Accessing hotter, deeper earth energy resources might open an opportunity to supply process heat for some of New Zealand’s higher temperature industrial applications. Benefits would include replacing fossil based carbon fuels that currently power these processes.
New Zealand currently uses its abundant geothermal earth energy for both electricity generation (providing 17% of New Zealand’s electricity) and directly as a heat supply. A wide range of diverse direct heat uses are possible, from bathing at low temperatures, up to large scale industrial processes at high temperatures. Our direct geothermal use spans sectors including tourism, industrial, horticulture, aquaculture, commercial and residential.
However, while conventional geothermal resources in the central North Island offer a low-carbon fuel source for a number of New Zealand’s industrial process needs, the highest temperature currently supplied from a geothermal resource is to the Miraka milk processing facility at Mokai: up to 220°C.
The following table displays some industrial processes that use geothermal heat directly, along with their fluid supply temperatures (from publicly available data).
What if geothermal could supply higher temperatures?
MBIE and EECA defined categories for industrial process heat use in the Process Heat in NZ Fact Sheet, as reproduced in the following table.
In 2016, around 55% of New Zealand’s process heat demand was supplied by burning fossil fuels, including those processes with the highest temperature requirements. Geothermal can supply significant quantities of energy, and offer a lower carbon alternative to fossil fuels – but can’t, yet, supply temperatures over 220°C.
In New Zealand’s geothermal research sector, investigations are underway to challenge this limitation.
The supercritical geothermal opportunity being investigated in the MBIE-funded “Geothermal, the Next Generation” research programme is looking at prospects with underground temperatures in excess of ~400°C, possibly as hot as 500°C, at depths down to ~6 km.
When extracted, these fluids will reduce in temperature as they move up a well bore. At the surface, available temperatures are still anticipated to be in the 350°C to 400°C range, making them suitable for the industrial process requirements for the MBIE ‘high temperature’ category.
So what is the opportunity? We are working to find this out. Keep track on the GNG work and watch this space as the research work progresses over the next 4 years.