How do we measure the wind on a site?

May 2011
by Baptiste Ruille

The wind measurement campaign is a critical step in the development of a wind energy project. Accuracy and consistency of measurements are instrumental in the design and optimization of the lay-out as well as in the feasibility analysis and eventually in the financing of a project. Several measuring solutions are implemented by wind resource analysts when it comes to collecting and analyzing wind data. Some of the most mature and widespread measuring techniques are presented in this article.

Met masts

This method consists of running on-site meteorological measurements using a mast of variable size fitted with measuring and data-collection equipment.

Depending on the project size and terrain complexity, several masts can be installed on a given site. The size of the mast should be at least equal to 2/3 of the hub height to reduce uncertainties on vertical wind profile extrapolations. Wind resource analysts assisted by project managers select the most appropriate location to install the equipment.

1. Anemometers

Anemometers are used to measure the wind speed. Depending on the size of the mast, 3 to 5 anemometers are installed at various heights in order to accurately calculate the vertical profile of the wind. Length of booms is set according to IEC 61400 standard.

Each anemometer is calibrated by a specialized institute in compliance with international standards (MEASNET). The calibration is performed before installation of the mast to ensure the quality of the campaign.

Anemometers used for energy predictions consist of three hemispherical cups revolving around a vertical axis. Best-in class sensors are used by FUTUREN for its wind measurement campaigns to avoid inaccuracy and over-speeding effects in the collected data.

2. Wind vanes

Measuring masts are equipped with two wind vanes which measure the wind direction. The vane must be positioned on a horizontal boom as high as possible but at sufficient distance below the top anemometer to avoid shadow effect. The offset of the vane is determined by using the boom orientation, a compass and a map.

3. Other meteorological factors

Humidity, air pressure and temperature influence energy production. Therefore, it is useful to collect these data during the measuring campaign.

Humidity measurements are particularly useful to predict risk of icing and therefore anticipate mitigation measures such as heating blade systems.

Air temperature affects air density and thus directly impacts energy production of the wind farm.

Sensors can be placed on the mast but data can also be collected from neighboring weather stations since these data usually require less accuracy.

4. Data collection equipment

Data produced by the sensors are then stored at regular time intervals in a logger placed in a steal cabinet in the lower section of the mast. Power needs of the electronic equipments are supplied using photovoltaic panels.

The logger is then connected to a telephone line or uses a GSM connection in order to transmit information. After collection, wind resource analysts carefully screen through the data and gaps in the time series are filled in.

Data are then computed into a specific wind calculation software in order to produce the energy assessment of the site.

Remote sensing instruments

A SODAR – which stands for Sonic Detection and Ranging – is a remote sensing instrument used for meteorological measurements.

Atmospheric data are calculated based on the speed of sound. Measurements are performed by sending out an acoustic signal. The return signal is then analyzed to evaluate wind speed, wind direction and atmospheric turbulences.

In a similar way, a LIDAR (Light Detection and Ranging) analyzes the wind profile through a laser signal. On the same principle as for the SODAR, a light beam is sent out in the atmosphere in a three dimensional cone. The Doppler shift of laser radiation backscattered by air particles is measured to define wind characteristics.

SODAR and LIDAR measurements offer the possibility to analyze the wind profile at various altitudes and over the rotor surface which is of interest mostly when the project is designed with large-size rotors and/or big hub heights.

Measuring data are stored in the SODAR/LIDAR and can be collected via email, internet or mobile connection.

Like measuring masts, remote sensing equipments can function as stand-alone applications. If SODAR can operate directly on photovoltaic panels, power requirements of a LIDAR are higher and require power supply from fuel cell or from the grid, making the use of this application more challenging in remote sites.

Measurement campaigns performed with SODAR and LIDAR usually last a few weeks and often complement mast measurements to extrapolate or correlate with existing data.

SODAR and LIDAR measuring techniques find various applications in the development of a project or operation of a wind farm such as power curve assessment, calculation of thermal effects on energy yield, lay-out design, complex site analysis, etc.

Limited encumbrance, quick deployment and the absence of administrative requirements before installation are some of the advantages of remote sensing equipments over traditional wind measurements. In some situations they can also prove to be a cost effective alternative to big size measuring masts.

Although remote sensing solutions are generating increasing interest among wind professionals, mast measurements are still considered mandatory in the development of a project. SODAR and LIDAR measurements are often used in complement of mast measurements and can offer significant benefits by refining existing data and improving the understanding of a wind profile in complex locations of a given site.

Vos réactions et Questions 8

    WITTIG
    2011-10-07 12:50:30
    J'apprécie beaucoup votre nouveau site qui permet de mieux comprendre l'énergie éolienne sur le plan technique et environnemental. Félicitations à toute votre équipe qui participe à son élaboration.
    chetan
    2011-11-10 07:28:23
    nice information.
    MAD
    2012-07-24 15:14:23
    Bonjour, Si je comprends bien, le lieu d’une implantation est très important. Il est reconnu, sans être expert, que les vents soufflent plus au bord de mer. La technique d’implantation d’éoliennes offshore doit être plus couteuse je suppose mais aussi plus rentable. Pourquoi ne pas exploiter cette voie ? J’habite dans le sud de la France et je peux témoigner sans aucun SODAR ni LINAR que le Mistral est bien au rendez-vous. Je suis conscient aussi des permis et autorisations d’implantations dans ses lieux très touristiques. Théolia est une entreprise à la pointe du progrès que je suis de très près et mes félicitations à toutes ces équipes d’ingénieurs et techniciens.
      FUTUREN
      2012-09-03 11:03:46
      Cher Monsieur, FUTUREN estime que la technologie éolienne offshore n’est aujourd’hui pas encore assez mature. Les parcs offshore actuellement développés présentent de nombreuses incertitudes, en particulier quant aux coûts de maintenance futurs. Aujourd’hui, il reste encore de nombreuses opportunités de développements éoliens onshore, notamment en France, pays qui est en retard par rapport aux objectifs nationaux affichés (à savoir l’exploitation de 19 000 MW éoliens onshore en France d’ici 2020) ou au Maroc, où nous développons actuellement un parc de 300 MW qui dispose de conditions de vent proches de celles des parcs offshore, mais avec beaucoup moins de risques. FUTUREN n’envisage donc pas à court terme de s’investir dans l’éolien offshore, mais suit attentivement les évolutions de ce marché. Bien cordialement, FUTUREN
    Benoit
    2013-02-11 16:19:13
    Messieurs, Idéalement, quelle est la distance maximum qu'il peut y avoir entre l'emplacement d'un mât de mesure et l'emplacement définitif du mât d'une turbine? En d'autres termes dans un rayon de combien de mètre une tour de mesures est-elle efficace? Cordialement
      FUTUREN
      2013-03-04 11:21:47
      Cher Monsieur, La distance maximale entre l’emplacement du mât de mesure et celui de l’éolienne dépend de plusieurs facteurs. Le terrain du site éolien joue un rôle important : plus celui-ci est complexe (en termes de rugosité, de topographie et d’obstacles présents), plus le mât devra être installé à proximité de l’emplacement de la future éolienne. Pour un terrain moins contraignant, le mât et la future éolienne peuvent être espacés de plusieurs kilomètres. Dans les cas les plus complexes, il est parfois nécessaire d’installer plusieurs mâts de mesure. La distance entre le mât de mesure et l’éolienne dépend également du modèle d’extrapolation des données de vent utilisé. Bien cordialement, FUTUREN
    A.
    2013-10-31 15:26:44
    Bonjour, C'est ma première visite du ce site web. je vous félicite pour la qualité de l'information que vous diffuser sur ce site. Pour THEOLIA quelle est la méthode utiliser pour estimer la production d’énergie éolienne dans le temps? Merci d'avance
      FUTUREN
      2013-11-04 11:05:52
      Madame, Monsieur, Pour estimer le potentiel de production des éoliennes, FUTUREN utilise des logiciels de modélisation complexes, tels que le modèle linéaire WAsP développé par l’institut danois Riso ou des modèles d’écoulement des fluides « CFD » (WindSim et WAsP-CFD). À partir du gisement éolien (lui-même établi en confrontant les données mesurées sur site à des données de vent long terme – consultez l’article de Benoît Buffard, « L’évaluation du gisement éolien d’un site »), ces logiciels permettent de réaliser des prévisions de production d’énergie éolienne sur plusieurs années. Bien cordialement, FUTUREN
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Authors

  • Baptiste Ruille

    Wind engineer. Masters degree in Environmental Engineering with major in meteorology.

  • Pierre Radanne and Emmanuel Guérin

    Pierre Radanne is an expert in energy and ecology, specialized in energy policies addressing climate change issues.  Emmanuel Guérin is Program Director at IDDRI (Institute for Sustainable Development and International Relations).

  • Benoît Buffard

    Wind engineer at FUTUREN France since October 2011. He graduated in Statistics Engineering with the ENSAI school of statistics (École Nationale de la Statistique et de l'Analyse de l'Information) and holds a Master's Degree specialized in "Renewable energies and their production systems" with the ENSAM engineering school (École Nationale Supérieure des Arts et Métiers).

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