Abstract The large penetration rate of renewable energy sources leads to challenges in planning and controlling the energy production, transmission, and distribution in power systems. A potential solution is found in a paradigm shift from traditional supply control to demand control. To address such changes, a first step lays in a formal and robust characterization of the energy flexibility on the demand side. The most common way to characterize the energy flexibility is by considering it as a static function at every time instant. The validity of this approach is questionable because energy-based systems are never at steady-state. Therefore, in this paper, a novel methodology to characterize the energy flexibility as a dynamic function is proposed, which is titled as the Flexibility Function. The Flexibility Function brings new possibilities for enabling the grid operators or other operators to control the demand through the use of penalty signals (e.g., price, CO2, etc.). For instance, CO2-based controllers can be used to accelerate the transition to a fossil-free society. Contrary to previous static approaches to quantify Energy Flexibility, the dynamic nature of the Flexibility Function enables a Flexibility Index, which describes to which extent a building is able to respond to the grid’s need for flexibility. In order to validate the proposed methodologies, a case study is presented, demonstrating how different Flexibility Functions enable the utilization of the flexibility in different types of buildings, which are integrated with renewable energies.
Abstract This paper gives a complete idea on the biofuel and its generation. In this fast-growing society there is a need of energies for survive. Biofuel, is the process where fossil fuel is replaced by organic material. It is an alternative source which can be also replaced the petroleum-based fuel. It is also the type of sustainable fuel derived from abundant biological sources called biomass. Biomass include a vast range of waste and plants. The objective of this paper is complete study of biofuel and its generation and find out the solution of other energy sources. The conclusion of this paper is that, algae is one of the greatest sources of energy and it can produce a lot of energy and can be replaced the fossil fuel. Biofuel and biomass are the only renewable sources which can replace the fossil fuel directly for the present and future energy restriction, because it is eco-friendly and renewable energy. The key finding of this review is biofuel can be the best substitute of fossil fuels.
Geothermal Energy is a very attractive source of naturally-occurring green renewable energy. Exploiting this natural resource is straightforward and causes almost no ill effects to the environment. But, while geothermal does not suffer the intermittence of other renewable sources, its extraction efficiency is fairly modest as compared to other sources. As a result, there has been significant interest recently in hybrid systems that integrate geothermal and other forms of energy to increase the output efficiency. This work will survey the different possible integrations involving geothermal energy. A review of the literature shows that the most common hybrid systems implementation involve the integration of geothermal with solar (45% of systems) followed by the integration of a cooling tower into the geothermal system (30% of systems). This work will also investigate the applications for geothermal hybrids and show that 44% of systems are designed for heating applications. Another 44% are used for cooling while only 12% are designed for electrical power generation. Complexity of control remains as the main obstacle facing hybrid multi-source energy systems including those involving geothermal energy.
Abstract Integration of different energy infrastructures (heat, electricity and gas vectors) offers great potential for better managing energy sources, reducing consumption and waste as well as enabling a higher share of renewables, lower environmental impact and lower costs. This paper aims at reviewing the state-of-the-art energy system infrastructures in order to provide a comprehensive overview of technologies, operational strategies, modelling aspects and the trends towards integration of heat, electricity and gas infrastructures. Various technological domains are taken into account, ranging from energy distribution networks (thermal, electric and gas), components for the energy vector conversion (e.g. combined heat and power, power to heat, power to gas, etc.) and energy storage. Furthermore, the aspects related to smart management in energy systems are investigated, such as integration of renewable energy sources and energy recovery systems.
Perseverance Dzikunu, Eugene Sefa Appiah, Emmanuel Kwesi Arthur
et al.
Abstract The increasing demand for cost-effective materials for energy storage devices has prompted investigations into diverse waste derived electrode materials for supercapacitors (SCs) application. This review examines advancements in converting waste into carbon-based SCs for renewable energy storage. In this context, different carbon-based waste precursor sources have been explored over the years as electrodes in SCs. These waste sources comprise of industrial, plastics and biowastes, including plant and animal wastes. The energy storage capabilities of the various waste derived SCs electrodes are highlighted to provide an understanding into the unique features that make them applicable to SCs. In addition, some challenges associated with the waste-derived SCs electrodes in terms of energy storage have been emphasized. Here, we also provided insights into the recent progress in SCs electrode synthesis techniques and their effects on electrochemical performance. SCs performance tailoring with material structures through the incorporation of different materials to form composites and optimized synthesis methods is an effective strategy. Hence, the synthesis methods outlined include pyrolysis, hydrothermal, microwave-assisted, template-assisted, and sol–gel techniques. The effect of the various synthesis methods on SCs performance has also been discussed. Overall, this review highlights waste valorization with future research directions and scaling challenges.
Adela Bâra, Irina Alexandra Georgescu, Simona-Vasilica Oprea
The paper examines the price volatility, key determinants, and autoregressive distributed lag (ARDL) framework of Romania’s Intraday Continuous Market (IDC) during the summer months. The stability of the ARDL-ECM coefficients is assessed using the cumulative sum (CUSUM) test. We explore the interaction between IDC and Day-Ahead Market (DAM) prices, alongside the influence of economic and environmental variables, including traded volumes, consumption, export/import and the generation mix. Using hourly data and econometric techniques, we identify significant short- and long-run relationships between IDC prices and their drivers. DAM prices exhibit a strong positive impact on IDC prices, reflecting tight market integration. Higher shares of Renewable Energy Sources (RES) such as wind and solar are associated with increased IDC prices, highlighting challenges in integrating intermittent resources. Conventional sources, particularly coal and oil/gas, also elevate prices due to higher marginal costs. Conversely, electricity consumption is negatively related to IDC prices, suggesting that anticipated demand patterns may contribute to system stability. The findings carry implications for policymakers, indicating a need for enhanced forecasting, flexible resources and improved inter-market coordination to ensure price stability and efficient integration of RES.
Despite their drawbacks, fossil fuels like gas, oil, and coal are widely used globally for energy purposes. On the contrary, nascent stages of the energy market are occupied by renewable energy sources such as solar, wind, and hydro, even though they are depletable and secure. Solar energy, which can be utilized on both small and large scales, is the purest form of renewable energy currently accessible. Accurate solar irradiance prediction is vital for sustainable solar energy use. Direct normal irradiance significantly influences solar power generation and can predict solar energy output. This study aims to develop a new hybrid model combining the grey wolf optimizer and extreme learning machine algorithm for accurate direct normal irradiance prediction
despite forecasting complexities. Ten input characteristics were chosen for the suggested model from a set of ten features that were gathered in Qinghai from June 30, 2023, to July 1, 2022. Following this, a feature selection process was conducted on these attributes, and the algorithms proceeded to process only the most significant ones. Upon comparing the alternative model utilized in this study to the suggested model its capability and effectiveness were unequivocally established. Consequently, employing the suggested model enables one to
reliably estimate direct normal irradiance for solar energy generation. Performance indicators for the proposed GWO-ELM model include RMSE of 63.17, MAE of 46.68, MSE of 3990.80, and RSE of 89.39. These findings show that the model can accurately and reliably estimate direct normal irradiance, despite the difficulties of solar energy forecasting.
Engineering (General). Civil engineering (General), Chemical engineering
The rock mass damage and failure induced by underground coal resource exploitation are strongly influenced by the confining pressure unloading (CPU) rate. However, the impact of CPU rate as a sole variable remains inadequately understood. This study utilizes discrete element numerical tests to explore the influence of CPU rate on the mesoscopic fracturing mechanism of sandstone. Homogeneous three-dimensional models with consistent mesoscopic parameters and constant axial pressure are subjected to varying CPU rates. By isolating the CPU rate as the sole variable, macroscopic failure patterns, mesoscopic damage evolution, and energy density distributions are investigated. The numerical results are validated against existing physical experimental results, confirming the rationality of the discrete element model parameters. The results show that lower CPU rates induce multistage, sudden, and progressive failure, characterized by stepwise increases in energy density, more abrupt fractures, and enhanced mobilization of local load-bearing capacity. The defined medium CPU rate results in distinct physical responses, attributed to particle rearrangement driven by unloading rate. Particle displacement is identified as a quantitative indicator of rock damage. The results underscore the importance of isolating the CPU rate effect to improve the understanding of rock fracturing mechanisms and associated physical properties.
Production of electric energy or power. Powerplants. Central stations, Renewable energy sources
For the dynamic analysis of floating offshore wind turbines (FOWTs) in realistic operating environment, this paper develops a coupled aero-hydro-mooring-servo model applicable to turbulent wind and irregular sea states with high computational efficiency. A modified rotor control strategy with platform motion feedback is proposed with a novel gain-scheduling technique to mitigate the negative damping effect on platform motions and decouple the rotor dynamics from the platform dynamics for better rotor operating performance. Firstly, the performance for the bottom-fixed wind turbine in steady uniform wind is validated and the turbulent wind tests show that using the rotor-disk-averaged wind speed for control is beneficial for reducing fluctuations of wind thrust and operational parameters compared with using the hub-height wind speed. For the FOWT, the negative damping phenomenon at above-rated wind speeds when using the baseline control is demonstrated through a range of wind and wave scenarios, and effects of control strategy and turbulent wind are investigated. The results indicate that the modified control strategy eliminates the negative damping effect on the platform pitch while maintaining small variations in rotor speed. Though the control including the blade pitch compensation from platform motion feedback with a constant gain can also eliminate the negative damping effect, it produces much larger fluctuations in rotor speed and causes larger overspeed exceeding the safety threshold of 20% at large wind speeds. Compared to steady wind, turbulent wind yields significantly larger low-frequency platform responses and increases the maximum rotor speed by 7.9% to 23.7% for the wind speeds considered.
We study the optimal green hydrogen production and energy market participation of a renewable-colocated hydrogen producer (RCHP) that utilizes onsite renewable generation for both hydrogen production and grid services. Under deterministic and stochastic profit-maximization frameworks, we analyze RCHP's multiple market participation models and derive closed-form optimal scheduling policies that dynamically allocate renewable energy to hydrogen production and electricity export to the wholesale market. Analytical characterizations of the RCHP's operating profit and the optimal sizing of renewable and electrolyzer capacities are obtained. We use real-time renewable production and electricity price data from three independent system operators to assess impacts from market prices and environmental policies of renewable energy and green hydrogen subsidies on RCHP's profitability.
In order to evaluate the insulation of two-phase immersion cooling in the HV power electronic package, the insulation degradation of the dielectric interface induced by bubbles is investigated. In this paper, a test strategy with 50 Hz unipolar DC and AC combined voltage for partial discharge (PD) at boiling interface of AIN ceramic is proposed. The insulation threshold of an AIN ceramic surface is acquired in several dielectric environments, such as air, FC-72 liquid (FC-72, a Fluorinert™ from 3M™), FC-72 vapor, and boiling state of FC-72. This reveals the deterioration of boiling on the insulation of the surface immersed in the dielectric refrigerant. To investigate the mechanism of the PD feature at the boiling interface, the PD patterns of the unrestricted bubble and the accumulated bubble are acquired and contrastively analyzed. Combined with the feature of the back discharge and the bubble behavior, the charged vapor-ceramic interface is relatively stable due to the accumulated vapor layer. This stability of the charged vapor-ceramic interface is broken if the bubble is unrestricted. Besides, it is discovered that the vapor-liquid interface inside the bubble may be another charged interface, which can also trigger a back discharge.