Windfarm growth exposes snag

A report commissioned by the Electricity Commission has found that more windfarms could mean more problems for power transmission.

The news comes as Transpower seeks community support for national power grid upgrades and as a new windfarm company seeks to raise money for its first development.

The report, written by Transpower, found that big changes in wind generation output from the Manawatu region (of 50 MW or greater in five minutes) were likely to occur about 20 times a year.

These sudden increases or decreases in generation change the power flows across the transmission grid and can power system frequency disturbances.

Wind power poses a challenge to an electricity transmission grid, since wind can suddenly drop away, meaning power to keep lights on must be instantly dispatched to cover.

The report says the challenge of integrating wind power into the system is compounded by three things:

* The power system has no interconnections to other power systems and cannot draw on other power systems resources.
* The long and stringy nature of the power system: generation and load are connected by long transmission lines.
* The nature of the wind resource: gusty and concentrated in certain areas rather than even flows and diversely spread across the country.

The report looks at the impact of windfarms on the Tararua Ranges on the national power grid, where TrustPower and Meridian have built New Zealand's largest windfarms.

NZ Windfarms yesterday registered its prospectus for an IPO, where it is seeking to raise money to build a new windfarm in the same area, not far from the TrustPower and Meridian farms.

Transpower often uses the example of wind power as a reason for upgrading the national power grid, saying new transmission lines, such as the controversial plan for a 400 kV line through the Waikato, are needed.

It says without the ability to connect windy places with population centres, the environmental benefits of wind power will be lost.

NZ Wind Energy Association chief executive James Glennie welcomed the report's acknowledgment of wind energy potential and the importance of "a flexible and robust national grid". He said the Transpower study had identified operational issues, "associated with the rapid uptake of wind energy, which it believed were manageable".

Glennie said wind could play a major role in meeting future electricity needs, but it should be carefully planned and supported by "strong, modern infrastructure".

The report says that when the level of wind generation penetration is small, the effects of its unpredictability and variability made little impact on the power system.

But with more wind generation connected to the power system, there came a point where the unpredictability and variability of wind generation became significant for the power system's operation.

Power points

* 170 megawatts (MW) of wind generation has been installed.
* Consent was given for 200MW of new capacity in the past 12 months.
* More than 600 MW is in the resource process.
* As a comparison, the Huntly Power Station, the country's biggest thermal plant, can generate 1000 MW.