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Transpower plays down congestion issue

Wind farms will have an impact on transmission congestion in Otago, according to national grid operator Transpower.

Contact Energy has called for new transmission capacity to be built before Project Hayes, the wind farm proposed for the Lammermoor Range, is commissioned, to prevent further congestion on the lines.

Transpower grid investment general manager Tim George said introducing wind farms into the area meant congestion was more likely.

The extent would depend on what hydro resources were being used, and the output of the wind farm at the time.

Even without the new wind farm, there could be periods where the existing transmission networks’ limits were reached.

“For example, if there is heavy rainfall, dams are spilling and all hydro generation is attempting to operate at maximum levels,” he said.

“Congestion in 2006 amounted to only about 10 hours or 0.1% of the time,” Mr George said.

If there was congestion, instead of spilling water from dams, hydro generation could be rescheduled to operate at times when the wind was not blowing, he said.

Contact Energy is concerned water will go to waste if it is forced to spill at its Clyde and Roxburgh dams.

There is little storage capacity on the Dunstan and Roxburgh hydro lakes and Contact operates “run of river”, using the water as it is available.

Contact spokesman Jonathan Hill said the company worked in a tight operating range, with 1m between minimum and maximum levels allowed in Lake Dunstan, and 1.8m in Lake Roxburgh.

Lake Hawea, the only storage lake in the Clutha River system, must remain between 338m and 346m above sea level, giving an 8m band.

Transpower does not believe there would be congestion problems resulting from the first stage of Project Hayes.

The existing grid could be upgraded at a reasonable cost and those options were being investigated, Mr George said.

However, a major increase in generation would require a new line, which would have to pass a “cost benefit” economic test. He could not put a figure on the likely price.

It was more likely in the initial stages of Project Hayes expected to have a final output of 150MW that hydro generation rescheduling would be the management tool used.

Meridian had consulted with Transpower from an early stage on the project’s development, external relations adviser Helen Morgan-Banda said.

Meridian believed there was capacity in the Central Otago transmission to handle extra generation and it was up to Transpower to decide on the amount.

By Diane Brown

Friday, 9th February 2007