Heatwave puts power supplies under threat

The Waikato River near Huntly, pictured last night, is only half a degree from the point where the station must shut down. Picture / Amos Chapple

Soaring power demand in Auckland has raised the prospect of summer power cuts.

With temperatures in the high 20s over the past two days, the situation reached crisis proportions on Wednesday when demand in the city reached 1500MW and available power supply to Auckland was just 1580MW.

The problem was compounded by high temperatures in the Waikato river which affected the Huntly station's production. The station operates under restrictions on how much river water - used to cool its plant - it can use.

Resource Management Act restrictions are designed to protect plant and fish life from an overheated river, which is warmed both by the hot, sunny weather and the warmer water discharged back into it from the power station.

Yesterday, water 1km downstream from the station was 24.5C, just half a degree below the limit at which the station must shut down.

Huntly is a major supplier of power to the upper North Island but has been running as low as 10 per cent capacity over the past two days.

Generation dropped to a measly 45MW when it has the capacity to generate 1000MW and usually generates between 500MW and 600MW at this time of year.

Richard Gordon, spokesman for Genesis Energy which runs the station, said power cuts this summer could not be ruled out.

"We can't say it's not going to happen," he said. "This was a little unexpected this year because the forecast had been for a moderate summer so the high temperatures have come as a bit of a surprise."

Parts of the upper North Island reached 30C yesterday, with Auckland on 28C and Hamilton 29C.

Hamilton reached 30C the day before, heating the river just as Aucklanders began turning on and turning up thousands of air conditioners in apartments and office blocks.

Genesis was counting on a North Island weather forecast for the next few days of showers or rain to give the river time to cool down, he said.

National grid minder Transpower has issued two warnings on each of the past two days of a "potential" power supply problem.

"The situation had to be managed pretty carefully," said spokesman Chris Roberts. "The forecast demand yesterday was getting pretty close to the supply available."

Genesis records show the last time the river was this hot was the summer of 1997-98, when Auckland was plunged into darkness as underground cables melted in the heat.

But Mr Gordon said this time the situation was different, a combination of rising water temperatures in the Waikato River and demand from air-conditioning units in Auckland, which had skyrocketed in number over the past few years. It takes three times as much electricity to cool a room as it does to heat it.

Mr Roberts said the situation backed his company's application for 220km of new transmission lines to feed power to Auckland and the Waikato from lower North Island stations and South Island hydro lakes. Supply on the lines from stations other than Huntly was running at capacity and could not be increased.

"North of Taupo the lines just aren't big enough," he said.

Genesis is also hoping a new $520 million gas-fired power station alongside the existing coal-fired station - and not dependent on cooling water from the Waikato River - will be commissioned by 2006.

A new cooling tower, to cool water before it's discharged back to the river, could also be operating by next summer, Mr Gordon said.

Most of the country basked in sunshine and blue skies yesterday, with parts of inland Canterbury reaching 33C. Temperatures in the North Island reached the high 20s, with Masterton reaching 31C.

The threat of a power crisis may be further eased with the likely onset of cooler weather.

A frontal rain band is expected to move over the South Island tonight, bringing heavy rain to some areas.

The front is then expected to move over the North Island tomorrow, bringing rain or showers to most areas.

Power crisis step-by-step

* Electricity grid minder Transpower issues instructions to lines companies to cut supply

* First target: water heaters in Auckland homes

* Second target: big industrial users

* Worst-case scenario: household power cuts of around two hours in parts of Auckland

* Areas with essential institutions such as hospitals and other critical services likely the last to get cuts