Wind Farm Placement
Global Mapper’s tools for terrain visualization and analysis, along with the ability to stream available data and convert data from one format to another, allow ample opportunity for suitability analysis. When considering the placement of a wind farm, the terrain, land cover, windspeed, airspace restrictions, and current land use need to be considered.
For this analysis, we will consider the wind power generation potential in a county of the US state of Vermont. To begin, terrain data is loaded into Global Mapper from the Online Sources dialog. This data from the USGS 3DEP program streams into Global Mapper as a 3D digital elevation model, but for faster rendering and analysis, data for the area of interest is exported to a local file. In this case, the data is saved to Global Mapper Grid format, a proprietary raster elevation format created to work with Global Mapper specifically.
To begin narrowing down suitable locations for a wind farm, ponds, rivers, and lake areas are removed from the dataset. Loading a Vermont hydrography shapefile into the workspace, these water features can be selected and used to cut holes in the terrain data. Through the Layer Options for the terrain model layer, the option to Cut Out Currently Selected Polygons(s) is chosen, leaving only the land areas of the terrain displayed.
Wind turbines are tall, and their construction requires a sturdy and relatively flat terrain. Generally, slopes below 10% (5.71 degrees) are acceptable to support wind turbines. The elevation model for this area can be shaded by slope, but for a clearer visualization of the 10% slope threshold, a custom shader is created in Configuration to highlight areas with slopes below 5.71 degrees.
To extract areas with acceptable slopes, Global Mapper Pro’s Vectorize Raster tool is used. This tool creates polygons bounding areas that lie within a specific slope or elevation range. In this case, it is used to create polygons enclosing areas with slopes below 5.71 degrees.
In order to generate power with wind turbines, there needs to be sufficient wind. A wind speed map from the National Renewable Energy Laboratory (NREL) provides data for an exploration of wind speeds at a certain height above the ground. Using a GeoTIFF layer representing wind speed 100 meters above ground, the average speed can be visualized.
The per-pixel values in this gridded raster layer are treated similarly to elevation values in Global Mapper, and, as with terrain data, customizing a shader and displaying the corresponding legend allows for a clearer look at the wind speeds over the area of interest. To remove areas in which wind speeds are not sufficient for a power-generating wind turbine, the corresponding pixels can be cropped in the Layer Options accessed through the Control Center. This allows for clear visualization of areas with sufficient wind speed. For optimal power production, wind speeds need to be at least 15 miles per hour, and speeds above 55 miles per hour risk damaging equipment. This range of ideal wind speed, 15 to 55 miles per hour, equates to 6.7 to 24.5 meters per second.
To convert this data into vector format, Global Mapper Pro’s Vectorize Raster tool is used again to extract the areas with sufficient wind speed as vector features. The use of vector data allows additional information to be stored as attributes, and using the spatial operations tool, the relationship between areas of optimal wind speed and other relevant vector datasets can be analyzed.
With areas of adequate wind speed and slope identified, Global Mapper’s Spatial Operations tool is used to create a new layer of polygons identifying areas that match both criteria. Using the Intersection operation, the areas covered by both the acceptable slope and ideal wind speed layers are created in a new layer.
Using the terrain and wind speed data to identify suitable areas for wind turbines provides a good start, but land use and restrictions need to be considered to further narrow down acceptable wind farm locations.
One factor to be considered when placing wind turbines is the impact on the surrounding airspace. Airspace restrictions around airports need to be considered as wind turbines reach into the airspace and have the potential to encroach on flight paths and runway approaches, and can cause air turbulence dangerous to air traffic.
By streaming freely available raster FAA sectional maps through Global Mapper’s built-in online source list, the airspace restrictions can be explored. Vector point features for each airport can also be loaded and used to generate range rings denoting restricted air space regions.
The Spatial Operations tool is then used to eliminate restricted airspace regions from the layer containing areas of suitable slope and wind. The difference operation identifies regions of one layer that do not overlap with features in another layer and is used to cut out the restricted airspace regions from the suitable terrain and wind layer.
Land Use Analysis
After determining the suitable locations in terms of wind potential and build-ability, current land use needs to be considered for any planned construction. Land cover data and parcel data for this county reflect the current land use and guide the suitability analysis.
The United States’ National Land Cover Dataset (NLCD) is a coarse raster layer describing the land cover in an area. As a palette image, each pixel color represents a specific type of land cover, and this information can be used to remove urban or developed areas from consideration for a wind farm site. Additional land cover types, such as wetlands and water, can also be removed as construction in these areas is impractical.
Available parcel data for this county is also loaded, and the attributes associated with this layer describe the parcels and land use. An attribute search can be used to preliminarily identify parcels that are not conducive to wind farm placement. These parcels include parks, schools, roadways, and current solar farms, among others.
Global Mapper Script
While the further filtering of suitable wind farm areas can be done manually through the Global Mapper user interface, the workflow can also be executed via Global Mapper Script. Global Mapper scripts can be created in any text editor or with the Script Editor tool in Global Mapper Pro.
As a first step, the raster land cover data is converted to vector areas using Global Mapper’s Create Equal Value Areas tool. This action vectorizes the raster data layer, allowing the analysis to continue using only vector polygon features.
Next, a complex Spatial Operation is defined and run. This can be done on the Scripting tab of the Spatial Operations tool or within a standard Global Mapper script. In this spatial operation, two feature sets are selected based on attribute values: one describing undesirable land cover types and the other describing unusable parcels. These selected features are found within a spatial operation but use the same attribute query syntax used in the Search Vector Data tool. The selected features from the land cover and parcel layers are placed in a single feature set defining the areas unusable for a wind farm. This set of unusable areas is then used with the Suitable terrain, wind, and airspace layer in a different operation to determine suitable and usable lands. Finally, it is important that the wind farm location can be connected to the existing power infrastructure. The set of suitable and usable land areas is used in an intersect operation with a layer of transmission lines to create a new layer of suitable areas with existing powerline infrastructure.
After creating a new layer with a Spatial Operation, key attributes from the land cover and parcel layers are copied to the generated suitable areas layer. This stores the needed information about land cover, parcel ID, and ownership with the suitable areas layer.
This multifaceted script is run through the user interface Script Editor in order to use the existing layers in the workspace, with minimal user input. Alternatively, this multi-step workflow can be manually completed within Global Mapper Pro’s user interface, an example of which can be seen here in a Solar Farm Placement analysis. When this script finishes processing, the resulting Suitable Wind Farm Areas layer appears in the workspace for continued analysis.
The final layer created from this script shows the suitable areas for wind farm development. These areas have met the outlined requirements, meaning they have adequate wind, buildable terrain, acceptable land cover, and generally available parcels. Additionally, the land cover types, parcel descriptions, and owner information have been added to the suitable wind farm area polygons to make further research and continued analysis easier.
WORK MADE EASY WITH GLOBAL MAPPER
As with any GIS workflow, the results of this wind farm suitability analysis can be exported to any supported format to be shared with colleagues and customers. This analysis can be taken further with additional feature measurements, Global Mapper Mobile, such as the surface area of each suitable location, proximity to nearby transmission lines, and even the planning of site visits and additional data collection with Global Mapper Mobile.
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Denholm, Paul, et al. “Land-Use Requirements of Modern Wind Power Plants ... - Nrel.” National Renewable Energy Laboratory, Aug. 2009, nrel.gov/docs/fy09osti/45834.pdf.
Haaren, Rob & Fthenakis, Vasilis. (2011). GIS-based wind farm site selection using spatial multi-criteria analysis (SMCA): Evaluating the case for New York State. Renewable and Sustainable Energy Reviews. 15. 3332-3340. 10.1016/j.rser.2011.04.010.
New York Wind Energy Guide for Local Decision Makers: Wind Energy Basics, NYSERDA.