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Mercury NZ Ngā Tamariki Expansion 2024–2026: New 46 MW Fifth Geothermal Unit to Power All Tauranga Homes

Mercury NZ Ngā Tamariki Expansion: Fifth Geothermal Unit to Deliver 46 MW of Clean Power by 2026


Mercury Ngā Tamariki Fifth Unit: +46 MW Geothermal Power NZ

Mercury NZ is building a fifth geothermal unit at Ngā Tamariki Power Station near Taupō. Adding 46 MW net (total 132 MW), enough to power all Tauranga homes or Christchurch residential load.
Mercury NZ Launches Ngā Tamariki Expansion – New Zealand’s Next Major Renewable Energy Project

In May 2024, Mercury NZ turned the first sod on one of the most significant geothermal developments in the country this decade: the Ngā Tamariki Expansion Project. This ambitious project will see a fifth generating unit added to the existing four-unit Ngā Tamariki Power Station, located 20 kilometres northeast of Taupō in the heart of New Zealand’s geothermal wonderland.

When completed in 2026, the new unit will deliver an additional 46 MW of net renewable capacity, lifting the station’s total output from 86 MW to an impressive 132 MW. That single expansion represents more than 50 % growth for the station and is a cornerstone of Mercury’s strategy to meet New Zealand’s fast-growing demand for clean, reliable electricity.

What the Numbers Really Mean for New Zealand Homes
To put the scale of this project into everyday terms:
The 46 MW added by the fifth unit alone will generate enough zero-carbon electricity to supply every residential home in Tauranga – a city of over 150,000 people.

Once complete, the entire 132 MW Ngā Tamariki station will produce sufficient renewable energy to power all residential homes in Christchurch, New Zealand’s second-largest city.
These are not abstract figures. They represent real households keeping the lights on, charging electric vehicles, heating homes in winter, and running heat pumps – all with 100 % renewable, geothermal baseload power that operates 24 hours a day, 365 days a year.

Geothermal: The Unsung Hero of New Zealand’s Renewable Mix

While wind and solar often grab headlines, geothermal energy remains the reliable backbone of New Zealand’s electricity system. Unlike weather-dependent sources, geothermal plants deliver firm, dispatchable power regardless of drought, cloud cover, or calm days. Ngā Tamariki already operates at capacity factors above 95 %, meaning it runs near full output almost all the time.

The new fifth unit will use proven binary cycle technology, which is highly efficient at converting lower-temperature geothermal fluid into electricity while reinjecting 100 % of the resource back into the ground. This closed-loop approach minimises environmental impact and ensures the geothermal field remains sustainable for generations.

A Truly Local Project – Keeping Skills and Spending in New Zealand
From day one, Mercury made a deliberate choice to keep the Ngā Tamariki Expansion as local as possible. More than 200,000 labour hours have already been delivered by Mercury’s own in-house teams based in Rotorua, Taupō, Cambridge, and Hamilton. These are the same skilled technicians, engineers, and project managers who have built and operated Mercury’s geothermal fleet for years.

Almost every major contractor and supplier on site is a New Zealand-owned company, with many headquartered in the central North Island. Civil works, piping, electrical, and turbine installation are all being carried out by firms that call the Bay of Plenty, Waikato, and Hawke’s Bay home. This approach not only boosts regional economies but ensures knowledge stays in the country for future geothermal developments.

Strong Partnership with Mana Whenua and the Taupō Community

The Ngā Tamariki station sits on land of deep cultural and historical significance. Mercury continues a long-standing relationship with local iwi, ensuring the project respects cultural values and delivers tangible benefits to the community. Employment opportunities, training programmes, and community funding are all part of the broader partnership that has become a model for resource development in New Zealand.

How the Fifth Unit Fits into Mercury’s Bigger Renewable Pipeline

The Ngā Tamariki Expansion is just one piece of Mercury NZ’s aggressive growth strategy. The company has consent for several more geothermal options in the Taupō and Kawerau areas, plus the multi-stage Kaiwera Downs wind farm in Southland. Together, these projects will add hundreds of megawatts of new renewable generation this decade – exactly what is needed as electrification of transport and industry accelerates.

By focusing on a mix of geothermal baseload and wind, Mercury is future-proofing supply against dry years while keeping downward pressure on wholesale electricity prices through increased competition and supply.

Technical Highlights of the New Unit

Technology: Single binary cycle turbine (ORMAT or similar)
Net capacity: 46 MW (parasitic load already deducted)
Expected capacity factor: >95 %
Cooling: Air-cooled condensers (zero water use)
Reinjection: 100 % of geothermal fluid returned to the reservoir
Commissioning target: Mid-2026
The plant will connect directly into the existing Ngā Tamariki switchyard and take steam and brine from wells already consented and drilled as part of the original development, minimising surface disturbance.

Why 2026 Could Be a Landmark Year for New Zealand Energy

When the fifth unit comes online, New Zealand will cross an important threshold: another large block of renewable baseload generation added at a time when demand is rising faster than it has in decades. Data centres, hydrogen projects, process heat electrification, and electric vehicle charging are all driving unprecedented growth in electricity consumption. Projects like Ngā Tamariki are the reason Mercury believes the country can meet that demand without resorting to coal or gas peaker plants.

Looking Ahead – More Updates from Site

Construction is now well underway. Well pad upgrades, piping installation, and turbine foundation work are all progressing on or ahead of schedule. Mercury has committed to regular photo and drone updates, and we’ll be bringing those to you as milestones are reached.

Ngā Tamariki Expansion at a Glance

Location: 20 km northeast of Taupō, Waikato
Current capacity: 86 MW (four units, commissioned 2013–2014)
New fifth unit: +46 MW net
Total post-expansion: 132 MW
Homes powered (additional): Every Tauranga residential connection
Homes powered (total station): Every Christchurch residential connection
Construction started: May 2024
Expected online: 2026
Ownership: 100 % Mercury NZ


New Zealand’s renewable energy future is being built right now – one turbine, one well, and one community partnership at a time. The Ngā Tamariki fifth unit is proof that world-class geothermal development is alive and thriving in Aotearoa.

Source:Mercury NZ

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