Technical Comments

A 2.5 Mw wind turbine is about 125m tall (410ft.) which is as high as a thirty storey building. The structure weighs about 325tonnes. The turbine will start to operate at a wind speed of about 10mph and increase its output up to about 35mph, above which the output will be constant. Wind turbines often freewheel at low wind speeds giving the impression that they are producing energy when they are not. The ‘load factor’ which is the percentage of the energy which is produced compared to that which would be produced if the turbine could run continuously, is about 25%. (DTI data). A 2Mw wind turbine with 25% load factor will support around 1,000 homes.

It is misleading to say that wind farms

Carland Cross (c RES)

generate no carbon dioxide. Because wind farms operate intermittently then the more wind farms there are, the more running-spare capacity of conventional power plant is needed to smooth out the variations. This action increases the carbon dioxide from the conventional plant. Wind farm developers usually quote a simple displacement value of carbon dioxide for the installed capacity of the wind farm which is therefore optimistic. Some scientists state that only half of the carbon dioxide is actually saved that the British Wind Energy Association claim.

 

The speed of the blade tip of a large wind turbine is in the range 150 – 190 mph.Opponents have said that a single wind turbine requires a foundation the size of a large swimming pool.  This is an exaggeration.  In normal circumstances a 2.5Mw turbine requires a base of 250 cubic metres of concrete, about 40 large wagon loads. The Went Edge is however a significant geological fault and it is possible that any turbine placed on the Westfield Lane site may require enlarged foundations.

A wind turbine would not normally be sited within 1,000m of dwellings. In Scotland there is new Planning Guidance which supports a separation distance of 2,000m

Dun Law (c Scottish Power)

between the edge of a town or village and large scale wind farm developments. The UK Noise Association recommend that they are not built within one mile of residential dwellings. Noise measurements in rural communities where ambient noise levels are low are very difficult to translate into potential for complaints.  Developers will say that their noise assessments meet Department of Trade and Industry guidelines but these guidelines were drawn up over ten years ago before any experience was gained with the huge machines now being built.  Low levels of background noise are not particularly relevant to actual noise complaints. With wind turbines it is the intermittent ‘blade pulsing’ or so called ‘whooshing’ which has proved so objectionable and yet this noise is barely determinable by average noise measurements. Noise is measure in decibels (dBA). A useful measure is that an increase of 3dBA is a doubling of the sound pressure level.

With large developments there are some precedents where the developer funds a local authority Environmental Impact Assessment to be used in parallel comparison with the developer’s own. This is a positive step since some assessments carried out on behalf of developers include carefully chosen wording to allay people’s concerns.

The ‘load factor’ which is the percentage of the energy which is produced compared to that which would be produced if the turbine could run continuously, is about 25%. (DTI data).A 2Mw wind turbine with 25% load factor will support around 1,000 homes. 

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