NZ could have more geothermal potential than previously recognised, particularly “low-temperature” geothermal energy. Until now, the focus has mainly been on high-temperature geothermal resources in the Central North Island but a team from GNS Science is about to begin a three-year project to study the country’s low-temperature geothermal resources. Low temperatures, in geothermal terms, are less than 150°C and in some cases down to 40°C. They include hot springs and boreholes, shallow aquifers, water and steam discharges from geothermal power plants, warm water associated with oil and gas wells, and flooded underground mines. There is also potential to harness heat contained in dry rock, using the same principle as larger-scale dry rock projects in Aust.

NZ Geothermal Energy Association Executive Officer Brian White says geothermal pockets occur in various parts of NZ but little is known about them. For example, around Christchurch there are known to be hot springs at the bottom of the Port Hills, which could potentially be tapped for heat. Furthermore, abandoned oil wells in regions such as Taranaki and the east coast of both islands are potential sources of low-temperature heat which could be tapped quite cheaply. These wells show rock temperatures increase by about 30°C for every km drilled, with one well reaching 180°C, a very useful temperature for heat supply or electricity generation.

It is also possible some of these resources could be sitting on top of much hotter geothermal fluids, which will only be discovered by drilling deeper.

NZ’s landmass is in fact a large source of heat, with different types of geothermal energy available for harnessing with the right technology in various locations. Overseas, low-temperature geothermal heat is used for heating homes and offices, domestic hot water, heat pumps, greenhouse heating, and aquaculture. For example, in Beijing geothermal fluid at just 40°C is used widely for home heating. Other uses overseas include food processing and numerous industrial applications, all of which could achieve substantial cost savings over traditional heating methods if they were adopted in NZ.

White believes for large-scale commercial heating, geothermal energy could stack up favourably against gas and electricity but NZ’s low population density makes geothermal home heating projects less viable. The GNS research will begin by compiling a nationwide inventory of low-heat energy sources. It will then address technical and scientific areas which will need development to enable the growth of this type of energy. The Foundation for Research, Science and Technology, which is funding the $2.6m project, believes the use of low-temperature geothermal resources is an economic opportunity that warrants further exploration in NZ. The Govt’s Energy Efficiency and Conservation Strategy includes a goal to increase the direct use of low-heat resources by at least 20% by 2025.

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