Scientists say what's called "deep geothermal" could generate 10 times the amount of energy that today's conventional geothermal can. Photo / NZ Herald
The key to driving New Zealand's emissions to net zero by 2050 may lie not above us but kilometres beneath our feet, a top geothermal geologist says.
A new project will explore how tapping deep and hot geothermal resources could yield an unlimited source of clean energy for the country, at a time it's searching for bold ways to decarbonise.
What's called deep geothermal - "supercritical" fluids trapped far below the Earth's crust - packed the potential to deliver 10 times more energy than conventional geothermal energy, GNS Science's Dr Isabelle Chambefort said.
To put that into context, New Zealand last year generated 43,041 gigawatt hours (GWh) of electricity, or enough to power five million homes.
Just 17.6 per cent of that came from geothermal energy - and around the same proportion came from non-renewable sources.
"New Zealand is using non-renewables at the same rate as geothermal, when our geothermal resources are so extensive, because, given current trends, conventional geothermal, hydro, solar and wind cannot replace non-renewables at a sufficient rate."
At the same time, the Government has been pushing toward a target of generating 100 per cent of our electricity from renewables by 2035 - and a slashing carbon emissions to net zero by mid-century.
"Given energy demand continues to grow, to achieve these targets, New Zealand must fundamentally transform its energy sector," she said.
"Geothermal energy is New Zealand's energy future."
Chambefort explained that New Zealand's unique tectonic setting, with its active rifting, produced voluminous magma, and from it, an outstanding amount of heat flow.
"It delivers exceptional opportunities for geothermal development and has placed New Zealand among the leaders in geothermal energy technology for the past 60 years," she said.
"Knowing that only geothermal can increase our renewable energy portion to the required levels, exploration over the next 20 years will inevitably move towards hotter and deeper supercritical resources."
So-called supercritical fluids existed at temperatures and pressures above the critical point where distinct liquids and gas phases didn't exist - for pure water, this was above 374C.
"They exhibit higher heat-content and lower density and so have the potential to generate around 10 times more energy than conventional geothermal for the same amount of extracted fluid."
Yet, she added, our scientific understanding of deep geothermal wasn't good enough to offer the solutions the energy industry needed.
That's been a challenge elsewhere in the world, although supercritical systems, hotter than 400C, had now been investigated in places like Italy, Iceland and the United States.
These probes had suggested the best supercritical resources lay closer to magmatic heat sources than conventional systems.
Scientists suspected New Zealand's own deep magmatic conditions, plunging to more than 6km below ground, didn't offer reservoirs that were permeable - allowing water and gas to pass through it - or drillable.
"However, we hypothesise that the presence of buried shear zones, or shallow intrusions favouring heat transfer from the deep magma reservoir to shallower conditions, provides drillable targets."
Her new project, supported through the Government's Endeavour Fund, first aimed to locate these reservoirs and study their distinct chemical characteristics.
That would lead the way to developing modelling for drilling, along with a new regulatory system.
Chambefort said she and her colleagues would also explore the potential for re-injecting any carbon dioxide from it, to enable emissions-free "deep heat" energy.
"Development of New Zealand's existing geothermal resources has depended in large part on laboratory research to determine the chemical behaviour of geothermal fluids, the effects of fluid-rock interaction, and predicted changes in rock properties during fluid extraction and injection," she said.
"We will leverage on this laboratory expertise combining it with international skills to acquire the foundational knowledge required."
Chambefort said she'd moved from Europe to New Zealand so she could understand how its world-renowned geothermal systems worked.
"They are a gift to New Zealand - and by respecting and understanding them, we may have a way to get a step closer to seeing a 100 per cent renewable country.
"I want to see that day and I believe we can."