Onshore Wind Methodology

How the capacity figures on the map are produced

Analysis grid: British National Grid, 50 m — 26,000 × 14,000 cells, each exactly 2,500 m²

Turbine: 5 MW on a 150 m rotor, spaced 5 rotor diameters (750 m) apart

Capacity method: turbines are placed on the surviving land and counted — no power density is assumed

Scenarios: 240 pre-computed combinations of the constraint settings

The tool answers one question: if a given set of constraints were applied, how much onshore wind could Great Britain physically hold? It does this by estimating where turbines can stand, not where wind farm boundaries would be drawn.

The grid

Everything is computed on a British National Grid raster at 50 m, so every cell is exactly 2,500 m². Setbacks are measured with a Euclidean distance transform, which means a 200 m buffer is 200 m in every direction.

Geotechnical & safety constraints

Always applied. These form the baseline available land: 79,059 km², about a third of GB.

Constraint	Rule
Wind speed	Excluded below 6 m/s at 100 m height
Slope	Excluded above 15°, computed from OS Terrain 50 directly onto the analysis grid
Airports	Within 2 km excluded
Roads	Within 200 m excluded — but not unpaved service tracks (OS Open Roads “Restricted Local Access Road”), which can exist because wind farms were built, not as a constraint on them. Including them excluded the land under 99.2% of GB’s existing turbines; excluding them takes that to 5.7%.
Railways	Within 200 m excluded
Overhead power lines	Within 200 m excluded (transmission only)
Waterbodies	Standing water excluded. Rivers and canals are not.
Forest	National Forest Inventory woodland plus a 50 m buffer excluded
Public green space	OS Open Greenspace — parks, playing fields, golf courses — excluded

Known problem — forest. This is the largest single exclusion, removing 32,038 km², and it is almost certainly too strict. 2.6% of the turbines standing in GB today are within 50 m of mapped forest, rising to 28.8% in Scotland, because commercial forestry is exactly where Scottish wind farms are built: plantations are felled around each turbine and replanted. Forest accounts for 68% of the real turbines the baseline still excludes. Not all forest is equal however: it may be viable to fell areas of plantation forest for onshore wind, but not old growth forest. To be conservative, all forest has been excluded.

Building setback: which addresses count

OS Open UPRN holds 41.6 million addressable locations, and it is not a map of buildings. Masts, car parks, bare land parcels, moorings and even wind turbines themselves all carry a UPRN. Buffering the raw layer carved a 250–1,250 m hole around every wind farm that already exists, and made this constraint remove roughly 4.7× more land than it should.

The layer is therefore filtered before buffering:

An address point is kept only if it falls inside, or within 10 m of an OS OpenMap Local building footprint. The 10 m tolerance is there because address seed points do not always sit within the drawn outline; across the removals the median gap to the nearest building is 10.6 m.
Address points that are a turbine’s own record are removed identified by being within 30 m of a known turbine and having almost no neighbours.
An improvement would be to use other building data products which include land classifcation with building objects, but many of these are not open access.

37,715,159 of 41,629,393 UPRNs survive (90.6%). At the 250 m setting this changes the share of geotechnically available land removed from 25.1% to about 5.4%.

Limitation: what survives is every building, not every dwelling. Barns, stables and farm outbuildings are kept, and no openly licensed dataset distinguishes them from houses. The setback is therefore a ceiling: the true figure for a dwellings-only rule would be lower.

Hard constraints

Toggled on or off by the user.

Biodiversity

Ramsar sites, plus a 2 km buffer
Special Protection Areas, plus a 2 km buffer
Sites of Special Scientific Interest
Special Areas of Conservation

These buffers are policy choices rather than technical limits: about one in ten existing GB turbines sits inside the 2 km SPA buffer.

World Heritage Sites

Site polygons excluded, with no buffer

Soft constraints

Landscape protection

Level 1: none

Level 2: National Parks

Level 3: + Areas of Outstanding Natural Beauty and National Scenic Areas

Level 4: + Green Belt

Listed buildings

Setback of 500 m, 1,000 m or 1,500 m

Distance from buildings

Setback of 250 m, 500 m, 750 m, 1,000 m or 1,250 m

From land to capacity

Earlier versions multiplied the surviving area by a flat 20 MW/km². That assumes every hectare is equally usable and is not tied to any particular machine. Turbines are now actually placed on the land:

Lattice. Turbines are laid on a hexagonal lattice at 750 m pitch — 5 rotor diameters for a 150 m rotor. Hex is the densest arrangement satisfying a minimum separation. A position is kept only if its cell survived every constraint.
Infill. A rigid lattice cannot use a corner whose lattice position happened to fall on an excluded cell. Every remaining available cell at least 750 m from all placed turbines becomes a candidate, and candidates are accepted in random order if they still clear 750 m from everything already placed. This adds about 53% more turbines, almost all of them along the narrow ribbons of land between constraints.
Grouping. Turbines within 2 km of each other are treated as one wind farm (chained, so a ridge-top string counts as a single site), and groups of fewer than three turbines are discarded as not developable.
Capacity is then simply the number of turbines multiplied by 5 MW.

The 2 km grouping distance is calibrated against reality rather than assumed: across the 424 REPD sites in GB, no real wind farm has an internal gap wider than 1,824 m, so 2 km holds every genuine site together.

Sensitivity: capacity depends on these choices as much as on the land. For the default settings, moving from 4 to 5 rotor diameters, or changing the grouping distance, moves the answer by tens of gigawatts. The turbine rating scales it linearly.

How much land wind farms actually occupy

The “land used” figure is a different quantity from the available land. A wind farm’s red-line boundary encloses the setback strips and unusable ground between its turbines, land this analysis excluded. To express the footprint of the farms themselves, capacity is divided by 10 MW per km² of red-line site area.

This is why the land-used figure can exceed the area the turbines were placed on, and the two should not be read as alternatives.

Geography on the map

Colour is carried by Westminster constituency (632 in GB), because capacity is extremely concentrated — a handful of Highland seats hold most of it, and a 27-zone map hides that entirely. Clicking any constituency groups it with the rest of its TNUOS transmission charging zone.

Zone outlines are drawn by dissolving constituencies onto their parent zone, so the two layers nest exactly. They are therefore approximations of the published TNUOS boundaries snapped to constituency edges, not the official geometry. The published file also has no zones for the Scottish islands, so Na h-Eileanan an Iar and Orkney and Shetland are assigned to the nearest mainland zone and flagged as such in the tooltip.

The colour scale is square-root rather than linear, again because of the concentration: on a linear ramp every constituency outside the top few would be the palest step.

Validation

The constraints were tested against 4,993 onshore turbines standing in GB today, by asking how many of them the model would forbid.

Test	Result
Real turbines on land the geotechnical baseline allows	67.0%
… under the most permissive full scenario	64.3%
Turbines within 50 m of mapped forest	22.6%
Turbines within 200 m of a road, excluding service tracks	5.7%
Turbines within 250 m of a filtered building point	5.5%

The remaining exclusions are dominated by forest, as described above.

The 33% of turbines which violate the geotechnical exclusions are primarily closer than 50m to a forest. Others are within 200m of a road, and a smaller number are within 200m of an overhead line. These exclusions should be more relevant to greenfield sites than existing sites.

What is not modelled

Radar and aviation safeguarding beyond the 2 km airport buffer — in practice a significant constraint on Scottish sites.
Grid connection capacity. Land is assessed as if it could be connected.
Planning and consent. This is a physical and policy-constraint map, not a forecast of what would be consented or built.
Farmland is deliberately not excluded, as wind is routinely deployed alongside agriculture.
Peat depth, aviation lighting, MoD low-flying areas, cumulative landscape impact.

Data sources and licensing

Data sources. OS Open UPRN, OS OpenMap Local, OS Open Roads, OS Open Greenspace, OS Terrain 50, OS Boundary-Line and Code-Point Open (Ordnance Survey); National Forest Inventory (Forest Research); protected site designations — Ramsar, SPA, SSSI, SAC — and landscape designations (Natural England, NatureScot, Natural Resources Wales); listed buildings and World Heritage Sites (Historic England, Historic Environment Scotland, Cadw); Green Belt (MHCLG); UK waterbodies (Taylor, P.J., Spatial inventory of UK waterbodies, UK Centre for Ecology & Hydrology); Renewable Energy Planning Database (DESNZ); TNUOS generation zones (NESO); wind speed at 100 m from the Global Wind Atlas; airports and railways from OpenStreetMap.

Contains public sector information licensed under the Open Government Licence v3.0.

Wind speed data from the Global Wind Atlas [version], a free, web-based application developed, owned and operated by the Technical University of Denmark (DTU), released in partnership with the World Bank Group, using data provided by Vortex and funding from the Energy Sector Management Assistance Programme (ESMAP). Licensed under CC BY 4.0.

Scenarios: the 240 combinations of the settings above are pre-computed, so the map responds immediately. Across all of them the capacity ranges from about 98 GW to 1,053 GW; the defaults shown on load sit near the bottom of that range.