Crest in front

The country’s most advanced and largest marine energy project is underway at the mouth of the Kaipara Harbour, writes LINDSAY CLARK.

The Auckland-based company Crest Energy’s plans to install tidal generators at Kaipara Harbour north of Auckland received a morale boost when it was the first to be helped out by the government’s Marine Energy Deployment Fund.

The fund was set up last year to help grow projects in this new renewable energy field and Crest was chosen by a panel, of largely overseas experts, to receive the maximum available in the first year, $1.85 million.

However, payment from the fund depends on a project being successful in resource consent. Crest director Anthony Hopkins says a decision on the company’s resource consent application was expected soon.

The 200MW power project is based on the largest harbour tidal flows around the country. 

The Kaipara, just north of the power hungry Auckland urban area, is one of the largest harbours in the world. Because of its large areas of mudflats, at the highest (spring) tides it stores 20 times as much water as Wellington harbour.

A massive flow out the tidal mouth on the outgoing tide is more than 92,000 cubic metres per second – or more than 20 times the maximum flood ever recorded on New Zealand’s biggest river by volume, Otago’s Clutha river.

A survey of current speeds done by Crest at the Kaipara mouth, recorded in its resource consent application, showed that harbour entrance currents in places exceeded two metres a second some 20 percent of the time during the full tidal phase.

Crest plans to place up to 200 1MW turbines completely underwater deeper than 30 metres in a 10 kilometres long section of the main channel near the North Head of the harbour entrance. The submerged turbines will be invisible and silent to anyone walking along the remote North Head Beach.  

Hopkins says that over the past year the company has decided to adopt a four-stage approach towards development of the project instead of building the generation plant all at once. This would avoid the big upfront expense of laying a 30 kilometre DC submarine cable across to the eastern side of the harbour towards Wellsford.

Instead, Crest now plans to supply power up from North Head towards Dargaville using present power lines at first. This will allow time for building bigger power line infrastructure later when more generation plants are in place.

Like the other tidal energy operators, Crest is keeping quiet about which manufacturer it will choose to supply turbines at a time when this embryonic industry around the world is bringing out new models.

The company estimates initial construction costs of about $40 million. The total cost over 10 years would be about $600 million, offset by modest, but growing, revenues from year three. The company says annual revenue from 200 turbines is theoretically up to $100 million at current wholesale electricity prices.