Wind Speeds

Wind Speeds

The relationship between energy yield and wind speed is cubic. Sites with slightly higher wind speeds have significantly higher energy yield for the same capacity installation than those with lower wind speeds.

Energy yield can be calculated using performance curves from different turbine models and measured wind speed data. Manx Utilities’ current energy yield estimates for the Earystane site use the Hadley data centre set to provide accurate energy yield estimates.

Manx Utilities have several different available sources of data for wind speed for Earystane:

• The Numeric Objective Analysis Boundary Layer (NOABL) Data set is a global wind resource model which includes data for the last thirty years from the Isle of Man meteorological office. This is the primary tool used by developers for estimating the energy potential of a site at the site selection stage and was used by Manx Utilities to support its decision making in selecting a site. The NOABL data set was compared to performance curves from known viable turbine models to determine energy yield estimates in the early stages of this project.
• The Hadley Centre Data set is a UK Met Office climate model resource, which provides accurate wind speed data over the last 5 years at 10 minute intervals. This data set is currently being used to determine accurate estimates for energy yield at the Earystane site.
• Data was collected by the Manx Electric Authority from an anemometer at the Round Table site, which is located 2km from Earystane, in 2000.
• A Sonic Detection And Ranging (SODAR) Device has been installed at Earystane since September 2023. This device samples a range of wind speeds at different hub heights from 50m to 200m at ten minute intervals. This data set will be required to provide assurance on the existing modelled data sets in order for a manufacturer to provide a warranty on energy yields for the site.

The average wind speeds from these studies are shown below:

Data Set	Earystane SODAR (2023/2024)				Hadley Centre Data Set	NOABL	Round Table Mast (2000)
Height	50m	100m	150m	200m	95m	45m	100m
Average Wind Speed (m/s)	10.62	11.69	12.68	13.37	11.4	10.1	9.2

The full SODAR data set from 6 September 2023 is available; the information will be updated as more data becomes available.

Earystane SODAR Data

What is a SODAR device and what is it used for?

A SODAR device works by emitting sound waves and recovering those which are reflected off moving, turbulent layers of air in the atmosphere.  An analyser within the device interprets the signal to calculate the different wind speeds in the package of air above the SODAR from 0m all the way up to 200m.

The average wind speeds identified for each site have been published in the Phase 1 Environmental Assessment report. The Earystane site also has the benefit of data from MEA studies in 2000.

The NOABL data set is considered suitable for windfarm feasibility purposes and is particularly useful when comparing sites; this is standard industry practice.

The windfarm design experts in Wardell-Armstrong have modelled energy yield for Earystane using a simulated data set generated by the Met Office using the Hadley Centre climate model. This dataset uses historical data from the island and the rest of the UK and spans a 5 year period with data extracts for every 10 minutes. This is set against manufacturer performance curves to accurately estimate power production for the site and consequently energy yield predictions. This energy yield also being directly validated by the data received from the SoDAR, however, a fully statistically valid wind assessment will not be possible until we have captured at least 12 months’ of on-site data.

 What is a wind rose?

A wind rose is essentially a vector diagram that illustrates wind direction and speed, measured at a specific site. It depicts the likelihood of every wind direction and its corresponding strength.

The wind rose diagram shows the wind speeds at the Earystane site in metres per second (m/s) against both cardinal and ordinal wind directions.

The length of each bar indicates the frequency of that direction. For instance, if only one bar is visible on the plot, it suggests that only one wind direction is possible. If several bars are present, all those directions will occur, with the longest bar representing the most frequent direction. It also shows the percentage (%) of time during which the wind blows in that direction.

A single bar may display several colours. These colours denote wind speed. In such cases, the colour occupying the longest segment of the bar indicates the most frequent wind speed for that direction.

 Below is a wind rose modelled from the Earystane site using data collected so far; this model is simplistically a vector diagram showing wind available from all directions, however the dominant direction of wind is from the south south-westerly direction, with the wind speeds greater than 20 m/s. This model is also consistent with the measured data being obtained from the SODAR device.

 

Fig. 1 Earystane Wind Rose