Electricity plans cut through city

The national grid operator is preparing to spend tens of millions of dollars to slice a new electricity path through Auckland City and stave off serious power shortages in the next seven years.

Transpower is considering options to build a string of pylons, install new overhead lines, bury cables under roads and even dig a deep tunnel south of the central business district.

The state-owned enterprise warns that if it fails to act now, north Auckland and Northland could face year-round power restrictions on hot days and cold nights by 2013.

Chief executive Ralph Craven said people had to "think beyond the switch" and consider how electricity got to their homes, businesses and communities.

"People in north Auckland and Northland need a secure electricity supply because it underpins their quality of life and their economic future."

The plans are independent from the controversial $600 million Waikato-to-Auckland giant pylon scheme, which is expected to be rejected by the Electricity Commission next month.

That is to address demand into Auckland. However, if that does not go ahead, Transpower warns that "supply into the north Auckland and Northland regions as a whole will be at risk".

The latest proposals would take power from Otahuhu to Albany, and address demand in north Auckland and Northland. There are two strands to the project, but each depends on the other.

Work has already begun on a route crossing the Waitemata Harbour from Penrose to Albany, which includes cables attached to the underside of the harbour bridge and further cables being attached to the North Shore busway.

It is expected to be completed by 2009, costing at least $200 million.

The other part of the project is a new link between the Otahuhu and Penrose substations and five possibilities have been identified.

They include new pylons up to about 40m high between Otahuhu and Penrose and a new substation in Onehunga. Other possibilities include upgrading existing lines, or laying cables under the road or in a deep tunnel between Otahuhu and Pakuranga. Costs range from $80 million to $130 million.

"The combined effect of these two projects would be a new transmission path between Otahuhu and Albany substations," said Transpower.

In a discussion document the company has called for potential alternatives to investment in the transmission network, such as micro-powerstations or management of demand for electricity.

The report said the options for cross-Auckland transmission did not prejudge the consultation process, "but rather show the scope and extent of a transmission alternative".

Transpower will continue to refine these options so they can be assessed against any non-transmission proposals.

Among the alternatives to transmission is the Top Energy geothermal plant at Ngawha, near Kaikohe, which is seeking resource consent to increase its output. But Transpower warns that even then, it would account for just 3 per cent of the peak load in north Auckland and Northland by 2010.

There are also plans for new plants at Rodney and Marsden, though neither of these have been given the go-ahead.

Transpower said these could defer the need for investment in transmission, but their "reliability would have to be taken into account".

Dr Craven said the company was calling for alternatives because it wanted a "complete picture before going any further".

But for the longer-term it had looked at a range of possible transmission options, costs and routes, he said.

Submissions close on July 28 and a preferred option should be announced by the end of the year. The Electricity Commission has the final say.