Construction of a geothermal power plant near Kaikohe is expected to finish eight months early and produce 25 per cent more electricity than originally planned.

Top Energy chief executive Russell Shaw said fast progress had been helped by a ''fantastic summer''.

Originally most of the earthworks at the Ngāwhā site were to have taken place over three summers but good weather meant it could be done in two.

As a result the new power station was now due to be handed over by Israeli renewable energy firm Ormat Technologies in October 2020, instead of June 2021 as originally planned.

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It would start producing energy around August 2020. Ormat would share the revenue from any power produced before the handover date so it had a strong incentive to get the job done early, Shaw said.

Top Energy's current geothermal plant at Ngāwhā — the only power plant in Northland apart Northpower's modest Wairua hydro station — generates 25MW, or just over a third of the Far North's peak energy consumption.

The new plant was originally designed to add another 25MW but design improvements had boosted that to 28MW.

Better than expected results from last year's well tests meant it was now expected to generate 31.8MW.

Steam billows from a test well at Ngāwhā. Photo / Top Energy
Steam billows from a test well at Ngāwhā. Photo / Top Energy

Shaw said the $182 million project had faced two main areas of risk which could have led to delays or cost over-runs.

The first was that poor weather could have hampered the earthworks; the second was that any of the geothermal wells drilled by Icelandic Drilling could have failed.

All, six, however, were successful.

Three wells would be used to extract hot fluids from 1.8km under the ground; the other three would be used to re-inject the fluids back into the geothermal field.

This week Whangārei firm Culham Engineering won the contract to build the many kilometres of pipes required to link the wells and the power plant, Shaw said.

The earthworks contract had also gone to a Whangārei company, United Civil.

Top Energy also has a consent to build a third power plant, but only if more than three years of monitoring showed no adverse effect on the geothermal field and nearby hot pools.

If it goes ahead it would also produce 32MW, bringing the total to 89MW — more than the Far North's winter evening peak power consumption of 70MW.

Power consumption was, however, expected to rise sharply in coming decades, Shaw said.

Factors included increasing numbers of electric cars and a switch by industry, such as dairy factories, from coal to renewable power as part of a drive towards a carbon-neutral New Zealand.

The Far North was also well placed to tap into solar power, which was already providing 10 per cent of the district's electricity needs at midday in summer.

Currently the Far North's biggest solar producer, at 102kW, was Kaitaia College. Kerikeri's Homestead Tavern has recently installed panels generating 34kW.