Searching for stronger winds

Engineers Australia
June, 2008 Page: 80

GHD is using software to conduct wind prospecting for Melbourne based energy company Wind Power. This will determine the optimum locations, or hotspots, to build wind farms. Software called CalMet will model the wind speed within a 100km x 100km area identified as having potential wind farm sites. The software simulates the wind speeds and therefore the energy output for a year. GHD has completed its data collection of the area and is in the process of identifying hotspots. Prospecting towers will then be built at the hotspots to confirm the software's predictions.

Without software, the client would have to make a decision based on topographical features and historic meteorological data to decide on where to build the tower. This is difficult, as available meteorological data, usually from the Bureau of Metereology and private companies, are not suited for this purpose.

"Another problem is, in Australia there are big data gaps. The software modelling allows us to fill in the gaps by collecting wind data outside the area of interest and then interpolating it back into the grid," said Barry Cook, GHD's team leader for air and noise assessments based in Melbourne. "This gives us a more accurate picture on where a wind prospecting tower should be built." The information can be used to influence the design of the turbines. A coastal cliff for example, would demand a different design to a site at a ridge line on the western side of the Great Dividing Range.

In simulating the wind conditions, the software builds a topographical model by considering elevation, pressure, temperature, humidity, and the land use type (water body, forested area, etc) which determine how rough the surface is. The software splits the vertical space into 20 levels, one of which is at the turbine hub height, across the 100km x 100km area. It then performs a conservation of mass and momentum calculation as it steps through each hour of the data for a year. This takes about a week to compute. It is then able to work out where the highest energy return will be by converting the wind speed into an energy output using a standard turbine.

Other projects might call for prognostic software such as TAPM (The Air Pollution Model) which was developed by CSIRO. "One of the challenges in wind modelling is deciding on the correct tool and this depends on what data inputs are available. The client originally wanted to see a TAPM run but we convinced them to use CalMet as the situation had better data coverage," Cook said.

Hotspots are ranked with considerations like land tenure or proximity to the electricity grid. Following the modelling the next stage is verification, where the tower is built. Once a site has been chosen, software can further be used in the form of computational fluid dynamics (CFD) to determine the best configuration for the turbines.

"When you find a hotspot, you're not going to put up one turbine, you're going to put up at least 15 to 20. These need to be built in lines at right angles to the prevailing wind so they don't interfere with each other," Cook said. "We use CFD models to find out the turbulence and wind speed calculated with greater accuracy as we can model factors such as backflows, eddies and turbulence dissipation."