Published in the National Business Review of 27 July 2007

Greater use of wind power is likely to mean more uncertainty in the electricity system, an issues paper from the Electricity Commission says.

Ironically for advocates of green electricity and those seeking to reduce greenhouse gases more wind turbines could result in more use of thermal stations.

The Electricity Commission and Transpower modeled four scenarios with the amount of wind power ranging from 420 MW to 2 250 MW. Increasing use of wind power would increase "the variability and unpredictability" in the system, according to the commission's paper.

Early findings from the study concluded that with gas supply contracts becoming less flexible the electricity would be less able to adjust quickly to changing climatic conditions.

Thermal power stations need time to fire up their boilers, and hydro stations need water immediately upstream or to release water from a reservoir "some hours ahead of time"

Hydro stations have been used to respond to short term changes in demand, but the Commission's study indicates that thermal stations would be used more frequently in future.

"Thermal plant might need to swing in response to wind variability on a day when hydro plant flexibility is already heavily utilised."

However operators would be reluctant to fire up thermal plant on a just in case basis, as they would get little or no revenue if the plant was not actually used.

Other problems with wind also came to light in the recent hearing of Meridian Energy's application for a resource consent to build 176 wind turbines in the Lammermoor range in Central Otago.

Contact Energy told the hearing that Meridian's scheme could see one source of renewable energy largely displacing another.

This is because of the transmission constraints in the lower half of the South Island and the way electricity is dispatched in the marketplace.

If Meridian got consent for its wind farm its electricity might move into the grid above electricity from Contact's hydro stations on the Clutha River.

If there were sufficient capacity to get power from wind and hydro away, this would not be a problem. But the transmission constraints meant hydro water that could not be used immediately often had to be spilled.