A new wind farm has been taking shape at Gouda in the Drakenstein Municipality of the Western Cape.
When Lynnette and I recently went to Porterville for the stargazing event at the Porterville Golfclub, organized by Nathalie Wagenstroom from the Porterville Tourism Office, I hadn’t been out that way for quite some time. I was therefore surprised to find that a new wind farm had sprouted up to the right of the R44 just past where it crosses the railway line.
This wind farm will consist of forty-six 100 m towers each carrying a 3 MW Acciona wind-power turbine so that the site can produce 138 MW at full capacity. The construction started in 2013 and was scheduled for completion in 2014 with the power being delivered to a 132 kV distribution network at the Windmeul substation near Wellington. Go here to read more about the project in the August edition of Engineering News. You will find a comprehensive overview of the project as summarized in the August 2013 NERSA public hearings. There is more information here on the webpage of Energy4Africa. Driving past there it was clear that they are way behind schedule.
The Gouda Wind Facility is the first wind farm in South Africa to use concrete towers. Steel towers are imported while concrete towers can be manufactured locally. Another advantage is that one can build taller towers, up to 120 m, at a reduced energy cost. The wind farm at Hopefield consists of thirty-seven, 95 m steel towers each carrying a 1.78 MW turbine from the Danish firm Vestas. The installation will produce 66 MW at full capacity. Go here to read about the installation in the May 2014 edition of Engineering News.
The Gouda installation was erected by Acciona Energy and Aveng while Sarens supplied the equipment to transport and lift the various sections of the towers as well as the turbine blades and the turbines. At full capacity Gouda will supply enough power for 146 000 low income homes or 60 000 medium income homes.
Each blade of the three-blade turbine is 50 m long and the pitch of the blades is increased as wind speed drops to increase the torque and maintain the rotation speed. If the wind speed increases the pitch will be decreased to reduce the torque. At wind speeds of around 20 m/s at the hub height (that is around 70 km/h) the turbines are shut down. In rural areas the turbine blades are required to generate no more than 35 decibels of sound which is classified as less noise than a normal conversation.
When one sees these turbine blades rotating they always look as if they are in slow motion. A bit of mathematics reveals that if the rotor is turning at 10 revolutions per minute the tips of those 50 m long blades are travelling at over 180 km/h. Low flying birds cannot judge the speed of those rotor tips correctly and, because the rotors taper, the tips are far less visible than the sections closer to the hub, so they fly into them, with fatal results. This is especially the case for large, slow birds like geese, pelicans, cranes and storks. Raptors tend to be watching for prey on the ground so they also often fall foul of the blades. From an environmental perspective, it is important that wind farms should not be built on the migration routes of these birds, or in areas where they congregate to feed or breed.