wind measurement campaign

One of the most important stages to successfully develop a wind farm is the wind measurement campaign.

Wind data should be collected according to wind industry best practices for at least one year to properly characterise the climatic conditions of the site and avoid seasonal bias. Although, sometimes, when the wind rose is not representative of the site, one year is not enough to characterise the wind regime. This stage is crucial because the development and design of the wind farm will be based on this data.

Unfortunately, it is common to find measurement campaigns that have not been well designed, leading to various problems affecting the profitability of wind farms. This article summarises the best wind monitoring campaign practices, the problems that may be encountered in wind measurement campaigns and the consequences they may have for the wind farm.

Mounting the meteorological mast

Mounting the met mast tower in accordance with IEC 61400-12-1 Annex G is crucial to minimise flow disturbance. This standard also highlights the importance of having control anemometers to check the consistency of the primary anemometer. To decrease the mast shadowing effect, depending on whether the tower is lattice or tubular, the standard recommends installing the meteorological mast booms at 45° or 90° respectively to the prevailing wind direction.

In addition, depending on the configuration of the tower, the standard recommends complying with particular configurations for the instrumentation (Boom distance, sensor support etc). It is possible to correct normal flow disturbances if control anemometers are available, but these are not always installed, which leads to greater uncertainty in the measurement process.

The number of meteorological masts needed is very particular to each site and the answer could be “as much of them to characterise the wind resource of the site”. According to Measnet evaluation of site-specific wind conditions guidance, the representativeness radius of a mast is 10 km in simple terrain and 2km in complex terrain. A reasonable number of measurement masts will help to adequately characterise the site wind resource, and hence to limit related uncertainties.

Height at which measurements are taken

Another important aspect to consider is the height at which the measurements are going to be taken. The minimum requirement is that the data is recorded at a height corresponding to at least two thirds of the hub height. Quite often the meteorological data are not recorded at hub height and a vertical extrapolation of the wind speed is required. Therefore, it is important to comply with this requirement to limit uncertainties due to this step. The greater the distance is, the greater the uncertainty is.

Regularly check measurement equipment

Once the assembly of the meteorological mast has been successfully completed, it is essential to regularly check the good functioning of the equipment in order to obtain as many valid records as possible.

Some meteorological masts have really low data recovery rates, which makes it difficult to correctly characterise the wind resource of the site. If the mast is to be located at a site with usual frosts, it is important to install heated anemometers (at least one), in order to increase the data availability during freezing periods. It is also recommended to recalibrate anemometers once a year, but this recommendation is seldomly followed in the industry. At least, once the measurement campaign is completed, the anemometers should be recalibrated to detect possible changes in measurement behaviour due to wear or improper functioning of the equipment.

Determining the wind turbine type

All the above is of vital importance because the recorded data will be used to determine the type of turbine that best fit to the site wind characteristics (Wind turbine class and turbulence category according to IEC 61400-1 design parameters) and so, the layout, hub height, and the wind farm energy production and revenues. Therefore, it is essential that the data is reliable and representative of the site. Bad quality data could result in significant operating costs for corrective maintenance as the turbine could be exposed to fatigue loads higher than expected, and for which the wind turbine has not been designed.

Looking at wind resource estimates, a well-designed measurement campaign will allow robustness when extrapolating wind speed to production. Relatively small speed errors can be very large in terms of production due to the gradient that relates the variation of energy as a function of speed.

Why measurement campaigns are so important

As a conclusion, it is possible to expect deviations of the wind farm predicted production between the operation phase and the development phase of 10% and even more if the measurement phase of the wind resource is played down. A good measurement campaign will allow for an adequate estimate of the P50 and limitations of the uncertainties, which will additionally reduce the difference between the P50 and the P90, of vital importance when making investment decisions. If the cost of developing a good measurement campaign is compared with the cost of developing the wind farm, the first one is negligible. Instead, a poor meteorological mast measurement campaign can condition a huge percentage of the project’s performance.

How can Greensolver help?

From Greensolver, we can help both in the construction and design process of meteorological mast campaigns with the aim of providing robustness in data collection, achieving greater representativeness of the measurements on the site, and reducing uncertainties. Get in touch to enquire!


Written by Carlos Sanchez Smith, Advisory Services Engineer.