Abstract

The first 10 gigawatts of geothermal generation took around 100 years to develop. It is mainly located in a handful of lucky countries with pristine, high-temperature systems found at relatively shallow depths. We hope the next 10 gigawatts will not take so long and will be developed across many more nations. For that to happen, we need to shift the envelope of what is considered an ‘economic’ resource, with a focus on bringing marginal systems into frame.

There are two ways to improve the economics of a geothermal resource: use better technology or leverage co-benefits to reduce your costs. On the technology development side, we have been investigating partially bridging multi-stage hydraulic fractures, a theoretical fracture design that improves the production and longevity of engineered reservoirs. While exotic fracture patterns are not new, we show how physics-informed models can be embedded within an economic framework to evaluate marginal resources. This kind of techno-economic modelling can help, at an early stage, discriminate which emerging technologies need further development.

Switching perspectives, in recent years, New Zealand geothermal companies have been exploring reinjection of their produced carbon emissions. Ngāwhā geothermal system currently injects 100 000 tonnes of produced CO₂ each year, which makes it carbon neutral. We have been investigating how such geothermal systems could be pushed even further to become carbon negative. This can be done through bioenergy hybridization and reinjection of flue gas, which boosts electricity and sequesters CO₂ from the atmosphere. Again, we use techno-economic models of the combined power cycle to explore which designs are thermodynamically feasible and, importantly, result in lower costs than geothermal alone. This is one example of how co-benefits – in this case, CO₂ removal and boosted power – can bring the marginal geothermal system above an economic threshold.

Bio

David Dempsey is an Associate Professor in the Department of Civil and Natural Resources Engineering at the University of Canterbury where he teaches groundwater engineering and serves as postgraduate director of studies. He completed his PhD in Geothermal Engineering at the University of Auckland and held postdoctoral positions at Los Alamos National Laboratory and Stanford University where he researched carbon sequestration and induced seismicity. David co-leads the Pūhiko Nukutū Green Hydrogen Geostorage research program and is a NZ representative on the IEA’s Hydrogen Technology Collaboration Program (IEA H2-TCP) Task-42 Underground Hydrogen Storage Research. On weekends, he enjoys fixing up the house, reading science fiction, and raising his two young daughters.

References

Yu, Dempsey & Archer (2022) “Techno-Economic feasibility of enhanced geothermal systems (EGS) with partially bridging Multi-Stage fractures for district heating applications”. ECM, https://doi.org/10.1016/j.enconman.2022.115405

Titus, Dempsey & Peer (2023) “Carbon negative geothermal: Theoretical efficiency and sequestration potential of geothermal-BECCS energy cycles”. IJGGC, https://doi.org/10.1016/j.ijggc.2022.103813