Renewable, but not exactly clean: Climate report hints at debate over NZ's newest power plant

The Ngawha Power Station reduces Northland's need to get power from elsewhere, but its emissions are significantly higher than most other geothermal stations. Photo / Top Energy

The Climate Change Commission's advice to the Government calls for a major change to electricity generation, with more wind and low-emission geothermal and less coal and gas.

But what about the high-emission geothermal?

Although considered renewable, geothermal electricity generation does create carbon emissions, as gases which cannot be turned back into liquid are released into the atmosphere.

In some cases, geothermal energy emits more carbon than equivalent-sized gas-fired electricity generation, and the commission's advice to the Government assumes that such plants should be closed within a decade.

"In our path these high emitting geothermal fields would close before 2030, reducing geothermal emissions by around 25 per cent while only reducing generation by 6 per cent.

While it is only mentioned in passing, the statement could have profound implications for New Zealand's newest electricity generation plant, which was billed as a "game-changer" by its developers for a region which has little easy alternative power sources.

Situated near Kaikohe in Northland, the Ngawha Power Station began generating in 1998 and was expanded in 2008 to be able to generate around 70 per cent of Northland's electricity.

In January, a $182 million project to more than double its generation was completed by Top Energy, the electricity network company owned by Northland's power consumers, allowing the region to produce its entire electricity needs, rather than drawing electricity from Huntly or hydro stations on the Waikato River.

But the nature of the geothermal resource that drives it means Ngawha is the highest emitting geothermal plant in New Zealand.

An analysis by the New Zealand Geothermal Association in 2018 found that most New Zealand geothermal stations emitted less than 100 grams of carbon dioxide equivalent for each kilowatt hour of electricity produced, but Ngawha, as well as Contact Energy owned Ohaaki produced more than 300 grams.

Top Energy chief executive Russell Shaw told the Herald that emissions from the stations were dropping as the geothermal field changed, and were a third of what they were when the first station began production.

"It is decreasing and has decreased significantly and we think with the new station, it will decrease further," Shaw said.

The company believed it was possible that emissions would fall to a point where it was considered "an outlier", however Shaw conceded that there was uncertainty over the fall.

Ngawha's emissions, having fallen to a third of historical levels, had now plateaued and there was no guarantee how much they would eventually fall to, or when.

"Whether it drops to a third of the current level, or another amount, and over what period, that's the uncertainty we face."

The commission's report was "extremely successful" at identifying some of the changes which needed to be made in both electricity generation and the transport sector and industrial heat users.

Shaw said closing Ngawha would be tragic.

"It would mean that we would go back to a situation that we were in 25 years ago, where we're totally reliant on power coming from the Waikato, up through Auckland, to get to the Far North."

Now, Northland was only reliant on power coming from Auckland 3 per cent of the time.

"Anyone who understands the electricity sector would say any generation north of Auckland has got to be a good thing," Shaw said.

"We're in a position now where we're effectively self-sufficient for power ... I'm fairly emotionally attached to it, but I would think it would be absolutely tragic if we're not allowed to continue like that."