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Challenges and Opportunities in the Global Clean Energy Transition
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Challenges and Opportunities in the Global Clean Energy Transition

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "B2: Clean Energy".

Deadline for manuscript submissions: 15 September 2025 | Viewed by 2083

Special Issue Editors

Dr. Nikolay Hinov

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Guest Editor
Faculty of Computer Systems and Technologies, Department of Computer Systems, Technical University in Sofia, 8 Ohridski Blvd., 1000 Sofia, Bulgaria
Interests: artificial intelligence; mathematical modeling; control theory and applications; smart cities and smart grids
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Georgi Todorov

E-Mail Website
Guest Editor
Faculty of Industrial Technology, Technical University of Sofia, 1000 Sofia, Bulgaria
Interests: virtual reality; virtual prototyping; virtual engineering; 3D printing; rapid prototyping; mechanical engineering and industrial systems; CAD /CAM /CAE technologies; FEA; vibration and noise; production technologies and materials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are pleased to invite you to participate in this Special Issue and join our team at the Centre of Excellence "Mechatronics and Clean Technology", Campus Technical University, Sofia. In our work toward the realisation of the centre, combining almost all areas of engineering, we focused on the creation, development, and implementation of innovative technologies and systems for sustainable development based on the use of green energy. As a result of accelerated development based on digital technologies, mechatronics and their systems are becoming key to combining growing energy needs and maintaining the ecological balance of the planet. The main themes of our research are computer modelling and the development of technologies and new materials for engineering and re-engineering; electronic, optical, sensor and bio-mechatronic systems and technologies; mechatronic systems and technologies; clean energy; and green technologies.

We hope that our combined efforts will give impetus to new ideas and collaborations between leading researchers in the field of engineering and will contribute to achieving synergies both at the level of individual research teams and institutions.

Dr. Nikolay Hinov
Prof. Dr. Georgi Todorov
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • energy harvesting
  • conversion and storage
  • energy effective and robotized manufacturing
  • green and smart transport
  • digital technologies for sustainable industry and society
  • innovations focused on improving the quality of life

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Published Papers (4 papers)

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Research

29 pages, 4571 KB  
Article
Parametric Evaluation of Coolant Channels for Proton-Exchange Membrane Fuel Cell Based on Multi-Pass Serpentine Flow Field
by Qingsheng Liu, Xuanhong Ye, Hai Huang, Junjie Cheng, Kai Meng, Qinglong Yu, Junyi Liu, Waqas Ahmad, Zulkarnain Abbas, Muhammad Aurangzeb, Muhammad Ahmed and Shusheng Xiong
Energies 2025, 18(16), 4264; https://doi.org/10.3390/en18164264 - 11 Aug 2025
Viewed by 344
Abstract
Proton-exchange membrane fuel cells (PEMFCs) stand out for their exceptional efficiency, high power density, and zero emissions, as they produce merely heat and water as byproducts. Appropriate and robust thermal management is the key to ensuring the maximum efficiency of the fuel cell [...] Read more.
Proton-exchange membrane fuel cells (PEMFCs) stand out for their exceptional efficiency, high power density, and zero emissions, as they produce merely heat and water as byproducts. Appropriate and robust thermal management is the key to ensuring the maximum efficiency of the fuel cell (FC) as its optimum operating temperature is 70~80 °C. The current study was designed for the parametric evaluation of coolant channels (CCs) based on the multi-pass serpentine flow field (MPSFF) to investigate the relationship between channel geometry and thermal performance in PEM fuel cells, offering novel insights into optimal design configurations for improved thermal management. Six 3D computational models of PEMFCs with varying numbers of coolant channels were created and evaluated using COMSOL 6.2. The acquired results suggested that longer channel lengths with more serpentine turns cause the maximum number of hot spots around turns and offer a maximal pressure drop, whereas increasing the number of channels results in a uniform thermal distribution and leads to a minimal pressure drop. The findings indicate that systematic variations in geometrical configurations of MPSFFs can significantly enhance thermal uniformity and minimize the pressure drop, offering valuable insights for improving the efficiency of PEMFCs. Full article
(This article belongs to the Special Issue Challenges and Opportunities in the Global Clean Energy Transition)
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27 pages, 1739 KB  
Article
Hybrid Small Modular Reactor—Renewable Systems for Smart Cities: A Simulation-Based Assessment for Clean and Resilient Urban Energy Transitions
by Nikolay Hinov
Energies 2025, 18(15), 3993; https://doi.org/10.3390/en18153993 - 27 Jul 2025
Viewed by 751
Abstract
The global transition to clean energy necessitates integrated solutions that ensure both environmental sustainability and energy security. This paper proposes a scenario-based modeling framework for urban hybrid energy systems combining small modular reactors (SMRs), photovoltaic (PV) generation, and battery storage within a smart [...] Read more.
The global transition to clean energy necessitates integrated solutions that ensure both environmental sustainability and energy security. This paper proposes a scenario-based modeling framework for urban hybrid energy systems combining small modular reactors (SMRs), photovoltaic (PV) generation, and battery storage within a smart grid architecture. SMRs offer compact, low-carbon, and reliable baseload power suitable for urban environments, while PV and storage enhance system flexibility and renewable integration. Six energy mix scenarios are evaluated using a lifecycle-based cost model that incorporates both capital expenditures (CAPEX) and cumulative carbon costs over a 25-year horizon. The modeling results demonstrate that hybrid SMR–renewable systems—particularly those with high nuclear shares—can reduce lifecycle CO2 emissions by over 90%, while maintaining long-term economic viability under carbon pricing assumptions. Scenario C, which combines 50% SMR, 40% PV, and 10% battery, emerges as a balanced configuration offering deep decarbonization with moderate investment levels. The proposed framework highlights key trade-offs between emissions and capital cost and seeking resilient and scalable pathways to support the global clean energy transition and net-zero commitments. Full article
(This article belongs to the Special Issue Challenges and Opportunities in the Global Clean Energy Transition)
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16 pages, 4298 KB  
Article
Investigation of Flame Structure and PAHs’ Evolution in a Swirl-Stabilized Spray Flame at Elevated Pressure
by Wenyu Wang, Runfan Zhu, Siyu Liu, Yong He, Wubin Weng, Shixing Wang, William L. Roberts and Zhihua Wang
Energies 2025, 18(15), 3923; https://doi.org/10.3390/en18153923 - 23 Jul 2025
Viewed by 399
Abstract
Swirl spray combustion has attracted significant attention due to its common usage in gas turbines. However, the high pressure in many practical applications remains a major obstacle to the deep understanding of flame stability and pollutant formation. To address this concern, this study [...] Read more.
Swirl spray combustion has attracted significant attention due to its common usage in gas turbines. However, the high pressure in many practical applications remains a major obstacle to the deep understanding of flame stability and pollutant formation. To address this concern, this study investigated a swirl spray flame fueled with n-decane at elevated pressure. Planar laser-induced fluorescence (PLIF) of OH and polycyclic aromatic hydrocarbons (PAHs) were used simultaneously, enabling the distinction of the locations of OH, PAHs, and mixtures of them, providing detailed information on flame structure and evolution of PAHs. The effects of swirl number and ambient pressure on reaction zone characteristics and PAHs’ formation were studied, with the swirl number ranging from 0.30 to 1.18 and the pressure ranging from 1 to 3 bar. The data suggest that the swirl number changes the flame structure from V-shaped to crown-shaped, as observed at both atmospheric and elevated pressures. Additionally, varying swirl numbers lead to the initiation of flame divergence at distinct pressure levels. Moreover, PAHs of different molecular sizes exhibit significant overlap, with larger PAHs able to further extend downstream. The relative concentration of PAH increased with pressure, and the promoting effect of pressure on producing larger PAHs was significant. Full article
(This article belongs to the Special Issue Challenges and Opportunities in the Global Clean Energy Transition)
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18 pages, 3631 KB  
Article
Analysis of Implementing Hydrogen Storage for Surplus Energy from PV Systems in Polish Households
by Piotr Olczak and Dominika Matuszewska
Energies 2025, 18(14), 3674; https://doi.org/10.3390/en18143674 - 11 Jul 2025
Viewed by 388
Abstract
One of the methods for mitigating the duck curve phenomenon in photovoltaic (PV) energy systems is storing surplus energy in the form of hydrogen. However, there is a lack of studies focused on residential PV systems that assess the impact of hydrogen storage [...] Read more.
One of the methods for mitigating the duck curve phenomenon in photovoltaic (PV) energy systems is storing surplus energy in the form of hydrogen. However, there is a lack of studies focused on residential PV systems that assess the impact of hydrogen storage on the reduction of energy flow imbalance to and from the national grid. This study presents an analysis of hydrogen energy storage based on real-world data from a household PV installation. Using simulation methods grounded in actual electricity consumption and hourly PV production data, the research identified the storage requirements, including the required operating hours and the capacity of the hydrogen tank. The analysis was based on a 1 kW electrolyzer and a fuel cell, representing the smallest and most basic commercially available units, and included a sensitivity analysis. At the household level—represented by a single-family home with an annual energy consumption and PV production of approximately 4–5 MWh over a two-year period—hydrogen storage enabled the production of 49.8 kg and 44.6 kg of hydrogen in the first and second years, respectively. This corresponded to the use of 3303 kWh of PV-generated electricity and an increase in self-consumption from 30% to 64%. Hydrogen storage helped to smooth out peak energy flows from the PV system, decreasing the imbalance from 5.73 kWh to 4.42 kWh. However, while it greatly improves self-consumption, its capacity to mitigate power flow imbalance further is constrained; substantial improvements would necessitate a much larger electrolyzer proportional in size to the PV system’s output. Full article
(This article belongs to the Special Issue Challenges and Opportunities in the Global Clean Energy Transition)
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