WHAT DO YOU DO WHEN WIND-FARM PLANS GO SOUTH, but the turbines and towers have been ordered? Ouch. This scenario played out not long ago in Oregon when the Federal government axed plans for a 10 turbine wind farm. It was too close to a military base, it said. Chinese OEM SANY was to supply the turbines and towers and the towers arrived first.
So now, nine good towers each capable of holding a 2-MW turbine, plus one damaged tower are sitting in the Port of Vancouver, Washington looking for a new home. To see if the 10th tower could be fixed, President of ph-consulting group inc. Peder Hansen was called in to provide an analysis. “It could be repaired but the owners considered the cost prohibitive,” he says. No big problem. Given the current building boom, the others should be easy to sell. Right?
Not exactly. “The nine good towers are still at the port because SANY is not selling this type of machines in the U.S. anymore, but wants to get rid of them,” says Hansen. However, there is a practical and a dynamic problem to the sale. The practical problem is that the bolt diameter in the top flange may not fit other turbines, and so would require an extra cost adaptor.
And the dynamic problem is one of natural frequency. If the vibrations generated by a different turbine are close to the natural frequency of the tower, it could eventually weaken by fatigue or embrittlement. “A solution would be to alter the speed of the turbine or add mass to the tower. Several people have suggested where to weld on more mass or add concrete ballast. Both fixes are widely viewed as unsatisfactory solutions,” he says.
Hansen suggests further that the tower fatigue problem will arise again as U.S. turbines reach their 20 year life. After two decades of vibration, they may not be capable of heavier loads from upgraded equipment.
In any case, one of the 10 towers will be scrapped or recycled, which brings up a larger problem for the wind industry. “We are talking about 100 to 200 tons of steel in each tower, some of it two-inches thick. Now consider the hundreds of towers under turbines that will soon reach their 20 year service life. If they are to be taken down to make room for taller towers and more productive turbines, the towers will have to be cut apart and hauled away, a job almost as difficult as transporting and erecting such large loads now.”
Hansen however, suggest other uses for the good towers. “Schools that train wind technicians might like a tower for its climbing, safety, and rescue classes. Then the dynamics of the tower are unimportant. Another thought was for an adventure company to let people experience the thrill and challenge in climbing and rappelling,. Hansen says he sure there are many other ideas. If you have one, let him know at firstname.lastname@example.org
Filed Under: Featured, Towers