Where can you put Turbines? – Practical Constraints
Wind Turbines will operate with wind as low as 4m/s: 7 mph (cut in speed) and will continue to operate up to about 25m/s: 50-60mph (cut out speed) when the potential damage due to a sudden gust starts to become a risk and the turbines shut down and wait for a reduction in wind speed before automatically entering operation again. By operating in this way wind Turbines are designed to withstand the onslaught wind of the frequent storms which reach our shores from the Atlantic.
It goes without saying that in order to be effective a wind site must have good exposure to the prevailing wind(s). The direction of prevailing wind is an obvious factor is turbine siting and design of the wind farm arrays but also the type of winds which are being captured is important. Most of the winds in Ireland and the UK are storm front driven not thermally driven as those appropriateness of the site but in principle Turbines can be put almost anywhere – from open farmland to mountain ridges, to lake shores and offshore.
Having said that a turbine can be sited almost anywhere there are obviously key practical or economic questions for any site
There are clearly practical limits to where turbines can be sited owing to their size and this will often form an important element of the selection criteria. A typical modern utility size wind turbine will have a tower height of anywhere from 50 and 80 metres and a rotor diameter of between 52 and 90 metres. The smaller machines would have an installed capacity of around 800kW each whilst the larger machines have a capacity of around 3000kW. Although turbines are commonly talked of as being small or large there is no escaping the fact that regardless of whether they are 800kW (or less) or 3000kW turbines they are all BIG machines.
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The difference in scale between turbines between either Big or very BIG is clear when you stand at the base of a tower but less so as one gets further away. It is often very difficult to tell what size turbine one is viewing from even quite moderate distances.
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Access: Each turbine requires an access track of around 5metres in width and a stable crane pad for the erection of the turbines. It is not uncommon to have to build several kilometres of road onto a site in order to access the turbines. Delivering the equipment over the Public road network also needs consideration since the access roads need to be suitable for both heavy and long transport vehicles. This may entail strengthening and widening elements of the public roads. Even a very high wind speed site may still prove uneconomic if the cost of getting the turbines to site and then getting them to their individual locations is prohibitive.
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Electricity Grid: Wind Turbines are often sited in semi-remote mountainous areas because of the available wind resource, but like access roads there is a limit to how far it is economic to build a power line to connect to the main grid. There is no simple answer to what is viable since it is dependent on the available wind speed (wind energy) and the size of the site e.g. 15km is a long way for 5 MW Wind Farm but not one of 50 MW or more.
Ground Conditions: Turbines are usually built with a so called gravity base or foundation which keeps the turbine up right by virtue of its weight. The size of this concrete base varies depending on the size of turbine, the maximum wind speed of the site and the type of ground conditions at the turbine base but would generally be around 12-14metres square and around 1-2metres deep.
With a gravity base all that is necessary is for the soil or peat to be excavated to a stable load bearing strata before the foundation is formed. They can therefore be sited in bog sites provided the depths are not too great but for deep peat foundations there are limits to what is economically feasible. On an ideal site the turbines would be placed on an open exposed area facing the prevailing wind with around 1 –2 metre depth of peat or soil before good bedrock.
Trees and Other Obstacles: Turbines can be sited in trees although this is not ideal since trees like any sizeable obstacle will slow the wind which reduces the energy captured and also introduce turbulence which can affect the machine life. The ideal vegetation cover for turbines is short grass which is provides little disturbance to the flow of wind across it.
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