Floating offshore wind turbines (FOWT) have attracted more and more attention in recent years. However, environmental loads on FOWTs have higher complexity than those on the traditional onshore or fixed-bottom offshore wind turbines. In addition to aerodynamic loads on turbine blades, hydrodynamic loads also act on the support platform. A review on the aerodynamic analysis of blades, hydrodynamic simulation of the supporting platform, and coupled aero- and hydro-dynamic study on FOWTs, is presented in this paper. At present, the primary coupling method is based on the combination of BEM theory and potential flow theory, which can simulate the performance of the FOWT system under normal operating conditions but has certain limitations in solving the complex problem of coupled FOWTs. The more accurate and reliable CFD method used in the research of coupling problems is still in its infancy. In the future, multidisciplinary theories should be used sufficiently to research the coupled dyna... [more]

Rockburst may cause damage to engineering equipment, disrupt construction progress, and endanger human life. To this day, the occurrence of rockburst remains complex and difficult to predict. This study proposes the D-P-Transformer algorithm to address this issue by improving the embedding structure of the Transformer for specific applications to rockburst data. To reduce the computational requirement, sparse self-attention is adopted to replace self-attention. A distilling operation and multiple layer replicas are simultaneously used to enhance the robustness and speed up the algorithm’s process. Taking all relevant rockburst factors into consideration, multiple experiments are conducted on seven large-scale rockburst datasets with different training ratios to verify the reliability of the proposed D-P-Transformer rockburst prediction algorithm. As compared to the original algorithm, the proposed algorithm shows average reductions of 24.45%, 46.56%, 17.32%, and 48.11% in the mean abso... [more]

Bellows are the key structures that compensate for and absorb the temperature-dependent displacement of a gas insulated switchgear (GIS) shell. It is of great engineering value to master the relationship between the temperature-dependent displacement behavior and various influencing factors. Based on the analysis of the influencing factors of the temperature variation displacement compensation ability of the GIS bellows, a bellows model was established. By coupling it with a shell having different degrees of bending through two layout methods, finite element simulation was carried out based on ABAQUS software to obtain the regular relationship between the temperature variation displacement compensation behavior of the bellows and various influencing factors. The results of the case study show that the temperature change displacement compensation ability of the bellows is most significantly affected by their own structural size. Reducing the wall thickness and increasing the wave height... [more]

Since there are no legally defined testing requirements for mobile positive pressure fans, they may be tested based on methods that do not correspond to their actual operating conditions. Adequate assessment of the technical and operating conditions for this type of equipment is particularly important for equipment used in rescue operations. Such units should be characterized by efficient and reliable operation. This article investigates the influence of measurement methods of the volumetric airflow rate on the performance of a power unit. The article shows that the applied measurement method, whether it is PN-EN ISO 5801 (test conditions in a pipe duct—Method A) or other methods, i.e., ANSI/AMCA 240-15 and testing of the characteristics of the velocity profile (tests in open flow—Method B), can cause differences in the power demand of fans of from 3.2% to 4.5%. The differences in the requirements of propulsion power translate into fuel consumption and emissions of harmful exhaust gase... [more]

In the hot-spot fault of photovoltaic modules, there is a low resistance hot-spot fault caused by crystal defects, such as internal crack and PN junction failure. When the faulty area is partially shaded, it will produce severe temperature rise, accelerate the aging of battery unit, and even cause fire, which will affect the safe operation of the photovoltaic system. In this paper, the low resistance hot-spot fault endangering the safe operation of photovoltaic modules is taken as the research object; the shunt effect of equivalent low resistance caused by crystal defects under local shadow occlusion is explained by using the reverse characteristic of PN junctions of battery units, and its failure mechanism is analyzed. The three working states of the power generation system and the formation conditions of hot-spots in the process of power generation are analyzed in detail. By building a simulation model, the heating power distribution characteristics of hot-spots under different exter... [more]

As one of the countries with the most rapid development of new energy, China has been committed to exploring countermeasures to the challenges of new energy consumption. After more than ten years of consideration and consultation, the “renewable portfolio standard“(RPS) for “renewable energy power consumption responsibility weighting” has landed in China. However, in the official affirmation issued by the National Energy Administration, theoretical support for the basis of the initial quota allocation is still lacking. In this study, we examine the efficiency of the weight allocation scheme for renewable energy power consumption responsibilities, which was announced by the National Energy Administration in 2018 and which is based on the BCC-DEA efficiency model. The results indicate that most provinces have low allocation efficiency under this allocation scheme. Therefore, we propose an optimal allocation scheme for a renewable energy consumption quota, based on the ZSG-DEA model. With... [more]

Rapid climate change and forecasted damage from fossil fuel combustion, forced researchers to investigate renewable and clean energy sources for the sustainable development of societies throughout the world. Biomass-based energy is one of the most important renewable energy sources for meeting daily energy needs, which are gaining in popularity daily. Gasification-based bioenergy production is an effective way to replace fossil fuels and reduce CO2 emissions. Even though biomass gasification has been studied extensively, there is still much opportunity for improvement in terms of high-quality syngas generation (high H2/CO ratio) and reduced tar formation. Furthermore, the presence of tar has a considerable impact on syngas quality. Downdraft gasifiers have recently shown a significant potential for producing high-quality syngas with lower tar concentrations. This article presents a comprehensive review on the advancement in biomass downdraft gasification technologies for high-quality s... [more]

Several physics-based enhancements are embedded in a low-fidelity general unducted rotor design analysis tool developed, py_BEM, including the local Reynolds number effect, rotational corrections to airfoil polar, stall delay model, high induction factor correction, polar at large angle of attack, exergetic efficiency calculation and momentum-based loss. A wind turbine rotor is analyzed in high fidelity designed from py_BEM using a 3D blade generator. It is a design derived from the NREL Phase VI rotor. Three design variations are analyzed using steady 3D CFD solutions to demonstrate the effect of geometry on aerodynamics. S809 and NACA 2420 airfoil properties are used for calculating the aerodynamic loading. Momentum, vorticity and energy transport are explained in depth and connected to entropy production as a measure of performance loss. KE dissipation downstream of the rotor is shown to be a significant contributor of entropy rise. Wake analysis demonstrates mixing with the free st... [more]

Worldwide growth in electric vehicle use is prompting new installations of private and public electric vehicle supply equipment (EVSE). EVSE devices support the electrification of the transportation industry but also represent a linchpin for power systems and transportation infrastructures. Cybersecurity researchers have recently identified several vulnerabilities that exist in EVSE devices, communications to electric vehicles (EVs), and upstream services, such as EVSE vendor cloud services, third party systems, and grid operators. The potential impact of attacks on these systems stretches from localized, relatively minor effects to long-term national disruptions. Fortunately, there is a strong and expanding collection of information technology (IT) and operational technology (OT) cybersecurity best practices that may be applied to the EVSE environment to secure this equipment. In this paper, we survey publicly disclosed EVSE vulnerabilities, the impact of EV charger cyberattacks, and... [more]

To obtain the price return and price volatility spillovers between renewable energy stocks, technology stocks, oil futures and carbon allowances under different investment horizons, this paper employs a frequency-dependent method to study the dynamic connectedness between these assets in four frequency bands. The results show that, first, there is a strong spillover effect between these assets from a system-wide perspective, and it’s mainly driven by short-term spillovers. Second, in the time domain, technology stocks have a more significant impact on renewable energy stocks compared to crude oil. However, through the study in the frequency domain, we find renewable energy stocks exhibit a more complex relationship with the other two assets at different time scales. Third, renewable energy stocks have significant spillover effect on carbon prices only in the short term. On longer time scales, other factors such as energy prices, climate and policy may have a greater impact on carbon al... [more]

The significant market growth of stationary electrical energy storage systems both for private and commercial applications has raised the question of battery lifetime under practical operation conditions. Here, we present a study of two 8 kWh lithium-ion battery (LIB) systems, each equipped with 14 lithium iron phosphate/graphite (LFP) single cells in different cell configurations. One system was based on a standard configuration with cells connected in series, including a cell-balancing system and a 48 V inverter. The other system featured a novel configuration of two stacks with a parallel connection of seven cells each, no cell-balancing system, and a 4 V inverter. The two systems were operated as part of a microgrid both in continuous cycling mode between 30% and 100% state of charge, and in solar-storage mode with day−night cycling. The aging characteristics in terms of capacity loss and internal resistance change in the cells were determined by disassembling the systems for regul... [more]

The energy transition is placing increased strain on power systems and making it challenging for Transmission System Operators (TSOs) to securely operate power systems. System Integrity Protection Schemes (SIPSs) are one of the solutions to address these challenges. SIPSs are a type of over-arching power system control; their goals are to increase the secure utilization of power system assets and to limit the impact of large disturbances on the system. Due to societal developments, the interest in utilizing SIPSs is increasing internationally, highlighting the importance of the standardization of terms and definitions to support collaboration between internationally interconnected power systems. This paper addresses the issue of increasing SIPS literature and the efficient exchange of knowledge about SIPSs by providing a new, up-to-date literature review and proposal for the standardization of SIPS terminology. The need for standardized terminology is highlighted by gathering various t... [more]

A review of different energy components is detailed, as a baseline of fundamentals for the new integrated energy concept idealization. This innovative solution is a Hybrid for Renewable Energy Network (Hy4REN) based on well-studied elements to produce the best final solution. This proposal has the objective of improving energy system sustainability, facing fossil fuel and climate change restrictions, and increasing energy network flexibility. The most mature energy storage technology, pumped hydropower energy storage (PHES), is used to support both the grid connection and stand-alone modes, as an integrated hybrid energy system. The hybrid system idealization is modular and scalable, with a complementary nature among several renewables, using sea water in offshore mode to build an integrated solution. By evaluating a variety of energy sources, complemented with economic analysis, the benefits associated are evidenced using this sustainable methodology based only on renewable sources. C... [more]

Over the years, the use of numerical simulations in the development of high voltage pulse generators has become a standard approach. Nevertheless, the modeling of spark-gaps, one of the most commonly used switching devices in such generators, has always been a weak point of the process, especially in coupled circuit and field simulations. Although the complex SPICE spark-gap models do exist, it is difficult or impossible to directly couple them with field simulations. Thus, in many cases, the spark-gap models used were elementary and required many assumptions, which led to the prolongation of the design process. Our paper describes the coupling of a realistic circuit model of an air spark-gap, with a Finite Element Method simulation, solving the wave equation in the time domain. The simulation describes the operation of a Blumlein transmission line as a pulse generator. One of the advantages of the proposed solution is that the input parameters of the empirical model are measurable phy... [more]

Photovoltaic technology mainly uses beam, diffused, and reflected solar radiation to produce power. To increase the photovoltaic power output, the surface of the solar panel must be at the optimal tilt angle. In this paper, a numerical study is carried out to investigate the optimal tilt angle for a 1 MW PV system installed at Sukkur IBA University (latitude = 27.7268° N, longitude = 68.8191° E). Moreover, power output, efficiency, and fill factor are calculated for polycrystalline and monocrystalline solar panels. Results obtained at different tilt angles are used to compare the solar gain from photovoltaic modules installed at the university. In conclusion, an optimal tilt angle is decided for both polycrystalline and monocrystalline solar panels used at Sukkur IBA University. It was found that the optimal tilt angle for the installed 1 MW systems is 29.5 degrees.

Transportation and installation of a wind turbine system is one of the main factors for business availability of offshore wind power due to its high cost and technical difficulty. The purpose of this study is to develop an innovative transportation and installation method for offshore wind turbines. We refer to this installation process as an All-In-One-Installation (A.I.O.I), and the special vessel used is referred to as a multipurpose mobile base (MMB). In this study, the short-range transportation and penetration and pull-out tests of the entire wind turbine system are performed before field demonstration. All the offshore wind turbine systems were transported and installed safely at one time. Field demonstration was conducted on the installation site approximately 15 km from the harbor in approximately 5 h using the suction method. In the actual A.I.O.I demonstration test, stable values were obtained. The respective changes in inclination at the center of the MMB and the tower were... [more]

The increasing number of residential buildings that are installing distributed energy resources enforces the need for schemes to facilitate a local energy balance. With the continuing evolution of Internet of Things (IoT) technology, Peer-to-Peer (P2P) energy trading is becoming a viable solution to incentivize prosumers and promote efficient energy sharing in a community. This paper develops a model to quantitatively analyze the potential benefits of P2P energy trading for residential buildings that have installed photovoltaic battery systems. The integration of the bidding strategy into a residential energy-management system is feasible to realize cost savings for prosumers. However, the coordination between the bidding strategy and the optimal scheduling of energy has received far too little attention. To better participate in the P2P market, we propose a novel separate bidding energy-management system (SBEMS) that can realize rolling optimal energy scheduling while determining ener... [more]

The purpose of the research presented in this paper was to develop an analytical instrument for measuring the efficiency of investing in renewable energy sources suitable for use by the average single-family homeowner. The paper develops an algorithm to quickly estimate the efficiency of small rooftop solar photovoltaic (PV) systems use by households. The algorithm is developed on the basis of the MS Excel software package. It is easy to use and allows estimation of the maximum efficiency of the installation of a photovoltaic system, taking into account the preferences of the household, the technical characteristics of the photovoltaic system, and the parameters of the building and location. The validation of the algorithm was carried out on the example of Opole Province (Poland). The selection of photovoltaic panels is based on 17 types of panels made in different technologies, which allows rational choice of modules based on consumer preferences according to the price/quality ratio.... [more]

Smart integration of different energy sectors on islands could serve as a key to achieve their energy independence and carbon neutrality goals and facilitate the large-scale penetration of renewables. Demonstration projects play a vital role in testing innovative sector-coupling solutions and exploring their synergies in the real-life environment. They also help to build the required market confidence and awareness, verify and enhance the societal acceptance, and identify and prevent unnecessary risks and complications. The aim of this paper is to provide the reader with a comprehensive review of 19 research projects, which concern the demonstration of sector-coupling technologies on European islands. The projects are funded by the European Commission and started between 2010 and 2020. The review focuses on the exploration of various technical aspects of 28 demo pilots. In addition, it addresses objectives, contributions, and novelty of the demonstrations and analyses barriers, challen... [more]

The article discusses the wind tunnel experimental investigation of two turbines (the downstream unit placed fully in the wake of the upstream one) at various turbulence intensity levels and wind turbine separation distances, at a Reynolds number of approximately 105. The velocity deficit due to the upstream turbine operation is reduced as the wake mixes with the undisturbed flow, which may be enhanced by increasing the turbulence intensity. In a natural environment, this may be provoked by natural wind gusts or changes in the wind inflow conditions. Increased levels of turbulence intensity enlarge the plateau of optimum wind turbine operation—this results in the turbine performance being less prone to variations of tip speed ratio. Another important set of results quantifies the influence of the upstream turbine operation at non-optimal tip speed ratio on the overall system performance, as the downstream machine gains more energy from the wake flow. Thus, all power output maximisation... [more]

State space models (SSMs) are important for multi-variable performance analysis and controller design of aero-engines. In order to solve the problems of the traditional state space modeling methods that rely on component-level models (CLMs) and cannot be carried out in real time, an aero-engine state space modeling method based on adaptive forgetting factor online sequential extreme learning machine (AFOS-ELM) is proposed in this paper. The structure of the extreme learning machine (ELM) is determined according to the form of the state space model, and the inverse-free ELM algorithm is used to automatically select the appropriate number of hidden nodes to improve the efficiency of offline initialization. The focus of the ELM on current operation performance is enhanced by the adaptive renewed forgetting factor, which reduces the impact of aero-engine history and deviated data on the current output and improves the accuracy of the model. Then, according to the analytical equation of the... [more]

In addition to the use of waste heat from the vessel’s exhaust gas to save energy onboard, reduce the carbon emissions of the ship, and combine the characteristics of ship waste heat, mathematical modeling and testing of ship waste heat temperature difference power generation were carried out in this study. Finally, an experimental platform for temperature differential power generation was established to assess the impact of influencing agents on the efficiency of temperature differential power generation. The results show that the effect of different thermally conductive greases on the efficiency of temperature differential power generation tablets is basically the same. In addition, the rate of flow of cooling water, the cooling plate area, and the heat source temperature have more significant effects on the open-circuit voltage and maximum output power. The results show that the maximum power output growth rate increases with increasing cooling water flow, reaching 8.26% at 4 L/min.... [more]

Recently, “power cuts” and “coal price surges” have been significant concerns of individuals and societies. The main reasons for a power cut are a recent rapid increase in power consumption, shortage of thermal coal or the large shutdown capacity of thermal power units, resulting in a tight power supply in the power grid. In recent years, the shortage of fossil resources has led to frequent energy crises. In the context of carbon peaks and carbon neutralization, how to better develop electric-energy substitution and eliminate the dependence on fossil energy has become a problem that needs to be solved at present. In this paper, the influencing factors of electric-energy substitution in Beijing are analyzed, and the indexes affecting the electric-energy substitution are outlined. By constructing various machine-learning models, the prediction is performed. The results show that the Gaussian kernel support vector machine model based on a grid search has a good prediction effect on the el... [more]

Brushless doubly fed reluctance generators (BDFRGs) are hopeful generators for using inside variable speed wind turbines (VSWTs), as these generators introduce a promising economical value because of their lower manufacturing and maintenance costs besides their higher reliability. For integrating WT generators, global networks codes require enabling these generators to stay connected under grid disturbances. The behavior of the BDFRG is strongly affected by grid disturbances, due to the small rating of the used partial power converters, as these converters cannot withstand high faults currents which leads to quick tripping of BDFRG. VSWTs can be safeguarded against faults using the crowbar. Usually, the conventual crowbar is shunt connected across the converter to protect it, but this configuration leads to absorbing reactive power with huge amounts from the grid, leading for more voltage decaying and more power system stability deterioration. This study proposes a simpler self-control... [more]

Studies of carbon emissions typically focus on price and tax effects or technology. We argue that the two are closely linked within an economy in disequilibrium. Our goals are twofold: (1) to examine the combined role of: low CO2 technology, fuel taxes and CO2 tax on taming CO2 emissions and (2) to build a counterfactual analysis by capturing anything else that causes emissions to diverge from the trend such as renewable energy, energy laws and the state of the economy. The equilibrium correction model (EqCM) suggests that emissions have a long-term relationship with economic growth, fossil fuel use, taxes and clean power sources. Both oil and gas extraction and economic growth raise Norway’s emissions, offsetting the mitigating effect of taxes. Sweden´s carbon fuel tax elasticity is 20%, a value far above Norway´s elasticity, even though these carbon taxes were phased-in under a period of macroeconomic instability, weakening their effectiveness. The income elasticity of emissions is n... [more]