Showing papers in "Wind Energy in 2005"

Beyond NIMBYism: Towards an integrated framework for understanding public perceptions of wind energy

Abstract: It is widely recognised that public acceptability often poses a barrier towards renewable energy development. This article reviews existing research on public perceptions of wind energy, where opposition is typically characterized by the NIMBY (not in my back yard) concept. The objectives of the article are to provide a critical assessment of past research and an integrated, multidimensional framework to guide future work. Six distinct strands of research are identified, summarized and critiqued: public support for switching from conventional energy sources to wind energy; aspects of turbines associated with negative perceptions; the impact of physical proximity to turbines; acceptance over time of wind farms; NIMBYism as an explanation for negative perceptions; and, finally, the impact of local involvement on perceptions. Research across these strands is characterized by opinion poll studies of general beliefs and case studies of perceptions of specific developments. In both cases, research is fragmented and has failed to adequately explain, rather than merely describe, perceptual processes. The article argues for more theoretically informed empirical research, grounded in social science concepts and methods. A multidimensional framework is proposed that goes beyond the NIMBY label and integrates previous findings with social and environmental psychological theory. Copyright © 2004 John Wiley & Sons, Ltd.

Tip loss corrections for wind turbine computations

Abstract: As an essential ingredient in the blade element momentum theory, the tip loss effect of rotors plays an important role in the prediction of wind turbine performance Various tip loss corrections based on the Prandtl tip loss function are analysed in the article Comparisons with measurements and theoretical analyses show that existing tip loss correction models are inconsistent and fail to predict correctly the physical behaviour in the proximity of the tip A new tip loss correction model is proposed that remedies the inconsistency Comparisons between numerical and experimental data show that the new model results in much better predictions of the loading in the tip region Copyright © 2005 John Wiley & Sons, Ltd

Further load reductions with individual pitch control

Abstract: Previous work has demonstrated that significant reductions in fatigue loading on a wind turbine can be achieved by using individual pitch control, in which the pitch of each blade is adjusted individually, in response to measured loads. The asymmetrical out-of-plane rotor load is measured and an additional pitch action (dominated by the rotational frequency of the rotor) is calculated for each blade in order to minimize this load. This results in the near-elimination of the dominant once-per-revolution (‘1P’) peak in the out-of-plane load spectrum seen by the rotating components, and fatigue loads can be reduced by 20%–40%. The load reduction is also transferred to the nacelle and tower, but here it is the low-frequency loads which are removed, resulting in a load reduction of a few per cent at best, since the fatigue on the fixed components is dominated by the peak at the blade passing frequency (‘3P’ for a three-bladed turbine), which is largely unaffected by the individual pitch control action. This article demonstrates a relatively straightforward addition to the individual pitch control algorithm which is capable of reducing the dominant load peak on the fixed components, resulting in significant fatigue load reductions on the whole structure. Copyright © 2005 John Wiley & Sons, Ltd.

Impact of hourly wind power variations on the system operation in the Nordic countries

Abstract: The variations of wind power production will increase the flexibility needed in the system when significant amounts of load are covered by wind power When studying the incremental effects that varying wind power production imposes on the power system, it is important to study the system as a whole: only the net imbalances have to be balanced by the system Large geographical spreading of wind power will reduce variability, increase predictability and decrease the occasions with near zero or peak output The goal of this work was to estimate the increase in hourly load-following reserve requirements based on real wind power production and synchronous hourly load data in the four Nordic countries The result is an increasing effect on reserve requirements with increasing wind power penetration At a 10% penetration level (wind power production of gross demand) this is estimated as 1·5%–4% of installed wind capacity, taking into account that load variations are more predictable than wind power variations Copyright © 2004 John Wiley & Sons, Ltd

Hourly wind power variations in the Nordic countries

Abstract: Studies of the effects that wind power production imposes on the power system involve assessing the variations of large-scale wind power production over the whole power system area. Large geographical spreading of wind power will reduce variability, increase predictability and decrease the occasions with near zero or peak output. In this article the patterns and statistical properties of large-scale wind power production data are studied using the data sets available for the Nordic countries. The existing data from Denmark give the basis against which the data collected from the other Nordic countries are benchmarked. The main goal is to determine the statistical parameters describing the reduction of variability in the time series for the different areas in question. The hourly variations of large-scale wind power stay 91%–94% of the time within ±5% of installed capacity in one country, and for the whole of the Nordic area 98% of the time. For the Nordic time series studied, the best indicator of reduced variability in the time series was the standard deviation of the hourly variations. According to the Danish data, it is reduced to less than 3% from a single site value of 10% of capacity. Copyright © 2004 John Wiley & Sons, Ltd.

On structural optimization of composite shell structures using a discrete constitutive parametrization

Abstract: In this article a novel method for structural optimization of laminated composite shell structures such as wind turbine blades is presented. The outer shape of a wind turbine blade is typically determined by aerodynamic considerations and therefore not subject to change. Furthermore, the thicknesses of the shell structures are also considered fixed. The design objective is chosen to be a global quantity such as maximum stiffness or lowest eigenfrequency with a constraint on the total mass, such that the cost of material can be considered. The design optimization method is based on ideas from multiphase topology optimization where the material stiffness (or density) is computed as a weighted sum of candidate materials, and the method is easy to implement in existing finite element codes. The potential of the method to solve the combinatorial problem of proper choice of material, stacking sequence and fibre orientation simultaneously for maximum stiffness or lowest eigenfrequency design is illustrated on both small test examples and a real-life main spar from a wind turbine blade. Copyright © 2004 John Wiley & Sons, Ltd.

Transient stability of DFIG wind turbines at an external short‐circuit fault

Abstract: The fast development of wind power generation brings new requirements for wind turbine integration into the network. After clearance of an external short-circuit fault, grid-connected wind turbines should restore their normal operation without power loss caused by disconnections. This article concentrates on the transient stability of variable speed wind turbines with doubly fed induction generators (DFIGs) at an external short-circuit fault. A simulation model of a MW-level variable speed wind turbine with a DFIG developed in PSCAD/EMTDC is presented and the control and protection schemes are described in detail. The transient process of grid-connected wind turbines with DFIGs at an external short-circuit fault is analysed, and in critical post-fault situations a measure is proposed for the voltage recovery of DFIG wind turbines after fault clearance. Simulation results demonstrate that in uncritical post-fault situations the control schemes are able to restore the wind turbine's normal operation without disconnections. It is also proved that the proposed measure is effective in re-establishing the voltage at the wind turbine terminal in critical post-fault situations. Copyright © 2005 John Wiley & Sons, Ltd.

International comparison of requirements for connection of wind turbines to power systems

Abstract: Power production from wind turbines has increased considerably during the lost decade. Therefore today's wind turbines, which are typically set up in wind farms, have a significant influence on the ...

Innovative Design Approaches for Large Wind Turbine Blades

Abstract: A preliminary design study of an advanced 50 m blade for utility wind turbines is presented and discussed. The effort was part of the Department of Energy WindPACT Blade System Design Study with the goal to investigate and evaluate design and manufacturing issues for wind turbine blades in the 1–10 MW size range. Two different blade designs are considered and compared in this article. The first is a fibreglass design, while the second design selectively incorporates carbon fibre in the main structural elements. The addition of carbon results in modest cost increases and provides significant benefits, particularly with respect to blade deflection. The structural efficiency of both designs was maximized by tailoring the thickness of the blade cross-sections to simplify the construction of the internal members. Inboard the blades incorporate thick blunt trailing edge aerofoils (flatback aerofoils), while outboard more conventional sharp trailing edge high-lift aerofoils are used. The outboard section chord lengths were adjusted to yield the least complex and costly internal blade structure. A significant portion of blade weight is related to the root buildup and metal hardware for typical root attachment designs. The results show that increasing the number of studs has a positive effect on total weight, because it reduces the required root laminate thickness. The aerodynamic performance of the blade aerofoils was predicted using computational techniques that properly simulate blunt trailing edge flows. The performance of the rotor was predicted assuming both clean and soiled blade surface conditions. The rotor is shown to provide excellent performance at a weight significantly lower than that of current rotors of this size. Copyright © 2004 John Wiley & Sons, Ltd.

Effect of energy storage on variations in wind power

Abstract: Powered by TCPDF (www.tcpdf.org) This material is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. Paatero, Jukka; Lund, Peter

Large‐scale wind power integration in Norway and impact on damping in the Nordic grid

Abstract: The Nordic energy market is in need of new power generation capacity. Norway is today in shortage of electrical energy, and the hydropower-based system must rely on importing electrical power from its neighbours in a normal year of hydro inflow. One solution to this problem is to invest in new generation capacity, e.g. by integrating more wind power into the Norwegian grid. The Norwegian government has announced that 1000 MW of wind power will be installed in Norway by 2010, corresponding to an eventual energy production of approximately 3 TWh year−1. This article investigates the impact of wind power integration in Norway on the damping of interarea mode oscillations in the Nordic grid. The impact on the interarea mode oscillations is tested for various types of generators. Results from computer analyses of a simplified yet realistic equivalent of the Nordic power system are used to compute the interarea mode oscillations. Copyright © 2005 John Wiley & Sons, Ltd.

Seismic analysis of wind turbines in the time domain

Abstract: The analysis of wind turbine loading associated with earthquakes is clearly important when designing for and assessing the feasibility of wind farms in seismically active regions. The approach taken for such analysis is generally based on codified methods which have been developed for the assessment of seismic loads acting on buildings. These methods are not able to deal properly with the aeroelastic interaction of the dynamic motion of the wind turbine structure with either the wind loading acting on the rotor blades or the response of the turbine controller. This article presents an alternative approach, which is to undertake the calculation in the time domain. In this case a full aeroelastic model of the wind turbine subject to turbulent wind loading is further excited by ground motion corresponding to the earthquake. This capability has been introduced to the GH Bladed wind turbine simulation package. The software can be used to compute the combined wind and earthquake loading of a wind turbine given a definition of the external conditions for an appropriate series of load cases. This article discusses the method and presents example results. Copyright © 2004 John Wiley & Sons, Ltd.

Voltage dips at the terminals of wind power installations

Abstract: This article gives an overview of the kind of voltage dips that can be expected at the terminals of a wind power installation The overview is based on the study of those dips at the terminals of industrial installations and provides a guideline for the testing of wind power installations against voltage dips For voltage dips due to faults, a classification into different types is presented Five types appear at the terminals of sensitive equipment and thus have to be included when testing the wind power installation against disturbances coming from the grid A distinction is made between installations connected at transmission level and those connected at distribution level For the latter the phase angle jump has to be considered Dips due to other causes (motor, transformer and capacitor switching) are briefly discussed as well as the voltage recovery after a dip Finally some thoughts are presented on the way in which voltage tolerance requirements should be part of the design process for wind power installations Copyright

Offshore wind resource estimation from satellite SAR wind field maps

Abstract: A wind resource estimation study based on a series of 62 satellite wind field maps is presented. The maps were retrieved from imaging synthetic aperture radar (SAR) data. The wind field maps were used as input to the software RWT, which calculates the offshore wind resource based on spatial averaging (footprint modelling) of the wind statistic in each satellite image. The calculated statistics can then be input to the program WAsP and used in lieu of in-situ observations by meteorological instruments. A regional wind climate map based on satellite SAR images delineates significant spatial wind speed variations. The site of investigation was Horns Rev in the North Sea, where a meteorological time series is used for comparison. The advantages and limitations of these new techniques, which seem particularly useful for mapping of the regional wind climate, are discussed. Copyright © 2005 John Wiley & Sons, Ltd.

An Improved BEM Model for the Power Curve Prediction of Stall-regulated Wind Turbines

Abstract: Blade element momentum (BEM) theory is the standard computational technique for the prediction of power curves of wind turbines; it is based on the two-dimensional aerodynamic properties of aerofoil blade elements and some corrections accounting for three-dimensional wing aerodynamics. Although most BEM models yield acceptable results for low-wind and pitch-controlled regimes where the local angles of attack are small, no generally accepted model exists up to date that consistently predicts the power curve in the stall regime for a variety of blade properties and operating conditions. In this article we present a modified BEM model which satisfactorily reproduces the power curves of four experimental wind turbines reported in the literature, using no free fit parameters. Since these four experimental cases comprehend a great variety of conditions (wind tunnel vs field experiments, different air densities) and blade parameters (no twist and no taper, no taper but twist, both twist and taper, different aerofoil families), it is believed that our model represents a useful working tool for the aerodynamic design of stall-regulated wind turbines. Copyright © 2004 John Wiley & Sons, Ltd.

A DFIG wind turbine ride‐through system. Influence on the energy production

Abstract: The influence of a voltage sag ride-through system on the energy production of a doubly-fed induction generator (DFIG) wind turbine is investigated. Using simulations, a candidate ride-through system based on insulated gate bipolar transistor (IGBT) modules with high current rating and with the option of having antiparallel thyristors, which can quickly disconnect the stator of the DFIG from the grid, is developed. It has been found that, by increasing the current rating of the converter IGBTs, the losses of the converter can be reduced. However, if antiparallel thyristors have to be connected between the stator and the grid in order to achieve a fast disconnection of the stator circuit, the overall losses of the total system increase instead. Copyright © 2005 John Wiley & Sons, Ltd.

Forecasting offshore wind speeds above the North Sea

Abstract: We investigate the expected performance of short-term wind power prediction systems for offshore sites in the German Bight and at Horns Rev. Despite the special meteorological situation over the North Sea, it is found that the accuracy of wind speed predictions provided by the numerical prediction model of the German weather service is comparable to that of onshore predictions. However, although relative forecast errors look promising, the absolute errors are fairly large, with a root mean square error up to 3 m s−1 for the 48 h forecast. Moreover, vertical wind profiles which are typically needed to calculate the wind speed at hub height are considered at Horns Rev. In all thermal conditions the measured profiles show significant deviations from the expected shapes. The reason for this has to be clarified. Assuming that the deviations are due to the physical processes in the marine boundary layer, we present an alternative approach to derive wind profiles over the ocean which involves the inertial coupling of the Ekman layers of atmosphere and sea via a wave boundary layer with constant shear stress. Profiles calculated by this method are compared with measured profiles, showing rather good agreement. Copyright © 2004 John Wiley & Sons, Ltd.

Large-scale Wind Power Farms as Power Plants

Abstract: The integration of large-scale wind power into weak power systems raises several issues that must be clarified. Typically these include the practical connection to the network, integration with the network system, system stability, system operation, necessary installations and extensions of the network, etc. At the same time, careful attention must be paid to the functional requirements such wind farms should meet in order to enhance system responses. Different wind power technologies have different characteristics and control possibilities. In this article, three technologies have been studied with respect to their dynamic performance, and a transient stability study has been performed in order to illustrate the differences in the three technologies. The results clearly show that there are differences in behaviour and in control possibilities. Hence there are also differences in how well they can meet functional requirements. When discussing to what degree strict requirements should be imposed on wind power, it should be kept in mind that some requirements can be met with small or moderate costs, while others may be expensive or difficult to meet. Some requirements may also mean a reduction in generation and hence in revenues. Rather than imposing strict requirements on wind turbines as such, ancillary services should be met in the most suitable way. It is not obvious that the same requirements should apply to wind power in hydro power-dominated systems compared with, for instance, systems with a large share of nuclear or thermal power. It may well be cheaper to incorporate primary power control and system-stabilizing equipment in other power plants or grid points than in many small wind turbine generators. General conclusions cannot be made on this, but the issue should be the focal point of system operators everywhere. Copyright © 2005 John Wiley & Sons, Ltd.

Influence of wave modelling on the prediction of fatigue for offshore wind turbines

Abstract: Currently it is standard practice to use Airy linear wave theory combined with Morison's formula for the calculation of fatigue loads for offshore wind turbines. However, offshore wind turbines are typically placed in relatively shallow water depths of 5–25 m where linear wave theory has limited accuracy and where ideally waves generated with the Navier–Stokes approach should be used. This article examines the differences in fatigue for some representative offshore wind turbines that are found if first-order, second-order and fully non-linear waves are used. The offshore wind turbines near Blyth are located in an area where non-linear wave effects are common. Measurements of these waves from the OWTES project are used to compare the different wave models with the real world in spectral form. Some attention is paid to whether the shape of a higher-order wave height spectrum (modified JONSWAP) corresponds to reality for other places in the North Sea, and which values for the drag and inertia coefficients should be used. Copyright © 2004 John Wiley & Sons, Ltd.

The effect of mean stress on damage predictions for spectral loading of fibreglass composite coupons

Abstract: In many analyses of wind turbine blades the effects of mean stress on the determination of damage in composite blades are either ignored completely or characterized inadequately. Mandell et al. have recently presented an updated Goodman diagram for a fibreglass material that is typical of the materials used in wind turbine blades. Their formulation uses the MSU/DOE fatigue database to develop a Goodman diagram with detailed information at 13 R-values. Using these data, linear, bilinear and full Goodman diagrams are constructed using mean and ‘95/95’ fits to the data. The various Goodman diagrams are used to predict the failure stress for coupons tested using the WISPERX spectrum. Three models are used in the analyses. The first is the linear Miner's rule commonly used by the wind industry to predict failure (service lifetimes). The second is a non-linear variation of Miner's rule which computes a non-linear Miner's residual strength based upon an exponential degradation parameter. The third is a generalized non-linear residual strength model that also relies on an exponential degradation parameter. The results illustrate that Miner's rule does not predict failure very well. When the mean full Goodman diagram is used, the non-linear models predict failures near the mean of the experimental data, and when the 95/95 Goodman diagram is used, they predict the lower bound of the measured data very well. Published in 2004 by John Wiley & Sons, Ltd.

A system for wind power estimation in mountainous terrain. Prediction of Askervein hill data

Abstract: In mountainous terrain, where the wind power potential is largest, the estimation of the local wind power can be done rationally by means of available information about the large-scale flow and the detailed terrain and numerical flow models for downscaling, provided that the numerical model estimates can be assigned sufficient confidence. In this study the confidence of a local model in such an estimation system is discussed. The model is based upon the Reynolds-averaged Navier–Stokes equations with (K, ϵ) turbulence closure and integrated with finite element numerical techniques. The model has previously been validated relative to complicated laboratory-scale flows and appears to predict some full-scale geophysical flows plausibly. Here its predictions are compared quantitatively with the full-scale Askervein hill experimental data. The model estimates the data to within the experimental uncertainty, which we judge to be comparable to 10%, as other comparable models also do. This contributes to assign confidence to the downscaling estimation system mentioned. Copyright © 2004 John Wiley & Sons, Ltd.

Investigation of spatial gusts with extreme rise time on the extreme loads of pitch‐regulated wind turbines

Abstract: It is assumed that the extreme loading of pitch-regulated turbines is caused by gusts with an extreme rise time rather than an extreme gust amplitude. A special kind of wind field simulation, so-called constrained stochastic simulation, is dealt with in order to generate the desired gusts. Just as in wind field simulation for fatigue purposes, it is assumed that turbulence is Gaussian; a possibility is mentioned of how to deal with non-Gaussian behaviour.On the basis of the presented theory it can be stated that the stochastic gusts produced in this way are, in a statistical sense, not distinguishable from gusts selected from a (very long) time series. An example of a spatial gust as well as the mean spatial gust shape is shown. For a reference turbine the maximum blade root flapping moment has been determined as a function of the gust centre in the rotor plane; the maximum response is obtained in the case where the gust hits one of the rotor blades at 75% of the radius. When the gust duration is large compared with the integral time constant of the controller, the controller can handle the gust as expected. However, even for small rise times it turns out that the maximum flap moment due to the gust is not significantly higher than that due to the background turbulence and 1P excitations. This may indicate that perhaps extreme rise time gusts do not lead to extreme loading of pitch-regulated wind turbines. For a final judgement a proper probabilistic approach is necessary; an outline of such an approach has been sketched. Furthermore, it is recommended to do research on other gust types in order to find out the type which leads to the extreme wind turbine loading.Copyright © 2004 John Wiley & Sons, Ltd. WIND ENERGY Wind Energ. 2005; 8:17–34 (DOI: 10.1002/we.139)

Design of robust converter interface for wind power applications

Abstract: As the amount of wind power and other distributed generation with power electronic interface in the grid grows, it becomes unacceptable to disconnect generating units every time a disturbance occurs, as was common practice in the past. Keeping the voltage source converter on-line during unbalanced voltage dips thus becomes a very critical issue. In this article the design of a robust converter interface for wind turbines is investigated. Based on the classification of unbalanced faults that can occur in the grid, resulting in voltage dips at the bus where the turbine is connected, the maximum current that the converter valves must be able to withstand is calculated. The effect of phase angle jumps during faults is also investigated. It is demonstrated that, ultimately, the converter design can be optimized by using statistics of voltage dips and the wind speed distribution for the specific site considered. This is shown by a design example. Copyright © 2005 John Wiley & Sons, Ltd.

Wind turbine generator trends for site‐specific tailoring

Abstract: Turbine optimization for specific wind regimes and climate conditions is becoming more common as the market expands into new territories (offshore, low-wind regimes) and as technology matures. Tailoring turbines for specific sites by varying rotor diameter, tower height and power electronics may be a viable technique to make wind energy more economic and less intermittent. By better understanding the wind resource trends and evaluating important wind turbine performance parameters such as specific power (ratio of rated power and rotor swept area), developers and operators can optimize plant output and better anticipate operational impacts. This article presents a methodology to evaluate site-specific wind data for turbine tailoring. Wind characteristics for the Tehachapi wind resource area in California were utilized for this study. These data were used to evaluate the performance of a range of wind turbine configurations. The goal was to analyse the variations in wind power output for the area, assess the changes in these levels with the time of day and season and determine how turbine configuration affects the output. Wind turbine output was compared with California statewide system electrical demand to evaluate the correlation of the wind resource site with local peak demand loads. A comparison of the commercial value of electricity and corresponding wind generation is also presented using a time-dependent valuation methodology. Copyright © 2005 John Wiley & Sons, Ltd.

Grid interaction of offshore wind farms. Part 2. Case study simulations

Abstract: Owing to an increasing penetration of wind turbines and large wind farms in electrical power systems, the wind turbines start influencing the overall power system behaviour. Dynamic wind farm models for power system studies have been presented in Part 1 of the article. In this contribution, these models are applied in a number of case studies to determine the impact of wind farms on the power grid. Four turbine concepts are evaluated with respect to their grid interaction. Case studies involving normal behaviour, voltage dip behaviour, voltage control capability and behaviour during frequency deviations will be presented. Copyright © 2005 John Wiley & Sons, Ltd.

Field tests and modelling of a wind farm with doubly fed induction generators

Abstract: Havoygavlen is Norway’s second wind farm and started operation in 2002. Several new wind farms are currently under planning at various sites along the Norwegian west coast. The Norwegian System Operator (TSO) Statnett SF and Sintef Energy Research have jointly developed a dynamic simulation model for Havoygavlen in order to analyse the interaction between wind farms and the transmission grid. Full-scale field tests have been conducted to verify the model by comparing simulations to measurements. This paper presents results from the field tests, model validation work as well as operating experiences for Havoygavlen wind farm.