SARAWAK METEOROLOGICAL MAST DATA
Recorded meteorological mast data was received from Jabatan Meteorologi Malaysia for four sites across Sarawak Sibu, Miri, Kuching and Bintulu airports. The location of these sites can be seen in the following Figure. The wind data provided was an hourly time series of mean wind speeds and direction covering the 2008 calendar year from 01/01/2008 to 31/12/2008 inclusive. The data received at Kuching Airport was at a height of 12.2 m AGL, the other three sites ‘anemometer heights were unknown although in HTC’s experience airport anemometers are generally between 10 m and 15 m AGL.
Figure: Sarawak map of prospective sites and mast data locations
Significant limitations are inherent in the mast data provided due to their placement at airports and low height of the anemometers above ground level. Significant uncertainties can occur as a result of turbulence created from wind flow around surrounding buildings and air traffic. The roughness of the ground can impact on the wind speeds by causing non-laminar flow. Due to the nature of airports it is often the case that obstacles are changing over time such as the addition of new buildings or changing surfaces. This can affect the wind speeds when measured at such a low level. Due to these limitations the data is only used to identify trends in the wind speeds such as the changing of magnitude of the wind with time to display diurnal (daily) and seasonal (monthly) variations.
In the absence of extensive site data, HTC has utilised the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) software package known as The Air Pollution Model (TAPM) Version 3 which predicts three-dimensional meteorology and air pollution concentration. TAPM takes high-level synoptic data and produces low-level grids (or time-series) of wind regimes across a defined region for a defined time period.
Studies have been undertaken that verify results against actual mast data to a reasonable degree, thus providing the confidence to apply the TAPM model to a high-level initial-investigation study such as this.
The synoptic data used in this study was sourced from the CSIRO for the year 2008. Output from the model can be extracted as low as 10 m and is also available at 25 m, 50 m 75 m, 100 m, 150 m and then numerous levels up to 3000 m above ground level.
For this study the hub heights of likely turbines are around 75 m above ground level. However, the modelled data is based on coarse resolution terrain and surface roughness classes so it is not recommended that data at this close to the surface be used. Verification studies by HTC have consistently shown that the wind speed predicted by TAPM best matches wind speeds measured by a mast at lower heights (i.e. wind speed at 75 m in TAPM does not equate to wind speed measured by a mast at 75 m).
Consequently, the approach taken was to extract data from the TAPM model at a height of 150 m to best represent the expected wind speed at an approximate 75 m hub height based on HTC experience.
Validation of the TAPM model was performed by comparing generated wind data sets with the supplied mast data. TAPM was used to create an hourly time series for the year of 2008 at a height of 10 m AGL at each of the four airport sites Sibu, Miri, Kuching and Bintulu, where mast data was received. This generated time series was then compared against actual mast data to observe relationships between the two datasets and identify any significant features.
The modelled TAPM wind speeds were extracted at 10 m and 150 m AGL for each mast location and plotted against the site data. Correlations between the data sets, as well as seasonal and diurnal (daily) trends were assessed.