Sorin Gabriel Vernica

The power temperature coefficient (γ) of a photovoltaic–thermal (PVT) collector is usually taken from the datasheet. Determining it outdoors is difficult because irradiance and temperature vary together. This study evaluates how reliably γ can be estimated from a few field observations. Thirty observations were collected during three campaigns in Bacău, Romania, in 2024 on a 240 Wp liquid-cooled PVT collector operated at a fixed pump setting. Power normalised to 1000 W/m² was regressed on front-surface temperature with campaign-specific intercepts. This conventional analysis yielded γ = −0.64%/°C (95% CI: −0.82 to −0.46), compared with the declared −0.45%/°C. The result was sensitive to model specification. Irradiance and panel temperature were strongly correlated (r = 0.84), and including irradiance as a covariate, which the data supported (p = 0.043), changed γ to −0.40%/°C (−0.72 to −0.09). Eleven specifications differing in covariates, first-observation exclusions and temperature variable produced estimates from −0.33 to −1.08%/°C. In one campaign, measured power averaged 19% above the nameplate-based expectation, indicating an inconsistency in the absolute measurement scale. In an hourly PVGIS-SARAH3 calculation for 2023, each 0.1%/°C change in γ altered annual electrical yield by 0.94%. The measurements are compatible with the datasheet coefficient but constrain it only to between about ±0.3 and ±0.7%/°C, depending on the specification.

The integration of hydrogen into natural-gas-fired gas turbines represents a promising transitional pathway for reducing greenhouse gas emissions in industrial power generation. This study presents a comparative thermodynamic and environmental assessment of a Solar Titan 130 gas turbine operating in combined heat and power (CHP) mode under two fueling conditions: conventional natural gas and a hydrogen-enriched CH₄/H₂ (80/20 vol.%) blend. The analysis combines validated operational data for natural gas with analytical thermodynamic modeling for the blended-fuel scenario to evaluate key performance indicators, including thermal efficiency, specific fuel consumption, power output, and carbon dioxide emissions. The results indicate that hydrogen enrichment leads to an increase in thermal efficiency from 34.1% to 36.6% and a reduction in specific CO₂ emissions by approximately 13.7%, while maintaining similar thermal input within the adopted steady-state modeling framework. Compressor power consumption decreases, and net electrical output increases slightly under hydrogen-enriched operation, contributing to improved overall energy performance. Although the hydrogen-blended regime is assessed through modeling, the findings suggest that moderate hydrogen addition can enhance efficiency and environmental performance in industrial gas turbines without fundamental structural redesign of the turbine core, assuming appropriate fuel supply and control system adaptation. The study provides practical insights into the feasibility of hydrogen-assisted operation in existing CHP installations and supports its role in near-term decarbonization strategies.

This paper provides a brief overview of the importance and how virtual power plants (VPPs) could participate in the Romanian electricity market in the future, as well as renewable energy integration into the Romanian Power System (RPS). Over the last decade, Romania has experienced a significant growth in its distributed energy resources (DERs) installed capacity base. VPPs concept aggregates diverse DERs, including solar photovoltaic (PV) arrays, wind turbines (WTs), battery energy storage systems (BESSs), and demand response units to operate as one big power plant which can trade on the same electricity market that today's suppliers do. VPPs integrate renewable energy and digitization based on Information and Communications Technologies (ICTs) and Artificial Intelligence (AI)-based predictive models to create a new energy platform for prosumers. VPPs solutions will process the energy production forecast and electricity price, then optimize the electricity sales plan, and if there is charge and discharges gathered, to obtain total profit.

This paper presents a comprehensive comparative study between conventional and condensing wallmounted boilers, focusing on energy efficiency, environmental impact, and practical installation outcomes. Experimental data was collected at the Thermoenergetics Laboratory of the Faculty of Engineering at 'Vasile Alecsandri' University of Bacau. Measurements include energy balance parameters, gas analysis, and heat exchange performance under standardized conditions. Based on the conducted energy balances, it was found that the efficiency of the condensing boiler is 8.1 % higher than that of the conventional boiler. This increase is primarily attributed to the recovery of latent heat from the flue gases through the condensation of water vapors.

Cogeneration is widely recognized as one of the most efficient methods of electricity generation, with gas turbine-based systems playing a critical role in ensuring reliability, sustainability, and consistent power output. This paper presents an energy efficiency analysis of a 14 MW high-efficiency cogeneration unit, featuring a modernized gas turbine as its core component. Since gas turbines often operate under varying loads due to fluctuating demand, this study examines their performance at 100%, 75%, and 50% load levels. It is observed that the efficiency of the gas turbine declines as the load decreases, primarily due to losses resulting from deviations from the design flow conditions. A detailed energy balance, Sankey diagram, and a comparative analysis of performance metrics against the manufacturer’s guarantees are provided for each load scenario. The results indicate that net thermal efficiency decreases by 10.7% at 75% load and by 30.6% at 50% load compared to nominal performance at full load. The performance at full load closely aligns with the values guaranteed by the gas turbine supplier. The gross electrical power output is 1.33% higher than the guaranteed value, and the thermodynamic circuit’s efficiency is 0.49% higher under real conditions. This study represents the initial phase of transitioning the turbine to operate on a fuel blend of natural gas and up to 20% hydrogen, with the goal of reducing CO₂ emissions. As a novel contribution, this paper provides a systematized method for calculating and monitoring the in-service performance of gas turbines. The mathematical model is implemented using the Mathcad Prime 8.0 software, which proves to be beneficial for both operators and researchers.

This work presents a comparative study of a step-down converter controlled through the algorithm MPPT Perturb and Observe (P&O) with or without a fuzzy logic controller supplied by a photovoltaic system. This study aimed at increasing the quantity of electric energy taken over from the photovoltaic systems by the load through the DC-DC convertor. To follow up the maximum power point where the transfer is performed from the photovoltaic system to the load at maximum power, the Perturb and Observe (P&O) method was used. Two programs were elaborated in MATLAB-Simulink R2018a to control the buck convertor commanded through the P&O algorithm with or without a fuzzy logic controller. The analysis of the results showed that a higher quantity of energy is transferred from the source to the receptor circuit in the case of the buck convertor controlled through the P&O algorithm with a fuzzy logic controller. The P&O algorithm was implemented on an experimental stand at the Laboratory of Electrical Machinery and Drives of the Engineering Faculty in Bacau, with the help of a program issued in the Arduino IDE programming environment. The analysis of the results showed that for an increase in the power conveyed to the receptor circuit, there will also be an increase in the filling factor of the PWM signal that controls the power transistor in the structure of the DC-DC convertor. The P&O algorithm with a fuzzy logic controller may also be implemented in the DC-DC converters in the structure of the driving systems of electric vehicles.

This paper offers a theoretical and experimental examination of the concurrent production of electricity and heat using photovoltaic thermal (PV/T) technology. The efficiency performance of the PV/T system is meticulously analyzed using MATLAB/Simulink software environments. Notably, the proposed PV/T system shows reliable performance, and its validity is confirmed through experimental validation on a test stand with a single PV/T panel positioned at a 45-degree angle to the horizontal and a 0-degree azimuth angle. The measurements were conducted during the summer season, and two models were suggested to calculate the overall efficiency of the PV/T system. The variance between the results obtained from the two models was minimal, below 5%. For the examined panel type, the following average values were derived: electrical efficiency = 12.01%, thermal efficiency = 47.21%, and overall efficiency = 59.23%.

Solar photovoltaic (PV) generation suffers from multiple serious issues, for example shading effects directly affect the performance of installed PV arrays. By studying these issues, it can play a key role in improving the limitations and performance of PV panels. The study of PV arrays under partial shading conditions is mentioned in many papers as a part of other studies and as an independent phenomenon. Therefore, it is essential to improve these studies and update them with new research and study this problem in detail to know how to limit the effects of partial shading irradiance conditions on PV arrays performances, including economical aspects. This paper proposes to study the effects of different partial shading irradiance conditions for a PV array in various configurations. The analysis is proved in detail through the simulation of the proposed PV array in the Matlab/Simulink environment. The obtained results show the performances of interconnected PV arrays under different partial shading irradiance and temperature conditions, including the solar array I-V and P-V characteristics. In addition, different PV array configurations with and without bypass and blocking protection diodes improve and minimize the effect of partial shading conditions and avoid the reductions in output power.

This paper offers a theoretical and experimental examination of the concurrent production of electricity and heat using photovoltaic thermal (PV/T) technology. The efficiency performance of the PV/T system is meticulously analyzed using MATLAB/Simulink software environments. Notably, the proposed PV/T system shows reliable performance, and its validity is confirmed through experimental validation on a test stand with a single PV/T panel positioned at a 45-degree angle to the horizontal and a 0-degree azimuth angle.