Peter Clive: Harnessing the wind's power is an exact science

Published on Friday 27 February 2009 19:44

WIND farms are an increasingly common sight on the Scottish landscape; however, it is simply not the case that you can erect a series of turbines anywhere and harness the power of the wind.

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 1 per cent is equivalent to about 1,250 households' electricity consumption.

Hills, forestry, lochs, 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.

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.

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 ten 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.

However, like most technology adapted for other uses, Lidar technology is continually evolving as the need to characterise wind and maximise the efficiency of wind farms becomes increasingly important.

First-generation Lidars allow for the measurement of wind directly above where the device is placed. The development of next-generation Lidar – such as SgurrEnergy's Galion Lidar – allows wind measurements to be made within a range of two kilometres.

So, for example, the development of next-generation machines allows multiple wind turbine locations to be surveyed from a single Lidar deployment site. And for the first time, the effect of the turbine rotor on the wind – its wake – can be directly measured instead of merely approximated, allowing assessment of its impact on other turbines.

&#149 Peter Clive is a renewable energy consultant with SgurrEnergy