Wind turbines have been a great addition to the energy mix. Due to exponential growth of wind energy in recent times, wind turbines are normally the first choice when looking at zero emission sources at our disposal.
In countries where areas of low air pressure dominates (i.e. near Sub polar low pressure zone latitude 60°), they are already achieving grid parity i.e. producing energy at a cost at which it is available from the grid. Their efficiency is steadily improving and costs are coming down.
Wind turbines can generate electricity indigenously in remote locations. They reduce the need of laying expensive grid infrastructure to faraway places.
Their utility as “zero emission” electricity producer alone is reason enough for many in a climate changing world.
The wind power technology has been moving towards larger wind turbines for several reasons. Firstly the technology in the larger turbines is more robust and economically viable compared to smaller counterparts. Large turbines also benefit from intercepting wind at higher speeds because of thier high sitting nacelle. It should be noted that wind speed increases as we move further away from the ground due to the presence of earth boundary layer. However as turbines get bigger, there are more considerations for their planning, installation and commissioning.
Factors to consider for Wind farm planning are as follows:
The first and foremost thing to consider is the wind potential of the proposed site. The windier the location is the higher the feasibility of installing wind turbine. Normally a yearlong study is carried out using the data obtained from weather station or Metmast on the site. The information regarding wind speed and direction is recorded.
It should be noted that steady high speed wind is better than gale force wind that rapidly changes direction. Turbulence intensity of wind is another parameter that has to be considered. High amount of turbulence can be caused by obstructions in the wind path as it approaches wind turbine. This can result in adverse forces and vibration on the turbine structure and machinery. Turbulence also causes high sheer in the blades.
Proximity to Energy Highways
If wind turbines are to be located far away from the population centres which they are to feed than it should be ensured that their location is in close proximity to energy highways (High power transmission lines). If not than the added cost of transmission of electricity from the wind farm can become prohibitive.
There are instances where energy companies have picked the tab for installing transmission lines to the wind farm. In such cases this cost is adjusted in the Power Purchase Agreement. Thus the benefit to the wind farm owner is reduced.
If the energy of the turbine is to be consumed locally than the issue to proximity does not arise.
Wind turbines can interfere with Radars. This becomes a significant concern if they are to be situated near the airports or in an area that is under defence surveillance. The movement of the blades produces a blink on the radar screen.
There have been instances where radar interference was not considered at the planning stage and it was during the later stages that their installation and commissioning was halted. This has resulted in huge loss to the owners of wind farm
Large wind turbines can rise nearly 200 meters above the ground. The tallest being Vestas V-164 that stands 220 meters tall in Osterlid Denmark. Therefore it has to be ensured that the turbines also do not affect the flight paths and are located well away from the line of approach.
A site has to be accessible for not only the turbine parts but for the groundwork machinery that needs to install it (diggers and cranes). This is a particularly big issue for larger wind turbines that can have blade sizes of more than 80 meters. These large components have to be transported on longer heavier vehicles (LHVs). These special trailers generally have a huge turning circle.
Thus it’s not just the presence of the roads leading to the site but the turning radius of the roads that can become a huge obstacle to the project. Similarly areas that may have a difficult terrain i.e. rocky and mountainous can also add to the cost,
Ideally the site around the wind turbine should be clear of any protruding features. If turbines are installed close to a wooded land than their performance can be severely hampered. Furthermore the turbulence intensity of the wind increases after getting past the trees which causes vibration problems as mentioned earlier.
Off-shore turbines benefit from winds with low turbulence intensity most of the times. Similarly turbines should not be installed in the wind shadow of a hill, particularly if the hill covers the prevalent wind direction. Furthermore provision should be made for one wind turbine not to be in the shadow of other wind turbines in the same farm.
Geology, Ground Works and Excavation
Power lines from the turbines to the substation in the wind farm have to be laid down (usually underground). Furthermore access roads and foundations have to be laid on the site.
There are also geological parameters such as the soil softness or rock strength that can add to the cost of the ground works. In places where geological parameters are unfavourable, deeper foundations have to be dug which adds to the cost. More concrete may be required for example.
Further information regarding wind turbine foundations can be accessed from here.
Historic or Touristic Interest
Although local council may grant planning permission for building a wind farm for a site but often it does not involve the consent of the locals. This can cause problems further down the line. People are generally sensitive about sites of historic interest, recreational spaces or ones that are popular with tourist such as national parks.
A proposed site may be a fair distance away but as long as the turbines are visible on the landscape or seascape, people may file complains against them. This can delay the project and at times even get it cancelled. In a famous case in Scotland for example, the renowned political candidate and real estate developer Donald Trump objected to a wind farm that was off-shore but was visible from his golf course.
Bird strikes are an issue in wind power industry. Often planning permission is not granted to a very windy site based on the fact that the proposed site lies in the path of migrating birds. The tip speeds of wind turbines are very high and can sever a bird in two.
In Scotland for instance the Golden Eagles are a protected species and therefore permissions for wind farms are denied for sites that are close to their habitat.
In many countries, the avian data (number of birds crossing the site every year) is also required for the permission to be granted. This can be measured by installation of avian radars.
There may be other factors that hinder wind farm planning that are site/region specific. It is clear from the above mentioned factors that wind turbine/s cannot be installed just anywhere and many areas can be ruled out because of unsuitability.
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