Wind Projects - Initial Site Selection

The initial site selection is the first phase in the development of any wind energy project. In this phase appropriate sites should be identified and their wind potentials should be estimated. By identifying environmental, technical, commercial and political constraints of the sites the project developer can decide whether a more extensive feasibility study should be conducted. As a starting point many developers visit the possible project sites, gathering first impressions about topography and infrastructure (roads, dwellings, grid-connection). A central task in this phase, available environmental and technical data must be collected.

First estimation of energy yields and related data requirements

The data requirements for a first energy-yield estimation of a wind project are defined by the following function

$E=\sum _{i=1}^{i=1}H(U_{i})P(U_{i})$

where H is the number of hours with windspeed U_i and P is the value of the power curve for the proposed wind turbine for the windspeed U_i.

A wind speed distribution function provides information about the frequency of different wind velocities occuring during a year. The generation of these distribution function requires long-time (for minimum one year) measurement. Thus for initial estimation, regional available data should be used, providing only rough information but keeping the initial costs low. The so-called power distribution function (PDF) can be obtained from a wind atlas (for example the NREL Oaxaca Wind Energy Atlas provides regional wind data for a state of Mexico). The US National Renewable Energy Laboratory (NREL) publishes information about wind speed distributions for many regions of the world on its Website[[3]]. PDFs are based on Weibull-Distributions and take into account local conditions like the roughness of the surrounding terrain (given by surface characteristics, obstacles and topology) are calculated for any wind direction using a divisions of 12 30° sectors. To use the values of the PDF in the function presented above, wind velocity values of all directions are integrated.

The power curve of a wind turbine depicts the energy output of the turbine at different wind speeds U_i. Paul Gipe suggests that the reliability of power curves especially for small wind turbines is limited, but for the initial estimation the available power curves are sufficient.

In case data availability is very limited (for instance only from remote weather stations), wind velocity modelling including meteorological data and site characteristics can be used.

Assessing local framework conditions

Information about grid-connection possibilities

If the wind project is supposed to be connected to the grid, it will be necessary to examine the local availability of the electricity grid. Local electricity suppliers have to be consulted concerning possible connection points, local grid capacity and likely costs of connection in the area. If only a short line to the next connection point has to be installed, costs of grid-connection will be low and the environmental impacts of this easiest case are small. In some areas the line connects the wind project directly with the next transformer station. In case the grid-capacity at the transformer-station is not sufficient for the connection of the wind project, the station has to be extended with an additional segment. Very big projects contain a separat transformer station required for the connection of the project to high-voltage grids. Taking into account this information the project developer knows, whether the grid-connection will cause high costs and environmental impacts due to a long distance to the next connection point. Thus it is important to initiate a dialogue with the local electricity supplier as early as possible.

Road access to the wind project site

Parts of industrial size wind turbines like Rotor blades or tower elements are transported by large trucks, which require appropriate roads. Routes between the site and the potential component suppliers have to be checked: Average bridge heights of 4,2 meters can be problematic for the transportation of the tower elements with the largest diameter and for the rotor blades of the biggest modern wind turbines, because some of them have a maximal width of 5,8 m. To avoid the closing of roads, rotor blades are normally transported in an position keeping the width of the whole transport vehicle low. Because of the high width of modern rotor blades a technique has been developed to turn the position of the blade in front of a bridge before the passage. Tight curves, often found in mountainous regions, can be a barrier for the long transport trucks, too. 

For the construction process, the site must have enough space to place at least one big and heavy crane. Usually the construction of big wind turbines is done by one very big main crane and a smaller 'assistant' crane. Besides space, construction machinery and vehicles need a high ground consistency for their operation.