Friday, March 05, 2010

You don't need a weatherman to know which way the wind blows

As the global wind energy industry continues to expand more companies and industries are becoming engaged in the wind energy supply chain. One of the major benefits of this development is that many companies are coming up with innovations that improve the performance of wind energy systems that ultimately translate into lower costs of electricity for ratepayers.

"Smart" wind energy systems connected to smart grids could be game-changers. (GW)

Smarting from the wind

The Economist

March 4, 2010

Turbines equipped with sensors can now “see” the wind before it arrives, and then take appropriate action

GATHERING energy from the wind may seem a straightforward process. Air whips past the blades of a turbine, forcing it to spin. The turbine turns a generator. The generator produces electricity. Yet in practice things are not so simple. Wind generators are, necessarily, erected in places where powerful winds are common. If they are not properly angled towards the more howling of these gales, they can be damaged or destroyed. Adjusting turbines so that their blades can harness the strongest air currents rather than be harmed by them is a normal part of turbine management. But technology being developed by Torben Mikkelsen, of Risoe DTU National Laboratory for Sustainable Energy in Denmark, and his colleagues should make the process easier. Dr Mikkelsen is working on a way for individual turbines to scan the air upwind and adjust their blades in anticipation.

The basic technology, called lidar (short for light detection and ranging) has been around since the 1970s. It is similar to radar in that it sends out electromagnetic waves and then analyses those waves that bounce back, to determine what they bounced off. The difference is that radar depends on radio waves. These have long wavelengths and therefore bounce only off large things. Lidar uses light waves. Light has a much shorter wavelength and is readily reflected from small objects—one reason that human vision relies on it. Crucially, the light waves used in wind lidar are reflected by tiny, naturally occurring particles like water droplets, dust, pollen and salt crystals that drift along at the precise speed of the wind.

Dr Mikkelsen and his colleagues worked out that they could use lidar to scan incoming wind and determine how it was behaving before it struck the turbine. To try this idea out, they first placed lidar devices at the base of 120-metre-tall wind turbines at Hovsore, the Danish test site for such devices. The device measured wind movement at 40, 60, 80, and 100 metres above the ground, and 100-200 metres in front of the turbine. The data it collected were then compared with wind measurements taken by cup anemometers in order to calibrate the lidar. That done, the computer which analyses the lidar data could be connected to the motors that adjust the pitch of the turbine blades, in order to maximise energy production and reduce damage.

The team found they were able to get accurate measurements at all heights around the turbine, but realised that installing the device on the ground was far from ideal. By shining the lasers into the air from below they were analysing a cone that had its point at the base of the turbine. This gave them an understanding of wind speeds, but little sense of how winds were changing as they closed the 200-metre distance to the turbine. To capture this important information, the cone of the lidar needed to be sent out from the centre of the turbine itself.

Placing a lidar in the centre of a turbine proved difficult, because of forces generated by the turbine’s rotation. To help the lidar cope, the researchers replaced their classic lidar device, which used mirrors to direct the light, with a newly developed fibre-optic system. The team also had to deal with electrical interference from the generator, which involved wrapping the lidar in shielding material.

The result is a system than can already improve electricity production by 5%. For a 4MW turbine, this is worth around $38,000 a year. Further benefits and savings come from increasing the life of the blades and the generator itself.


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