Monday, 19 August 2013

Visibility of Wind Farms

There is much discussion of how wind farms are affecting views of the landscape.

I suspect I'm in a similar position to many people. I like the idea of renewable energy. I don't want to see some fine landscape trashed. I know enough about it to realise that these positions are not entirely compatible. I don't know enough about it to understand how the conflict can be resolved in practice. However, I do think it's important to have the debate . 

So I was particularly struck recently by pictures of Dunstanburgh Castle, taken from the sea, which show Middle Moor Wind Farm looming over the iconic ruins. We walk along the coastal path here fairly regularly, and I hadn't noticed the turbines myself, so I thought I needed to explore a bit more. As the above map shows, the reason I hadn't noticed the turbines was that they are not visible from the coastal path, though they are from further inland, and, of course, from out to sea.

I'm not qualified to enter into a debate on the benefits of wind farms, or where they should be sited, but it does seems to me that a lot of people might find it useful to plot the degree to which they are visible. Some might want to find and visit beautiful landscapes that aren't affected by wind farms, some might want to highlight particularly bad examples as part of a campaign, and some might want to understand what effect different proposals are going to have. 

This is how I went about it:
  • You will need a copy of Quantum GIS, which is available here. To be honest you also need to be reasonably familiar with how to use QGIS. Plotting the visibility of wind farms probably isn't the best place to start. So if all of this is completely new, it might be a good idea to get experience with QGIS, or to get help before proceeding much further.
  • You will need some background maps for positioning everything. I used the QGIS OpenLayers plugin to apply a base Open Street Map layer in order to get myself started. For the image above I have replaced this with the full colour raster version of OS VectorMap District from OS OpenData
  • You will need to know the location and the height (above ground level) of the wind turbines, and you need elevation data for the surrounding area. For elevation I used the OS Terrain 50 elevation data from OS OpenData
  • You need the "Visibility" Plugin for QGIS, which is available on the "contributed" repository - here. You obtain and install this from the Plugins->Manage Plugins menu. 
First, install the Visibility plugin, unpack and organise all the bits and pieces that you have collected, and get yourself positioned in the right general area in QGIS. I don't think this is essential, but things seemed to go more smoothly if I used OSGB projection for everything (27700) since this is what all the OS data uses.

Create a single elevation layer from the various tiles provided with  Terrain50. The Raster->Miscellaneous->Merge menu guides you through the process, and I used Raster->Extraction->Clipper to trim down the area a bit, which speeds up the subsequent analysis. It's useful at this stage to set transparency on this layer quite high, so that you can see the underlying map when you get to the next stage. Personally I also found it useful to stretch the grey-scale on this layer to get some idea of the shape of the terrain, but this isn't essential to the process, and I didn't use it in the final map. 

Initiate the analysis, using the Plugins->Visibility menu. This asks for the position of the viewpoint (i.e. where the wind farm is, in this case). You do this by pointing and clicking on the map. You will also need to enter the height of the masts. What you are actually plotting here is which parts of the ground surface are visible from the top of a mast. What we really want to know is where a substantial chunk of the mast is visible to walker or cyclist (at eye level), from inside a vehicle, or from a bedroom window. I don't know what best practice is for determining the height in these circumstances. In the plot above I've used the total height to the tip of the blades as a "worst case", and 50% of that as a "normal case", then I plotted the two layers with different colours to give some indication of how much variation there is. My guess is that I'me being a little harsh, but not too far away from what most people would expect.

The final step was to set the properties of the different overlays so that areas with no visibility are completely transparent, while areas that we think have visibility of the wind turbines are both brightly coloured, and partially transparent. 

All this seems to work reasonably well over a fairly broad landscape. At a more local level, trees and buildings rather confuse the picture. I wouldn't want to get into an argument about what is visible from where without actually going and having a look on the ground. But at least this gives some indications of what to expect, and it might save a lot of wandering about.

And finally, I've just been figuring this out as I went along - so any suggestions of how to improve the process would be very welcome.