This paper presents a comparative analysis of different battery charging strategies for off-grid solar PV systems. The strategies evaluated include constant voltage charging, constant current charging, PWM charging, and hybrid charging. The performance of each strategy is evaluated based on factors such as battery capacity, cycle life, DOD, and charging efficiency, as well as the impact of environmental conditions such as temperature and sunlight. The results show that each charging strategy has its advantages and limitations, and the optimal approach will depend on the specific requirements and limitations of the off-grid solar PV system. This study provides valuable insights into the performance and effectiveness of different battery charging strategies, which can be used to inform the design and operation of off-grid solar PV systems. This paper concludes that the choice of charging strategy depends on the specific requirements and limitations of the off-grid solar PV system and that a careful analysis of the factors that affect performance is necessary to identify the most appropriate approach. The main needs for off-grid solar photovoltaic systems include efficient energy storage, reliable battery charging strategies, environmental adaptability, cost-effectiveness, and user-friendly operation, while the primary limitations affecting these systems encompass intermittent energy supply, battery degradation, environmental variability, initial investment costs, fluctuations in energy demand, and maintenance challenges, emphasizing the importance of careful strategy selection and system design to address these factors. It also provides valuable insights for designing and optimizing off-grid solar PV systems, which can help to improve the efficiency, reliability, and cost-effectiveness of these systems.

The article examines the role of green hydrogen in reducing CO₂ emissions in the transition to climate neutrality, highlighting both its benefits and challenges. It starts by discussing the production of green hydrogen from renewable sources and provides a brief analysis of primary resource structures for energy production in European countries, including Romania. Despite progress, there remains a significant reliance on fossil fuels in some countries. Economic technologies for green hydrogen production are explored, with a note that its production alone does not solve all issues due to complex and costly compression and storage operations. The concept of impure green hydrogen, derived from biomass gasification, pyrolysis, fermentation, and wastewater purification, is also discussed. Economic efficiency and future trends in green hydrogen production are outlined. The article concludes with an analysis of hydrogen-methane mixture combustion technologies, offering a conceptual framework for economically utilizing green hydrogen in the transition to a green hydrogen economy.

Shifting towards renewable energy sources is essential for achieving sustainability goals. This research aims to develop and practically validate an integrated photovoltaic (PV) system with battery storage and electric vehicle (EV) charging, combined with smart energy management, to optimize energy use and minimize fossil fuel reliance. Conducted in Constanta, Romania, the study presents a novel practical solution involving a real-world grid-connected PV system leveraging battery storage to effectively retain excess solar energy for future consumption, thereby enhancing self-sufficiency and grid independence. Utilizing PV*SOL for system simulation and Global Solar Atlas for solar irradiance data, the authors provide accurate assessments of energy yield, economic feasibility, and environmental benefits. Results demonstrate a high energy autonomy level, with solar energy covering 92.2% of total consumption, alongside a notable annual reduction of 6239 kg in CO₂ emissions. The study significantly contributes to the field by providing an empirically validated model that bridges theory and practice, offering a scalable blueprint for sustainable and economically viable renewable energy systems.

The transition to renewable energy is a crucial step toward sustainability and integrating photovoltaic (PV) systems with battery storage and electric vehicle (EV) charging plays a key role in optimizing energy consumption and reducing reliance on fossil fuels. This study examines the design, performance, and impact of a grid-connected PV system in Constanta, Romania, assessing its ability to enhance energy efficiency, improve self-sufficiency, and contribute to environmental sustainability. By leveraging battery storage, surplus solar power is retained for later use, reducing dependency on the grid and ensuring a stable electricity supply. The study further investigates the economic and environmental benefits of renewable energy integration, including reductions in carbon emissions and operational costs. The analysis was conducted using PV*SOL for system simulation and performance evaluation, while Global Solar Atlas provided solar irradiance data for accurate energy yield assessment. The results demonstrate that integrating PV systems with battery storage and EV charging significantly enhances energy independence, with 92.2% of total consumption covered by solar energy and a reduction of 6239 kg in CO₂ emissions annually. This research provides a comprehensive model for renewable energy adoption, supporting the transition toward a cleaner and more sustainable energy.

The paper concludes that the choice of charging strategy depends on the specific requirements and limitations of the off-grid solar PV system, and that a careful analysis of the factors that affect performance is necessary to identify the most appropriate approach. Also provides valuable insights for designing and optimizing off-grid solar PV systems, which can help to improve the efficiency, reliability, and cost-effectiveness of these systems.

With the development of an energy sector based on renewable primary sources, structural changes are emerging for the entire national energy system. Initially, it was estimated that energy generation based on fossil fuels would decrease until its disappearance. However, the evolution of ${CO}_2$ capture capacity leads to a possible coexistence for a certain period with the renewable energy sector. The paper develops this concept of the coexistence of the two systems, with the positioning of green hydrogen not only within the renewable energy sector but also as a transformation vector for carbon dioxide captured in the form of synthetic fuels, such as $C{H}_4$ and $C{H}_{3}OH$. The authors conducted pilot-scale research on ${CO}_2$ capture with green $H_2$, both for pure (captured) ${CO}_2$ and for ${CO}_2$ found in combustion gases. The positive results led to the respective recommendation. The research conducted by the authors meets the strict requirements of the current energy phase, with the authors considering that wind and solar energy alone are not sufficient to meet current energy demand. The paper also analyzes the economic aspects related to price differences for energy produced in the two sectors, as well as their interconnection. The technical aspect, as well as the economic aspect, of storage through various other solutions besides hydrogen has been highlighted. The development of the renewable energy sector and its demarcation from the fossil fuel energy sector, even with the transcendent vector represented by green hydrogen, leads to the deepening of dispersion aspects between the electricity sector and the thermal energy sector, a less commonly mentioned aspect in current works, but of great importance. The purpose of this paper is to highlight energy challenges during the current transition period towards climate neutrality, along with solutions proposed by the authors to be implemented in this phase. The current stage of combustion of the $C{H}_4-H_2$ mixture imposes requirements for the capture of the resulting ${CO}_2$.