Windflow sound solution achieved
15 July 2004
Windflow Technology has solved the sound level problem of its wind turbine at Gebbies Pass (near Christchurch), and Chief Executive Officer Geoff Henderson is confident it can now operate within the terms of the Company's Resource Consent. The wind turbine, with a modified gearbox was reinstalled earlier this week, and the Company has been monitoring its sound emissions.
"Our early monitoring shows that we're now operating within our Resource Consent requirements," said Mr Henderson. "While we have yet to confirm it with the District Council, this is very good news."
Earlier this year, the Company identified that gearbox vibration was the source of the noise problem, and it returned the prototype gearbox to the Auckland-based supplier for a series of modifications. The effects were measured on a $200,000 test rig that Windflow has manufactured to factory-test the prototype and all future gearboxes for the Windflow machines.
"The problem noise was caused by vibrations at 311 Hz being amplified by the rotor. That gave rise to a tone at that frequency in the windmill's sound spectrum. Factory testing has shown that our modifications have totally removed these vibrations," said Mr Henderson. "And now our field monitoring has confirmed that we have eliminated this tone. The residual sound levels are much lower, and importantly, tonal characteristics are absent."
The local council, Banks Peninsula District, has a maximum sound level of 40 dBA for night-time rural environments. "During the Resource Consent consultation process, we identified that the neighbouring McQueens Valley has a uniquely quiet environment," said Mr Henderson. "So we offered to comply with a maximum level of 30 dBA at all times. We now believe that our gearbox ranks among the world's quietest wind turbine gearboxes."
The Company will now ask the Council to have its independent acoustic consultant verify its readings before resuming normal operation. "In the past we have not taken this step because our own readings showed we had a problem," said Mr Henderson.
Next week, Windflow will invite neighbours and media to a 'Public Hearing' of the Gebbies Pass windmill.