The Ngawha geothermal power station can generate 25MW of power. That's about 70 per cent of the Far North's existing power requirement. It does this by extracting water and steam from the ground at 190C and using it to generate electricity.
The water then flows back into the ground at a temperature of 93C, only slightly lower than boiling point, and flows back over the underground heat source to be reheated.
Top Energy's Ray Robinson, who manages the Ngawha power station, describes it as a "beautiful" process.
"It's totally cyclical, fully sustainable and completely renewable," he said. "We're taking nothing out of the earth that we don't put back, and the underground heat source simply reheats the water in an instant.
"The simplicity of the process is what really appeals to me."
The Ngawha field is the only high temperature geothermal resource in New Zealand outside the Taupo Volcanic Zone and is thought to be between 20 and 40sq km in area. The springs at Ngawha village are among the very few external signs of the huge natural boiler buried deep below.
Sheer pressure is what forces the water up to the surface through Top Energy's wells. The only pumping involved takes place at the pilot station when the water is injected back underground at the end of the cyclical process. This helps ensure the long-term sustainability of the resource.
Robinson said the Ngawha geothermal plant had a complex resource consent. It's subject to continual audit by the Northland Regional Council and also to peer review by an independent panel of environmental experts.
Top Energy has been monitoring a wide variety of data points, including natural fluctuation in things such as water pressure and temperature, every 15 minutes since 1998.
"Every 15 minutes for 16 years. Can you imagine that? Can you imagine the amount of data we have for this place? But generally levels have stayed the same all that time," Robinson said.
The landscape covering the several hundred hectares of Top Energy's Ngawha estate is also sampled constantly for evidence of man-made change.
"This is a massive field and our operations have zero impact on the impressive thing Mother Nature has created," Robinson said. "We'll keep looking and testing, though, because it's not something we want to take for granted."
About 17,000 litres of water flows up into the Ngawha plant every minute from a depth of between one and two kilometres, with the same amount being pumped back down into the ground. That's equivalent to nearly one Olympic-sized swimming pool every 2.5 hours.
Top Energy is planning to expand the plant in a move that it says has the potential to attract new employers to the Kaikohe area and to create about 200 new jobs.
"We've been conducting scientific research and modelling since 2007 to understand how much geothermal resource might be available," Chief Executive Russell Shaw said. "Although we won't know exactly what we have until we explore through test drilling, we believe there could be enough resource for an additional 100MW of energy."
That's four times the amount being generated at the moment and Shaw says it's enough to power every household in the Far North and to export power south to the rest of Northland.
"New Zealand is currently searching for clean ways to produce the energy we'll need in the future, so this is an incredibly important resource for the country and opportunity for Northland," he said.
Top Energy is working with the Far North District Council to attract an industry that could use the additional electricity or the heat from the water and steam.
"As well as electricity, industries like wood processing, dairy processing and aquaculture use significant amounts of heat for their industrial processes," Shaw said.
"Our modelling shows we can increase the fluid take and reinjection without reducing our ability to continue heating the fluid. That's important not only to the local community but also to us. We're about making decisions today for the long-term benefit of our business and our region."
Top Energy plans to lodge a resource consent application in 2015 for additional Ormat binary power stations, similar to the units currently at Ngawha. These could start generating electricity from as early as 2020 and Shaw says this is timed well with a forecasted increase in national demand for electricity.
In the rolling hills around Kaikohe there's a Northland success story not many people have heard about. That may be about to change.
Peter Heath is contracted to do public relations work for Top Energy.
