The influence of non‐logarithmic wind speed profiles on potential power output at Danish offshore sites

Motta, Maurizio; Barthelmie, R.J.; Vølund, P.

doi:10.1002/we.146

Cited by 102 publications

(108 citation statements)

References 12 publications

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“…less than 15 m s -1 ), non-neutral atmospheric stability is prevailing as well. [2] It is, therefore, important to include atmospheric stability in wind turbine simulations involving loads and annual energy production.…”

Section: Introductionmentioning

confidence: 99%

A new k‐epsilon model consistent with Monin–Obukhov similarity theory

2016

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A new k-ε model is introduced that is consistent with Monin-Obukhov similarity theory (MOST). The proposed k-ε model is compared with another k-ε model that was developed in an attempt to maintain inlet profiles compatible with MOST. It is shown that the previous k-ε model is not consistent with MOST for unstable conditions, while the proposed k-ε model can maintain MOST inlet profiles over distances of 50 km.

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Section: Introductionmentioning

confidence: 99%

A new k‐epsilon model consistent with Monin–Obukhov similarity theory

2016

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“…Moreover, as shown by Motta et al (2005), the diurnal and seasonal variation of the static stability depends on the upwind surface, e.g. offshore or onshore wind.…”

Section: Static Stability Of the Ablmentioning

confidence: 99%

Accounting for the speed shear in wind turbine power performance measurement

Wagner¹,

Courtney²,

Gottschall³

et al. 2011

Wind Energy

146

109

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Abstract:The power curve of a wind turbine is the primary characteristic of the machine as it is the basis of the warranty for it power production. The current IEC standard for power performance measurement only requires the measurement of the wind speed at hub height and the air density to characterise the wind field in front of the turbine. However, with the growing size of the turbine rotors during the last years, the effect of the variations of the wind speed within the swept rotor area, and therefore of the power output, cannot be ignored any longer. Primary effects on the power performance are from the vertical wind shear and the turbulence intensity. The work presented in this thesis consists of the description and the investigation of a simple method to account for the wind speed shear in the power performance measurement. Ignoring this effect was shown to result in a power curve dependant on the shear condition, therefore on the season and the site. It was then proposed to use an equivalent wind speed accounting for the whole speed profile in front of the turbine. The method was first tested with aerodynamic simulations of a multi-megawatt wind turbine which demonstrated the decrease of the scatter in the power curve. A power curve defined in terms of this equivalent wind speed would be less dependant on the shear than the standard power curve. The equivalent wind speed method was then experimentally validated with lidar measurements. Two equivalent wind speed definitions were considered both resulting in the reduction of the scatter in the power curve. As a lidar wind profiler can measure the wind speed at several heights within the rotor span, the wind speed profile is described with more accuracy than with the power law model. The equivalent wind speed derived from measurements, including at least one measurement above hub height, resulted in a smaller scatter in the power curve than the equivalent wind speed derived from profiles extrapolated from measurements at hub height and below only. It is well established that the turbulence intensity also influences the power performance of a wind turbine. Two ways of accounting for the turbulence were tested with the experimental data: an adaptation of the equivalent wind speed so that it also accounts for the turbulence intensity and the combination of the equivalent wind speed accounting for the wind shear only with the turbulence normalising method for turbulence intensity suggested by Albers. The second method was found to be more suitable for normalising the power curve for the turbulence intensity. Using the equivalent wind speed accounting for the wind shear in the power performance measurement was shown to result in a more repeatable power curve than the standard power curve and hence, in a better annual energy production estimation. Furthermore, the decrease of the scatter in the power curve corresponds to a decrease of the category A uncertainty in power, resulting in a smaller uncertainty in estimated AEP.The thesis is submitted to the Danish Tec...

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“…The k value can best be estimated by using the approximate relationship for (14) as given by Justus and Mikhail [17], that is:…”

Section: Weibull Distribution Parameter Extrapolationmentioning

confidence: 99%

“…Wind speed extrapolation might be regarded as one of the most critical uncertainty factor affecting the wind power assessment, when considering the increasing size of modern multi-MW wind turbines. If the wind speed measurements at heights relevant to wind energy exploitation lacks, it is often necessary to extrapolate observed wind speeds from the available heights to turbine hub height [1], which causes some critical errors between estimated and actual energy output, if the wind shear coefficient, n, cannot be determined correctly. The difference between the predicted and observed wind energy production might be up to 40%, due to turbulence effects, time interval of wind data measurement, and the extrapolation of the data from reference height to hub heights [2].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Wind Velocity Vertical Extrapolation by Extended Power Law

Şen

Altunkaynak

Erdik

2012

Advances in Meteorology

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Wind energy gains more attention day by day as one of the clean renewable energy resources. We predicted wind speed vertical extrapolation by using extended power law. In this study, an extended vertical wind velocity extrapolation formulation is derived on the basis of perturbation theory by considering power law and Weibull wind speed probability distribution function. In the proposed methodology not only the mean values of the wind speeds at different elevations but also their standard deviations and the cross-correlation coefficient between different elevations are taken into consideration. The application of the presented methodology is performed for wind speed measurements at Karaburun/Istanbul, Turkey. At this location, hourly wind speed measurements are available for three different heights above the earth surface.

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The influence of non‐logarithmic wind speed profiles on potential power output at Danish offshore sites

Cited by 102 publications

References 12 publications

A new k‐epsilon model consistent with Monin–Obukhov similarity theory

A new k‐epsilon model consistent with Monin–Obukhov similarity theory

Accounting for the speed shear in wind turbine power performance measurement

Wind Velocity Vertical Extrapolation by Extended Power Law

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