Big NZ Geothermal Plant Kicks Into Gear

A Nevada company has completed the largest geothermal power plant of its type ever, in New Zealand, bringing online the Ngatamariki plant – variously characterized as 82 megawatts and 100 megawatts — for Mighty River Power. But this could be it for new New Zealand’s most aggressive pursuer of geothermal for a while.

“The completion of Ngatamariki also means the significant capital expenditure – of more than $1.4 billion – that the company has invested in geothermal assets in New Zealand over recent years is at an end, with Mighty River Power unlikely to build a new large power station here in the next three to five years due to the current weak electricity demand outlook,” general manager for development Mark Trigg said in a statement.

new zealand geothermal

The Ngatamariki plant during construction (image via RCP)

But that’s not to say the company isn’t happy with the outcome of the project, which apparently came in at budget and with more power than anticipated..

“We’re delighted with a project of this scale – the largest of its type in the world – to see it successfully completed, and with power output now expected to be 3MW (4%) higher than spec, which will be positive for the plant’s economics and cash flow into the future. We also expect the project to come in slightly under the total cost forecast,” chief executive Doug Heffernan said.

The plant is expected to produce close to 700 gigawatt-hours of electricity. That’s the equivalent of what a 318-MW solar PV plant operating at 25 percent capacity factor or a 228-MW wind farm operating at 35 percent capacity (typical figures for such utility-scale plants) would turn out in a year. And, of course, it has the big advantage that geothermal offers: It isn’t intermittent. It’s 24-hour-a-day.

By the way, the “type” of geothermal that we’ve referred to for Ngatamariki is called binary. What that means is that unlike dry steam and flash steam systems, the water or steam from the geothermal reservoir never comes in contact with the turbine/generator units. As the DOE explains:

“Low to moderately heated (below 400°F) geothermal fluid and a secondary (hence, “binary”) fluid with a much lower boiling point than water pass through a heat exchanger. Heat from the geothermal fluid causes the secondary fluid to flash to vapor, which then drives the turbines and subsequently, the generators.”

The DOE also notes that binary cycle power plants are closed-loop systems, so except for water vapor, they have no emissions. and virtually nothing (except water vapor) is emitted to the atmosphere.

The United States is the world leader in geothermal power in terms of installed capacity of 3,386 MW as of the end of last year. But New Zealand, with less than 1,000 MW, nonetheless is now getting around 14 percent of its electricity from geothermal.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.

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