Wind Resource Evaluation Research Articles

Investigation of the Wind Resource Assessment over 2D Continuous Rolling Hills Due to Tropical Cyclones in the Coastal Region of Southeastern China

The effect of tropical cyclones on the turbulent flow over 2D continuous rolling hills was numerically investigated based on a field test analysis of the coastal region of Southeast China. A computational fluid dynamics (CFD) method was first developed and verified using previously published experimental results. Then two typical beneficial and destructive cyclone cases were studied above different locations of the hills. Results showed that the continuous hilly flow was much more drastic and variable than previously reported normal wind; the mean and turbulent magnitudes became the strongest around the hill top, with the maximum speed-up ratio, turbulence intensity and gust-speed ratio of 1.1, 0.32 and 1.6; the flow over lower hill was greatly affected by the nearby higher hills; the mean and fluctuating quantities were mostly smaller than the corresponding single hill case. These phenomena were considered to be related with the rather strong detachment and attachment of the cyclone flow around the two hills. In addition, the mean and fluctuating wind velocities were found to be underestimated by at least 20% if the widely accepted IEC standard equations were utilized, suggesting the necessity to supplement the field test analysis in the standard for more reasonable wind resource evaluation within the Southeast China coastal area.

Wind resource modelling in complex terrain using different mesoscale–microscale coupling techniques

Wind resource evaluation in two sites located in Portugal was performed using the mesoscale modelling system Weather Research and Forecasting (WRF) and the wind resource analysis tool commonly used within the wind power industry, the Wind Atlas Analysis and Application Program (WAsP) microscale model. Wind measurement campaigns were conducted in the selected sites, allowing for a comparison between in situ measurements and simulated wind, in terms of flow characteristics and energy yields estimates.Three different methodologies were tested, aiming to provide an overview of the benefits and limitations of these methodologies for wind resource estimation. In the first methodology the mesoscale model acts like “virtual” wind measuring stations, where wind data was computed by WRF for both sites and inserted directly as input in WAsP. In the second approach, the same procedure was followed but here the terrain influences induced by the mesoscale model low resolution terrain data were removed from the simulated wind data. In the third methodology, the simulated wind data is extracted at the top of the planetary boundary layer height for both sites, aiming to assess if the use of geostrophic winds (which, by definition, are not influenced by the local terrain) can bring any improvement in the models performance.The obtained results for the abovementioned methodologies were compared with those resulting from in situ measurements, in terms of mean wind speed, Weibull probability density function parameters and production estimates, considering the installation of one wind turbine in each site. Results showed that the second tested approach is the one that produces values closest to the measured ones, and fairly acceptable deviations were found using this coupling technique in terms of estimated annual production. However, mesoscale output should not be used directly in wind farm sitting projects, mainly due to the mesoscale model terrain data poor resolution. Instead, the use of mesoscale output in microscale models should be seen as a valid alternative to in situ data mainly for preliminary wind resource assessments, although the application of mesoscale and microscale coupling in areas with complex topography should be done with extreme caution.

A Practical Approach in the CFD Simulation of Off-shore Wind Farms through the Actuator Disc Technique

In this work a practical approach to Computational Fluid Dynamics (CFD) simulations in wind resource evaluation is proposed in a test case of the IEA project (task 31) “Wakebench” focused on the benchmarking of wind wakes models. The proposed method uses an easy wake model, the Actuator Disc (AD), in a CFD approach, in order to understand the wind behavior in a complex wind farm of 18 turbines sited in the northern part of Netherlands, with a sustainable computational load. In order to optimize the simulation results a useful tool that automates the parameters evolution was developed; such tool is able to improve the control of the engineering parameters and is useful to prepare advanced post processing. The study was mainly focused on the analysis of the single wake; also simulations on the double wake case and other tests on larger wind farm were performed with success using the same automatic approach. Results are in quite good agreement with experimental data and the differences between the predicted and experimental results are to be addressed to: global effect of stability, turbine inferences in the actual wind farm and to some lacks in physical wake model.

The Reliability Evaluation Methods of the Wind Farm

The evaluation methods of wind farm in China are not perfect enough, and there are a few differences between analyze and evaluate. The reliability evaluation of wind resources and generated energy can improve wind resources evaluation level and estimating generated energy accurately. How to evaluate wind farm is the emphases. The paper brings forward the reliability analyze of the wind turbine, and the methods of the evaluation wind farm. The reliability evaluation could improve the generated efficiency and economic benefits.

Improving the Representation of Resolved and Unresolved Topographic Effects on Surface Wind in the WRF Model

AbstractThe Weather Research and Forecasting (WRF) model presents a high surface wind speed bias over plains and valleys that constitutes a limitation for the increasing use of the model for several applications. This study attempts to correct for this bias by parameterizing the effects that the unresolved topographic features exert over the momentum flux. The proposed parameterization is based on the concept of a momentum sink term and makes use of the standard deviation of the subgrid-scale orography as well as the Laplacian of the topographic field. Both the drag generated by the unresolved terrain and the possibility of an increase in the speed of the flow over the mountains and hills, where it is herein shown that WRF presents a low wind speed bias, are considered in the scheme. The surface wind simulation over a complex-terrain region that is located in the northeast of the Iberian Peninsula is improved with the inclusion of the new parameterization. In particular, the underestimation of the wind speed spatial variability resulting from the mentioned biases is corrected. The importance of selecting appropriate grid points to compare with observations is also examined. The wind speed from the nearest grid point is not always the most appropriate one for this comparison, nearby ones being more representative. The new scheme not only improves the climatological winds but also the intradiurnal variations at the mountains, over which the default WRF shows limitations in reproducing the observed wind behavior. Some advantages of the proposed formulation for wind-resource evaluation are also discussed.

Wind resource evaluation in six selected high altitude locations in Nigeria

This paper presents an assessment of wind energy potentials of six selected high altitude locations within the North-West and North-East geopolitical regions, Nigeria, by using 36-year (1971–2007) wind speed data subjected to 2-parameter Weibull distribution functions. The results showed that the maximum mean wind speed is obtained in Katsina as 9.839 m/s while the minimum value of 3.397 m/s is got in Kaduna for all the locations considered. The annual wind power density and energy variation based on the Weibull analysis ranged from 368.92 W/m 2 and 3224.45 kWh/m 2/year to 103.14 W/m 2 and 901.75 kWh/m 2/year in Kano and Potiskum for the maximum and minimum values respectively. Furthermore, Katsina and Kano will be suitable for wind turbine installations while Gusau will only be appropriate for wind energy utilization using taller wind turbine towers whereas Kaduna, Bauchi and Potiskum will be considered marginal for wind power development based of their respective annual mean wind speeds and power densities.

High-frequency field measurements and time-dependent computational modelling for wind turbine siting

Field measurements by cup anemometer at a sampling frequency of 1 Hz and computational modelling were used for characterisation of the wind conditions at a region of complex orography. Because the wind rose displayed low wind occurrences and high turbulence intensity for specific wind directions, spectral analysis of computational data was performed which showed the existence of preferred time scales for some wind directions, in agreement with spectral analysis of field data. Empirical orthogonal functions and frame by frame analysis of the time-dependent computational data showed that these time scales were related with a pair of vortices in the lee of a mountain. We concluded on the appropriateness of the methodology being used, which enabled the determination of these structures without reverting to the use of more complex and time consuming techniques. This study, initiated as part of a wind resource evaluation and possible installation of a wind farm, also proves the need for more detailed determination of the wind conditions, compared with the standard practice in wind turbine siting.

Evaluation of wind resource using numerically optimized data in the southwestern Korean Peninsula

The wind distribution over the Korean Peninsula was analyzed using numerically optimized wind data to reduce the uncertainties in estimating the wind resources. The simulated data were validated by a comparison with surface wind observations and three statistical indexes. According to the simulated surface winds, mesoscale circulation, such as land-sea breeze and mountain-valley winds affect the wind characteristics of the hub height at coastal and inland regions. However, the prevailing winds are strongly associated with the synoptic forcing at the island and mountainous regions, not the regional circulation. On the other hand, the atmospheric stability definitely affects the strength of the daytime and nocturnal wind speed at a hub height. Overall, there was a significant difference between the numerical and logarithmic method to estimate the wind energy at hub height. Moreover, the discrepancy in the wind density estimated using the two methods becomes clear over inland and mountainous areas.

Review of Methodologies for Offshore Wind Resource Assessment in European Seas

The wind resource offshore is generally larger than at geographically nearby onshore sites, which can offset the higher installation, operation and maintenance costs associated with offshore wind parks. Successful offshore wind energy development relies to some extent on accurate prediction of wind resources, but since installing and operating a meteorological mast in situ is expensive, prospective sites must be carefully evaluated. Accordingly, one can conceptualize the wind resource assessment process as a two-phase activity: (i) an evaluation of wind resources at the regional scale to locate promising wind farm sites and (ii) a site specific evaluation of wind climatology and vertical profiles of wind and atmospheric turbulence, in addition to an assessment of historical and possibly future changes due to climate non-stationarity. Phase (i) of the process can involve use of in situ observations of opportunity derived from ships, lighthouses and buoys in conjunction with model tools and remote sensing products. The reliability of such data sources has been extensively investigated in different national and European projects especially in Northern Europe, and the results are summarized herein. Phase (ii) of the project often still requires in situ observations (which may or may not be supplemented with ground-based remote sensing technologies) and application of tools to provide a climatological context for the resulting measurements. Current methodologies for undertaking these aspects of the resource assessment are reviewed.

Simulation and measurement procedures for effective isolated wind and hybrid system development in south Patagonia

This paper presents results of experience with simulation and measurement systems applied to local wind and hybrid (wind-diesel) isolated systems in south Patagonia, especially in Santa Cruz and Chubut provinces (Argentina) and the XII Region of Magallanes in Chile. Wind resource evaluation with a network of automatic loggers is discussed. Performance measurements include an integrated power curve evaluation system for small wind turbines. Some of the power, energy (early so-called SISMED systems) and commercial wind measurement systems have been operating in the region since 1999 or earlier, and their data provides important insight regarding best practices for sizing criteria in local wind and climate regimes. The data collected has been of value for validating simulations using NREL's free HOMER software. The more recent Small Wind Turbine – Power Curve Evaluation System (SWT-PCES) addresses the special requirements involved in power curve measurement for small wind turbines, and has been deployed for very low-power isolated systems in Chubut province (Argentina). Data and operational aspects from systems installed are shown and discussed.

The 44-year Mediterranean HIPOCAS wind database: A useful tool to analyse offshore extreme wind events from a long-term regional perspective

Nowadays, many efforts are leading to use the high potential offshore wind energy resources. A detailed assessment of the offshore wind resources arises as a first-rate requirement. Most of such assessment is based on extreme offshore wind atlas generated mainly from global reanalysis and satellite data. Both sort of data show certain shortcomings related, among others, to coarse spatial resolution and time inhomogeneity issues, respectively. This snag seems to be crucial over areas such as the Mediterranean Basin, which is characterized by a complex land–sea distribution and a significant orography. The HIPOCAS Mediterranean long-term (1958–2001) wind database comes to overcome the aforementioned reanalysis shortcoming and provides a Mediterranean wind data set useful to perform extreme wind analysis. This contribution also deals with a statistical extreme wind analysis over the whole Mediterranean offshore areas. Extreme return periods and levels are obtained from annual maxima using a number of distributions. Additionally, an alternative regional statistical method based on regional L-moment statistics is also proposed. The regional technique is applied to reduce uncertainty and allows a higher number of measurements to be included in the analysis, using data from a homogeneous region instead of from a single location. The herein performed extreme wind analysis provides a detailed assessment of high wind offshore areas over the Mediterranean and constitutes a subject of great interest for evaluation of wind resources.