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This paper presents a systematic literature review of urban wind energy harnessing in built environments. In line to foster decarbonisation in urban areas of tropical countries with decentralised renewable energy technologies, such as small wind turbines in buildings, this research has been carried out. To provide a comprehensive foundation on the topic, urban wind assessment research for various purposes was reviewed, where 48 studies for energy harnessing purposes were classified by country, region and methods. The methodologies are divided into six stages, of which environmental assessment and resilience analysis are scarce. Due to tropical countries being exposed to atmospheric events that historically cause human and material losses, potential future research could be made in line with resilience analysis through metrics that are key to the proper mass deployment of building-integrated wind turbine systems. Of 66 methods for wind prospecting, the most used are on-site measurement, computational fluid dynamics simulation and numerical climate prediction, which represent 49 %, 22 % and 17 %, respectively. Other decision-making techniques are presented with the aim of addressing new ways in strategic planning to promote the use of this technology. [Display omitted] • Urban wind energy research does not deem energy resilience analysis. • Few evaluations of urban wind energy have been carried out in the tropics. • Hurricanes represent a hazard for building-integrated wind turbines. • On-site measurement and CFD simulation are the most adopted methods. [ABSTRACT FROM AUTHOR]

Abstract The recent recurrence of wind curtailment in China underscores the rigidity and vulnerability of China's electricity regulatory regime. Using the theory of "fragmented authoritarianism", this paper identifies key institutional barriers causing wind curtailment in China and develops a framework for analyzing China's electricity regulatory regime. Specifically, the fragmented institutional authorities and responsibilities lead to departmentalism and coordination problems, both vertically and horizontally. The resulting mismatches in the investment, generation, and distribution of the electric power sector reflect direct causes for China's wind curtailment. This paper recommends that an electric power system reform with established regional spot markets is needed to fix China's wind curtailment problem. Highlights • Complex reasons lie behind serious wind curtailment in China. • Wind curtailment has its roots in the electricity regulation regime of China. • Fragmented authority causes coordination problems in the power sector. • Mismatches permeates the investment, generation and distribution of power. • A regional power spot market is needed to fix the wind curtailment problem. [ABSTRACT FROM AUTHOR]

As a result of the growing global demand for energy, together with the depletion of resources and the growing emphasis on mitigating climate change and greenhouse gas emissions, an urgent need for an evolution of the renewable energy resources has emerged. On the architectural scene, we have become accustomed to seeing buildings incorporated with photovoltaics and wind turbines. Despite the great contribution of biomass as a clean energy producer, the integration of biomass into architecture is quite modest and still in its initial phases. Microalgae, as a plant-based biomass, can outperform other renewable resources with their potential to absorb CO 2 , recycle wastewater, and release O 2 . The limited experience regarding building-integrated microalgae photobioreactors (PBRs) requires shedding light on some issues. So, this paper aims to explore the following: 1) the proper types of PBRs for integration with buildings, 2) the overall bioprocess and the design considerations regarding PBRs and their technical requirements, 3) the environmental and energetic performance of PBRs, 4) their challenges, and 5) their prospects. Thus, the paper's methodology consists of 1) reviewing the promulgated literature concerning microalgae and PBRs, 2) reviewing and analyzing three building-integrated PBRs and three urban-integrated PBRs, and 3) reviewing the environmental and energetic performance of building-integrated PBRs. The paper has concluded that the symbiosis between PBRs and façades encounters some challenges, including 1) the biorefinery infrastructure, 2) the provision of a source of CO 2 , and 3) the high initial cost. On the other hand, the multifaceted environmental prospects of building-integrated PBRs are represented in 1) energy savings; 2) GHG emissions reduction; 3) oxygen and hydrogen release; 4) biofuel production; and 5) wastewater treatment. The unique benefits of the bio-façades through the combination of the technical and biological cycles within buildings inaugurate an innovative approach to sustainability by integrating environmental, energetic, and iconic values. [ABSTRACT FROM AUTHOR]

This paper evaluates the potential of wind energy in six coastal locations in the Kingdom of Morocco, namely Al Hoceima, Tetouane, Assila, Essouira, Laayoune and Dakhla. First, a literature review of recent wind energy potential studies in different locations worldwide has been conducted. Thereafter, the status of wind energy development in Morocco along with its achievements and challenges has been reported. A comprehensive literature review of the mathematical distributions used to fit wind data and procedures employed to estimate the shape and scale parameters of the Weibull distribution is as well presented. The second part of this paper investigated the statistical analysis of wind data based on hourly wind speeds and directions considered for a period of five years between 2011 and 2015. The analysis has shown that the Weibull model independently of the used algorithms for estimation scale and shape parameters, presented an accurate description of the frequencies of actual wind data. By the end, annual energy outputs and capacity factors were derived for wind turbines of various sizes between 225 and 900 kW. The results showed that Dakhla is the most suitable location for harnessing the wind power, while Laayoune has been identified as the second most suitable site. Both Dakhla and Laayoune were found to be suitable for the grid-connected wind energy conversion system while Assila and Essouira have been categorized to be appropriate for the stand-alone wind power applications. [ABSTRACT FROM AUTHOR]

This paper presents an innovative scaled suction caisson (SSC) for fixing offshore wind turbines (OWTs) to enhance its anti-overturning bearing capacity. The outer wall of the SSC is constructed with a scaled bionic structure referring to snakeskin scales, reducing resistance to installation and increasing pullout capacity, which is verified by model tests that the SSC requires less applied suction and provides higher horizontal bearing capacity in sandy soil compared with the traditional suction caisson (TSC) under the same caisson diameter and height. Also, model test results reveal that the SSC can reduce the height of soil plug and the scaled structure can effectively limit the SSC inclination in comparison to the TSC. Additionally, numerical results show that the ultimate bearing capacity for the SSC increases rapidly when the friction factor λ between the caisson wall-soil interface ranges from 0 to 0.2. Moreover, the sidewall of the SSC dissipates less energy than that of the TSC due to the small displacement of soil near the sidewall. This study confirms that the SSC can eliminate grouting in the space between the top of the soil plug and the bottom of the cap, thus reducing the construction period, construction costs and avoiding marine pollution. [Display omitted] • Bionic design concept of the SSC is proposed. • Penetration behavior of the SSC is revealed. • Bearing capacity and failure mechanism of the SSC are obtained. • SSC can eliminate grouting, and at the same time compensate the bearing capacity. [ABSTRACT FROM AUTHOR]

Wind turbine structures are key components for modern transformation into free energy and greener environment. In recent years, a rapid growth in the development and installation of wind turbines has been witnessed. Moreover, the increase in capacity and size of wind farms worldwide triggers wide concerns about their safety and reliability. Therefore, structural health monitoring (SHM) and damage identification of wind turbines has become a major research focus. Particularly, wind turbine blades (WTBs) are major wind turbine components that are vulnerable for different types of damage due to various environmental effects, fatigue loadings, etc. Therefore, researchers have utilized SHM and non-destructive testing (NDT) techniques for developing effective damage detection tools for WTBs. Such techniques can play a great role to increase reliability, maximize the output profit, and manage maintenance strategies of wind turbines. In the view of recent developments and the lack of comprehensive survey that can summarize and classify the state-of-the-art damage detection of WTBs, in addition to illustrate the research gaps and unsolved problems, an urgent review of the topic of damage detection of WTBs is required. Thus, this paper presents an up-to-date review based on five research areas: signal responses, features, sensors, NDT techniques, and testing methods. The paper aims to provide a big picture and summarize the previous studies, including the classification and analysis of representative studies. Moreover, future research directions are discussed to provide researchers with new research ideas and highlight the gaps in the literature under the title of damage identification of WTBs. • A survey of recent advances of damage detection in wind turbine blades (WBTs) is conducted. • This survey is classified into five categories, namely the signal responses, features, sensors, NDTs, and testing methods. • This paper aims to summarize the previous research, including the classification and analysis of representative studies. • Future scope of WTBs' inspection is discussed to provide new research ideas and highlight the research gaps. [ABSTRACT FROM AUTHOR]

Semi-submersible foundation, as one of the most feasible platform supporting the floating offshore wind turbine, is developing at a fast pace with the offshore wind turbines moving to deep waters (water depth range: 50–300 m). This paper presents a rather comprehensive review on the semi-submersible foundation. At first, this paper reviews the design of semi-submersible foundations, which includes both the conceptual design and the projects currently under operation. Afterwards, a number of simulation tools employed in previous researches to investigate the dynamics of semi-submersible foundations are summarized. In detail, wind-wave basin tests and numerical simulations concerning the dynamic responses of the semi-submersible foundation under the excitations of wind-wave loads are included. As for basin test, key techniques for simulating the realistic wind-wave fields and for accurately modeling different part of a floating wind turbine are reviewed. As for numerical studies, the free-vortex wake model is outlined, which was introduced to overcome the defects of the conventional blade element momentum theory used commonly in estimating the wind load on the wind turbine blades. Additionally, a novel technique coupling a three-dimensional flow solver EllipSys3D with FLEX5 is discussed. [ABSTRACT FROM AUTHOR]

In this paper, the authors investigate four original methodologies for sizing a battery bank inside a passive wind turbine system. This device interacts with wind and load cycles, especially for a stand-alone application. Generally, actual wind speed measurements are of long duration which leads to extensive processing time in a global optimization context requiring a wide number of system simulations. The first part of this article outlines two sizing methodologies based on a statistical approach for the sizing of the electrochemical storage device of a stand-alone passive wind turbine system. Two other efficient methodologies based on the synthesis of compact wind speed profiles by means of evolutionary algorithms are described in the second part of this paper. The results are finally discussed with regard to the relevance of the battery bank sizing and in terms of computation cost, this later issue being crucial to an Integrated Optimal Design (IOD) process. [ABSTRACT FROM AUTHOR]

Wind turbine wakes are one of the most important aspects in wind power meteorology because they decrease the power production and increase the loading of downstream wind turbines. Therefore, there is a continuous need to find a ‘good’ wake model to properly plan wind power plant-level control strategies, predict the performance and understand the fatigue loads of turbines. In this paper, six widely used approaches of wake modelling (Jensen, Larsen, Dynamic Wake Meandering, Fuga and, Ellipsys3D LES and RANS together with their interpretations) that were developed at Technical University of Denmark, are described and the model subcomponents are analysed. The models are evaluated using data from the Sexbierum (onshore) and the Lillgrund (offshore) wind farms to understand how to best utilize them. The paper provides a comprehensive conceptual background to wake modelling combined with the overview of the state-of-the-art models including their implementations on operating wind farms. [ABSTRACT FROM AUTHOR]

Several theoretical studies have been reported in recent years which have indicated that large-scale wind farms can have an impact on local and regional meteorology, possibly on climate. Now evidence of it based on field observations has also begun to emerge. The present paper traces the evolution of this knowledge. It discusses the theoretical studies on the possibility of wind turbines effecting climate change, and summarizes the emerging confirmation of those predictions. The concluding part of the paper assesses the implications of these findings in the context of the world׳s past experience on global warming and its present thrust to meet substantial portions of its energy needs with renewables. [ABSTRACT FROM AUTHOR]

For isolated power networks supplied by intermittent energy sources, several doubts have emerged regarding the impact of the uncertainties on the networks reliability. This paper performs optimal sizing for a hybrid power system with wind/energy storage sources based on stochastic modeling of historical wind speed and load demand. The autoregressive moving average is used to stochastically model the uncertainty of the load demand/wind speed and, the sequential Monte Carlo simulation is performed to chronologically sample the system states. The contribution of the paper can be summarized as follows: (1) an objective function based on self-adapted evolutionary strategy in combination with the Fischer–Burmeister algorithm is proposed to minimize the one-time investment and annual operational costs of the wind/energy storage sources; and (2) the effect of the cycle efficiency and charging/discharging rate of different energy storage units on the system cost is investigated under different reliability and load shifting levels. The computational performance of the proposed optimization solver is proven in order to obtain the minimum possible investment cost. The presented case studies in this paper provide the decision makers with the flexibility to choose the suitable capacity installation at different values of reliability and load shifting levels. [ABSTRACT FROM AUTHOR]

The demand for electricity is increasing day by day, which cannot be fulfilled by non-renewable energy sources alone. Renewable energy sources such as solar and wind are omnipresent and environmental friendly. The renewable emulnergy sources are emerging options to fulfill the energy demand, but unreliable due to the stochastic nature of their occurrence. Hybrid renewable energy system (HRES) combines two or more renewable energy sources like wind turbine and solar system. The objective of this paper is to present a comprehensive review of various aspects of HRES. This paper discusses prefeasibility analysis, optimum sizing, modeling, control aspects and reliability issues. The application of evolutionary technique and game theory in hybrid renewable energy is also presented in this paper. [ABSTRACT FROM AUTHOR]

Since the early 1980s, wind power technology has experienced an immense growth with respect to both the turbine size and market share. As the demand for large-scale wind turbines and lor operation & maintenance cost continues to raise, the interest on condition monitoring system has increased rapidly. The main components of wind turbines are the focus of all CMS since they frequently cause high repair costs and equipment downtime. However, vast quantities of their failures are caused due to a bearing failure. Therefore, bearing condition monitoring becomes crucial. This paper aims at providing a state-of-the-art review on wind turbine bearing condition monitoring techniques such as acoustic measurement, electrical effects monitoring, power quality, temperature monitoring, wear debris analysis and vibration analysis. Furthermore, this paper will present a literature review and discuss several technical, financial and operational challenges from the purchase of the CMS to the wind farm monitoring stage. [ABSTRACT FROM AUTHOR]

Wind power is the most reliable and developed renewable energy source over past decades. With the rapid penetration of the wind generators in the power system grid, it is very essential to utilize the maximum available power from the wind and to operate the wind turbine (WT) at its maximal energy conversion output. For this, the wind energy conversion system (WECS) has to track or operate at the maximum power point (MPP). A decent variety of publication report on various maximum power point tracking (MPPT) algorithms for a WECS. However, making a choice on an exact MPPT algorithm for a particular case require sufficient proficiency because each algorithm has its own merits and demerits. For this reason, an appropriate review of those algorithms is essential. However, only a few attempts have been made in this concern. In this paper, different available MPPT algorithms are described for extracting maximum power which are classified according to the power measurement i.e. direct or indirect power controller. Merits, demerits and comprehensive comparison of the different MPPT algorithms also highlighted in the terms of complexity, wind speed requirement, prior training, speed responses, etc. and also the ability to acquire the maximal energy output. This paper serves as a proper reference for future MPPT users in selecting appropriate MPPT algorithm for their requirement. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive review of various techniques employed to enhance the low voltage ride through (LVRT) capability of the fixed-speed induction generators (FSIGs)-based wind turbines (WTs), which has a non-negligible 20% contribution of the existing wind energy in the world. As the FSIG-based WT system is directly connected to the grid with no power electronic interfaces, terminal voltage or reactive power output may not be precisely controlled. Thus, various LVRT strategies based on installation of the additional supporting technologies have been proposed in the literature. Although the various individual technologies are well documented, a comparative study of existing approaches has not been reported so far. This paper attempts to fill this void by providing a comprehensive analysis of these LVRT methods for FSIG-based WTs in terms of dynamic performance, controller complexity, and economic feasibility. A novel feature of this paper is to categorize LVRT capability enhancement approaches into three main groups depending on the connection configuration: series, shunt, and series–shunt (hybrid) connections and then discuss their advantages and limitations in detail. For verification purposes, several simulations are presented in MATLAB software to demonstrate and compare the reviewed LVRT schemes. Based on the simulated results, series connection dynamic voltage restorer (DVR) and shunt connection static synchronous compensators (STATCOM) are the highly efficient LVRT capability enhancement approaches. [ABSTRACT FROM AUTHOR]

United States’ Wind Vision report envisions wind energy to generate 20% and 35% of nation׳s electricity by 2030 and 2050 respectively. Taking in to account of the aforementioned vision, the electric power industry is promoting generation of wind power and integration into the US interconnection grids. Over the last decade, this fast growing grid connected wind power generation has raised several new technical, regulatory and economic concerns for grid operations and electricity markets. Therefore, it becomes essential to perform research study and determine possible solutions for the integration of high penetration levels of wind power with the power grid. This paper focuses on the grid integration issue associated with deteriorated frequency response of power system when significant levels of wind power generation is present in the total generation mix. A brief review of the recently introduced frequency response regulatory standards and requirements for wind power plants in United States is presented along with the turbine manufacturer׳s advanced grid technology upgrade options to maintain the power system reliability. This paper evaluates the provision of ancillary services such as Emulated Inertial Response (EIR) and Primary Frequency Response (PFR) by wind generation resources, and investigates the impact of different control architectures on frequency response metrics. Further, it discusses the costs, benefits and other economic impacts associated with the various frequency control techniques of wind power plants. Finally, guidelines and priorities for wind turbine manufacturers, generating entities, balancing authorities and regulators are provided to ensure the increased reliability without additional costs. [ABSTRACT FROM AUTHOR]

In current offshore wind turbine designs, many are basic concepts using standard land-based wind turbines ‘marinised’ using a platform from the offshore oil and gas industry with additional anti-corrosion and structural stiffness. These projects are also focused on fixed offshore wind turbines at depths of less than 50 m. The design conservatism observed is present to avoid many changes to the proven technology on land-based wind turbines and offshore fixed foundations, to assure technical feasibility and economic viability in the short term. However, exportation of onshore technology directly to the offshore environment may not be entirely advantageous. There are opportunities in new designs or configurations, which can potentially lower cost of energy in a less restrictive offshore environment. This paper aims to review the current offshore wind technology and discusses comprehensively some of the factors and opportunities in selecting a downwind configuration for offshore wind turbines. In addition, current industry, research and developmental trends for downwind offshore wind turbines are described. Various technical challenges and gaps foreseen for this design motivation are also highlighted in the paper. [ABSTRACT FROM AUTHOR]

Wind energy has played an increasingly vital role in renewable power generation, driving the need for more cost-effective wind energy solutions. Health monitoring of turbines could provide a variety of economic and other benefits to aid in wind growth. A number of commercial and research health monitoring systems have been implemented for wind turbines. This paper surveys these systems, providing an analysis of the current state of turbine health monitoring and the challenges associated with monitoring each of the major turbine components. This paper also contextualizes the survey with the various potential benefits of health monitoring for turbines. [ABSTRACT FROM AUTHOR]

Wind energy is an important contributor of modern power systems as a renewable energy source. However, wind energy poses new challenges because of its unique characteristics, such as limited predictability, short-term and long-term variability and close-to-zero marginal cost. This paper puts forward the critical aspects of wind energy systems in respect to the transformation of the power system into a “smart grid”. Issues discussed include the electro-mechanical matters like the selection of wind turbine technology, the structure of wind system, the robustness of mechanical parts (gear box and blades) and fault diagnosis. In addition, the system operational challenges such as complexity, instability, unbalance loading, grid interactive problems and impact of wind energy on power system are discussed in this paper. Moreover, the economical subjects such as investment costs and energy management, communication requirements, and security are involved as important titles. Finally, environmental aspects of wind energy are also highlighted to show that the wind energy is an environmentally friendly energy source since it is sustainable, clean and safe. [ABSTRACT FROM AUTHOR]

Domestic wind turbine manufacturing sector in China has experienced development stages starting from scratch to mass production. During the 11th FYP period (2006–2010), the main goal of wind power policy in China is to promote the commercialization of wind power by large-scale deployment of wind farms. This goal has been realized to a great extent and now the cost of wind power generation is nearly comparable to coal-fired power generation in China. The industry policy, which devotes to mass production of domestic wind turbines, is also largely successful. The purpose of the paper is to provide an overview on wind turbine manufacturing sector in China. The policy evolution in different stages, achievements and challenges pertinent to the sector are addressed in the paper. Key findings are that the misleading industry policy, which provides strong incentive to blind entrance and “competition for scale and price” and restrains innovation as well, is the key obstacle for the sustainable development of the sector. Deficient technology standard and qualification system and the misplaced franchise bidding system also indulge vicious competition and oversupply. Creating a level playground for all turbine supplies, providing strong incentive to innovative manufacturers, establishing thorough and practicable standard and qualification system, and fine-tuning the directive of the franchise bidding system towards technology and service are the primary policy implications proposed by our study. [ABSTRACT FROM AUTHOR]

Renewable energy becomes an asset to the world׳s energy resource for its eco-friendly and low cost energy production feature. As an important renewable energy source, wind turbine technology has become a significant contributor to the world energy production because of its feasible production cost, reliability and efficiency. Researchers are very active to optimize the effectiveness of wind turbines which may lead to increase the productivity of this source of energy. Vibration in the wind turbine system affects the productivity and thus reduces efficiency. Vibration of a system cannot be destroyed but can be reduced or converted to energy using appropriate strategies. Vibration control system improves structural response of wind turbines and reliability which has impact on lifetime of the components. Lowering the vibration amplitude of a system will provide a lesser amount of noise, assure user and operating comport, maintain the high performance and production efficiency. These will assist the system to prolong the lifetime of an industrial structure or machinery. Also vibration control enhances the performance of wind turbines providing suitable work environment without external disturbance. This paper presents an ample review on performance enhancement of the wind turbines by vibration mitigation. The aim of this review is to provide a concise point for researchers to assess the current trend to control vibration of wind turbines technology. This paper will focus on main vibration control techniques of wind turbine structures. It provides the applications of passive, active and semi-active and vibration control strategies for structures, especially for wind turbines. Besides, this paper reviews on damping devices needed for vibration mitigation of structures. These damping devices have been implemented extensively in wind turbines for increasing their efficiency by mitigating vibration. This paper also reviews and assesses the performance of different control policies to control the system input and power input of damping devices. [ABSTRACT FROM AUTHOR]

Over the past decade, there has been rapid increase in the offshore wind turbine installations. The future installations will see a progression from shallow to deep waters. It necessitates the development of innovative floating platforms to support the offshore wind turbines capable of resisting coupled wind and wave forces to meet the exponential growth of energy demand. The floating offshore wind turbine (FOWT) is a complex dynamic system. There exists coupling and interaction between aerodynamics, hydrodynamics, servodynamics, structural dynamics and mooring dynamics. Various analysis methods have been developed over the time to model the complex behaviour of FOWT system and to accurately predict its response. These methods can be classified as uncoupled, partially coupled and fully coupled methods based on their degree of coupling. Each of these methods can be utilized in the specific stages of the design. This paper provides an integrated review of the recent advances in the experimental and numerical methods used for the dynamic analysis of the FOWT. Various software tools used for the numerical analysis of FOWT are also reviewed in this paper. Fully coupled experimental analysis is usually carried out using real-time hybrid simulation (RTHS) in the laboratory environment. Several possible configurations of RTHS based on different partitioning schemes are also discussed. This paper encapsulates the different methods available in the literature and will be useful for further building up the research in the analysis of FOWTs. Finally, this paper is complemented with the technical challenges and future scope identified based on the review. • Analysis and design specifications for FOWT • Methods for evaluation of hydrodynamic and aerodynamic loads on FOWT • Uncoupled, partially coupled, fully coupled dynamic analysis of FOWT • Real Time Hybrid Simulation and control methods of FOWT • Technical challenges and future scope of FOWT [ABSTRACT FROM AUTHOR]

Given the abundant availability of resources, the market potential, and their cost competitiveness, onshore wind farms and photovoltaic units are expected to drive the overall growth of renewable energy sources in the next decade. However, Europe is a small and densely populated continent, which results in many countries experiencing a severe shortage of suitable land sites for installing new wind and photovoltaic facilities. This, combined with the fact that many existing wind turbines and photovoltaic units reach the end of their operational lifetime, has laid the groundwork for 'repowering'. Repowering includes upgrading or retrofitting renewable energy sources' components and exploits existing land sites, in which renewables are operating for years. This paper intends to emphasise the multiple dimensions of repowering, also delving in its surrounding socio-economic context in various European countries, to identify its barriers and allies as well as gather best practices and lessons learnt from its implementation. Considering data availability, extent of spatial use and bulk equipment, and consequent attention in literature and practice, the analysis mainly orbits around repowering of wind projects, rather than solar photovoltaics. Finally, the paper presents key directions toward wider future exploitation of repowering. • Land scarcity problem with high renewable energy potential addressed by repowering. • In-depth socio-economic extensions of repowering are discussed. • Semi-quantified evaluation highlighting main implementation pillars of repowering. • Best practices and lessons learnt from the implementation of repowering. • Legislative barriers against the wider implementation of repowering. [ABSTRACT FROM AUTHOR]

Rural electrification has been a long-standing goal in Kenya, but there is still a long way to go with only 7% rural access to electricity. Therefore, there lies great potential for small wind turbines (SWT) in areas with sufficient wind resources. This paper presents a review of the SWT sector in Kenya. The review consists of a description of the status of the sector and a more in-depth investigation into factors and dynamics that hinder sector growth. This investigation is performed by using a combination of two theoretical approaches: Strategic Niche Management (SNM) and the Multi-Level Perspective (MLP). The main insights from this review are that the SWT sector in Kenya is growing but is characterized by one-time experiments, fragmented learning experiences, lack of focus and low quality products and services. The weakly aligned network with many underperforming actors and unaligned expectations is the main cause of the weak current status of the sector. Despite the low rural electricity access and growing electricity demand, niche upscaling remains cumbersome due to external factors such as corruption, poverty, lack of innovation and an anti-entrepreneurial mind-set. The results of this review serve as inputs for recommendations for all niche actors on what can be done to make the niche grow. In addition, the paper includes ideas on how the SNM and MLP approaches could become better suited for reviewing and analyzing renewable energy technologies in developing countries such as SWTs in the Kenyan context. [ABSTRACT FROM AUTHOR]

This paper presents a critical review on the self-excitation process and steady state analysis of a self-excited induction generator driven by the wind turbine. The physics of self-excitation is crucial for the interpretation of the voltage build-up process of self-excited induction generators (SEIGs). During the initial phase of build-up the machine behaves as if it be a synchronous machine with weak permanent magnet in the form of remnant magnetization. In this paper the MMF approach as well as the synchronous resonance approach has been proposed to know the fact that how the machine relinquishes the initial synchronous mode and enters into the final asynchronous mode. The process of self-excitation is initiated by the resonating interaction between the terminal capacitor and machine׳s magnetizing reactance. The steady state analysis has been reviewed and proposed based on input/output impedance method to find the steady state reactive VAR need of the SEIG. The minimum and maximum critical capacitance has been evaluated theoretically. Finally the value of critical speed and critical load impedance has been evaluated. [ABSTRACT FROM AUTHOR]

Wind energy is rapidly growing in recent years. Among different types of wind turbines, due to several advantages, permanent magnet synchronous generator (PMSG) is attractive concept. Since the penetration level of wind power in the grid is increased, therefore, wind power can influence to the grid and vice versa. Some of the important problems in the grid are fault condition and voltage sags. These conditions may affect the operation of wind turbine. In order to enhance low voltage ride through (LVRT) capability in PMSG-based wind turbines, various approaches have been proposed in the last years. In this paper, the review and comparison of several LVRT capability enhancement methods is performed. The two foremost types of LVRT capability enhancement methods are external devices based methods and modified controller based methods. The main objectives of this paper are to introduce performances of different LVRT capability enhancement methods and use of some LVRT capability enhancement methods in PMSG based wind turbine which are applied in other kind of wind power generators. The external devices based methods can be effective but some of these methods are of significant cost. According to the literatures, modified controller based methods can reduce the LVRT capability enhancement cost. Several modified controller based methods have been proposed for LVRT capability enhancement. To compare the mentioned methods, several simulations are performed in MATLAB software. From the review of simulation results, series connection of FACTS devices and modification of back-to-back converter controllers are the highly efficient LVRT capability enhancement approaches. [ABSTRACT FROM AUTHOR]

Wind turbines have been developed fast in the recent years and at the same time have brought some problems. It is important to maintain the healthy condition of the running turbine because the consequences after faults are miserable for both the company and owner. There is a constant need to reduce the costs of operating and maintaining the turbines. Therefore, it is very important to detect the faults/failures early so as to minimize downtime and maximize productivity. This paper reviewed the structure of wind turbines and analyzed the different components of wind turbines in order to detect the faults that may happen. Meanwhile, this paper mainly reviewed fault diagnosis methods of wind turbines in the last three years. The main purpose of this paper is to supply some information on structure healthy condition monitoring (SHCM) and fault diagnosis in wind turbines for related researchers. [ABSTRACT FROM AUTHOR]

In recent years, an increasing number of Chinese wind power firms have been going international in search of global market for development channels. By employing qualitative research and case study methods, this paper examines the export scale and markets of China’s wind turbines, the market entry modes and location choices of China’s outward foreign direct investment (FDI) in the wind power sector, identifies the determinants and prospects of Chinese wind firms’ internationalization, as well as provides policy implications. It is found that Chinese wind power firms has chosen to internationalize very differently from the Uppsala model in that the exports and FDI of Chinese wind power firms both took place around 2008, and the exports and FDI of Chinese wind power firms are closely linked. The determinants of Chinese wind firms’ internationalization are the competitive advantages of leading Chinese wind firms and the intensified domestic market competition, followed by Chinese government support for internationalization and the attractive overseas market. The prospects of Chinese wind firms’ internationalization are bright but challenging. Drawn on this analysis, conclusions and three policy implications are provided at the end of the paper. This paper contributes to the study of China’s wind power sector from a new perspective. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive literature review on the estimation of effective wind Speed (EEWS), and EEWS based control techniques applied to wind turbine (WT). Several numbers of good publications have reported the EEWS based control of wind turbine. Wind speed is a driving force for the wind turbine system. In general wind speed measurement is carried out by anemometer which is located at the top of the nacelle. The optimal shaft speed is derived from the exact measurement of wind speed to extract the optimal power output at below rated wind speed. The wind speed provided by the anemometer is measured at a single point of the rotor plane which is not the accurate effective wind speed. At the same time anemometer increases the overall cost, maintenance and reduce the reliability of the overall system. So an accurate EEWS based control technique is required for WT systems to get the optimal power output. In this paper, a detailed description and classification of EEWS and some EEWS based control techniques have been discussed which is based on control strategy and complexity level of WT system. All most all previous work estimates the wind speed using EEWS techniques such as Kalman filter (KF), extended Kalman filter (EKF), neural network (NN) etc., and then different control techniques are applied. In the last section of this paper integral sliding mode control (ISMC) of a WT at below rated speed region is considered. Operating points are determined by proper estimation of effective wind speed, and modified Newton Raphson (MNR) is employed to estimate this. Finally simulation results are presented with a comparison between proposed ISMC, sliding mode control (SMC) and classical controllers such as aerodynamic torque feed forward (ATF) and indirect speed control (ISC). [ABSTRACT FROM AUTHOR]

Wind turbine nacelles are complex machines that are designed to operate under extreme loads and harsh environments. Extensive tests are performed throughout their development process to ensure that they can operate with high reliability. As both onshore and offshore wind turbine systems have rapidly evolved, so have the methods for testing the nacelle systems and subsystems. This paper presents the state of the art in wind turbine nacelle testing and the development trends in this field. It discusses the existing test requirements for certification and the different levels of testing that form part of a nacelle system's development. The latest changes to the nacelle certification requirements are highlighted, along with several important research activities related to drivetrain testing. Future challenges for nacelle testing are identified and their potential solutions are proposed. [Display omitted] • The state of the art of nacelle system and subsystem testing are described. • The current industrial approach on nacelle testing during the development process is discussed. • Advances made in nacelle system testing and certification relevant tests are described. • Major challenges in nacelle testing of modern wind turbines are highlighted. • Solutions to tackle some of the identified challenges in nacelle testing are suggested. [ABSTRACT FROM AUTHOR]

Floating offshore wind turbines have arisen as a promising option to access massive wind energy resources in deep water, where the existing fixed-type offshore wind turbine is no longer practical. However, due to the nature of the oceanic environmental conditions, large uncertainties are involved in the aerodynamic/hydrodynamic calculations, which are coupled with those within the structures and materials. This not only threatens its reliability but also drastically increases the manufacturing cost of floating offshore wind turbines. To understand the uncertainty within the system and properly predict its reliability, first, the uncertainties involved in the environments and subsystems need to be defined. Therefore, this paper aims to provide an extensive review of the uncertainty models involved in the structural design of floating offshore wind turbines. The presented uncertainties within the structures include those inherent in the material and geometrical/mechanical properties of the wind turbine, floating structures, and mooring lines. The uncertainties within hydrodynamics include empirical parameters and nonlinearities involved with the hydrodynamics modeling of the floaters. Within the environmental loads, the parameter uncertainties as well as the randomness of wind and wave loads are presented. The uncertainties growing over time caused by fatigue, corrosion, and climate hazards are also discussed. In addition, the correlation between the random variables, such as the correlation of the wind and wave, is presented. Finally, the method of treating those uncertainties is discussed, including the probabilistic model which incorporates the uncertainties and the correlations between the random variables, as well as modeling errors. • Various sources and types of uncertainties that affect the structural reliability of floating offshore wind turbines are presented. • An extensive review of the uncertainty models for the parameters involved in the estimation of the reliability of the floating offshore wind turbines is provided. • The correlations between the parameter uncertainties are discussed when applicable. • Growing uncertainties over the lifecycle, including those caused by fatigue and corrosion, are discussed along with their impact on structural reliability. • Various existing reliability analysis methods, that can be used for the floating offshore wind turbine structures are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Wind power is one of the main sources of renewable energy. New applications of this technology are currently under development through small vertical axis wind turbines, allowing energy production in small spaces even at low wind speeds. Therefore, creating an effective turbine design methodology tailored to these operating conditions has been the subject of extensive research. The Savonius-type vertical axis wind turbine is one of the most widely used due to its low cost and easy manufacturing. Several works have examined the effect of various geometric parameters on the performance of the Savonius-type wind turbine. However, there are no published overarching conclusions about these works. Thus, this paper aims to review and discuss in a concise way experiments and simulations carried out by several authors evaluating the effect of some geometric parameters on the maximum power and torque coefficient of Savonius vertical axis wind turbines. The paper also discusses additional experiments that should be performed in future work. • The effect of geometrical parameters of Savonius-type vertical axis wind turbine rotor on its efficiency is reviewed. • Power and torque coefficients response to variation of four geometrical parameters are discussed. • Geometrical parameters as aspect ratio, twist angle, overlap ratio, number of blades, and number of stages are explored. • Diverse experimental and numerical researches are explored and maximum power and torque coefficients found are graphically presented as function of each geometrical parameter. [ABSTRACT FROM AUTHOR]

OWT (Offshore Wind Turbine) support structures are exposed to harsh ocean environment with significant uncertainties in soil properties and environmental loads. Reliability assessment of OWT support structures taking into account those uncertainties is crucial in the development of more cost-effective OWT support structures. This paper presents a state-of-the-art reliability assessment of OWT support structures, providing a comprehensive review on the structural reliability, reliability-based calibration of codes, fatigue reliability and the implementation of reliability assessment. The current and future developments of reliability assessment of OWT support structures, such as reliability-based design optimisation, multi-hazard reliability analysis and risk-based inspection, are also presented. This paper has been written for both 1) researchers new to this research area through providing a comprehensive review on the latest research and summarising underlying theory; and 2) experts in this research area through presenting a comprehensive list of relevant references where the details of analysis methods can be acquired. • Comprehensive review of the reliability assessment of OWT support structures. • Structural reliability, reliability-based calibration and fatigue reliability are discussed. • Implementation of reliability assessment of OWT support structures is presented. • Future developments of reliability assessment of OWT support structures are outlined. [ABSTRACT FROM AUTHOR]

Blades are critical components in wind turbines (WTs) for power generation, and condition monitoring (CM) of WT blades is a crucial and challenging issue under operating conditions. Several methods have been developed to assess blade health status, and some of them have the potential to achieve in-situ CM. Nevertheless, there is a lack of critical and comprehensive survey concerning CM techniques for operational WT blades, as well as unsolved problems and research prospects. In this paper, typical causes and types of blade damage that deserve to be considered during the running time are presented. Besides, in-situ CM techniques for WT blades are reviewed in terms of four sub-targets: damage detection, localization, classification, and evaluation. Further, the investigation and development timeline of in-situ CM methods and types of damage that have been verified to be recognizable in field tests are concluded for the first time. The paper ends with discussions on research impediments and prospects that indicate promising development tendencies. • In-situ condition monitoring methods for wind turbine blades are reviewed. • Typical causes and types of blade damage are discussed. • Damage detection, localization, classification, and evaluation are considered. • Relationships between techniques and detectable damage are revealed. • Research challenges and development tendencies are summarized. [ABSTRACT FROM AUTHOR]

This paper studies the dynamic behavior of doubly fed induction generators (DFIGs) modeled with the stator flux orientation regarding rotor- and grid-side converter control strategies. The investigations include modal and sensitivity analysis, and using them to identify and characterize the instability mode, stator dynamics analysis, and time domain simulations. The paper first deals with the modal analysis of the DFIG for different control strategies and operating conditions. Then the dynamic and transient performance of the DFIG under voltage dips and large disturbances are investigated, and the effects of rotor and grid-filter control strategies on the DFIG transient behavior are examined. Increasing the rotor and grid-filter closed loop bandwidths, rotor current active damping, and compensation of back-emf voltages can improve the rotor and grid-filter dynamics, decrease tracking error and limit the rotor current transients. However they can lead to poorly stator modes and deteriorate the DFIG transient performance. Thus, appropriate selection of rotor controller parameters has an important effect on the DFIG transient performance, and consequently on the future interconnected power system. [ABSTRACT FROM AUTHOR]

Wind energy continues to stand out as a more established and mature technology to offset a large proportion of power. Efforts aimed at improving wind energy use to meet the energy demand in turbulent urban wind environment have been the main technical focus. In previous studies on wind resource and behavior in urban environment, different designs of horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs) have been reviewed. This paper vividly captures the fact that wind resource has a great potential to be fully explored and developed in the urban environment. Varying ways of application and application techniques being applied for electrical generation, ventilation and pollution dispersion, onshore cooling and dehumidification of coastal urban cities, and economics and environmental benefits of applying wind energy in urban environments are summarized. Although many new ideas and solutions that factor technical, economical and environmental sustainability in urban areas are coming up every day, challenges in design are gradually being solved to take advantage of urban low and turbulent wind speed characteristics, installation space challenges, vibration and noise reduction, among others. Some of the unique solutions that have been and are being developed in the applications of wind energy technology in urban environments are also reported in this paper. [ABSTRACT FROM AUTHOR]

The paper presents a detailed analysis of the dynamics and control of air turbines and electrical generators in oscillating-water-columns (OWCs). The aim is to explain the performance of an OWC device based on the physical behaviour of each system component. The Mutriku wave power plant was chosen as the test case. The power plant is a breakwater located in the Bay of Biscay, in Basque Country, Spain. The contributions of the work are: i) development of a hydrodynamic model of the power plant in the frequency domain; ii) implementation of a non-linear time-domain wave-to-wire model; iii) real-valued implementation of the Prony method for the computation of the wave-radiation force; iv) a detailed generator model based on experimental data to assess the influence of the generator efficiency on the power take-off performance; v) a critical performance comparison of the Wells and biradial turbines; vi) a sensitivity analysis of the control parameters of the turbine/generator set; and vii) an explanation of the comparative performance of both turbines based on statistical data. The turbine performance curves were taken from developers' published experimental data. The results were obtained with a simplified model of the wave climate off the Mutriku test site comprising 14 sea states. • Non-linear time-domain wave-to-wire model of the Mutriku OWC-breakwater was developed. • Experimental electrical generator efficiency was mapped versus rotational speed and shaft torque. • The performances of Wells and biradial turbines were compared based on statistical data. • A sensitivity analysis of the control parameters of the turbine/generator sets was performed. • The biradial turbine was found to be more efficient and less sensitive to the control parameters. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach based on fuzzy multi-criteria decision-making tools for assessing sustainable alternatives of power generation in San Andrés Island, Colombia. In the first stage, the energy system was established. A fuzzy multi-objective decision approach based on a mixed-integer linear model was implemented to obtain a set of alternatives, including solar photovoltaic, wind turbines, and the diesel plants currently used. Subsequently, the total cost and the CO 2 emissions of the energy system were minimized all while considering design, operational, and efficiency constraints. The CO 2 emissions and the total present value of the alternatives of energy, together with social, technological, economic, and environmental factors assessed through expert opinions were used as input in the fuzzy multi-criteria decision phase, where a novel fuzzy logic model was employed for selecting the most sustainable alternative. The results indicate that the current diesel capacity in San Andrés Island prevails; with a maximum participation of 3% and 4% of solar and wind systems, respectively. • An efficient tool to select a suitable alternative for power generation in isolated areas of Colombia was proposed. • The approach allowed the relationship among criteria and a new sustainability index for choosing the best Pareto alternative. • The economic criterion has the greatest variability compared to the sustainability index, mainly due to its increase. [ABSTRACT FROM AUTHOR]

A 30 kW fixed-guide-vanes biradial turbine-generator set was designed by Instituto Superior Técnico (IST) and manufactured by Kymaner, within the framework of the H2020 European project OPERA, for open sea testing at the Mutriku breakwater oscillating water column (OWC) power plant and at the IDOM MARMOK-A-5 OWC spar-buoy, deployed at BiMEP, Basque Country, Spain. The paper reports the design and construction of the prototype, and its dry testing at IST, in a variable-flow test rig, simulating the oscillating flow induced by irregular waves. Results show that the turbine exhibits a peak efficiency of 70% under steady-state conditions and an average efficiency of 56% for the control laws tested. [ABSTRACT FROM AUTHOR]

The reduction of operation and maintenance cost plays a significant role in decreasing the cost of energy generated by offshore wind farm, which can be realized through better design of maintenance strategy. This paper proposes a dynamic opportunistic condition-based maintenance strategy for offshore wind farm by using predictive analytics. In the strategy, a new maintenance basis is developed by considering the varying maintenance lead time to make maintenance decisions for different wind turbine components. Meanwhile, the strategy also considers the economic dependence between the wind turbines and the components. We then present a maintenance model to derive the optimal maintenance plans for various turbine components under different weather and operation load conditions. A numerical example is used to illustrate the effectiveness of the maintenance model. It is found that the varying maintenance lead time has a significant effect on the annual maintenance cost which demonstrates the reasonableness of our proposed maintenance basis. Compared to the widely employed and the simple maintenance strategies, the proposed strategy can help reduce the annual maintenance cost by 39.24% and 32.46% respectively. • A dynamic opportunistic condition-based maintenance strategy is formulated. • The varying maintenance lead time effect on the maintenance decision is analyzed. • A new maintenance basis is proposed to make maintenance plans for components. • We find that the maintenance cost is affected by the varying maintenance lead time. • The comparative analysis illustrates the capability of the proposed strategy. [ABSTRACT FROM AUTHOR]

Abstract Subsynchronous control interaction (SSCI) associated with wind farms has become one of the major challenges for maintaining the stability and reliability of modern power systems. SSCI is mainly caused by the active participation of fast-acting wind turbine converter (WTC) controls in the phenomenon. It can damage the system equipment, reduce the amount of power generation, and degrade the power quality. Thus, it is urgent to develop practical mitigation techniques for the SSCI in order to achieve a smooth and reliable operation of grid interfaced wind farms. This study presents an overview of potential SSCI mitigation techniques at various stages of the power system, including system planning, operation, control, and protection phases at both network and generation sides. In particular, this paper reviews the active damping controls utilizing flexible ac transmission systems (FACTS) and WTC controls. Finally, it outlines the challenges and future work in studying SSCI mitigation techniques in practical wind power systems. Highlights • SSCI mitigation techniques: planning, operation, control and protection stages. • Review of active damping control techniques in network and generation sides. • Challenges and limitations of various SSCI mitigation techniques are discussed. • WTC control modifications and shunt-VSC using filters are recommended approaches. [ABSTRACT FROM AUTHOR]

Abstract This paper evaluates the potential for co-location of offshore wind turbines at sites being developed for tidal stream arrays as a method for reducing the cost of electricity. It is shown that for a typical tidal site, MeyGen in the Pentland Firth, UK, increasing the wind turbine capacity reduces the cost of electricity compared to operating tidal stream arrays alone. This is due to increased energy yield combined with reduction of capital expenditure based on the use of common grid connection and shared support structures. Assessment is made using tidal, wave and wind resource data for a three year period. The overturning moment about the base of a monopile supporting a wind turbine with two tidal turbines is only 8% larger than for a wind turbine alone in a strong current typical of tidal farms. The increased cost of infrastructure is small relative to the increased energy yield and for all array configurations of practical interest, the levelised capital cost of energy is estimated to be 10–12% less from a co-located farm than from a tidal turbine farm alone. Highlights • Cost of electricity by co-locating wind turbines with tidal stream arrays is evaluated. • Energy yield and peak loads are modelled for array layouts in the Pentland Firth. • Peak loads for a shared support are 60% greater than typical offshore wind turbines. • For the same cost, co-location generates 20% more yield than tidal-only arrays. • Co-location offers 10–12% lower levelised cost compared to a comparable tidal array. [ABSTRACT FROM AUTHOR]

Abstract Offshore wind is a source of clean, renewable energy of great potential value to the power industry in the context of a low carbon society. Rapid development of offshore wind energy depends on a good understanding of technical issues related to offshore wind turbines, which is spurring ongoing research and development programmes. Foundations of offshore wind turbines present one of the main challenges in offshore wind turbine design. This paper reviews the present state of knowledge concerning geotechnical and structural issues affecting foundation types under consideration for the support structures of offshore wind turbines, and provides recommendations for future research and development. Highlights • Reviews the technology development and designs of offshore wind turbine foundations. • Discusses geotechnical and structural issues affecting the foundations. • Provides recommendations for future R&D to improve the effectiveness of different designs. [ABSTRACT FROM AUTHOR]

Abstract At present, the UK government is driving the survival of the wind energy industry by using interventions that encourage investment in the sector. The use of a Contract for Difference (CfD)/Strike price model by the UK government supports the wind industry and guarantees that wind energy generators have a stable premium over a period of 15–20 years; however, this may not last forever. The growth and stability of the wind industry will depend essentially on continued reductions in wind energy cost, even below that of fossil-fuel based energy sources. Huge cost reduction beyond the present strike price of £ 57.50/MWh for some projects to be delivered in 2022/2023 may be achieved quickly through efficient and optimized turbine support structure. Consequently, the offshore wind industry is currently making enormous efforts to upscale wind turbines (WTs) from 8 MW to 9.5MW,10MW and then 12 MW HAWT (Horizontal Axis Wind Turbine). This level of upscaling no doubt creates tough challenges because the mass of the turbine increases linearly with the cube of the rotor radius. Monopiles having diameters larger than 7 m have been proposed, with a wall thickness section in the range of 70–110 mm. It is generally thought that Thermo-Mechanical Controlled Process (TMCP) steels are well suited for extra-large (XL-WTs). This paper reviews the present status of WTs and critically assesses the material factors in the structural integrity concerns that may confront the use of XL steel plates in the design of XL-WT support structures. [ABSTRACT FROM AUTHOR]

Abstract Condition monitoring in wind turbines aims at detecting incipient faults at an early stage to improve maintenance. Artificial neural networks are a tool from machine learning that is frequently used for this purpose. Deep Learning is a machine learning paradigm based on deep neural networks that has shown great success at various applications over recent years. In this paper, we review unsupervised and supervised applications of artificial neural networks and in particular of Deep Learning to condition monitoring in wind turbines. We find that – despite a promising performance of supervised methods – unsupervised approaches are prevalent in the literature. To explain this phenomenon, we discuss a range of issues related to obtaining labelled data sets for supervised training, namely quality and access as well as labelling and class imbalance of operational data. Furthermore, we find that the application of Deep Learning to SCADA data is impeded by their relatively low dimensionality, and we suggest ways of working with higher-dimensional SCADA data. Highlights • An overview of recent applications of artificial neural networks and Deep Leaning. • Most approaches in the literature are unsupervised. • Supervised methods that use high-dimensional input data are quite successful. • Supervised approaches are impeded by issues with operational data. • These regard quality, availability, dimensionality, labels, and class imbalance. [ABSTRACT FROM AUTHOR]

More and more wind farms are reaching the end of their useful lifetimes, so it is necessary to consider the need and/or suitability of dismantling or repowering them. This paper presents an analysis from the point of view of the potential environmental impact and benefit of a wind farm repowering process. The study has been performed by developing a life cycle assessment model of the repowering process of an old wind farm with low-power wind turbines. The results show the advantages of repowering wind farms of this type, especially in terms of increased capacity for electrical power generation from renewable sources and extending the useful lifetimes of wind farms. The main impact of the repowering process comes from the wind turbines, which show values of 2.43E + 07 kg CO 2 eq. in the Global Warming category, followed by the substation and electrical line (5.14E + 05 kg CO 2 eq.). These impacts are clearly offset by the benefits of increasing electrical power generation from renewable sources, which show values of − 9.03E + 08 kg CO 2 eq. Therefore, from the point of view of the decision-making process, the repowering of old wind farms with low-power wind turbines provides environmental benefits that must be taken into account when evaluating the future of wind farms approaching the end of their useful lifetimes. [ABSTRACT FROM AUTHOR]

Using floating platforms to support offshore wind turbines will be necessary for many countries to reach their Net-Zero targets, since much of the wind resource is located at water depths at which fixed offshore wind turbines are uneconomic or technologically unfeasible. However, floating platforms for wind turbines are still at an early stage of development, and there are a wide range of platform designs. This paper reviews the current state-of-the-art of floating offshore wind turbine platform designs which currently have or have previously had a prototype, demonstration, or farm scale project at sea. The most common design goals for the platforms and the corresponding design features of platforms used to achieve those goals are reviewed. Past, current and projected future levelized cost of energy values for floating offshore wind are reviewed and discussed. The development of each platform design is described, including evolving design goals and resulting changes in platform features. Finally, overall trends in platform designs are discussed and divided into three phases, defined by changing goals: (i) influences from the offshore oil and gas industry, (ii) specialization to floating offshore wind, and (iii) further specialization to local environment. [Display omitted] • Floating offshore wind turbine platform designs with a device at sea are reviewed. • Common design goals and associated design features of platforms are summarized. • Levelized cost of energy for floating offshore wind turbines is discussed. • Evolution and trends in design drivers and platform designs are summarized. [ABSTRACT FROM AUTHOR]

Control algorithms for wave energy conversion technologies with air turbines require contingency tools to prevent the rated power and maximum rotational speed from being exceeded. Survival problems limit energy conversion when the available power is too large compared to the turbo-generator-rated power. Short-term predictions require information from local wave-measuring buoys, which raises reliability concerns. Wave groups in the ocean result in extremely high wave power peaks that cannot be smoothed by low-inertia power-take-off (PTO) systems, leading to survival problems. The most common strategy to cope with this situation is to set the rated power of the PTO several times more than the annual average produced electrical power. The PTO is shut-down when the available power is excessive. These two engineering decisions have a detrimental impact on the capacity factor and the energy cost. The paper shows a new control algorithm for wave energy oscillating-water-column (OWC) devices that can control the shutter position of a fast-acting valve to dissipate the pneumatic energy excess. Hence, the PTO can operate even when the available power is significantly larger than the generator's rated power. The algorithm was validated with the 30 kW biradial turbine prototype from the OPERA H2020 European project under real sea conditions at Mutriku's wave power plant. Results show the algorithm's effectiveness in real situations and during a generator failure simulated during the experimental campaign. This new concept may reduce the energy cost from wave energy and open a new field of design possibilities for OWC wave energy converters. • First-of-a-kind hardware to perform peak shaving in OWC wave energy devices. • Algorithm tested at Mutriku's wave power plant in real sea conditions. • Generator's rated power and maximum rotational speed are prevented from being exceeded. • The algorithm protects the power take-off system in the case of a generator failure. • Novel peak shaving control can reduce the OWC WECs energy costs. [ABSTRACT FROM AUTHOR]

Rapidly increasing demand for electricity, rising costs of fossil fuels, and growing environmental concerns are driving research into alternative energy sources. Wind energy has experienced significant growth in recent years. Extensive research has been conducted to efficiently generate electricity from wind energy. However, due to limitations such as space and maintenance, it is very difficult and unsafe to install wind turbines for research and educational purposes. A lab-scale wind turbine emulator has many advantages, including independence from prevailing wind conditions, a greater degree of control, and freedom from space constraints. In this article, authors have reviewed and analyzed over 140 technical articles related to wind turbine emulators. It provides comprehensive information on prime movers, generators, and controls used in wind turbine emulator (WTE) research. Additionally, this paper discusses the strengths and weaknesses of various WTE prime movers, generators, and control algorithms used in the literature review. This article will serve as a good reference for the researchers to choose the right technique for WTE according to their needs. [Display omitted] • Overview of the importance of Wind Turbine Emulators (WTE) in wind energy research. • Comparison of different types of wind turbine emulators. • Discussion of recent advances in wind turbine emulation technology. • Analysis of the current state of wind turbine emulation research. [ABSTRACT FROM AUTHOR]

With the unprecedented growth in recent voltage source converter-based high voltage direct current (VSC-HVDC) integrated offshore wind power plants, frequency regulation of onshore systems and their stability has been crucial. Offshore wind farms cannot directly provide frequency support to the onshore AC grid as back-to-back converters in variable speed wind turbines and HVDC grid decouple the two ending terminals. It prevents the kinetic and electrostatic energy from mitigating the frequency transients in the onshore AC grid. Low inertia contributes to an increase in the rate of change of frequency with a further decrease in frequency nadir that undermines the onshore AC system's reliability. However, variable speed wind turbines and voltage source converter stations with appropriate control strategies can efficiently participate in the onshore AC grid's frequency regulation. This paper provides an in-depth review of the frequency support strategies for offshore wind power plants and the voltage source converter stations in a multi-terminal HVDC system, including a comparison of the related approaches and the potential gaps present in the existing literature. This paper also provides guidelines and serves as a reference for researchers focused on the frequency support strategies for such an integrated system. • A comprehensive review on power system frequency regulation through VSWTs and VSC stations is presented. • SFD occurs during rotor speed recovery if no other power is available to compensate for power shortage at that moment. • Use of ESS could be a viable alternative to compensate for the energy shortage during rotor speed recovery. • AFC-based coordinated control in VSC-HVDC is the preferred practicing technology due to its simplicity and robustness. • New protocols need to be defined to cyber secure the offshore wind power plant-based power systems. [ABSTRACT FROM AUTHOR]