Wind Shear Model Research Articles

Wind Shear Model Considering Atmospheric Stability to Improve Accuracy of Wind Resource Assessment

An accurate wind shear model is an important prerequisite in extrapolating the wind resource from lower heights to the increasing hub height of wind turbines. Based on the 1-year dataset (collected in 2014) consisting of 15-minute intervals collected at heights of 2, 10, 50, 100, and 150 m on an anemometer tower in northern China, the present study focuses on the time-varying relationship between the wind shear coefficient (WSC) and atmospheric stability and proposes a wind shear model considering atmospheric stability. Through the relationship between Monin–Obukhov (M-O) length and gradient Richardson number, the M-O length is directly calculated by wind data, and the WSC is calculated by combining the Panofsky and Dutton (PD) models, which enhances the engineering practicability of the model. Then, the performance of the model is quantified and compared with two alternative methods: the use of annual average WSC and the use of stability change WSC extrapolation. The analysis demonstrates that the proposed model outperforms the other approaches in terms of normal root mean square error (NRMSE) and normal bias (NB). More specifically, this method reduces the NRMSE and NB by 24–29% and 76–95%, respectively. Meanwhile, it reaches the highest extrapolation accuracy under unstable and stable atmospheric conditions. The results are verified using the Weibull distribution.

Wind power in forested regions: Power law extrapolation vs. lidar observation

As the increasing hub height of modern wind turbine, wind shear model is generally adopted as a useful tool to extrapolate wind speed available to higher levels for wind power assessment. This paper conducts a data-driven study to examine the power law model in assessing the wind power in forested regions featured with seasonally-varied roughness. Specifically, wind speeds are observed using a laser lidar mounted in forested regions in the northeast of China, ranging from 80 m to 200 m with a constant interval of 20 m. Subsequently, comparisons are made between the wind profiles established based on the power law model and field observations. The exponents used include the empirical exponents and the fitted exponents, the former are derived from the standard codes, and the latter are fitted based on the seasonal and annual data collections. Results indicate that the power law model is unable to fully capture the vertical distribution of wind speed in forested regions, it is the exponent that plays a decisive role influencing the reliability representing the real wind profile. Compared with the empirical exponents, the seasonally-fitted exponents exhibits much better suitability for wind speed extrapolation in forested regions, as well as for the wind power assessment.

Review on Wind Resistance for Quadrotor UAVs: Modeling and Controller Design

Micro-Unmanned Air Vehicles (Micro-UAVs), especially quadrotor UAVs, have been widely used in recent years because of their simple structure and convenient operation. However, due to under-actuated and strongly-coupled characteristics, their flight performance is not perfect when suffering external uncertainty such as wind disturbance. Therefore, in this paper, the literature is reviewed related to wind acting on UAVs and makes some conclusions. First, we review the wind field model of quadrotor operation and decompose it into wind turbulent model, wind shear model, and other typical wind field models. Then we focus on the mathematic model of wind disturbance on UAVs and divide it into effect on rotors and effect on the fuselage. Finally, various control laws are used to study the wind resistance of quadrotors. We review the promising works which have been done before and determine the research emphasis to be focused on in the future.

Characterisation of the Vertical Wind Profile According to the Stability Classes of the Atmosphere in Conakry, Guinea

The characteristics of the vertical wind profile and the wind potential study on the Conakry site for each atmospheric stability class were investigated in this study. Wind speed and air temperature data recorded over the period from January 2001 to December 2019 at 10 m and 50 m above the ground at daily (50 m) and hourly (10 m) scales were used. The wind shear parameters were determined from the logarithmic and power law. Based on the Newman and Klein wind shear model, a new formulation of this parameter was proposed as a function of the Obukhov length at order 2 and calibrated from the measurements using the simplex algorithm of Nelder and Mead. From the Weibull parameters obtained for the stable and unstable period of the atmosphere, the available wind potential at Conakry was estimated from 10 m to 80 m. The results indicate that the annual average of the ground roughness length is 1.7 x 10-2 m. The annual average of the ground friction velocity is 0.19 m.s-1. The atmosphere remains stable at the Conakry site from 09 p.m. to 10 a.m. and unstable from 10 a.m. to 09 p.m. The proposed wind shear formulation gives a better estimation of the wind speed in function of altitude with the lowest values of RMSE and MAE (4.5x10-4 ; 3.8x10-4) m.s-1 in stable and unstable periods (0.09 ; 0.07) m.s-1 compared to some models found in the literature. The mean annual wind shear coefficient in stable period is 0.26 and in unstable period 0.28. The annual mean shape parameter from 10 m to 80 m above ground in stable period is between 1.25 and 1.64, and during unstable period, it varies from 1.55 to 2.07. The annual mean scale parameter at 10 m and 80 m above ground is (3.9; 7.10) m.s-1 (unstable atmosphere) and (2.45; 4.41) m.s-1 when the atmosphere is stable. The annual average of the energy production under a convective atmosphere at 10 m and 80 m is estimated at 72 W.m-2 and 301 W.m-2 respectively. During the night cycle, this annual production varies from 28 W.m-2 (10 m) to 93 W.m-2 (80 m). Based on these results, the Conakry site is suitable to host medium-sized wind power plants for electricity and water production.

INFLUENCE OF WIND SHEAR ON AERODYNAMIC CHARACTERISTICS AND WAKE SHAPE OF WIND TURBINE BLADES

A wind turbine usually operates in unsteady conditions, and the aerodynamic performance and wake of the rotor will change with the change of working conditions. Wind shear is the most common and long-term environment of wind turbine. It often affects the aerodynamic load, the shape of the wake and the overall performance of the wind turbine. So it is important to analyze the aerodynamic performance of blade of the wind turbine under the wind shear condition. In this paper, a time-marching free vortex wake method, which coupled with the wind shear model, is used to calculate the aerodynamic coefficient, thrust and wake shape change under different wind shear factors. At the same time, the influence of the wake shape variation on the induced velocity of the rotor rotating plane and the aerodynamic performance of the wind turbine blade are studied. The results show that: under the condition of wind shear inflow, with the increase of the wind shear factor, the fluctuation amplitude of aerodynamic coefficient of the wind turbine, which fluctuates periodically with time is increased, the average thrust decreases gradually, the tilted degree of wake increases and the tilted degree of wake under the center of hub is more obvious. The distortion of wake shape makes the distribution of the axial induced velocity factor in the rotational plane uneven, and makes the overall performance of wind turbine decrease and deviate greatly. There is a distinct difference of the induced effect on the rotational plane between the tilted wake and the symmetrical wake. The fluctuation amplitude of the aerodynamic coefficient induced by the tilted wake is larger than that induced by the symmetrical wake, and the deviation of the wave trough is more obvious than the wave crest. The more tilted the wake is, the more obvious the load asymmetry in the rotating plane is.

Wind speed analysis based on the logarithmic wind shear model: a case study for some brazilian cities

The wind power’ share in electricity generating capacity has increased significantly in recent years. Due to the variability in wind power generation, given the variations in wind speed and considering the increase in wind participation in the Brazilian energy matrix, a fact that reinforces the relevance of the source, this article aims to present the methods used to analyze the wind speed more used in the literature and to analyze the wind speed in several Brazilian cities. The logarithmic wind shear model was used to analyze mean wind speeds based on historical data of twelve Brazilian cities available to the public on the ESRL database for a period of eight years 2010 to 2018. The study showed that in localities such as Uruguaiana/RS, Campo Grande/MS, Uberlândia/MG, São Luiz/MA and Corumba/MS, mean wind speeds are strong in all altitudes of reference, with a gain of ± 2m/s of wind speed as the operational altitude increases. The logarithmic wind gain in high altitudes or low altitudes can be seen in z = 100 meters, where the mean wind speed found was Wn ≈ 8 m/s in Uruguaiana/RS and Campo Grande/MS, whereas in Manaus it was Wn ≈ 5 m/s. In Porto Alegre (RS), Florianópolis (SC), Curitiba/PR and Brasília/DF, the mean wind speed in altitudes ≥ 250 m becomes significant, allowing the implementation of wind farms if the technology proves to be economically feasible.

Load Calculation and Performance Analysis of Mega-MW Wind Turbine Based on Cloud Edge Computing

With the continuous development of megawatt-scale wind turbines, the impact of bladevibration on the dynamic stability and vibration of wind turbines cannot be ignored. However,there is currently no method capable of effectively analyzing the load and performance ofwind turbines. In order to improve the load calculation accuracy and performance of windturbines, this paper selects small base stations (SBS) as the research object of cloud edgecomputing, and explores the load analysis and performance analysis of megawatt-scale windturbines. In this paper, wind shear model, turbulence model, blade icing model andaerodynamic model of blades under icing conditions are established, and the effect of icing onthe dynamic load of blades of megawatt wind turbines is explored. It was found that the icinghad the greatest effect on the load in the direction of the blade array, followed by the load inthe swing direction, and the least in the torsional direction. In this paper, a load analysis isperformed on the blades of a megawatt wind turbine. When the blade speed increases, thefirst-order modal frequency deviation coefficient changes from -1.28% to 52.09%, and thethird-order modal frequency deviation coefficient changes from -0.77% to 48.67%. The speedof the wind wheel has a great influence on the first and third-order vibration frequencies of theblades of the wind turbine, but it does not have a great influence on the vibration frequenciesof the other steps.

Effect of atmospheric stability on the wind resource extrapolating models for large capacity wind turbines: a comparative analysis of power law, log law, Deaves and Harris model

Abstract To observe certain wind climate from the available met mast measured wind data at different heights an accurate wind shear model is necessary. Since WAsP and windPRO is software package which provides the better representation of wind profile over homogeneous terrain only. Though, a separate module named as WAsP CFD has been added in both of the software to predict correct wind resource in complex terrain also. Nowadays wind resource assessment has been widely dependent on terrain and becomes a key issue for the researchers. It has been found experimentally from earlier work that Deaves and Harris model shows a better representation of wind profiles on flat terrain at higher heights in comparison to other models such as the PL (power law), the LogL (log law) and the LogLL (Log-linear law). This study presents a comparative analysis of three different wind extrapolation models. Based on 2 year measured wind data from the met mast the at 10 m, 50 m, 80 m, 100 m and 102 m heights, results were compared in different stability classes using Monin-Obukhuv similarity theory. The RMSE (root mean square error) and NRMSE (normalized root mean square error were found to be least in case of log linear model which is 0.11 and 0.01784 respectively in compare to the PL and Deaves and Harris models.

Review of dynamic soaring: technical aspects, nonlinear modeling perspectives and future directions

In this paper, we present a comprehensive and detailed review of dynamic soaring process, and in particular, its application to unmanned aerial vehicles (UAVs). We start by explaining the biological inspiration that comes from soaring birds and how researchers have tried to utilize the dynamic soaring phenomenon/maneuver and apply it to UAVs. We present and discuss the fundamentals of wind shear models in both the linear and nonlinear cases. Moreover, a comprehensive parametric characterization of the key performance parameters for the dynamic soaring maneuver is given. Numerical methods for nonlinear trajectory optimization are summarized and methodologies capable of generating rapid solutions suitable for real-time implementation, are presented. Additionally, the paper introduces mathematical modeling and procedure to generate the optimized dynamic soaring trajectory. Through this paper, a consolidated platform is built, which not only covers technical aspects of advancements made over the passage of time, but also identifies and discusses the existing challenges. These challenges which are encountered by UAVs curtail the potential utility of dynamic soaring. Integrating dynamic soaring with morphology and inclusion of nonlinear control theory in the flight control system are introduced as a possible future research directions that may overcome the existing limitations.

Use of spatio-temporal calibrated wind shear model to improve accuracy of wind resource assessment

Wind shear models are commonly used to predict the wind speed at wind turbine hub heights from the wind data collected at the elevation of the monitoring station. In many cases, the model parameters are based on empirical values recommended by design specifications that reflect the site conditions. This paper evaluates the benefits of incorporating site-specific wind data to calibrate the wind shear model parameters. Wind speed data collected by a ZephIR® Light Detection and Ranging (LiDAR) system over a 2-year (Oct. 2010–Sept. 2012) period are used for the analyses. The atmospheric stability is found to have appreciable effects on the wind shear parameters, i.e. wind shear coefficients (WSC) for the power law model and roughness lengths for the logarithmic law wind shear models. The calibrated wind shear model parameters by the monitored wind data during the first year are presented in the format of a contour map to demonstrate the spatio-temporal variations, which shows daily and seasonal variations. The calibrated wind shear models are then validated by the wind data collected during the second year, which demonstrates decent performance. The accuracy and performance of incorporating site-specific wind shear model calibration to predict the wind energy resource is evaluated, where six different methods are compared. The results show that the consideration of spatio-temporal variations of wind shear model parameters achieved improve performance over the application of the empirical or yearly-averaged wind shear model parameters in extrapolating the wind speed. It is also found that the performance of considering spatio-temporal wind shear parameters are even better at higher elevations. Furthermore, the analyses find that the use of empirical wind shear model parameters underestimates the wind energy output at the studied sites. Site-specific calibration of the wind shear models could further improve the accuracy of wind energy assessment by considering the site condition and the variability in the atmospheric stability.

Comparative study of wind speed extrapolation methods for sites with different roughness

An accurate wind shear model is crucial to extrapolate the observed wind resource from the available lower heights to the steadily increasing hub height of modern wind turbines. That is why several studies have been made to determine the best suited formula for wind speed extrapolation. This work is aimed at preceding the research issue addressed within a previous study, where some extrapolation models were tested and compared by extrapolating the energy resources at different heights. In this context, this paper deals with the assessment of several wind speed extrapolation laws by comparing the analytical results obtained with real data for three different meteorological. The comparison has led to the following results: for an extremely roughs site, the one seven law is a very efficient law for the extrapolation of the wind speed and Weibull parameters of reference altitude at higher altitudes, for a site of average roughness, the modified power law 2 is recommended for the best extrapolation. The logarithmic power law provides a good level of accuracy for a site of mild roughness.

Power fluctuation and power loss of wind turbines due to wind shear and tower shadow

The magnitude and stability of power output are two key indices of wind turbines. This study investigates the effects of wind shear and tower shadow on power output in terms of power fluctuation and power loss to estimate the capacity and quality of the power generated by a wind turbine. First, wind speed models, particularly the wind shear model and the tower shadow model, are described in detail. The widely accepted tower shadow model is modified in view of the cone-shaped towers of modern large-scale wind turbines. Power fluctuation and power loss due to wind shear and tower shadow are analyzed by performing theoretical calculations and case analysis within the framework of a modified version of blade element momentum theory. Results indicate that power fluctuation is mainly caused by tower shadow, whereas power loss is primarily induced by wind shear. Under steady wind conditions, power loss can be divided into wind farm loss and rotor loss. Wind farm loss is constant at 3α(3α–1)R2/(8H2). By contrast, rotor loss is strongly influenced by the wind turbine control strategies and wind speed. That is, when the wind speed is measured in a region where a variable-speed controller works, the rotor loss stabilizes around zero, but when the wind speed is measured in a region where the blade pitch controller works, the rotor loss increases as the wind speed intensifies. The results of this study can serve as a reference for accurate power estimation and strategy development to mitigate the fluctuations in aerodynamic loads and power output due to wind shear and tower shadow.

Comparative study of wind speed extrapolation methods for sites with different roughness

An accurate wind shear model is crucial to extrapolate the observed wind resource from the available lower heights to the steadily increasing hub height of modern wind turbines. That is why several studies have been made to determine the best suited formula for wind speed extrapolation. This work is aimed at preceding the research issue addressed within a previous study, where some extrapolation models were tested and compared by extrapolating the energy resources at different heights. In this context, this paper deals with the assessment of several wind speed extrapolation laws by comparing the analytical results obtained with real data for three different meteorological. The comparison has led to the following results: for an extremely roughs site, the one seven law is a very efficient law for the extrapolation of the wind speed and Weibull parameters of reference altitude at higher altitudes, for a site of average roughness, the modified power law 2 is recommended for the best extrapolation. The logarithmic power law provides a good level of accuracy for a site of mild roughness.

Extending the diabatic surface layer wind shear profile for offshore wind energy

In this research the diabatic surface layer wind shear model is extended for offshore wind energy purposes to higher altitudes based on Gryning's wind profile and the resistance functions proposed by Byun. The wind profile is in theory applicable up to the boundary layer height, which is parametrized with the Rossby-Montgommery equation. The coefficient c of the Rossby-Montgommery equation is found to be stability dependent with decreasing values up to 0.04 for stable conditions and increasing values up to 0.17 for unstable conditions. The proposed shear profile has been validated with 1 year of offshore observation data, and a significant improvement in accuracy is found compared to traditional surface layer shear profiles or power laws. The influence of adopting this extended shear profile for wind energy is analysed in terms of the kinetic energy flux and blade root fatigue loads experienced by a wind turbine. It is found that, especially for stable conditions, results deviate significantly compared to using the traditional surface layer shear profile. The kinetic energy flux decreases by up to 15%.

Estimating atmospheric stability from observations and correcting wind shear models accordingly

Atmospheric stability strongly influences wind shear and thus has to be considered when performing load calculations for wind turbine design. Numerous methods exist however for obtaining stability in terms of the Obukhov length L as well as for correcting the logarithmic wind profile. It is therefore questioned to what extend the choice of adopted methods influences results when performing load analyses. Four methods found in literature for obtaining L, and five methods to correct the logarithmic wind profile for stability are included in the analyses (two for unstable, three for stable conditions). The four methods used to estimate stability from observations result in different PDF's of L, which in turn results in differences in estimated lifetime fatigue loads up to 81%. For unstable conditions hardly any differences are found when using either of the proposed stability correction functions, neither in wind shear nor in fatigue loads. For stable conditions however the proposed stability correction functions differ significantly, and the standard correction for stable conditions might strongly overestimate fatigue loads caused by wind shear (up to 15% differences). Due to the large differences found, it is recommended to carefully choose how to obtain stability and correct wind shear models accordingly.

Model of wind shear conditional on turbulence and its impact on wind turbine loads

AbstractWe analyse high‐frequency wind velocity measurements from two test stations over a period of several years and at heights ranging from 60 to 200 m, with the objective to validate wind shear predictions as used in load simulations for wind turbine design. A validated wind shear model is thereby proposed for flat terrain and that can significantly decrease the uncertainty associated with fatigue load predictions for wind turbines with large rotors. An essential contribution is the conditioning of wind shear on the 90% quantile of wind turbulence, such that the appropriate magnitude of the design fatigue load is achieved. The proposed wind shear model based on the wind measurements is thereby probabilistic in definition, with shear jointly distributed with wind turbulence. A simplified model for the wind shear exponent is further derived from the full stochastic model. The fatigue loads over different turbine components are evaluated under the full wind measurements, using the developed wind shear model and with standard wind conditions prescribed in the IEC 61400‐1 ed. 3. The results display the effect of the Wöhler exponent and reveal that under moderate turbulence, the effect of wind shear is most pronounced on the blade flap loads. It is further shown that under moderate wind turbulence, the wind shear exponents may be over‐specified in the design standards, and a reduction of wind shear exponent based on the present measurements can contribute to reduced fatigue damage equivalent loads on turbine blades. Although the influence of wind shear on extreme loads was found to be negligible, the IEC 61400‐1 wind shear definition was found to result in non‐conservative estimates of the 50 year extreme blade deflection toward the tower, especially under extreme turbulence conditions. Copyright © 2014 John Wiley & Sons, Ltd.

Predictive Controller for Aircraft Landing under Wind Shear

Low altitude wind shear badly threatens aircrafts’ flight safety. Since flight states change rapidly during flying through wind shear, it is deficient to design an optimization controller by off-line analyse. A ring-vortex microburst wind shear model and B747 aircraft flight dynamics model were built. For glide slope tracking under wind shear, an off-line controller was designed by linear quadratic method. Furthermore, a model predictive controller with sequential optimization was designed. Simulation results show the on-line sequential optimization controller possess better tracking performance.

On the Structure and Adjustment of Inversion-Capped Neutral Atmospheric Boundary-Layer Flows: Large-Eddy Simulation Study

A range of large-eddy simulations, with differing free atmosphere stratification and zero or slightly positive surface heat flux, is investigated to improve understanding of the neutral and near-neutral, inversion-capped, horizontally homogeneous, barotropic atmospheric boundary layer with emphasis on the upper region. We find that an adjustment time of at least 16 h is needed for the simulated flow to reach a quasi-steady state. The boundary layer continues to grow, but at a slow rate that changes little after 8 h of simulation time. A common feature of the neutral simulations is the development of a super-geostrophic jet near the top of the boundary layer. The analytical wind-shear models included do not account for such a jet, and the best agreement with simulated wind shear is seen in cases with weak stratification above the boundary layer. Increasing the surface heat flux decreases the magnitude and vertical extent of the jet and leads to better agreement between analytical and simulated wind-speed profiles. Over a range of different inversion strengths and surface heat fluxes, we also find good agreement between the performed simulations and models of the equilibrium boundary-layer height, and of the budget of turbulent kinetic energy integrated across the boundary layer.

EVALUATION OF THE ADEQUACY OF THE WIND SPEED EXTRAPOLATION LAWS FOR TWO DIFFERENT ROUGHNESS METEOROLOGICAL SITES

Increasing knowledge on wind shear models to strengthen their reliability appears as a crucial issue, markedly for energy investors to accurately predict the average wind speed at different turbine hub heights and thus the expected wind energy output. T his is particularly helpful during the feasibility study to abate the costs of a wind power project. The ext rapolation laws were found to provide the finest representation of the wind speed according to heigh ts, thus avoiding installation of tall towers, or e ven more expensive devices such as LIDAR or SODAR. The proposed models are based on theories that determine the vertical wind profile from implicit r elationships . However, these empirical extrapolation formulas have been developed for specific meteorolo gical conditions and appropriate sites for wind turbines; reason that several studies have been mad e by various authors to determine the best suited formula to their own conditions. This study is aime d at proceeding the research issue addressed within a previous study, where some extrapolation models were tested and compared by extrapolating the energy resources at different heights. However, comparable results are returned by the power law and the log law which indeed proved to be preferable. In this c ontext, this study deals the assessment of several wind speed extrapolation laws (six laws), by comparing t he analytical results obtained with real data for t wo different meteorological Sites, different roughness , different altitudes and different measurement per iods. The first site studied is an extremely rough site w ith daily measurements of March 2007, wind speed measurements are available at four different height s of Gantour/Gao site, obtained by the water, energ y and environment company Senegal. The second site studied is a feeble rough site with monthly measurements for 2005, wind speed measurements are available at three different heights of Kuujjuarapi k Site obtained by Hydro-Quebec Energy Helimax Canada. The study aims to determine the effectiveness and concordance between the extrapolation laws and the real measured data. The results show that the adjusted law is efficiently adequate for an extreme ly rough site and the modified laws with two other laws are efficiently adequate for a feeble rough si te. The experimental results and numerical calculat ions exploited for the evaluation of the Weibull paramet ers fall the shape factors k greater than 9. The increase in altitude often causes an increase in the Weibull parameters values, however, our results show that the shape factor k can take lower values to those estab lished in the reference altitude.

Extrapolating wind speed time series vs. Weibull distribution to assess wind resource to the turbine hub height: A case study on coastal location in Southern Italy

Increasing knowledge on wind shear models to strengthen their reliability appears as a crucial issue, markedly for energy investors to accurately predict the average wind speed at different turbine hub heights, and thus the expected wind energy output. This is particularly helpful during the feasibility study to abate the costs of a wind power project, thus avoiding installation of tall towers, or even more expensive devices such as LIDAR or SODAR.The power law (PL) was found to provide the finest representation of wind speed profiles and is hence the focus of the present study. Besides commonly used for vertical extrapolation of wind speed time series, the PL relationship between “instantaneous” wind profiles was demonstrated by Justus and Mikhail to be consistent with the height variation of Weibull distribution. Therefore, in this work a comparison is performed between these two different PL–based extrapolation approaches to assess wind resource to the turbine hub height: (i) extrapolation of wind speed time series, and (ii) extrapolation of Weibull wind speed distribution. The models developed by Smedman–Högström and Högström (SH), and Panofsky and Dutton (PD) were used to approach (i), while those from Justus and Mikhail (JM) and Spera and Richards (SR) to approach (ii). Models skill in estimating wind shear coefficient was also assessed and compared.PL extrapolation models have been tested over a flat and rough location in Apulia region (Southern Italy), where the role played by atmospheric stability and surface roughness, along with their variability with time and wind characteristics, has been also investigated. A 3-year (1998–2000) 1–h dataset, including wind measurements at 10 and 50 m, has been used. Based on 10–m wind speed observations, the computation of 50–m extrapolated wind resource, Weibull distribution and energy yield has been made. This work is aimed at proceeding the research issue addressed within a previous study, where PL extrapolation models were tested and compared in extrapolating wind resource and energy yield from 10 to 100 m over a complex–topography and smooth coastal site in Tuscany region (Central Italy). As a result, wind speed time series extrapolating models proved to be the most skilful, particularly PD, based on the similarity theory and thus addressing all stability conditions. However, comparable results are returned by the empirical JM Weibull distribution extrapolating model, which indeed proved to be preferable as being: (i) far easier to be used, as z0–, stability–, and wind speed time series independent; (ii) more conservative, as wind energy is underpredicted rather than overpredicted.