Estimating Wind Speed for a Wind Turbine Site
Estimating wind speed is one of the first steps in reviewing whether a small wind turbine site may be technically worthwhile. This guide explains how terrain, grid reference location and historic NOABL data can be used to form an early-stage view.
Why Wind Speed Estimation Matters
An early wind speed estimate helps indicate whether a site may be suitable for a wind turbine before more detailed work is carried out.
Wind turbine performance depends heavily on the local wind regime. Before committing to a project, it is sensible to form an early view of the likely annual mean wind speed at the proposed site.
At early stage, this is often done by combining a grid-reference-based estimate with a practical review of the surrounding terrain. Open ground, hilltops and exposed ridges generally perform better than valley bottoms or sites surrounded by trees and buildings.
This kind of estimate is useful for screening sites, but it should always be understood as an approximation rather than a direct on-site measurement.
Assess the Nature of the Surrounding Land
The character of the land around the turbine affects how much the wind is slowed before it reaches the rotor.
The surrounding landscape has a direct effect on wind speed because the surface of the land creates friction. Smooth and open ground slows the wind less, while features such as hedges, trees, woodland, buildings and rising terrain can reduce wind speed and increase turbulence.
Historically, this has been accounted for by applying terrain-based correction factors to the annual mean wind speed. The rougher and more obstructed the site surroundings, the greater the likely reduction in useful wind.
A sensible rule is to consider the site and the surrounding land character over roughly 1 kilometre, rather than judging the turbine position in isolation.
Find the Site Grid Reference
A grid reference is needed to identify the correct area for early-stage wind speed lookup.
To estimate wind speed for a proposed turbine site, you first need the site grid reference. This allows the site to be linked to the relevant mapped wind dataset.
For ease you can use postcodes on our calcualator to find the relevant data. Then you can download a google earth file which covers a 3 by 3km grid around that postcode.
The traditional format used for this process is the standard Ordnance Survey style grid reference, typically made up of two letters followed by six digits. For practical use, the letters are kept at the front and the digits are separated into equal easting and northing groups.
This step does not measure the wind directly. It simply locates the site within the correct reference square for the next stage of the estimate.
Use Historic NOABL Data as an Early Indicator
The NOABL dataset has historically been used to obtain an annual mean wind speed estimate for the relevant 1 km grid square.
The NOABL database has traditionally been used to provide a long-term annual mean wind speed estimate for a location. We still use it as the basis for early screening.
The estimate relates to the 1 kilometre grid square containing the site rather than to a direct measured point at the turbine position. That means the result is useful as an indicator, but it should not be treated as a precise site-specific measurement.
The original source is no longer available in its former public form, we have created the following tool, to access this data.
Why the Result Can Differ From Reality
A mapped wind estimate is useful, but there are several reasons why the actual turbine position may perform differently.
A site can sit within a 1 kilometre grid square that has a reasonable wind speed estimate, yet still perform poorly if the actual turbine position is in a sheltered hollow or below surrounding tree cover. Equally, a turbine on a nearby exposed ridge may see better wind than the wider square average would suggest.
Terrain effects also matter over distance. Wind is slowed not only by immediate obstacles close to the turbine, but also by the wider land cover and roughness around the site. The result is that an average figure alone is never enough to describe the real operating conditions fully.
For that reason, wind estimation should always be combined with practical site judgement, terrain review and, where justified, more detailed follow-up assessment.
Main reasons for variation include:
The result is based on a 1 km grid square rather than a measured point
Hilltops and ridges may be windier than the square average
Valley floors and sheltered positions may be less windy than the square average
Trees, buildings and rough land can reduce useful wind speed
The estimate may overstate or understate the real site conditions
Early-stage wind speed estimation is best used as a screening tool. It helps identify whether a site may be promising, but it does not replace engineering judgement or site-specific review.
A Sensible Early-Stage Sequence
The most reliable early view comes from combining mapped wind data with practical site assessment.
Supporting Insight Pages
Wind speed estimation is strongest when considered alongside siting and wider early-stage project review.
Need Help Reviewing a Wind Turbine Site?
SJ1 Renewables can support early-stage wind site review, turbine siting assessment and wider feasibility work for rural renewable energy projects.