Turn Key Wind Farms

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A wind farm development is usually a complex, collective effort where several different companies are involved – the developer, the financing institutions,  the WTGs manufacturer, the companies doing the BoP and installation and several other.

As many tasks are performed in parallel, often is not very clear to people who are not in the wind industry who is doing what and where.

Luckily, my friend Alberto from ACWA sent me this enlightening step by step guide. It has been developed by K2, a management company active in the business.

As you might imagine sometime the borders between activities are sometime blurry and some task might be shuffled. For instance, the environmental impact study in some countries is done very late (you will probably have to work only with some preliminary document), or the land lease agreement can be closed very late in time. We’ve been forced to relocate quite a few turbines in projects ready for construction where landowners where very reluctant to close a deal.

Also, as I’m obsessed with engineering and construction, I do disagree with the construction line, where  the “Balance of Plant Completed” comes in parallel (and terminates before) with the “Detailed Design Complete”. The implication of this structure is that you could start construction without having construction drawings, which is usually not a good idea )although is something that I see recurrently).

However the scheme is very instructive – I hope you will find it useful for your business.

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LIDAR topography is the best available solution available nowadays.

We have used it in several wind farms and I’m enthusiast of the results. It can be used to define earthworks with great precision.

Basically it is made with an airplane flying with a laser, a digital camera and a GPS.

The laser “sweep” the requested area and a receiver on the plane register the laser beam waves reflected by all the surfaces. At the same time high quality digital pictures are taken, and the position of the plane is registered thanks to the GPS.

This is how the equipment used looks like:

After the flight, the cloud of point obtained is filtered: first of all points are divided in classes, depending on the type of reflection (“echoes”). Groups of points representing trees, bushes, buildings and so on can be defined.

In the second filtering the intensity of the reflected beams is considered (vegetation and ground reflect with very different intensity).

The next step is to calculate a mean between different laser passages, as the same point may appear in slightly different coordinated.

This kind of mistake introduces a noise in the results, and contour lines may results as broken lines instead of smooth lines:

As a result of this data cleaning process, all the point can be classified as belonging to a type surface (trees, grass, building, and ground) and it’s possible to visualize them with a different color.

You can see in the following image some examples. In the first, an agricultural area is mapped. In green you can see the trees and in brown the ground:

In this other example, we mark in green the ground, in violet the trees and in brown the buildings:

In this final example, you can see as a whole town would look like in a cloud of points:

Control point are manually selected identifying them in the picture. They are used to put the data in the correct absolute coordinates:

Finally, a digital terrain model is produced using the Delaunay triangulation, to maximize the area of the triangles.

As you can see, the results are often exceptional:

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The components of a typical, utility size wind farm are:

  • One or more rows of turbine perpendiculars to the prevailing wind direction, with a distance between them of 2 or more diameters. For instance, if the diameter of the rotor is 100 meters, the distance would be from 200 to 300 meters. This distance is necessary to avoid induced turbolences to the rotor, than can affect the life of the generator. The number of turbine installed depend of the chosen model: a wind analysis is made, to define the WTG with the best fit for the location.
  • An underground power collection system, normally around 20kV-30kV. Sometimes an above ground medium voltage power collection system is used, although it happens very rarely due to the visual impact. Here there is a trade off between greater spacing between the WTGs (=more production) and greater cables length (=more energy losses and cable cost).
  • Civil works (roads, crane pads, foundations)
  • A substation transformer
  • An operation and management (O&M) building, to store spare parts and perform maintenance. Can be integrated in the substation.
  • A SCADA system, to collect and transmit data from the wind farm to the stakeholders.
  • A high voltage interconnection line to the grid. The distance from the substation to the grid can vary greatly, and if the wind resource is sufficiently high longer distance can be feasible. The interconnection point to the utility line can be co-located in the substation: in this case (frequent when the wind farm connects to an existing substation) there is no need for an overhead line.

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San Anton is a small wind farm (4 WTGs) located in Lillo, Toledo (Spain).

I had the opportunity to follow this project from the beginning visiting the site very often. I collected several picture to show the main phases of a wind farm construction.

First of all a met mast is installed, and wind data is collected. If there is enought wind in the area and the investment is profitable, an authorizative project is developed and transmitted to the authorities. Normally this project is developed using existing information, that is without developing a new cartography or other field works.

When this project is approved and it start to become reality, than the first work on site is the geotechnical report, done to define the subsoil conditions trought several in situ and laboratory test: here in the picture a trial pit is open to see the materials in the subsoil

Trial pit

A trial pit opened using a backhoe

With this information and a document provided by the seller of the wind turbine with the load transmitted to the base (shear, moment and vertical loads), a preliminary (or sometimes directly a constructive project) of the foundation is developed.

Afterwards, a topographical survey is developed. This can be done using standard field topography, a flight or LIDAR (a laser system that can provide a very dense cloud of point).

The following picture show the first step of the construction phase: topsoil stripping, an operation that consist in the removal of the first layer of fertile vegetal terrain that will be stocked and piled separately and used at the end of the works to revegetate the site area.

Topsoil stripping

Topsoil stripping

The next step is what is called earthworks: the construction of embankments and cuts. For instance in the image below a crane pad is under construction. Several thousands of cubic meters can be moved during this operation.

Earthworks

Crane pad earthworks

In parallel, the foundation for the met mast is constructed. The mat foundation is smaller than a WTG foundations: it is around 7 x 7 meters. It has 3 pedestal where the met mast will be connected.

Met mast foundation

Met mast foundation

After, the circular holes for the turbine foundation are opened: here you can see the topographer checking the dimension and horizontality of the hole. Several days of work are necessary to open the hole, depending on the hardness of the excavated material.

Foundation hole

The internal roads are continuously washed with water, to avoid accumulation of dust in the air due to the traffic of heavy trucks and other machinery.

Roads watering

The following step is to pour the blinding concrete, to assembly the anchor cage and to position the steel reinforcement bars (rebars). More info here.

This is how it looks a completed foundation:

Meanwhile, the operation and maintenance building is built nearby. It will host the SCADA equipment and the medium voltage switchgear:

O&M Building

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