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Over recent years there has been a multitude of wind turbines sprouting up over the countryside. Whether you feel that these are monstrous beasts or elegant mechanisms rotating in the breeze depends on your view point but Britain is well situated for wind power generation as the following map shows:
Most of Scotland has average speeds of more than 8 m/s and a large part of England has favorable wind conditions.
More accurate data can be obtained from the British Wind Energy Association web site www.bwea.com where wind data at a location specified by a Grid Reference is tabulated . Another alternative is to set up an anemometer at the proposed site and measure the windspeed over several months and one such device has been set up at the author's home.
Windspeeds were monitored for the year 2006 and, as expected, the winds are stronger in the winter months than in summer time.
It must be noted that the anemometer, for these results, was not placed at a height of 50 m above the ground nor was it placed in an open area so the results only give a yearly average of about 2.8 m/s.
To determine what power is available we need to make a calculation and this will be for the IDEAL situation when all the energy in the wind is extracted:
Any moving mass has kinetic energy, K.E., given by the equation : K.E. = ½mv2
For a cylindar of air with area A and length L we have mass = A L x density
If L is numerically equal to v, the speed of the wind then all the air passes out of this cylindar in one second
So we have Power = ½ A x density x v3
The density of air is 1.2 kg per cubic metre and one can consider a blade size of 1m ; area A is then 3.14 m2 and the power generated is 41.3 Watts. (if the windspeed was 6 m/s the power increases to about 400 Watts)
We can see that the power is proportional to the CUBE of the windspeed thus, high windspeeds are very important if we need high outputs from this type of energy source.
Realistically, the power output is much lower than that calculated above and a more complete theory is given in a publication from the Intermediate Technology Development Group (ITDG) - web site www.itdg.org - there is a search box and one can type "windpower" in this box.
The good feature about windpower is that it is a sustainable source. Whereas with the heat pump (section 10) an electricity supply is needed, windpower is a primary source and what energy we do not "trap" today will be lost forever.
Most homes in suburbia will not have a suitable site at which to install a wind turbine and it is not envisaged that B&Q generators will appear on chimney pots all over towns and cities as did, say, satellite dishes. In the countyside there is more likely to be an opportunity to make use of wind power.
The most useful leaflet for advice on wind energy is that produced by Segen, www.segen.co.uk.; it gives a step by step guide to site selection, planning, funding, purchase and erection of a turbine and then discusses the proceedures for connection to the "mains" so that you can export any excess electricity!
On a larger scale it is felt that the country must exploit off-shore sites as these do not spoil the countryside and give us a much needed renewable source of electricity.
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