Key Points:

The company behind a multimillion-dollar tidal power scheme on the Kaipara Harbour is "delighted" to have been granted resource consent for the project.

But Crest Energy, whose emission-friendly electricity venture has been three years in the planning, would be wise to leave the champagne on ice a little longer.

A number of hurdles remain before it can begin installing the first of up to 200 enormous turbines on the harbour floor. Opponents have a fortnight left in which to lodge an appeal in the Environment Court.

Te Uri o Hau, the local hapu acknowledged as guardians of the harbour, said this week that it was considering doing so on the basis that the scheme contravenes the Foreshore and Seabed Act. Even if unsuccessful, an appeal could delay plans by up to a year.

Te Uri o Hau is just one of 118 objectors to the scheme, which was the subject of a Northland Regional Council consent hearing in May. There were an equal number of submissions in support.

Last week the council granted Crest the 11 resource consents required.

But because the power plan is a restricted coastal activity, it requires two further consents from the Minister of Conservation - one letting the company place its turbines on the seabed and the other to allow it to bury two 7km underwater cables between the turbines and the Northpower electricity network. The council recommends the minister grant those.

The Department of Conservation and Director General of Conservation are backing the scheme, so the odds are the Minister will rubber-stamp it. On top of that, Energy Minister David Parker in May awarded Crest $1.85 million from the Marine Energy Deployment Fund, on condition of it getting resource consent.

It's quite an accomplishment to have got this far. As lawyer Sue Simons, who argued Crest's case at the consent hearing, says, "this is the first of its kind in the world - it's really an exciting project."

Te Uri o Hau's Russell Kemp describes it slightly differently, saying it's "a mad scientist's experiment" involving turbines the size of a three-bedroom house with benefits that are not conclusive.

There are certainly plenty of unknowns, which the council is attempting to allow for by setting strict conditions on the project. The turbine placement will happen in four stages, with 20 being installed initially. Even before the first instalment, Crest will have to take baseline measurements relating to tidal currents, water quality and fish numbers, among others things. As the project proceeds there will be ongoing monitoring and the council will be able to call a halt if it is having an unacceptable impact.

The Kaipara is an important snapper nursery, and local fishing and boating groups made submissions against the project for fear of its effect on the fishery.

Rodney Bridge, who has a Helensville-based charter boat operation, doesn't oppose the plan - "we have to get energy from somewhere" - so long as it doesn't interfere with navigation of the harbour. But that's where there could be trouble.

The Northland harbourmaster has indicated the 9km by 1km area where the turbine array will be placed will be a no-go area for boats. Te Uri o Hau is considering whether that would be a violation of the Foreshore and Seabed Act and could be grounds for an appeal.

For Bridge, it's a safety issue. He wants to see an open channel left through the array. "If you're chartering out on the coast and it comes up rough, we would have to come through that channel to come back inside."

The array zone coincides with an area of the harbour known as "the graveyard", where scores of vessels have sunk.

The council didn't deal with the exclusion zone issue, although it gave Crest consent to prohibit anchoring, fishing and diving in the turbines' vicinity.

Once it's clear all the consent hurdles have been crossed, choosing turbines will be the first step for Crest in a nine to 12-month "pre-construction" phase. Director Anthony Hopkins says there are two or three designs being considered for manufacture in New Zealand.

Each would be about 25m high and, driven by the Kaipara's 9km/h tidal stream, would generate 1MW of power. The full array - costing hundreds of millions of dollars - would produce electricity for about 250,000 Northland homes.

Hopkins says about $1 million has been spent on the project so far, not including the work half a dozen Crest directors and consultants are being paid for in company equity.

He says and he's not dwelling on the possibility of work being delayed by consent appeals. "That's democracy. [People] may well choose to appeal and that's their right to do so."

Anthony Doesburg is an Auckland technology journalist.