi
Dr. Elisa Sani
Dr. Mario Petrollese
Guest Editors

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Keywords

solar energy and thermal energy storage systems
concentrated solar power
solar thermal and PV systems
thermal energy storage
solar desalination
solar heating
air heaters
solar industrial process
solar residential uses
solar water treatment
solar gasification
solar propulsion
solar cooling
solar chemical processes
integrated solar energy systems
numerical simulations
optic

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Published Papers (9 papers)

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Research

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21 pages, 7270 KiB

Open AccessArticle

Overcoming Power Limitations of Electric Heating in a Solar Salt Thermal Storage by Microwave Heating

by Roberto Grena, Mattia Cagnoli, Roberto Zanino and Michela Lanchi

Energies 2025, 18(8), 2059; https://doi.org/10.3390/en18082059 - 17 Apr 2025

Viewed by 202

Abstract

The expected increase in energy production from VRE (Variable Renewable Energy) requires a significant increase in energy storage capacity, with thermal storage potentially offering a key contribution. However, heat transfer mechanisms can limit the maximum power instantaneously transferable to the storage medium, posing a significant operational challenge. An analysis is presented here of the power limitations that arise when molten salt thermal storage adopting Solar Salt (NaNO₃/KNO₃, 60/40%wt) is heated by electrical resistances (Joule heating), and a possible alternative—the volumetric heating of the salt mass by microwaves—is discussed. Results show that microwave heating is an interesting path to overcome the power limitations of Joule heating. A first, theoretical analysis indicates a potential increase of more than 10 times in the maximum power transferable per unit area. Thermal-fluid-dynamic and electromagnetic models have been developed to numerically test the performance of a one-tank thermocline system endowed with a microwave heater. The proposed heating system showed limitations in terms of the maximum power that can be transferred to the salt because of the high temperatures established in the boundary layer. Finally, it performs in a comparable way with respect to an (ideal) heating system based on the Joule effect. However, many design improvements can still be adopted to enhance the performance of the proposed technology, likely overcoming the performance reachable using Joule heating systems. Full article

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

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25 pages, 6814 KiB

Open AccessArticle

Dynamic Investigation of Thermochemical Heat Upgrade and Alternative Industrial Heating Technologies

by Christos Sammoutos, Angeliki Kitsopoulou, Panagiotis Lykas, Dimitra Gonidaki, Evangelos Vidalis, Dimitrios Korres, Hamid Reza Rahbari, Christos Tzivanidis and Evangelos Bellos

Energies 2025, 18(8), 1990; https://doi.org/10.3390/en18081990 - 12 Apr 2025

Viewed by 302

Abstract

Industrial process heat production is critical to achieving sustainability in our society. Avoiding fossil fuels and reducing electricity consumption for heat production are critical aspects of creating sustainable industries. Exploiting waste heat streams by upgrading them into useful high-temperature heat is an interesting idea for reducing the CO₂ footprint industrial processes. In line with this, the present study’s main objective is to investigate a novel thermochemical heat upgrade system based on the SrBr₂/H₂O working pair for the petrochemical industry, which is practically driven only by low-temperature waste heat streams. This innovative system, which exploits a waste heat stream of 200 °C and upgrades it to 250 °C to make it suitable for industry utilization, achieves a nominal coefficient of performance of 0.605. The examined system is compared with three other alternatives, including a natural gas boiler with 86% efficiency, a hybrid solar thermal unit with an auxiliary natural gas boiler, and a high-temperature heat pump with a coefficient of performance of two. The nominal industrial heat production is 2.2 MW for the thermochemical heat upgrade system. The dynamic investigation is conducted under the climate conditions of Denmark and Greece. The high-temperature heat pump’s annual electricity consumption is 6.94 GWh. In contrast, the annual heat consumed by the natural gas boiler is 16.12 GWh, without integrating the solar thermal unit. For the hybrid system, the maximum daily contribution of the solar thermal system is 87% for the climate conditions of Denmark, and the annual useful heat generated by the concentrating solar system is 1.30 GWh for the Danish climate conditions and 2.82 GWh for the Greek climate conditions. Full article

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

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30 pages, 10836 KiB

Open AccessEditor’s ChoiceArticle

A Preliminary Experimental and Numerical Analysis of a Novel Solar Dryer

by Pio Francesco Muciaccia, Alessandra Nigro, Alessia Aquilanti, Sebastiano Tomassetti, Matteo Muccioli and Giovanni Di Nicola

Energies 2024, 17(23), 6059; https://doi.org/10.3390/en17236059 - 2 Dec 2024

Cited by 1 | Viewed by 1177

Abstract

In this study, a novel solar dryer is presented and analyzed experimentally and numerically. The proposed device is a small, passive, indirect solar dryer that works in an unconventional way. The product is mainly heated by irradiation from the walls of the drying chamber, while its moisture is removed by an airflow caused by natural convection. In addition, it is a low-cost solar dryer made of readily available materials and has a variable geometry that allows it to increase its thermal performance. Two types of experimental tests were conducted to analyze its performance. Thermal tests without load were carried out to assess the suitability of the drying chamber temperatures. Load tests with various masses and types of food were carried out to evaluate its drying performance. The results of the experimental tests demonstrated that the solar dryer achieved temperatures suitable for food drying and was able to dry the tested foods. Finally, a Computational Fluid Dynamics (CFD) model was developed to predict the performance of the proposed solar dryer. The validation of the numerical model with experimental data confirms their reliability in accurately predicting the temperatures within the dryer. Full article

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

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19 pages, 4742 KiB

Open AccessEditor’s ChoiceArticle

Storing Excess Solar Power in Hot Water on Household Level as Power-to-Heat System

by Ivar Kotte, Emma Snaak and Wilfried van Sark

Energies 2024, 17(20), 5154; https://doi.org/10.3390/en17205154 - 16 Oct 2024

Cited by 1 | Viewed by 1164

Abstract

PV technology has become widespread in the Netherlands, reaching a cumulative installed capacity of 22.4 GWp in 2023 and ranking second in the world for solar PV per capita at 1268 W/capita. Despite this growth, there is an inherent discrepancy between energy supply and demand during the day. While the netting system in the Netherlands can currently negate the economic drawbacks of this discrepancy, grid congestion and imbalanced electricity prices show that improvements are highly desirable for the sustainability of electricity grids. This research analyzes the effectiveness of a Power-to-Domestic-Hot-Water (P2DHW) system at improving the utilization of excess PV electricity in Dutch households and compares it to similar technologies. The results show that the example P2DHW system, the WaterAccu, compares favorably as a low cost and flexible solution. In particular, for twelve different households differing in size (1–6 occupants), PV capacity (2.4–8 kWp), and size of hot water storage boiler (50–300 L), it is shown that the total economic benefits for the period 2024–2032 vary from −€13 to €3055, assuming the current net metering scheme is abolished in 2027. Only for large households with low PV capacity are the benefits a little negative. Based on a multi-criteria analysis, it is found that the WaterAccu is the cheapest option compared to other storage options, such as a home battery, a heat pump boiler, and a solar boiler. A sensitivity study demonstrated that these results are overall robust. Furthermore, the WaterAccu has a positive societal impact owing to its peak shaving potential. Further research should focus on the potential of the technology to decrease grid congestion when implemented on a neighborhood scale. Full article

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

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21 pages, 22649 KiB

Open AccessArticle

Energy, Economic and Environmental (3E) Analysis for an Optimal CSP Technology Integration in Morocco

by Nabil Ammari, Ahmed Alami Merrouni, Abderrahmane Mendyl, Elmiloud Chaabelasri and Tamás Weidinger

Energies 2024, 17(12), 3020; https://doi.org/10.3390/en17123020 - 19 Jun 2024

Cited by 1 | Viewed by 933

Abstract

Among the existing solar technologies, Concentrating Solar Power (CSP) stands out as the most efficient and adaptable option for base load applications, primarily due to its thermal storage capabilities. However, despite its potential, the implementation of this technology still lacks competitiveness compared to Photovoltaic (PV) systems. Therefore, optimizing the plant components and operational factors becomes crucial for its cost-effective utilization, particularly in the desert regions of Morocco. Hence, the objective of this study comprised two main aspects: first, to conduct a parametric analysis aimed at selecting the optimal configuration for a parabolic trough collector (PTC)-based power plant suitable for the Moroccan context. Subsequently, an environmental analysis was performed to assess the impact of soiling on the plant operation. This step aimed to refine the precision of the techno-economic analysis and enhance the project’s bankability. High-quality in situ meteorological data and soiling measurements were utilized for these analyses. Furthermore, to ensure the reliability of the results, the results from the employed simulation tool were validated against real data obtained from an operational power plant. The results indicate that Morocco holds significant potential for the integration of large-scale CSP plants. A capacity of 1 MW utilizing PTC technology could yield an annual electricity production of up to 33 GWhe, with a levelized cost of electricity (LCOE) estimated at 0.1465 EUR/kWh. However, accounting for soiling effects in the yield analysis, which is recommended for precise yield calculations, revealed a decrease in the annual production to 28 GWhe for the same 1 MW capacity. This reduction represented a 20% loss from the nominal conditions, resulting in a corresponding increase in electricity cost by 30.6 €/MWh. Full article

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

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13 pages, 3753 KiB

Open AccessArticle

Performance Evaluation of Air-Based Photovoltaic Thermal Collector Integrated with Dual Duct and Semicircular Turbulator in Actual Climate Conditions

by Byeong-Hwa An, Seong-Bhin Kim, Hwi-Ung Choi and Kwang-Hwan Choi

Energies 2024, 17(11), 2752; https://doi.org/10.3390/en17112752 - 4 Jun 2024

Cited by 1 | Viewed by 898

Abstract

An air-based photovoltaic thermal collector (PVTC) is a system that generates both electricity and heat using air flowing over a photovoltaic (PV) module. This system offers the advantage of easy maintenance; however, it suffers from lower thermal efficiency compared to other PVTCs, mostly owing to the low heat capacity of air. Thus, this study introduces a novel PVTC incorporating dual ducts and semicircular turbulators, which were experimentally evaluated under actual weather conditions in the Republic of Korea. The proposed PVTC was compared with two other types of PVTC: one is a single-duct PVTC with semicircular turbulators, and the other is a dual-duct PVTC without turbulators. The results showed that the thermal efficiency of the proposed PVTC increased by approximately 88.7% compared to the single-duct PVTC with a turbulator and by 9.3% compared to the dual-duct PVTC without a turbulator. The electrical efficiency showed a slight decrease of about 7.2% compared to the single-duct PVTC but an increase of 1.4% compared to the dual-duct PVTC without a turbulator. Overall, the total efficiency of the proposed PVTC increased by 54.2% and 7.7% compared to the single-duct PVTC and the dual-duct PVTC without a turbulator, respectively. These experimental results demonstrate that attaching dual ducts and semicircular turbulators to an existing PVTC increases the daily thermal energy output, which ultimately enhances the total daily energy output. Full article

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

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24 pages, 8713 KiB

Open AccessFeature PaperArticle

Optimizing Nanofluid Hybrid Solar Collectors through Artificial Intelligence Models

by Safae Margoum, Bekkay Hajji, Stefano Aneli, Giuseppe Marco Tina and Antonio Gagliano

Energies 2024, 17(10), 2307; https://doi.org/10.3390/en17102307 - 10 May 2024

Cited by 5 | Viewed by 1408

Abstract

This study systematically explores and compares the performance of various artificial-intelligence (AI)-based models to predict the electrical and thermal efficiency of photovoltaic–thermal systems (PVTs) cooled by nanofluids. Employing extreme gradient boosting (XGB), extra tree regression (ETR), and k-nearest-neighbor (KNN) regression models, their accuracy is quantitatively evaluated, and their effectiveness measured. The results demonstrate that both XGB and ETR models consistently outperform KNN in accurately predicting both electrical and thermal efficiency. Specifically, the XGB model achieves remarkable correlation coefficient (R²) values of approximately 0.99999, signifying its superior predictive capabilities. Notably, the XGB model exhibits a slightly superior performance compared to ETR in estimating electrical efficiency. Furthermore, when predicting thermal efficiency, both XGB and ETR models demonstrate excellence, with the XGB model showing a slight edge based on R² values. Validation against new data points reveals outstanding predictive performance, with the XGB model attaining R² values of 0.99997 for electrical efficiency and 0.99995 for thermal efficiency. These quantitative findings underscore the accuracy and reliability of the XGB and ETR models in predicting the electrical and thermal efficiency of PVT systems when cooled by nanofluids. The study’s implications are significant for PVT system designers and industry professionals, as the incorporation of AI-based models offers improved accuracy, faster prediction times, and the ability to handle large datasets. The models presented in this study contribute to system optimization, performance evaluation, and decision-making in the field. Additionally, robust validation against new data enhances the credibility of these models, advancing the overall understanding and applicability of AI in PVT systems. Full article

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

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13 pages, 2776 KiB

Open AccessArticle

Experimental Characterization of Commercial Scroll Expander for Micro-Scale Solar ORC Application: Part 1

by Maurizio De Lucia, Giacomo Pierucci, Maria Manieri, Gianmarco Agostini, Emanuele Giusti, Michele Salvestroni, Francesco Taddei, Filippo Cottone and Federico Fagioli

Energies 2024, 17(9), 2205; https://doi.org/10.3390/en17092205 - 3 May 2024

Cited by 3 | Viewed by 1348

Abstract

In order to reduce greenhouse gas emissions and achieve global decarbonisation, it is essential to find sustainable and renewable alternatives for electricity production. In this context, the development of distributed generation systems, with the use of thermodynamic and photovoltaic solar energy, wind energy and smart grids, is fundamental. ORC power plants are the most appropriate systems for low-grade thermal energy recovery and power conversion, combining solar energy with electricity production. The application of a micro-scale ORC plant, coupled with Parabolic Trough Collectors as a thermal source, can satisfy domestic user demand in terms of electrical and thermal power. In order to develop a micro-scale ORC plant, a commercial hermetic scroll compressor was tested as an expander with HFC-245fa working fluid. The tests required the construction of an experimental bench with monitoring and control sensors. The aim of this study is the description of the scroll performances to evaluate the application and develop optimization strategies. The maximum isentropic effectiveness is reached for an expansion ratio close to the volumetric expansion ratio of the scroll, and machine isentropic effectiveness presents small variations in a wide range of working conditions. The filling factor is always higher than one, due to leakage in the mechanical seals of the scroll or other inefficiencies. This study demonstrates that using a commercial scroll compressor as an expander within an ORC system represents a valid option for such applications, but it is necessary to improve the mechanical seals of the machine and utilize a dedicated control strategy to obtain the maximum isentropic effectiveness. Full article

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

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Review

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53 pages, 4256 KiB

Open AccessReview

Nanofluids in Thermal Energy Storage Systems: A Comprehensive Review

by Mohamed Shameer Peer, Mario Cascetta, Luca Migliari and Mario Petrollese

Energies 2025, 18(3), 707; https://doi.org/10.3390/en18030707 - 4 Feb 2025

Cited by 2 | Viewed by 829

Abstract

Nanofluids, which consist of nanosized particles dispersed in a base fluid, represent a promising solution to improve the performance of thermal energy storage systems. This review offers a comprehensive overview of nanofluids and their applications in thermal energy storage systems, discussing their thermal properties, heat transfer mechanisms, synthesis techniques, and application in latent heat storage systems. Various types of nanofluids are examined, including metal oxide, carbon-based, and metallic nanofluids, highlighting their effects on thermal conductivity, latent heat and the phase change temperature. A review of experimental and numerical studies showcases the performance of thermal energy storage systems incorporating nanofluids and the factors influencing their thermophysical characteristics and energy storage capacity. Finally, the key findings of current research are summarized, as well as the challenges and the potential future directions in nanofluid-based thermal energy storage systems research, emphasizing the need to optimize nanoparticle concentration and long-term durability. Full article

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

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