Author: Alicia Webb
Wind farm layout design is all about putting your turbines in the best possible locations within your site boundary. Defining these 'best possible' locations takes into account lots of factors, including wind speed, appropriate spacing of the turbines and various constraints which may be discovered during your detailed assessment phase.
Generally layout design is done by wind engineering consultants, the same people who will analyse your wind data and calculate the expected energy output of your wind farm. Their software can optimise the layout for the best possible energy output, taking into account the topography of your site. If you provide the consultant with additional restraints as your detailed assessment studies reveal them, they can adjust the layout and recalculate the energy output.
The wind farm layout refers to the positions of the wind turbines in your wind farm site. Exactly where they are located is very important, and needs to take into account a long list of factors, described below.
Wind speed
The first and most important factor to consider when locating your turbines is wind speed. Generally the wind farm layout will be designed by technical experts using wind modelling software. This software will take into account the topography of your site and your monitored wind data, and calculate the best places to put turbines for the fastest wind speeds. It will also account for obstacles around the site like other hills and trees, etc.
Wake effects
When the wind blows through a turbine, spinning it to make electricity, the wind downstream from the turbine becomes slower and more turbulent. If this slower and more turbulent wind blows immediately through another turbine, the second turbine would generate a lot less energy than the first. For this reason, it's important to space turbines apart. Spacing them apart gives the slower, turbulent downstream wind a chance to disperse and mix with the fast winds that didn't hit the first turbine. While spacing is important, it means that not all of your turbines will be able to take advantage of the fastest locations on your site. Again, these calculations will be done by technical experts using software.
Spacing for wake effects is related to the length of the turbine's blades. New layouts and energy calculations will need to be completed for the different types of turbines you are considering for installation.
Construction feasibility
Technical wind modelling experts will be able to calculate the best places for turbines, based upon the results of a computer simulation. However, you will still need to consider practical construction issues. Firstly, very steep hill sides present access issues for the trucks which carry enormous turbine components. Secondly, the hills on which you intend to put wind turbines need to have adequate flat space for a 'hard stand'. A hard stand is a flat area adjacent to a turbine location which is used in construction. The crane will stand on it, and the turbine blades will be put together there too. The size of the hardstand is determined by the type of turbine, so ask the manufacturers of any turbine models you're considering. If your location can't accommodate the hardstand, your layout will need to be adjusted.
Grid considerations
As your project progresses you will continue to develop grid connection constraints which may determine how many turbines you can have. If grid constraints mean that your layout has too many turbines, it will need to be adjusted and energy calculations will need to be re-run.
Other constraints
Having taken into account wind speed and wake effects, your turbine layout will be the best it can be based on your site boundary and topography. The expert consultant will have calculated the energy that will be produced based on your monitored wind data, and you will have designed a layout for your wind farm.
This, however, is rarely the end of the story. Planning requirements dictate that you must complete a long list of studies to investigate the effect a wind farm will have on its environment and the community. Many of these studies will have the potential to affect your layout, and in that case the new layout constraints must be given to your layout consultant who will adjust the layout and recalculate your expected energy output.
For example, if your cultural heritage study finds that you have located a turbine right on top of a site of cultural significance, you will have to move it away. The cultural heritage study will draw a boundary or exclusion zone and the turbine will be moved. This move might change the wake effect on the other turbines, so the worst case scenario is that the whole wind farm may be adjusted. New energy calculations will feed into a new business case and inform a new feasibility for your project.
There are several types of studies that have the potential to cause an adjustment of your layout. These include flora and fauna, visual assessment, electromagnetic impact assessment, noise and shadow flicker assessments, and the geotechnical assessment.
Balance of plant design
On a wind farm, turbines aren't the only things that needs to be built. In addition you'll need under ground cables, roads, and some sort of substation in order to connect the turbines to the electrical grid. Depending on the various constraints governing their positions, you might need to reconsider your layout.
Planning considerations
As discussed, wind farm layout tends to be an evolving part of the wind farm design. Because you will be working on your planning application in parallel with your detailed technical assessments, you might apply for planning approval without having completely firmed up your layout.
In this case, it is normal to submit a siting 'envelope', whereby you apply for approval to build wind turbines within a certain area on your site. This can be a series of big circles with a 100 m radius, centred where you think each turbine will be sited. This provides certainty to the approving authority as well as flexibility for changing siting constraints. How well defined your layout is at the time of planning application will depend on the authority reviewing it.