Wind Farms Planning Services
Figure 1 shows the flow chart from planning to the completion of the project as well as the phases from the operation to the dismantling of the turbines. The planning phase is divided into three parts:
Services Details
A wind power project can basically be divided up into three phases:
- Planning,
- Erection, and
- Operation of the wind turbines.
In each phase, three important points have to be kept in mind:
- Technical aspects,
- Permits and legal aspects, and
- Economic aspects,
Planning of a wind farm
- Initial investigations,
- Site analysis, and
- Actual planning procedure.
During initial investigations, the basic feasibility of the project at the site selected is examined before moving on to additional formal steps of site analysis and planning that entail costs.
Technical planning aspects
Estimation of wind conditions
An estimation of local wind conditions is especially crucial in the selection of the site. If the wind speeds are 10% smaller than expected, the energy yield will fall short by more than 30%, which can quickly cause economic problems. In addition to an evaluation of the wind speed based on general meteorological data, wind prediction also requires an analysis of the orography of the site selected, i.e. the structure of the terrain, the roughness of the surface, and the type and size of the terrain's boundaries. Furthermore, any individual obstacles - such as rows of trees, buildings, and any other wind turbines - must be registered accurately. Already at this stage, an experienced expert must be consulted to help determine how to continue and which methods will be used to accurately determine the potential of local wind energy production. Various methods are commonly used to measure, simulate, and evaluate wind conditions. Depending on local conditions and the quality of any wind and data available for the region - such as from measuring stations - a methodology will be chosen, and a decision will be made as to whether additional wind measurements are required to corroborate the initial findings.
Initial estimates of installed capacity and energy yield
The space available and, above all, the access to the grid are decisive factors in determining how many turbines with which nominal power output should be used.
Therefore, the local grid operator has to be asked for the maximum possible wind power feedable into the grid has to, how far away the next feeding point is, and what the voltage level is for a connection to the grid. For large wind parks (> 20 MW), it may make sense or even be necessary to set up you’re a separate transformer station. The number and nominal power output of the wind turbines to be installed can be determined from these two boundary conditions (the available space and great capacity). This estimation then serves as the basis for the first energy yield prediction.
The expected yield is determined under consideration by wind direction sector using the frequency distribution of the wind speed determined for each wind direction sector and the performance characteristics of the wind turbines. This calculation is needed to find the optimal arrangement of the turbines within the wind farm so as to produce the greatest overall energy yield and minimize the inevitable effect that the wind turbines will have on each other (mutual shelter effect or 'wind shade'). Figure 2 shows the layout of the wind farm based on such considerations.
Draft layout of a wind farm
Of course, the ultimate goal in looking for the optimal arrangement of wind turbines on a given site is the highest possible energy yield of the entire wind farm over its service life. On the other hand, the conditions and costs of installation -- such as construction of power lines from the turbines to the transformer and interconnection stations or roads for assembly, maintenance, and service vehicles -- also play a role in the arrangement of the turbines. Today, a number proven of planning tools are developed -- such as software like WinPro, Windfarmer, etc. -- for providing an optimal layout of wind farms efficiently and quickly.
Additional restrictions on the layout of the wind farm -- such as prescribed distances to buildings, environmental protection regulations, or maximum building heights -- are not only the result of technical considerations, but also of laws and regulations imposed by public officials. It is best to find out about what restrictions apply right away lest such conditions make time-consuming, expensive changes in planning necessary in order to get permits.
General local frameworks
Find out who owns the property, and sign leasing agreements (or at least preliminary agreements) with the property owners. The general local frameworks are studied mainly to ensure the practical implementation of the project. Find out:
- Whether the turbines can be set up stably,
- Whether the site can be reached by all of the vehicles required, and
- To what extent transmission lines are needed to feed power to the grid.
In addition, access must be ensured to all turbines for servicing, maintenance, and repairs over their entire service life.
The soil must be studied for each wind turbine to ensure that the subsoil can handle the loads of the foundations. The shape of the foundation is based on these studies. Generally, flat gravity foundations are used, with pile foundations being used if the soil is too soft.
Access and transport roads for construction should be investigated, as should the locally available space for cranes. Buildings (some of which may be of historic value), underpasses, overhead lines, traffic signs, train lines, antennas, curved alleys lined with trees, bodies of water, etc. may all represent obstacles towards the delivery of large system components, such as tower sections and rotor blades. Furthermore, such climatic conditions as seasonal heavy rains and storms must be taken into consideration.
The location and type (such as voltage level) of grid access must be determined. In simple cases, a short stub cable can be used to connect the wind farm to the feeding point. The power cables may also sometimes be directly connected to the next transformer station where enough grid capacity is available; if none is available in the nearest station, a dedicated cell can be added for the farm. Very large projects often require their own transformer station so the wind farm can feed into high-voltage grids.
The distances and types of cable routes used must be selected with respect to technical and economic aspects. If the cable routes are long, planning may be more intricate and require an environmental impact assessment.
2. Permit aspects
Local construction law determines what is required for a wind farm or a single wind turbine to be eligible for a permit.
In addition, the environmental impact of the turbine generally has to be assessed as early as the planning phase in most countries. Generally, an environmental impact assessment is then conducted.
The ecological impact of wind turbines
There must be a determination of whether the impact that the construction and operation of wind turbines will have on the environment is acceptable in terms of nature conservation. Additional reports may be required to assess the impact on flora and fauna, such as in areas where birds build nests or migrate.
Local authorities check whether any considerable, undesirable effects on the environment are expected with consideration of the legally applicable criteria. If an environmental impact assessment has to be conducted, maps of biotopes, plants, and animal species -- such as the breeding grounds and habitats of migratory birds or bats -- are included along with an assessment of the visual impact of the wind farm.
The following items are some of the indicators of how the wind turbines will affect humans and the environment:
- A map of areas with rare birds,
- Other aspects of animal and plant protection,
- Noise impact reports,
- Reports on shadow casting caused by rotors, and
- Heritage and landscape conservation.
Noise pollution from wind turbines
There are legal limits for noise pollution at different times of day in residential areas, industrial areas, rural areas, etc. Measurements of the noise pollution from wind turbines are part of the general testing to fulfill, for instance, IEC 61400-11. For each type of turbine, the sound power level, frequency (dominant individual tones), and pulses (low-frequency 'rhythms') are determined. People generally find such characteristics, which are generally caused by the gears, generator, or inverter, to be especially annoying. The noise pollution on site can be forecast based on the findings of noise pollution measurements for a specific type of turbine.
The level of noise pollution than a wind turbine produces is not constant but rather varies according to the current output, i.e. the wind speed. Generally, the noise (sound power level) generally increases by around one dB(A) for each meter per second of wind speed. However, the wind noise caused by trees and bushes also increases accordingly, usually even more so than the noise from the machine. The noise caused by turbines is also stronger in specific directions, which is taken into account in the measurements of independent testing institutes and in the wind farm planning software.
The noise level is indicated in logarithms. An increase of 3.01 dB(A) indicates that the perceived noise level doubled.
During planning, maps of isophones -- lines indicating a specific noise level -- are created for the planned site (see Figure 3). The overall noise level of all of the turbines is the product of the overlapping of the individual noise levels of each turbine. Thus, the areas with the highest levels of noise can be identified and measures taken to reduce these levels by changing the arrangement of the turbines and the types of turbines used in order to comply with legal limits.
If local residents cast doubt on these predicted noise levels, officials will measure the levels themselves. If they then impose conditions -- such as at night when the wind blows in a certain direction -- variable-speed turbines with adjustable pitch can be used to reduce the noise by slowing the speed of the rotors during operation. Turbines that run at a fixed speed and whose rotor blades cannot be pitched in and out of the wind do not offer this option. In the worst case, the operator might then have to switch off the turbines at night, which would reduce the energy yield considerably over long periods. Therefore, it pays to have a prudent forecast of noise levels and generous safety distances.
Shadow casting of wind turbines
Another aspect that may affect the issuing of permits is whether the rotor blades cast a shadow on adjacent structures, creating a sort of 'disco effect' as the sun light passes through the blades. This item should also be investigated for the 'worst case' in planning; in other words, full sunlight without clouds should be assumed. The calculations are based on the local orbit of the sun across the seasons, the height of the hub, and the diameter of the rotors.
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