What is the end use for ultra-hot geothermal energy in Aotearoa New Zealand?

Abstract

Abundant, proven high-temperature geothermal resources give Aotearoa New Zealand a distinctive advantage in transitioning to a low-carbon energy sector and economy. Geothermal energy has been decarbonising New Zealand’s electricity and process heat sectors for over sixty years and has capacity for increased utilisation. Along with expansion of the nation’s geothermal electricity generation from conventional geothermal systems (<350°C, ~3.5 km deep) which will see the 170 MWe Tauhara II power plant commissioned in 2023 and others beyond that, what opportunities open if deeper drilling (4-6 km) encounters 400 to 600°C geothermal conditions? Research is underway through the Geothermal: the Next Generation Research programme to evaluate and identify ultra-hot geothermal resources in the Taup? Volcanic Zone (TVZ) that might become the focus of exploratory well drilling, testing and subsequent development activities.

It is proposed that the most likely sector in New Zealand to utilise ultra-hot geothermal is the electricity sector supplying a large user(s) or supplying into the electricity market. Process heat might be a secondary taker of energy from an electricity facility but the process heat industry itself is unlikely to be the primary developer / operator of an ultra-hot geothermal energy supply because of the larger quantities of heat energy that are required for an electricity generation facility and the much smaller amounts utilized by a process heat facility.

Higher temperatures should enable more efficient use of the extracted geothermal energy. The efficiency achieved from an ideal heat engine is computed across a range of temperatures from 150 to 500 °C showing the theoretical efficiency increase as temperature increases.

The paper has been written to encourage dialogue and ideas exchange on end use and the processes that might need to be scoped in seeking to better refine the future utilisation of ultra-hot geothermal energy in New Zealand.