TrustPower plans $500m windfarm

TrustPower plans to build New Zealand's largest windfarm for $500 million and hopes to start using hydro energy as a backup for wind power.

TrustPower chief executive Keith Tempest said the site of the new Dunedin wind farm, close to the company's largest hydro storage lake and its associated Waipori power stations, provided a huge opportunity for it to benefit from the "natural synergy" between hydro and wind.

Adding a windfarm to an existing hydro station meant better security of power supply, which would be particularly useful in winter.

"The ability to retain water when the wind is blowing for use when it is not, plus the availability of added peaking capacity provided when both resources are available, will give the best of both worlds in terms of sustainable generation," he said.

Boosting power generation is becoming increasingly important, as consumption growth is outstripping the addition of new generation capacity.

The country's high reliance on hydro power also means power supply can be squeezed in drought years.

If the project proceeds, it could have an installed capacity of up to 300MW. The farm would probably be built in 100MW increments.

The company said the site at Lake Mahinerangi, south of Dunedin, had shown the potential for a world-class windfarm, capable of reaching the same kind of performance seen at its Tararua site near Palmerston North.

That farm is regarded as the world's best performing commercial windfarm.

TrustPower says it expects to apply for resource consents for the Dunedin scheme later this year.

TrustPower, listed on the NZSX and 35 per cent owned by listed investment company Infratil, is one of the pioneers of wind generation here.

This idea of combining windfarms with hydro-electric power schemes is becoming increasingly popular, with state-owned Meridian Energy leading the charge. Its Te Apiti farm near Palmerston North is the country's largest, rated at 90.75MW.

Meridian owns and operates all the hydro dams on the Waitaki River, which runs from central Otago to the coast near Oamaru. At its heart is the Benmore Dam, where power is fed into the high-voltage direct current (HVDC) link that connects the South Island hydro generation to the high power-using areas in the North Island.

Meridian chief executive Keith Turner has floated the idea of a huge 1000MW windfarm in Otago at Rocklands.

This would be connected to the HVDC link at Benmore, helping save water in the southern hydro system for use only when there is no wind blowing.

"Backing up" windfarms with hydro may also help solve some of the technical problems that come with generating electricity from the wind.

Wind flows can grow strongly and quickly, before dropping off suddenly, putting huge amounts of energy suddenly into a network.

Wholesale electricity prices are set at different locations around the country and too much variable wind energy can lead to wild fluctuations in prices.

Technical problems like this have caused Meridian to delay construction of a 58MW windfarm at White Hill, near Lumsden in Southland. .

The farm would be connected to the network run by Powernet, a local powerlines company.

Because this network is small, there would be times when it would "have difficulty recovering from faults" because of the 58MW of electricity being put into it by the windfarm.

Winding up
* The windfarm could have an installed capacity of up to 300MW.
* The farm would probably be built in 100MW increments.
* The site at Lake Mahinerangi, south of Dunedin, has shown the potential to be as successful as the Tararua site near Palmerston North.
* That farm is regarded as the world's best-performing commercial windfarm.