Definition of the Subject
The utilization of wind energy requires an ability to assess the wind conditions with a high degree of certainty, being paramount for obtaining low risks and high reliability in wind energy project planning. This in turn requires a profound understanding of how atmospheric motions affect the use of wind energy: From the design and operation of the turbines to the spatial integrated renewable energy systems, say, from the dynamic inflow conditions at the turbine rotor to regional resource assessments. The activities necessary for solving the inherent problems in making use of the kinetic energy available in air that passes through the rotor of a large wind turbine during normal operation – or – respectively minimize the problems, has required a huge effort on analytical formulations, experimental activities, and the...
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Abbreviations
- Atmospheric boundary layer (ABL):
-
Also known as planetary boundary layer (PBL), it is the bottom layer of the atmosphere that is in contact with the surface of the Earth. It extends from 100 m or less in a clear nighttime condition to more the 2 km on a convective sunny day.
- Atmospheric surface layer:
-
The atmospheric layer closest to the ground up to 50–100 m and where the pressure and Coriolis forces can be neglected in the parameterization of meteorological variables such as the wind profile. The fluxes of the momentum and heat are nearly constant with height.
- CFD models:
-
Computational Fluid Dynamics models which are mainly used for engineering purposes such as aerodynamic calculations for the flow around a wind turbine blade. They are currently being developed for use for wind studies in very complicated topography.
- Climatology:
-
The average weather experienced at a place in the course of some chosen run of years.
- Coriolis force:
-
As air moves from high to low pressure in the northern hemisphere, it is deflected to the right by the Coriolis force. In the southern hemisphere, air moving from high to low pressure is deflected to the left by the Coriolis force. The Coriolis force is caused by the rotation of the Earth.
- Downscaling methods:
-
The concept of downscaling large-scale analysis and forecasts of weather and climate, such that small-scale features are estimated based on input about large-scale structures of the atmosphere. Two concepts are used: dynamical and statistical.
- Dynamic downscaling:
-
Use of mesoscale meteorological models to generate high-resolution climate statistics for a specific region and period of time based on, for example, the Global data archive.
- Dynamic statistical downscaling:
-
Use of mesoscale meteorological models to generate high-resolution climate statistics for a specific region and period of time based on a selected number of weather situations from, for example, the Global data archive.
- Geostrophic wind:
-
The wind which is in balance between the pressure and the Coriolis forces. It is often close to the wind observed above the PBL by radiosondes and can be calculated from surface pressure measurements.
- Global data archive:
-
Global or near-global covering climatological and topographic data.
- Hub height:
-
Height above the ground at the center of the rotor – usually the same as the tower height.
- IEC 61400–1:
-
International Standard published by the International Electrotechnical Commission. The Standard specifies essential design requirements to ensure the engineering integrity of wind turbines. Its purpose is to provide an appropriate level of protection against damage from all hazards during the planned lifetime.
- Lib files:
-
Tables of the two Weibull parameters given for a number of wind direction sectors, heights above ground and terrain roughness classes used in the wind atlas methodology.
- Lidar:
-
Light detection and ranging. Wind measurement device based on laser – Doppler technology.
- Mesoscale model:
-
Numerical meteorological models based on the full set of dynamical fluid equations usually covering a region of a few hundred of kilometers and a grid resolution of 2–10 km. An example is the PSU/NCAR mesoscale model (known as MM5) which is a limited-area, nonhydrostatic, terrain-following sigma-coordinate model designed to simulate or predict mesoscale atmospheric circulation.
- Microscale model:
-
Numerical flow models that can be based on the dynamical fluid equations, for example, CFD models or be based on a linearized version of the fluid equations. An example of a linearized flow model is the BZ (Bessel-zooming-grid) model in WAsP.
- Orography:
-
The height variations of a terrain.
- Power curve:
-
Gives the relationship between the net power output of a wind turbine and the wind speed measured at hub height averaged over 10 min.
- Reanalysis dataset (Global Data):
-
Time series of the large-scale meteorological situation covering decades. These datasets have been created by assimilating measurement data from around the globe in a dynamical consistent fashion using large-scale numerical models. The primary purpose for the generation of the dataset is to provide a reference for the state of the atmosphere and to identify any features of climate change. For wind energy, the application of the dataset is as a long-term record of large-scale wind conditions.
- Reference wind:
-
Usually the extreme 10-min average wind speed with a recurrence period of 50 years at turbine hub height. Used in IEC 61400–1 [1] together with the turbulence intensity to define classes for structural loading calculations.
- Regional resource assessment:
-
Regional resource assessment of wind energy resources means estimating the potential output from a large number of wind turbines distributed over a region. Ideally, this results in detailed, high-resolution, and accurate resource maps, showing the wind resource (yearly and seasonal), the wind resource uncertainty, and areas of enhanced turbulence.
- Roughness length:
-
The roughness of a terrains commonly parameterized by a length scale called the roughness length. For the logarithmic wind profile, it is the height where the wind is zero.
- Siting:
-
Siting is a process that includes estimating the mean power produced by specific wind turbines at one or more specific locations. Proper siting of wind turbines with respect to the wind resource requires proper methods for calculating the wind resource, the turbulence conditions, the extreme wind conditions, and the effects of rotor wakes.
- The wind atlas method:
-
The conventional method used to produce estimates of wind resource on national scales is to analyze wind measurements made at a number of sites around the country as in, for example, the European Wind Atlas [2]. In order for this method to work there needs to be a sufficient quantity of high quality data, covering the country.
- Topography:
-
The description of shapes and features of the Earth’s surface such as orography, land cover, and buildup areas (especially their depiction in maps).
- Turbulence:
-
The fast variations of the wind vector in all three directions: longitudinal, lateral, and vertical.
- Turbulence intensity:
-
The ratio between the mean horizontal wind and the standard deviation of the turbulence fluctuations usually measured over a period of 10 min.
- WAsP:
-
Wind Atlas Analysis and Application Program. Commonly used computer program for siting and regional resource assessment. Developed for the European Wind Atlas.
- Weibull probability density function:
-
Two-parameter probability density function which very often fits measured wind speed observations well. Is determined by the scale parameter A, which is close to the mean value and the shape parameter k. For k = 1 the function is Exponential for k = 2 it is the Rayleigh distribution and for k = 3 it is close to the Gaussian distribution.
- WENE-048 predictions:
-
Prediction of the power output from a wind farm hours and days ahead. This term is treated in a separate chapter.
- Wind profile:
-
The increase of the wind speed (horizontal component of the wind vector) above terrain. In strong wind in an overcast situation (called thermally neutral conditions), it follows a logarithmic law in the lowest 50–100 m. It deviates from the logarithmic when thermal effects become noticeable (stable and unstable conditions). The industry and the IEC 61400–1 often use a power law to describe the height variation. The power 1/7 may be used to represent neutral conditions and a roughness length of 0.03 m.
Bibliography
Primary Literature
IEC (2005) Wind turbines. Part 1: design requirements, International Standard 61400–1. International Electrotechnical Commission, Geneva
Troen I, Petersen EL (1989) European wind atlas. Risø National Laboratory. Published for the EEC, Roskilde, 688 pp (Also in Italian, French, Spanish and German)
Krohn S, Poul-Erik Morthorst P-E, Awerbuch S (2009) The economics of wind energy. European Wind Energy Association, Brussels, 155 pp
Petersen EL, Mortensen NG, Landberg L, Højstrup J, Frank HP (1998) Wind power meteorology. Part 1: climate and turbulence. Wind Energy 1:2–22
Petersen EL, Mortensen NG, Landberg L, Højstrup J, Frank HP (1998) Wind power meteorology. Part 2: siting and models. Wind Energy 1:55–72
Kaimal JC, Finnigan JJ (1994) Atmospheric boundary layer flows. Their structure and measurement. Oxford University Press, New York, 289 pp
Warner TT (2011) Numerical weather and climate prediction. Cambridge University Press, Cambridge, UK, 526 pp
Petersen EL, Troen I, Frandsen S, Hedegaard K (1981) Danish wind atlas. A rational method of wind energy siting. Risø-R-429. Risø National Laboratory, Roskilde, 229 pp
Badger M, Badger J, Nielsen M, Hasager CB, Pena Diaz A (2010) Wind class sampling of satellite SAR imagery for offshore wind resource mapping. J Appl Meteor Climatol 49(12):2474–2491, American Meteorological Society
Nielsen M, Jørgensen HE, Frandsen ST (2009) Wind and wake models for IEC 61400–1 site assessment, 2009. In: European wind energy conference, Marseilles. 6 p
Books and Reviews
EWEA (2009) Wind energy, the facts. European Wind Energy Association, Brussels
In general: The conference proceedings published yearly by the European Wind Energy Association (EWEA), The American Wind Energy Association (AWEA) and the British Wind Energy Association (BWEA)
Jensen NO, Petersen EL, Troen I (1984) Extrapolation of mean wind statistics with special regard to wind energy applications. Report No. WCP–86. World Climate Programme, WMO, Geneva, 85 pp
Wyngaard JC (2010) Turbulence in the atmosphere. Cambridge University Press, Cambridge, UK, 393 pp
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Petersen, E.L., Madsen, P.H. (2013). Meterology and Wind Power. In: Kaltschmitt, M., Themelis, N.J., Bronicki, L.Y., Söder, L., Vega, L.A. (eds) Renewable Energy Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-5820-3_77
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