Mercury NZ Limited (MCY), listed on both the NZX and ASX, has officially opened its new fifth generation unit at the Nga Tamariki Geothermal Station near Taupo. Mercury generates electricity from 100% renewable sources, including hydro, geothermal, and wind, and is also a retailer of electricity, gas, broadband, and mobile services. The $220 million expansion project, first announced in 2023, was completed in just under two years.
The expansion lifts the station’s annual average generation output to approximately 1120GWh, enough to power the equivalent of all residential homes in Christchurch. Mercury Chief Executive Stew Hamilton and the Associate Minister of Energy Shane Jones opened the new generation unit with mana whenua, Ngati Tahu Ngati Whaoa, Tauhara North #2 Trust, landowners, community leaders, and some of the 300 contractors and staff who worked on the project. The new 55MW unit has more than twice the capacity of each of the original units commissioned at Nga Tamariki in 2013.
In conjunction with the project, Mercury has drilled two new geothermal wells; one to provide additional steam supply for the new generation unit and the second for injection of geothermal fluid to support the sustainability of the reservoir. This provides the added ability to reinject non-condensable gases, mainly carbon dioxide, back into the geothermal reservoir, instead of these gases being released into the atmosphere. The company expects to achieve a 70% reduction in the station’s carbon emissions by 2030.
Mr Hamilton stated that increasing capacity at Nga Tamariki supports system resilience because geothermal provides steady baseload supply, helping meet winter peaks and stabilise the national grid. He added that the expansion will help deliver 3.5 TWh of new generation by 2030, about 8% of New Zealand’s annual energy demand. Mercury also has two wind farms under construction expected to begin generating electricity by the end of 2026, representing a $1 billion investment in new renewable generation.
