Wind Turbines: Does Height Matter?

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There is a lot of negativity towards wind turbines, which are often accused of being ‘blights on the landscape’. This may be because the first image that springs to mind when you think of a turbine is that of one of the giant turbines employed on offshore and onshore wind farms.  Sadly, this negative attitude seems to have rubbed off onto the much smaller, stand-alone turbines which are becoming ever more popular for powering farms and businesses.

This begs the question: does size and height really matter? In fact, it does.  However, domestic and agricultural turbines don’t need to generate anywhere near as much power as one of the wind farm giants and height can be tailored to need.

To really understand why height is so significant to turbine performance, you need to understand what drives it.  The wind is a naturally occurring element, arising from air being pushed from high pressure areas to low pressure areas.

Additionally to features which may cause wind turbulence (such as trees and buildings) friction from the surface of the Earth slows wind speed down – especially at night when there is no heat from the sun.  Even the difference of a meter in height can make a large difference to wind speed.  The reason that meter is so valuable is because the ‘wind speed to power generated ratio’ is not 1:1.  Energy generation is measured by the wind speed cubed. In other words, if you double the wind speed you get eight times the energy.

The wind, as we know, can be extremely destructive. Not all turbines can cope with high wind speeds and most carry an automatic cut-out, protecting the turbine from damage.  The cut-out speed varies from turbine to turbine and in the case of these turbines additional height may not be so useful.

However, there are turbines that have no cut out; the KW6 Kingspan wind turbine is a good example. The small KW6 has an innovative design to help it cope with high wind speeds using a unique over-speed protection system. The blades of the turbine pitch and cone in high winds, negating the need for brakes and allowing uninterrupted operation. The KW6 tower height can range from a diminutive 9m up to 20m, allowing prospective owners a better opportunity to hit maximum power generation from the turbine.

While the KW6 is extremely robust, it only has a peak power generation of 6.1kw. The KW6 is expected to generate around 9,000kwh per year based on a 10m height and the assumption that the turbine will not operate at maximum capacity continually – this is around the same height as a two storey house and smaller than most older trees.

9,000kwh is about half the energy that your average family household will use annually and in terms of emissions, equates to a saving of around 5 tonnes of carbon per year.

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