Thursday, 20 October 2011

The end of shadow flicker?

Probably not!. Vestas, the wind turbine manufacturer have been trialling a system that assesses the likelihood of shadow flicker occurring. If certain parameters are met (and thus, the likelihood of shadow flicker is considered high), the turbine is put into idle mode. Some more details on this system can be found here and here.

Sounds good? I thought so at first - but now, I'm not so sure. The first point to note is that shadow flicker can be completely eliminated if sensible turbine setback distances are adopted; such an approach would completely negate the need for such a system in the first place. However, neighbours of wind farms are often ignored when it comes to turbine sighting. Adopting an apparently sensible approach such as this would require a fundamental paradigm shift from wind farm developers and I see no sight of that on the horizon.

Now, looking at the first article referenced above, I see two problems with this system. First of all, shadow flicker does not only occur around dawn and sunset. In northern latitudes, the sun stays very low in the sky during winter and sometimes almost appears to track horizontally during its transit. However, this system apparently relies upon light sensors placed on the east and west facing sides of the turbine, completely ignoring the bit of sky in the middle. Let's not forget that the position of apparent sunrise and sunset is dependant on the latitude and elevation of the observer and the time of year. It can vary considerably. I hope those sensors have a wide field of view (both vertically and horizontally).

The second major issue I see is that shadow flicker is an observed phenomena; that is, it is an observer that experiences it not the turbine itself. Instead of a system bolted to the turbine, why are sensors not placed at properties potentially susceptible to this phenomena? The sensors could be linked to a control box containing the necessary software to detect the shadow and strobing effect, which in turn is linked to a 'phone line. If a shadow effect is detected, an appropriate signal could be sent down the line to the control centre. Such an approach would not rely upon the positioning and cleanliness of the sensors on the turbines or the quality and sophistication of the modelling software; it would actually detect when the problem was occurring allowing the necessary corrective steps to be taken. Too simple I suppose.

Unfortunately, if the Vestas system works as described I think it could actually make the situation far worse. Currently a lot of developers rely far too heavily on the 10 rotor diameter rule of thumb to 'eliminate' shadow flicker at the design stage. I can foresee situations where developers could use this system as a green light to site turbines even closer to residential properties than before, using the excuse that shadow flicker can be 'eliminated' by this system. As a result, I am deeply suspicious of this - to me, it looks like they are coming at the problem from quite literally the wrong angle in terms of solving it and I actually see this as a mechanism to sell a few more turbines.

Finally it is worth noting that by developing this system the manufacturers are essentially saying that wind farm developers are indeed placing turbines too close to residential properties.