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Harmonic Current Predictors for Wind Turbines  [PDF]
Jen-Hao Teng,Rong-Ceng Leou,Chuo-Yean Chang,Shun-Yu Chan
Energies , 2013, DOI: 10.3390/en6031314
Abstract: The harmonic impact caused by wind turbines should be carefully investigated before wind turbines are interconnected. However, the harmonic currents of wind turbines are not easily predicted due to the variations of wind speed. If the harmonic current outputs can be predicted accurately, the harmonic impact of wind turbines and wind farms for power grids can be analyzed efficiently. Therefore, this paper analyzes the harmonic current characteristics of wind turbines and investigates the feasibility of developing harmonic current predictors. Field measurement, data sorting, and analysis are conducted for wind turbines. Two harmonic current predictors are proposed based on the measured harmonic data. One is the Auto-Regressive and Moving Average (ARMA)-based harmonic current predictor, which can be used for real-time prediction. The other is the stochastic harmonic current predictor considering the probability density distributions of harmonic currents. It uses the measured harmonic data to establish the probability density distributions of harmonic currents at different wind speeds, and then uses them to implement a long-term harmonic current prediction. Test results use the measured data to validate the forecast ability of these two harmonic current predictors. The ARMA-based predictor obtains poor performance on some harmonic orders due to the stochastic characteristics of harmonic current caused by the variations of wind speed. Relatively, the prediction results of stochastic harmonic current predictor show that the harmonic currents of a wind turbine in long-term operation can be effectively analyzed by the established probability density distributions. Therefore, the proposed stochastic harmonic current predictor is helpful in predicting and analyzing the possible harmonic problems during the operation of wind turbines and wind farms.
Probabilistic Load Flow Considering Correlation between Generation, Loads and Wind Power  [PDF]
Daniel Villanueva, Andrés Feijóo, José Luis Pazos
Smart Grid and Renewable Energy (SGRE) , 2011, DOI: 10.4236/sgre.2011.21002
Abstract: In this paper a procedure is established for solving the Probabilistic Load Flow in an electrical power network, considering correlation between power generated by power plants, loads demanded on each bus and power injected by wind farms. The method proposed is based on the generation of correlated series of power values, which can be used in a MonteCarlo simulation, to obtain the probability density function of the power through branches of an electrical network.
Design Mining VAWT Wind Farms  [PDF]
Richard J. Preen,Larry Bull
Computer Science , 2015,
Abstract: The small body of previous work considering the design of wind farms has used arrays of turbines originally intended to operate alone, optimising the layout of homogeneous turbines essentially as an afterthought in the design process. In this paper, we consider designing wind farms composed of collaborating wind turbines. Computational intelligence is combined with rapid prototyping whereby candidate designs are physically instantiated and evaluated under fan-generated wind conditions. It is shown possible to use surrogate-assisted coevolutionary algorithms to aerodynamically optimise the potentially heterogeneous morphology of an array of 6 small scale and closely positioned vertical-axis wind turbines using the total angular kinetic energy of the array as the objective. This approach performs optimisation in the presence of complex inter-turbine wake effects and multi-directional wind flow from nearby obstacles, which is extremely difficult to achieve accurately under high fidelity computational fluid dynamics simulation. The general approach is equally applicable to the design of other forms of sustainable energy where the characteristics of the environment and/or materials involved are too difficult to accurately simulate.
Response of cooling towers to wind loads  [PDF]
G. Murali,C. M. Vivek Vardhan,B. V. Prasanth Kumar Reddy
Journal of Engineering and Applied Sciences , 2012,
Abstract: This paper deals with the study of two cooling towers of 122 m and 200 m high above ground level. These cooling towers have been analysed for wind loads using ANSYS software by assuming fixity at the shell base. The wind loads on these cooling towers have been calculated in the form of pressures by using the circumferentially distributed design wind pressure coefficients as given in IS: 11504 - 1985 code [1] along with the design wind pressures at different levels as per IS:875 (Part 3) - 1987 code [2]. The analysis has been carried out using 8-noded shell element (SHELL 93) with 5 degrees of freedom per node. The results of the analysis include membrane forces, viz., meridional force (Nf) and hoop force (Nq), and bending moments, viz., meridional moment (Mf) and hoop moment (Mq). The vertical distribution of membrane forces and bending moments along 0o and 70o meridians and the circumferential distributions at base, throat and top levels have been studied for both the cooling towers. For circumferential distribution, non-dimensional values have been obtained by normalizing the membrane forces and bending moments using the reference values at 0o meridian. Similarly, the reference values at the base have been used for vertical distribution. These non-dimensional curves for both the cooling towers have been compared in the present study for the feasibility of any generalisation.
The impacts of wind farms on animal species
Ster?e Jana,Poga?nik M.
Acta Veterinaria , 2008, DOI: 10.2298/avb0806615s
Abstract: Wind farms are constructed in various areas without considering the protected animal species that are present there. In problem areas, there are some mitigation measures taken. In 55% of the studies, bird mortality rates ranges from 0.0 to 2.0 fatalities/turbine/year. 79.4% of the evaluated mortality rates for raptors range from 0.0 to 0.1 fatalities/ turbine/year. The highest number of wind turbine fatalities has been recorded with a raptor Buteo jamaicensis, followed by seagull Larus argentatus, passerine Eremophila alpestris and domestic pigeon Columbia livia. The only species that has been recorded as a wind turbine fatality and is a part of the IUCN Red list of Threatened Species is red kite (Milvus milvus). The European wind power studies pay more attention to the disturbance of particular species. The species that are most commonly considered threatened are the raptors (common buzzard, common kestrel and red kite), grassland birds (common quail, corn crake, lapwing, ringed plover), migrating birds (migrant goose, crane, lapwing, golden plover) and waterbirds (geese species). Bat annual mortality rates range from 0.0 to 47.5 fatalities/turbine/year at different wind farms. The highest mortality rate has been reported for bat species Laisurus cinereus, Lasiurus borealis, Lasionycteris noctivagans and Nyctalus noctula.
Numerical prediction of wind loads on low buildings
S Ahmad, M Muzzammil, I Zaheer
International Journal of Engineering, Science and Technology , 2011,
Abstract: In the present study, 2-D numerical simulation of wind loads on low-rise buildings has been carried out. The simulation was carried out under FLUENT package environment in which full-scale Reynolds number, boundary layer and turbulence properties have been simulated. Wind loading effect numerically obtained on flat roof (TTU building) and pitched roof is compared with wind tunnel data. It was found that there is fair agreement between the numerical predictions and measurements for time-averaged wind loads on buildings. The computed pressure coefficients have been validated with wind tunnel TTU building model results on 1:100 scale within an average error of 20%. The effect of roof pitch for 10°, 20° & 30° on pressure coefficients for gable roof has also been investigated and the results were compared with the available wind tunnel results for 15°, 26° & 35° roof pitch. The present study shows that the numerical simulation of wind loads hold a great potential for extending codes of practice for wind loads.
Effect of Wind Turbine Classes on the Electricity Production of Wind Farms in Cyprus Island  [PDF]
Yiannis A. Katsigiannis,George S. Stavrakakis,Christodoulos Pharconides
Conference Papers in Science , 2013, DOI: 10.1155/2013/750958
Abstract: This paper examines the effect of different wind turbine classes on the electricity production of wind farms in two areas of Cyprus Island, which present low and medium wind potentials: Xylofagou and Limassol. Wind turbine classes determine the suitability of installing a wind turbine in a particulate site. Wind turbine data from five different manufacturers have been used. For each manufacturer, two wind turbines with identical rated power (in the range of 1.5?MW–3?MW) and different wind turbine classes (IEC II and IEC III) are compared. The results show the superiority of wind turbines that are designed for lower wind speeds (IEC III class) in both locations, in terms of energy production. This improvement is higher for the location with the lower wind potential and starts from 7%, while it can reach more than 50%. 1. Introduction Renewable energy sources (RESs) are clean, inexhaustible, and environmental-friendly alternative energy sources with negligible fuel cost. The worldwide demand for renewable energy is increasing rapidly because of the climate problem, and also because oil resources are limited. Wind energy appears as a clean and good solution to cope with a great part of this energy demand. Wind turbines present several advantages over conventional generation technologies for electricity generation. Reduction of greenhouse gases that contribute to global climate change and to local air quality is one of their major advantages. Additionally, they reduce the risk of fossil-fuel price fluctuations and decrease the electricity-sector dependency. However, developing a utility-scale wind project is a complicated and time-consuming process involving developers, landowners, utilities, the public, and various local authorities. Although each wind energy project is unique and has different characteristics, basic features and related steps are common. In practice, the steps are iterative and overlap with one another depending on the specific project circumstances. The key steps of development and planning for a wind farm are site selection, detailed wind assessment, feasibility, construction, and operation [1]. This paper examines the effect of different wind turbine classes in the electricity production of wind farms in two areas of Cyprus Island that present low and medium wind potentials: Xylofagou and Limassol. Wind classes determine which turbine is suitable for the normal wind conditions of a particular site. Turbines with higher wind classes have larger blades and produce more energy in low and medium winds [2], but they are more sensitive in
Wind Loads of Solar Water Heaters: Wind Incidence Effect  [PDF]
Chin-Cheng Chou,Kung-Ming Chung,Keh-Chin Chang
Journal of Aerodynamics , 2014, DOI: 10.1155/2014/835091
Abstract: For applications of solar thermal energy, solar water heaters (SWHs) are becoming common. In this study, the effect of a crosswind on the aerodynamic characteristics of residential (an inclined flat plate with a horizontal cylinder) and large-scale SWHs (an inclined flat plate only) is experimentally investigated. The tests are conducted in a low speed wind tunnel and the relative wind direction with respect to the test model, , ranges from 0 to 135?deg. Measurements of the mean and fluctuating pressures are presented. These results demonstrate that higher suction and fluctuating pressure are observed near the upwind corner, particularly for the test case of ?deg. 1. Introduction The use of renewable energy technologies represents an opportunity to reduce global warming. In this respect, SWHs are rapidly becoming an integral part of worldwide measures to combat the effects of climate change. Previous studies [1, 2] found that the wind loads on solar collectors are significantly reduced by the sheltering effect of the first row of collectors and of the building itself. For a residential SWH (an inclined solar collector with a horizontal water storage tank), normal to the direction of smooth uniform wind, the study by Chung et al. [3, 4] demonstrated that localized wind loads at a tilt angle?α of 15–30?deg. are significant near the front edge and reach a minimum value at a distance of approximately one-third of the total length from the leading edge. Reynolds number independence was also noted. For a large-scale SWH (inclined solar collector or flat plate only), Chung et al. [5, 6] indicated that there is a higher suction force on the lower surface over the first half of the inclined solar collector and a stronger positive mean longitudinal differential pressure coefficient is observed. Kopp et al. [7] further pointed that the presence of the building changed the aerodynamic loads substantially compared to ground-mounted systems. There is a complex interaction between building generated vortices and the flow induced by solar arrays. Wind incidence has an important influence on the aerodynamics of bluff bodies [8]. Certain oblique wind directions, , correspond to the critical case for wind loads. Wood et al. [9] demonstrated that the orientation of the solar collectors with respect to the wind direction and the proximity of the panels to the leading edge have a significant effect on the pressure distributions measured. Kopp et al. [7] found that the largest wind loads are associated with vortex shedding from in-line solar collectors. The peak system torque
Calculating carbon budgets of wind farms on Scottish peatlands
D.R. Nayak,D. Miller,A. Nolan,P. Smith
Mires and Peat , 2010,
Abstract: The reliability of calculation methods for the carbon emission savings to be achieved in Scotland by replacing power generated from fossil fuels (and other more conventional sources) with that produced by large-scale wind farm developments is a cause for concern, largely in relation to wind farms sited on peatlands. Scottish Government policy is to deliver renewable energy without environmental harm, and to meet biodiversity objectives including the conservation of designated wildlife sites and important habitats such as peatlands. The implications for carbon emissions of developing a wind farm are, therefore, just one aspect of the suite of considerations that the planning system takes into account. This paper presents a simple methodology for prospectively calculating the potential carbon emission savings to be realised by developing wind farms on peatland, forestland or afforested peatland. The total carbon emission savings of an individual wind farm are estimated by accounting emissions from the power source that will be replaced by wind power against: loss of carbon due to production, transportation, erection, operation and dismantling of the wind farm components (the infrastructure overhead); loss of carbon due to backup power generation; loss of carbon stored in peat and forest; loss of carbon-fixing potential of peatland and forest; and carbon savings due to habitat improvement. Most of the carbon losses are determined by national infrastructure, but those from peat soil and plants are influenced by site selection and management practices. The extent of drainage around each constructed element of the wind farm is a major factor for greenhouse gas emissions. Consideration of an example site with a low extent of drainage, where management practices that minimise net carbon losses (e.g. undrained floating roads, habitat improvement and site restoration on decommissioning) were used indicates that emissions from the soil and plants may cancel out as little as < 6% of the potential carbon savings, even on peatland. However, if the soil had a high extent of drainage and management practices that minimise carbon losses were abandoned, greenhouse gas emissions from the soil and plants could amount to 77% of the wind farm’s gross carbon savings; in other words, even though the development would not be a net cost in terms of greenhouse gas emissions, it would not provide much benefit. Thus, the development of wind farms on peat as opposed to mineral soils incurs a much greater risk that the potential net saving of greenhouse gas emissions will be signific
Principal wind turbines for a conditional portfolio approach to wind farms  [PDF]
Vitor V. Lopes,Teresa Scholz,Frank Raischel,Pedro G. Lind
Quantitative Finance , 2014, DOI: 10.1088/1742-6596/524/1/012183
Abstract: We introduce a measure for estimating the best risk-return relation of power production in wind farms within a given time-lag, conditioned to the velocity field. The velocity field is represented by a scalar that weighs the influence of the velocity at each wind turbine at present and previous time-steps for the present "state" of the wind field. The scalar measure introduced is a linear combination of the few turbines, that most influence the overall power production. This quantity is then used as the condition for computing a conditional expected return and corresponding risk associated to the future total power output.
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