Selection of Small Wind Turbine Installation Site

The choice of installation site for small wind turbines is very important. A very high performance wind turbine will not work if there is no wind, and a less powerful wind turbine will be fully functional if the site is well chosen. Some countries, such as the United States, have published monographs on the site selection of wind turbines because of the complex factors involved in the siting of small wind turbines. In principle, locations with very little wind and turbulence during the year should be best, but it is sometimes difficult to pick such locations.

 

First, the site selection principle

1. The site should choose the rich area of wind energy as described above, the greater the annual average wind speed of the installation site of wind turbines, the better, the general figures are: annual average wind speed of more than 3m/s, 3-20m/s effective wind speed accumulated time of more than 3000h, annual average effective wind energy density of 3 20m/s more than 100W/m2. As long as the first condition is met, small wind turbines can be considered economically sound.

2. The site should have a more stable prevailing wind direction. Prevailing wind direction refers to the wind direction with the highest current frequency. The meteorological upwind direction is generally expressed in 16 directions. The length and number of each azimuth arrow is the average wind speed in that direction and graphically plots the wind roses. In countries with strong monsoons, the prevailing wind direction changes in different seasons. The location of the site is expected to be more stable prevailing wind direction and facilitate the consideration of the favorable effect of the terrain.

3. Within the height range of the fan, "wind shear" should be small (wind shear should be small). "Wind shear" refers to the large change of wind speed and wind direction within a short distance. Therefore, the fan should avoid the strong shear area, install on the windward slope, or raise the tower.

4. The influence of meteorological factors should be considered

(1) Turbulence. Turbulence is a dramatic change in air speed, including changes in wind direction. Often the two factors are mixed together. Turbulence can affect the power output of a wind turbine, and at the same time make the whole device vibrate and damage the fan. Small turbulence is mostly caused by obstacles on the ground, so it is important to avoid such areas when installing wind turbines.

(2) Extremely strong wind. The wind speed at sea can reach more than 30m/s, sometimes more than 20m/s inland is called extremely strong wind. Of course, the installation site of wind turbine should choose high wind speed. The wind field at the top of the flat ridge becomes stronger. However, if the fan is used in the area prone to extremely strong wind, the unit should have sufficient strength. Once there is extremely strong wind, the wind turbine will become the object of attack.

(3) Freezing and sticking snow. Wind turbines located on the border between mountains and land are prone to freezing and snow sticking. Once the blade is frozen, its weight distribution will change, and the change of wing shape will cause intense vibration and even damage.

(4) Ray. Lightning strikes often occur because wind turbines are installed higher in flat areas where there are no obstacles. Therefore, it is advisable to install lightning protection devices for wind turbines.

(5) salt spray damage. When installing wind turbines within 10 to 15km of the coastline, precautions must be taken to prevent salt spray damage. Because salt spray can eat into metal parts like blades, and it can damage the insulation inside the device.

(6) Dust and sand. In dusty areas, the blade life of wind turbine is shortened obviously. The method of protection is usually to prevent the damage of the leading edge of the blade and to treat the leading edge surface. But dust can sometimes invade the inside of machinery, so that bearings and gear mechanism and other mechanical parts are damaged. In the factory area, harmful gases floating in the air will also corrode the metal part of the wind turbine, which should be paid attention to.

 

Second, site selection of flat terrain

According to the wind rose chart, which shows the relationship between wind direction and wind speed, if there is no obstacle on the windward side with the most wind direction, the site is generally considered to be flat. In the case of the so-called installation of wind turbines on flat land, the following two conditions should be considered:

(1) With the setting site as the center, there should be no obstacles in the circle with a radius of 1km.

(2) If there is an obstacle, the height of the wind turbine shall be more than three times the height of the highest obstacle. This condition is extremely strict, but can be relaxed for small wind turbines (for example, the radius can be set at 400m).

 

Third, site selection of ridge or hilltop terrain 

The ridge and the top of the mountain have a natural tower effect, and as the air flow approaches the ridge, due to the wind tunnel effect, the air flow is approximately streamlined and accelerated, and the energy increases accordingly. However, the direction of the wind and the direction of the ridge have a great effect on the speed of the wind, and the direction of the main wind is ideally at right angles to the direction of the ridge. Otherwise, with the acceleration of the terrain wind gradually smaller.

The wind speed usually decreases to a fairly small level at the base of the ridge and increases gradually as it moves towards the top of the mountain, where it is maximum. As a result, if a wind turbine is installed outside the midpoint of a ridge, the wind speed will not be increased. But the ideal place to be is behind a ridge where the wind is causing turbulence.

 

Four, the site selection of the terrain above or near the building

Although it is desirable to put wind turbines on pylons in flat, open areas, they may not be built on buildings near homes, in and around urban centers. In this case, it is necessary to understand what effect the building has on the airflow and what changes occur in the output power. The flow creates a small turbulent flow behind the building and a horseshoe around it. When the wind turbine is set on the windward side of the building, the spacing of at least 2 times the height of the building should be maintained; In the downwind side of the setting, to leave at least 10 times the height of the building spacing; When set above the building, the height of the fan must be more than 2 times the height of the building.