IN-DEPTH: Using meteorological info to select sites with best wind generating potential

Measuring wind at the site of a proposed wind farm development is vital for assessing the available wind resource, predicting the energy yield, and investigating the mechanical fatigue loading that may be imposed on wind turbines by the prevailing wind regime.

Typically one or more temporary meteorological masts are erected. These may be from 40m to 80m tall and are instrumented with wind vanes and anemometry at several heights.

The wind rose, which describes the distribution of wind speeds and directions recorded at a measurement mast locations, is a necessary input into computer models and statistical procedures which predict the long term distribution of wind speeds and directions throughout the proposed wind farm site.

This in turn informs the design of a wind farm layout: the turbines can be situated to minimise the effect of wakes on production and maximise the extent to which the available resource is exploited.

A wind farm is of course subject to multiple constraints including the mitigation of environmental and noise impacts and consideration of visual obtrusiveness, but the determination of the available resource by a process involving direct measurement of the wind and the configuration of the wind farm to exploit this resource remains central to wind farm development.

In addition to wind speed and direction, other parameters that relate directly to the cost of operation are measured, such as turbulence and wind shear.

The attractiveness of otherwise promising wind turbine locations may be modified if it transpires that they would be subject to adverse stresses arising from, for example, turbulence or wind shear caused by topography or forestry.

“In general, a proposed wind farm site needs to be classified in terms of the wind resource and wind regime that characterises it, as indicated by measurements such as wind speed, direction, turbulence, shear, veer and flow inclination, and the selection of suitable turbines and the design of the wind farm conducted with reference to this classification,” says Peter Clive, Technical Development Officer, Sgurr Energy, who is scheduled to speak during European Wind Farm Site Selection Summit to be held on 1-2 April in Hamburg.

(Clive is scheduled to speak about the best methods to assess wind conditions over a potential site).

Understanding the conditions from which turbines generate power

Wind farms are an increasingly common sight; however, it is simply not the case that you can erect a series of turbines anywhere and harness the power of the wind, points out Clive.

He added, “To be able to get the most out of a wind farm you need to understand the conditions from which turbines generate power and their response to these conditions. There are a number of new techniques that can deliver enhanced performance and reduce carbon emissions as a result. For example, improving the performance of a 50 megawatt wind farm by one percent is equivalent to about 1,250 households’ electricity consumption.”

Hills, forestry, bodies of water, complex terrain, even other turbines, all influence the wind.

These effects must be characterised to allow the selection of suitable turbines and inform where they are best located. Wear and tear can thus be minimised, and power production maximised. This requires precise data about the wind and the turbines' response to it.

This need is becoming acute as the size of wind turbines increases, as they are installed in less accessible locations – including offshore, with its operation and maintenance challenges – and as turbine technology adapts to meet these challenges.

Wind engineering requires a higher degree of precision than other wind-related disciplines, including scientific research, according to Clive.

“An atmospheric scientist may, in many circumstances, be content to know wind speed plus or minus one metre per second. That degree of precision could equate to plus or minus £1 million of annual revenues for a wind power project. Therefore, the instruments used by wind power experts go further, for example with the adoption of Lidar technology,” he said.

“In recent years this has established itself as an innovative method of measuring wind, often in locations where measurements would otherwise be impossible. Lidar (light detection and ranging) is a trusted technique in other fields and has been used for decades to analyse the composition of the atmosphere and the oceans, as well as monitoring turbulence at airports to clear aircraft for landing. In 2008, a Lidar was deployed to Mars on board Nasa's Phoenix Lander. Lidar works in a similar way to radar. Electromagnetic emissions from the device are scattered by objects in their path, and the device detects the scattered emissions. Analysis of these indicates some properties of the objects that the emissions encountered. Lidar emissions have a much smaller wavelength than radar. Whereas radar emissions are scattered by objects the size of a car, Lidar emissions are scattered by molecules and microscopic airborne particulates that move with the wind.”

The motion of these relative to the device imposes a change in wavelength, which indicates wind speed.

The development of fibre lasers over the past 10 years has enabled this highly successful technology to meet the demands of the wind power industry.

This has led to the development of products that are increasingly compact and highly deployable in the remote and poorly accessible locations typical of many wind farm developments. Once there, they operate with a high degree of autonomy, acquiring valuable and accurate data.


European Wind Farm Site Selection Summit

Peter Clive, Technical Development Officer, Sgurr Energy is scheduled to speak during European Wind Farm Site Selection Summit, which is scheduled to take place on 1-2 April in Hamburg this year.

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or Contact: Pete Carkeek by email