Micrositing of Small Wind Turbines
Choosing the right type of wind turbine (WTG) and its exact position are very important part. This process is called as micrositing.
During micrositing many aspects have to be considered.
- Wind conditions (past & present data concerning wind speed, wind speed average and preferably wind speed distribution)
- Any municipality rules/requirements regarding installation/height requirements(e.g. distance from building, distance from airports, sensitive areas etc. )
- Ownership of the full installation area.
- Accessibility to the site.
- Influence of the turbine on the environment(e.g. shadow flickering, noise emission) It is important to keep a distance to next residence in order to not disturb the inhabitants by noise emission and shadow flickering of the turbine. Normally there have to be at least 200m between turbine and next residence.
- The following points are important for proper siting & good power generation.
- Distances between the individual turbines (if multiple turbines are installed) distance should be atleast 7XD where D is the diameter of the rotor. This ensures that the WTG at the front does not block wind flow to the WTG behind it. A rotor of WTG causes high turbulence that reduces the energy output of the next turbine. Compared with single stand alone turbine there are also higher loads on the following turbine because of the increased turbulence. Therefore the minimum distance between two turbines depend on the wind conditions and may be 7 rotor diameters (D) in the main wind direction and 5 diameters in other direction.
- To allow smooth flow of air and avoid turbulent flow to the turbine rotor, turbines should be placed at a distance twice or more times the height of any man made structure. The turbulent wind flow created by the structure generally extends vertically to twice the height of the structure. so small structure may not have any impact on tall turbines. Please see diagram no. A & C below.
- Avoid areas of steep slope. The wind on steep slope tends to be turbulent and has vertical component that can affect the turbine. Also the construction cost for steep slope are greatly increased.(pls. see the diagram D below)
- On the ridgelines and hilltops, set the turbines back from the edge to avoid the impact of the vertical component of the wind. (pls. see the diagram )
- Preferably select site with flat terrain where there are no significant obstacles around the proposed location of wind turbine up to a distance of 8L where L=2.25D+/-0.25 and D is the rotor diameter of the wind turbine.
The knowledge of wind conditions is very important for installation of wind turbine. It is always best to have measured data of the planned site for a period of at least two years .But this is not always possible for small WTG installation where the cost of measurement may exceed the price of the WTG system. In case of shorter measurement of period wind consultant can find out the condition by an interpolation of long term measurement of nearby weather-station.
Based on the information about the wind condition and the exact load it is possible to choose the type and capacity of turbine which provides the highest energy production while meeting the external requirements. Based on realistic forecast of the energy production it is possible to decide whether to invest in wind energy or not.