Windy Miller

Site Location

• Wind conditions• Meteorological data

– In most cases using meteorology data directly will underestimate the true wind energy potential in an area

• Look for a view– Wide open spaces without obstacles

• Grid connection• Grid reinforcement

– a larger cable, perhaps connected closer to a higher voltage transformer station

• Soil conditions – foundations and delivery

Off-shore Sites

• The surfaces of seas and lakes are obviously very smooth, thus the roughness of a seascape is very low (at constant wind speeds). With increasing wind speeds some of the energy in the wind is used to build waves, i.e. the roughness increases. Once the waves have been built up, the roughness decreases again

• It may therefore be most economic to use fairly low towers of perhaps 0.75 times the rotor diameter for wind turbines located at sea

• The wind at sea is generally less turbulent than on land. Wind turbines located at sea may therefore be expected to have a longer lifetime than land based turbines.

Landscape

• Wind turbines are always highly visible elements in the landscape. Otherwise they are not located properly from a meteorological point of view

• In flat areas it is often a good idea to place turbines in a simple geometrical pattern which is easily perceived by the viewer

• In hilly landscapes it is rarely feasible to use a simple pattern, and it usually works better for the turbines to follow the altitude contours of the landscape, or the fencing or other characteristic features of the landscape.

• To a large extent it is a matter of taste how people perceive that wind turbines fit into the landscape.

Hill Effect• On hills, one may also experience

that wind speeds are higher than in the surrounding area. This is due to the fact that the wind becomes compressed on the windy side of the hill, and once the air reaches the ridge it can expand again as its soars down into the low pressure area on the lee side of the hill.

• The wind in the picture starts bending some time before it reaches the hill, because the high pressure area actually extends quite some distance out in front of the hill.

• The wind becomes very irregular, once it passes through the wind turbine rotor

Park Effect• Each wind turbine will slow down the wind

behind it as it pulls energy out of the wind and converts it to electricity.

• Ideally, we would therefore like to space turbines as far apart as possible in the prevailing wind direction.

• On the other hand, land use and the cost of connecting wind turbines to the electrical grid would tell us to space them closer together.

• The turbines (the white dots) are placed 7 diameters apart in the prevailing wind direction, and 4 diameters apart in the direction perpendicular to the prevailing winds

Wind Obstacles• Obstacles to the wind such as

buildings, trees, rock formations etc. can decrease wind speeds significantly, and they often create turbulence in their neighbourhood.

• As you can see from this drawing of typical wind flows around an obstacle, the turbulent zone may extend to some three time the height of the obstacle. The turbulence is more pronounced behind the obstacle than in front of it.

Towers

• The price of a tower for a wind turbine is generally around 20 per cent of the total price of the turbine. For a tower around 50 metres' height, the additional cost of another 10 metres of tower is about 15,000 USD. It is therefore quite important for the final cost of energy to build towers as optimally as possible.

• Clearly, we cannot sensibly fit a 60 metre rotor to a tower of less than 30 metres. But if we consider the cost of a large rotor and a large generator and gearbox, it would surely be a waste to put it on a small tower, because we get much higher wind speeds and thus more energy with a tall tower.

Rotor Diameter• The picture gives you an

idea of the normal rotor sizes of wind turbines: A typical turbine with a 600 kW electrical generator will typically have a rotor diameter of some 44 metres (144 ft.). If you double the rotor diameter, you get an area which is four times larger (two squared). This means that you also get four times as much power output from the rotor

Sound• Each square measures

43 by 43 metres, corresponding to one rotor diameter. The bright red areas are the areas with high sound intensity, above 55 dB(A). The dashed areas indicate areas with sound levels above 45 dB(A), which will normally not be used for housing etc

• As you can see, the zone affected by sound extends only a few rotor diameters' distance from the machine.

Birdies• Birds often collide with high voltage overhead lines, masts, poles, and

windows of buildings. They are also killed by cars in the traffic. • Birds are seldom bothered by wind turbines, however. Radar studies

from Tjaereborg in the western part of Denmark, where a 2 megawatt wind turbine with 60 metre rotor diameter is installed, show that birds - by day or night - tend to change their flight route some 100-200 metres before the turbine and pass above the turbine at a safe distance.

• A study from the Danish Ministry of the Environment says that power lines, including power lines leading to wind farms, are a much greater danger to birds than the wind turbines themselves.

• Some birds get accustomed to wind turbines very quickly, others take a somewhat longer time. The possibilities of erecting wind farms next to bird sanctuaries therefore depend on the species in question. Migratory routes of birds will usually be taken into account when siting wind farms.

Energy Payback Period

• Modern wind turbines rapidly recover all the energy spent in manufacturing, installing, maintaining, and finally scrapping them. Under normal wind conditions it takes between two and three months for a turbine to recover all of the energy involved.

• This is one of the main results of a life cycle analysis of wind turbines done by the Danish Wind Industry Association.

• The study includes the energy content in all components of a wind turbine, and it includes the global energy content in all links of the production chain

Offshore Energy Payback• Offshore wind turbines may have a slightly more favourable

energy balance than onshore turbines, depending on local wind conditions. In Denmark and the Netherlands, where wind turbines onshore are typically placed in flat terrain, offshore wind turbines will generally yield some 50 per cent more energy than a turbine placed on a nearby onshore site. The reason is the low roughness of the sea surface.

• On the other hand, the construction and installation of foundations require 50 per cent more energy than onshore turbines.

• It should be remembered, however, that offshore wind turbines have a longer expected lifetime than onshore turbines, in the region of 25 to 30 years.

Analysis of 1980 Vintage Turbines

• 1980 wind turbines do surprisingly well in the studies of the energy balance. The analysis shows that while small Danish 1980 turbines of 10-30 kW took almost a year to recover the energy spent in manufacturing, installing and decommissioning them, turbines of 55 kW took some 6 months to recover all of the energy

Wind Map

• Purple strongest• Blue weakest

Denmark Wind Map