Showing papers in "Wind Energy in 2003"
TL;DR: The possibility of using pitch-regulated wind turbines as a way of reducing loads has been suggested many times over the years, but the idea has yet to gain full commercial acceptance as discussed by the authors.
Abstract: If a pitch-regulated wind turbine has individual pitch actuators for each blade, the possibility arises to send different pitch angle demands to each blade. The possibility of using this as a way of reducing loads has been suggested many times over the years, but the idea has yet to gain full commercial acceptance. There are a number of reasons why this situation may be set to change, and very significant load reductions can result. Copyright © 2002 John Wiley & Sons, Ltd.
665 citations
TL;DR: In this article, the authors present a review of techniques for the control of wind turbines during power production, including pitch control, torque control, and additional sensors such as accelerometers and load sensors.
Abstract: This article reviews techniques for the control of wind turbines during power production. Pitch control is used primarily to limit power in high winds, but it also has an important effect on structural loads. Particularly as turbines become larger, there is increasing interest in designing controllers to mitigate loads as far as possible. Torque control in variable-speed turbines is used primarily to maximize energy capture below rated wind speed, and to limit the torque above rated, but it can also be used to reduce certain loads. The design of the control algorithms is clearly of prime importance. Additional sensors such as accelerometers and load sensors can also help the controller to achieve its objectives more effectively. By controlling the pitch of each blade independently, it is also possible to achieve important further reductions in loading. It is important to be able to quantify the benefits of any new controller. Although computer simulations are useful, field trials are also vital. The variability of the real wind means that particular care is needed in the design of the trials. Copyright © 2003 John Wiley & Sons, Ltd.
436 citations
TL;DR: In this article, the authors present a review of wind turbine blade design trends and design drivers, as well as the ways these design drivers have changed, and some possible directions for future blade design options are presented, namely new planforms, aerofoils and aeroelastic tailoring.
Abstract: Wind turbine blades continue to be the target of technological improvements by the use of better designs, materials, manufacturing, analysis and testing. As the size of turbines has grown over the past decade, designers have restrained the associated growth in blade weight to less than would have been possible through simple scaling-up of past approaches. These past improvements are briefly summarized. Manufacturing trends and design drivers are presented, as are the ways these design drivers have changed. Issues related to blade material choices are described, first for the currently dominant glass fibre technology and then for the potential use of carbon fibres. Some possible directions for future blade design options are presented, namely new planforms, aerofoils and aeroelastic tailoring. The significant improvement in sophistication of stress analysis and full-scale blade testing are also discussed. Copyright © 2003 John Wiley & Sons, Ltd.
247 citations
TL;DR: In this article, the authors give an overview of the different ways the wind resource at a site can be estimated, and the advantages and disadvantages of each of them are discussed in detail.
Abstract: This article gives an overview of the different ways the wind resource at a site can be estimated. Eight separate ways have been identified. Each of these will be described in some detail, and advantages and disadvantages of each of them will be discussed. Copyright © 2003 John Wiley & Sons, Ltd.
208 citations
TL;DR: A detailed description of a wide range of electrical methods for allowing variable-speed operation of large-scale wind turbines is provided in this article, where a number of these designs and their histories are described.
Abstract: Early wind turbines used for performing mechanical work (pumping, grinding and cutting) optimized aerodynamics by being allowed to run at variable speed. Some of the earliest DC electric wind turbines were allowed to run at variable speed. With the advent of grid-connected AC turbines, rotational speeds were limited in order to control the wind turbine AC frequency output to equal the grid frequency. With the advent of semiconductor devices, attempts began as early as the 1970s to allow variable-speed operation of large-scale turbines. The introduction of a new generation of high-voltage, high-speed power electronic components allows a wide range of variable-speed operation for very-large-scale machines. Over the past 30 years a number of designs have been tested, a few of which have entered commercial operation. A number of these designs and their histories are described. A detailed description of a wide range of electrical methods for allowing variable-speed operation is provided. Copyright © 2003 John Wiley & Sons, Ltd.
205 citations
TL;DR: In 2003, the European Commission funded a project, "Concerted Action on Offshore Wind Energy in Europe" (CA-OWEE), which aimed to gather, evaluate, synthesize and distribute knowledge on all aspects of offshore wind energy, including offshore technology, electrical integration, economics, environmental impacts and political aspects as mentioned in this paper.
Abstract: After several decades of theoretical developments, desk studies, experimental wind turbines and prototype wind farms, the first large-scale commercial developments of offshore wind farms are now being built. To support and accelerate this development, the European Commission funded a project, ‘Concerted Action on Offshore Wind Energy in Europe’ (CA-OWEE), which aimed to gather, evaluate, synthesize and distribute knowledge on all aspects of offshore wind energy, including offshore technology, electrical integration, economics, environmental impacts and political aspects. The partners are from a wide range of fields and include developers, utilities, consultants, research institutes and universities. This article reports on the final conclusions of this project, with the complete report being available online at http://www.offshorewindenergy.org. Copyright © 2003 John Wiley & Sons, Ltd.
193 citations
TL;DR: An overview of the different methods used today for predicting the power output from wind farms on the 1-2 day time horizon is given in this article, where the authors describe the general set-up of such prediction systems and also give examples of their performance.
Abstract: This article gives an overview of the different methods used today for predicting the power output from wind farms on the 1–2 day time horizon It describes the general set-up of such prediction systems and also gives examples of their performance Copyright © 2003 John Wiley & Sons, Ltd
193 citations
159 citations
146 citations
TL;DR: In this article, the authors used dynamic computer simulations with turbulent inflow to show that twist coupling substantially decreases fatigue damage over all wind speeds, without reducing average power, and significant decreases in fatigue damage are observed at lower wind speeds and smaller decreases at higher wind speeds.
Abstract: The prospect of installing blades that twist as they bend and/or extend on horizontal axis wind turbines provides opportunities for enhanced energy capture and/or load mitigation. Although this coupling could be achieved in either an active or a passive manner, the passive approach is much more attractive owing to its simplicity and economy. As an example, a blade design might employ coupling between bending and twisting, so that as the blade bends owing to the action of the aerodynamic loads, it also twists, modifying the aerodynamic performance in some way. For reducing loads the blades are designed to twist towards feather as they bend. For variable-speed pitch-controlled rotors, dynamic computer simulations with turbulent inflow show that twist coupling substantially decreases fatigue damage over all wind speeds, without reducing average power. Maximum loads also decrease modestly. For constant-speed stall-controlled and variable-speed stall-controlled rotors, significant decreases in fatigue damage are observed at the lower wind speeds and smaller decreases at the higher wind speeds. Maximum loads also decrease slightly. As a general observation, whenever a rotor is operating in the linear aerodynamic range (lower wind speeds for stall control and all wind speeds for pitch control), substantial reductions in fatigue damage are realized. Copyright © 2002 John Wiley & Sons, Ltd.
78 citations
TL;DR: In this article, the main uncertainties within aeroelastic modeling of wind turbines that have been hard to resolve over the years of research, and also presents perspectives for the new aero-elastic challenges, both from the viewpoint of the researchers at Riso National Laboratory.
Abstract: Aeroelasticity is a key issue in the continuing development of wind turbines towards large, flexible, highly optimized machines. The steadily increasing technology level is reflected not necessarily by the complexity of the turbines, but by the level of knowledge and advanced principles that are taken into account during the design process and incorporated in the final optimized design. This article examines some of the main uncertainties within aeroelastic modelling of wind turbines that have been hard to resolve over the years of research, and also presents perspectives for the new aeroelastic challenges, both from the viewpoint of the researchers at Riso National Laboratory. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the impact of wind turbines on voltage quality and power system stability in distribution grids is discussed. But the authors focus on the impact on slow voltage variations, flicker, voltage dips and harmonics.
Abstract: This article gives an overview of grid integration of wind farms with respect to impact on voltage quality and power system stability. The recommended procedure for assessing the impact of wind turbines on voltage quality in distribution grids is presented. The procedure uses the power quality characteristic data of wind turbines to determine the impact on slow voltage variations, flicker, voltage dips and harmonics. The detailed assessment allows for substantially more wind power in distribution grids compared with previously used rule-of-thumb guidelines. Power system stability is a concern in conjunction with large wind farms or very weak grids. Assessment requires the use of power system simulation tools, and wind farm models for inclusion in such tools are presently being developed. A fixed-speed wind turbine model is described. The model may be considered a good starting point for development of more advanced models, hereunder the concept of variable-speed wind turbines with a doubly fed induction generator is briefly explained. The use of dynamic wind farm models as part of power system simulation tools allows for detailed studies and development of innovative grid integration techniques. It is demonstrated that the use of reactive compensation may relax the short-term voltage stability limit and allow integration of significantly more wind power, and that application of automatic generation control technology may be an efficient means to circumvent thermal transmission capacity constraints. The continuous development of analysis tools and technology for cost-effective and secure grid integration is an important aid to ensure the increasing use of wind energy. A key factor for success, however, is the communication of results and gained experience, and in this regard it is hoped that this article may contribute. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, an approach based on the simplified Reynolds equation with eddy viscosity closure is chosen to describe the wake behind one rotor in an axisymmetric wake model.
Abstract: The wind farm layout program FLaP estimates the wind speed at any point in a wind farm and the power output of the turbines The ambient flow conditions and the properties of the turbines and the farm are used as input The core of the program is an axisymmetric wake model describing the wake behind one rotor Here an approach based on the simplified Reynolds equation with eddy viscosity closure is chosen The single-wake model is combined with a model for the vertical wind speed profile and a wind farm model, which takes care of the interaction of all wakes in a wind farm The wake model has been extended to improve the description of wake development in offshore conditions, especially the low ambient turbulence and the effect of atmospheric stability Model results are compared with measurements from the Danish offshore wind farm Vindeby Vertical wake profiles and mean turbulence intensities in the wake are compared for single-, double- and quintuple-wake cases with different mean wind speed, turbulence intensity and atmospheric stability It is found that within the measurement uncertainties the results of the wake model compare well with the measurements for the most important ambient conditions The effect of the low turbulence intensity offshore on the wake development is modelled well for Vindeby wind farm Deviations are found when atmospheric stability deviates from near-neutral conditions For stable atmospheric conditions both the free vertical wind speed profile and the wake profile are not modelled satisfactorily Copyright © 2003 John Wiley & Sons, Ltd
TL;DR: In this paper, the authors developed analytical tools for modeling the turbine loads and fatigue damage due to the vessel motion, which can be used for the optimization of candidate supporting vessels by evaluating the motion response directly.
Abstract: The location of wind turbines on floating structures offshore would allow an immense resource to be tapped without the drawbacks large developments can have on public opinion. There are, however, potentially significant technical and cost drawbacks. This article describes the theory and results of research work aimed at developing analytical tools for evaluating the performance of floating offshore wind farms. The principal problem addressed here is the development of analytical tools for modelling the turbine loads and fatigue damage due to the vessel motion. The effect that the motion would have on the wind turbine is found by calculating the aerodynamic and inertial loads on the blades in a two-dimensional state domain representing the blade and the vessel motion respectively. Using a double Fourier transform, discrete deterministic frequency spectra of the loads are found and the fatigue damage is evaluated. Undertaking the calculations for vessel motion in each degree of freedom allows appropriate weightings to be developed, which can be used for the optimization of candidate supporting vessels by evaluating the motion response directly. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the Navier-Stokes-based aeroelastic stability analysis of individual blade sections subjected to combined pitch/flap or flap/lead-lag motion has been attempted by the present consortium in the framework of the concluded VISCEL JOR3-CT98-0208 Joule III project.
Abstract: The recent introduction of ever larger wind turbines poses new challenges with regard to understanding the mechanisms of unsteady flow–structure interaction. An important aspect of the problem is the aeroelastic stability of the wind turbine blades, especially in the case of combined flap/lead–lag vibrations in the stall regime. Given the limited experimental information available in this field, the use of CFD techniques and state-of-the-art viscous flow solvers provides an invaluable alternative towards the identification of the underlying physics and the development and validation of sound engineering-type aeroelastic models. Navier–Stokes-based aeroelastic stability analysis of individual blade sections subjected to combined pitch/flap or flap/lead–lag motion has been attempted by the present consortium in the framework of the concluded VISCEL JOR3-CT98-0208 Joule III project. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, a reliability-based approach to determine the extreme response distribution of offshore wind turbines is presented, based on hindcast data, the statistical description of the offshore environment is formulated.
Abstract: In this article a reliability-based approach to determine the extreme response distribution of offshore wind turbines is presented. Based on hindcast data, the statistical description of the offshore environment is formulated. The contour lines of different return periods can be determined. Simulations are carried out for a prototype design of a 3 MW offshore wind turbine. Statistical methods are applied to determine the distribution of the extreme responses. Three approaches are used here. In the MAX approach, only the maximum of each simulation is taken into account. The POT (peak over threshold) approach takes also local maxima into consideration. The process model uses the statistical properties of the process to predict the extremes. All three methods show similar results, but POT and the process model require fewer simulations. Comparison is made for the 100 year response between these reliability-based models and a deterministic model. For this specific turbine the deterministic model underestimates the maximum flap moment but overestimates the maximum overturning moment of the support structure compared with the estimates of the reliability-based methods. The application of the reliability-based model can be extended to include other extreme load situations and achieve a more efficient structural design. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, the role of wind energy in the electricity generation of the European Union during the next two decades is defined and an estimation of the costs involved is performed, with special reference to the avoided external costs.
Abstract: Wind energy is the fastest-growing electricity-generating technology. The wind energy targets set during the last decade have all been surpassed. New targets are proposed for 2010 and 2020, since the existing European Commission and European Wind Energy Association targets do not reflect the trends in the market. The new targets and projections are used to define the role of wind energy in the electricity generation of the European Union during the next two decades. Estimation is made of the emission reductions which could be achieved with the use of wind energy by each Member State, and the contribution that wind energy could have in the process of the fulfilment of their Kyoto commitments is investigated. Finally an estimation of the costs involved is performed, with special reference to the avoided external costs. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, the VISCEL JOR3-CT98-0208 Joule III project was used to determine the aerodynamic characteristics as well as the aeroelastic behaviour of wind turbine blades across their broad range of operational conditions, from attached to highly separated flow regimes.
Abstract: Aerodynamic modelling of HAWT rotors by means of “engineering methods” has reached a saddle point, where no further development can be expected without a breakthrough in understanding the physics of unsteady, rotating three-dimensional flows. However, such a breakthrough becomes ever more necessary, as the size of the wind turbines increases. With the experimental work in that direction being mostly limited to observing the phenomena and interpreting the associated mechanisms, and its increased cost, alternatives are being sought. The use of CFD techniques and state-of-the-art Navier–Stokes solvers is considered a very serious contender, a belief shared by the members of the present consortium, which has worked on the VISCEL JOR3-CT98-0208 Joule III project. This project's goal was to determine the aerodynamic characteristics as well as the aeroelastic behaviour of wind turbine blades across their broad range of operational conditions, from attached to highly separated flow regimes. The work programme included specific tasks for the validation and assessment of existing 3D solvers, for the parametric study of 3D flow around realistic blades and for the investigation of aeroelastic stability, at the blade section level. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the concept of sliding mode control is employed to guarantee global stability and optimize the efficiency of a wind electrical water-pumping system, where the measurement of wind speed is avoided.
Abstract: Wind energy conversion systems have been receiving increasing attention in recent years, particularly in remote areas, where power from the utility is not available or is costly to install. Among many applications, wind electrical systems are successfully used for pumping water. Owing to the non-linear characteristics of these systems, their control is essential to attain high efficiency. In this work, concepts of sliding mode control are employed to guarantee global stability and to optimize the efficiency of a wind electrical water-pumping system. The measurement of wind speed is avoided. A thorough analysis of stability and dynamic behaviour is realized. Simulation results are presented. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors estimate the wind climatology at a platform located 15 km offshore of Venice based on 7 years of data and compare it with the wind climate obtained by five different methods using the long-term data from four coastal meteorological stations, Venezia Tessera,Venezia San Nicolo, Ronchi and Rimini.
Abstract: Relatively few studies have been performed on the evaluation of offshore wind resources, and these have been conducted mostly in Northern Europe. In Mediterranean areas the lack of such studies is mainly linked to (1) the difficulty of meteorological monitoring in deeper waters, (2) the complex orography, frequently extending down to the coasts, (3) the sea breeze wind regimes and (4) local winds such as the Bora, Mistral and Sciroc. In the North Adriatic Sea, a shallow basin of the Mediterranean, the first reason is not applicable, but the others are sufficient to make the evaluation of wind speed methods challenging. In this article we estimate the wind climatology at a platform located 15 km offshore of Venice based on 7 years of data and compare it with the wind climatology obtained by five different methods using the long-term data from four coastal meteorological stations, Venezia Tessera, Venezia San Nicolo, Ronchi and Rimini. We discuss the applicability of these methods and find that the WAsP® model of Riso National Laboratory is still the best tool for wind climate estimates. The results of two new methods are promising, but the methods still require some development. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: The use of an automatic code generating system is an alternative for relevance of the two key issues, the code and the design optimization, and can be used for rapid generation of codes of particular wind turbine simulation models.
Abstract: For many reasons the size of wind turbines on the rapidly growing wind energy market is increasing. Relations between aeroelastic properties of these new large turbines change. Modifications of turbine designs and control concepts are also influenced by growing size. All these trends require development of computer codes for design and certification. Moreover, there is a strong desire for design optimization procedures, which require fast codes. General codes, e.g. finite element codes, normally allow such modifications and improvements of existing wind turbine models. This is done relatively easy. However, the calculation times of such codes are unfavourably long, certainly for optimization use. The use of an automatic code generating system is an alternative for relevance of the two key issues, the code and the design optimization. This technique can be used for rapid generation of codes of particular wind turbine simulation models. These ideas have been followed in the development of new versions of the wind turbine simulation code VIDYN. The equations of the simulation model were derived according to the Lagrange equation and using Mathematica®, which was directed to output the results in Fortran code format. In this way the simulation code is automatically adapted to an actual turbine model, in terms of subroutines containing the equations of motion, definitions of parameters and degrees of freedom. Since the start in 1997, these methods, constituting a systematic way of working, have been used to develop specific efficient calculation codes. The experience with this technique has been very encouraging, inspiring the continued development of new versions of the simulation code as the need has arisen, and the interest for design optimization is growing. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this article, the effect of the sea surface height on the wind shear profile of an offshore wind turbine in the North Sea has been investigated and shown to be small and there is considerable scatter in the data.
Abstract: The rise and fall of the sea surface due to the tide effectively moves an offshore wind turbine hub through the wind shear profile. Offshore wind farms are being built around the coasts of Europe, including in the Baltic and the North Sea. Tidal ranges in the North Sea are greater than those in the Baltic, and the potential effect on the wind shear profile of the change in sea surface height is likely to be more significant. This article seeks to identify the effect of tidal height on the shear profile at a mast off the east coast of the UK where the maximum tidal range is 7 m. Definite evidence for the effect of tidal height on wind shear is presented, though the effect is small and there is considerable scatter in the data.
TL;DR: In this paper, the sampling of series of mean wind speeds from consecutive rotor rotations, followed by unweighted and weighted averaging, is shown to have a positive bias on the long-term mean wind speed, which is at least one order of magnitude larger than the positive bias from the weighted averaging.
Abstract: The cup anemometer signal can be sampled in several ways to obtain the mean wind speed. Here we discuss the sampling of series of mean wind speeds from consecutive rotor rotations, followed by unweighted and weighted averaging. It is shown that the unweighted averaging creates a positive bias on the long-term mean wind speed, which is at least one order of magnitude larger than the positive bias from the weighted averaging, also known as the sample-and-hold method. For a homogeneous, neutrally stratified flow the first biases are 1%–2%. For comparison the biases due to fluctuations of the three wind velocity components and due to calibration non-linearity are determined under the same conditions. The largest of these is the v-bias from direction fluctuations. The calculations pertain to the Riso P2546A model cup anemometer. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: A study conducted at Northern Arizona University investigated the barriers and opportunities facing Native American tribes in the West when considering development of their renewable energy resources in order to reduce regional haze as discussed by the authors.
Abstract: A study conducted at Northern Arizona University investigated the barriers and opportunities facing Native American tribes in the West when considering development of their renewable energy resources in order to reduce regional haze. This article summarizes some of the findings of that work with special attention to wind energy. Background information is presented concerning the Regional Haze Rule and the Western Regional Air Partnership, and some of the circumstances surrounding development of tribal energy resources. An assessment of tribal energy issues revealed that many Native American tribes are interested in developing their renewable resources. However, this development should occur within the context of maintaining and strengthening their cultural, social, economic and political integrity. Furthermore, it is shown that Native American lands possess an abundant wind resource. A list of potential actions in which tribes may participate prior to or during development of their wind or renewable resources is provided. Copyright © 2003 John Wiley & Sons, Ltd.