Is geothermal really green energy?

• Date: 22 June 2021
• Published date: 22 June 2021

But for carboNZero Certified electricity retailer Ecotricity, geothermal energy is dirty energy.

It says low emissions are not good enough and because geothermal runs continuously, its carbon volume is a problem.

“New Zealand really needs to reduce its emissions that come from the electricity sector, which includes coal, gas and geothermal,” says Ecotricity chief executive Al Yates.

“We see that wind and solar in particular are the best ways to reduce emissions for New Zealand at a rapid pace.

“By introducing more geothermal into the grid it is going to take a much longer period to get the emissions outof the New Zealand energy sector.”

The geothermal industry sees itself in the vanguard of decarbonising the energy sector, but NZ Geothermal Association president Paul Siratovich says geothermal fields would emit carbon dioxide anyway.

“One thing that we have to consider is that any geothermal field, whether you put a power station on it or if it lives on its own, emits carbon dioxide,” says Siratovich.

“When we extract power from them we do bring up a little bit more CO2, but over the life of those geothermal fields we actually have modelling that shows it is more or less neutral from what it would do on its own.”

He says large-scale surveys from Rotorua show a lot of natural CO2 comes from the ground.

At the Wairakei field, first harvested in the 1950s, carbon emissions have fallen over time, likely because a pocket of gas has vented.

The emissions gap narrows further between geothermal and hydro, solar and wind when whole-of-life emissions are taken into account instead of just operating emissions.

But two geothermal fields measure alarmingly high. The worst is Ohaaki power station north of Taupō, recording carbon emissions almost as high as some fossil fuel electricity plants.

Built in the 1980s, Contact Energy’s Ohaaki power station is a landmark with its large cooling tower.

“I think it’s best to look at geothermal as a spectrum rather than picking just the outliers,” says Contact Energy head of geothermal generation John Clark.

“As an industry we are relatively low carbon emissions.

“We are not zero – we do acknowledge our operations release carbon.

“CO2 occurs naturally in the reservoir and our processes help release that. We are looking to how we can reduce our carbon footprint over time with our emissions.

“We are looking to do a trial at our Te Huka station on the other side of Taupō this year, where we will be trying to reinject that CO2 back...