Mercury Energy has powered up its new geothermal generator near Taupō, which is now delivering electricity generation to the national grid.
Built at a cost of $220 million, the new unit is expected to be fully operational by March.
Mercury said the unit will add a further 46 megawatts of renewable energy - enough to power about 55,000 homes - ahead of winter, lifting the station's installed capacity from 86 MW to 132 MW.
At full capacity, Mercury said the Ngā Tamariki power station would generate around 1120 gigawatt hours of electricity a year, enough to supply about 158,000 average homes - more than all residential homes in Christchurch.
The station is powered by nine geothermal wells drilled more than 3000 metres below the surface, where temperatures reach up to 290 degrees Celsius.
Mercury chief executive Stew Hamilton said the expansion is part of a $1 billion investment in three renewable generation developments planned by the company.
"These include the Ngā Tamariki expansion, stage two of the Kaiwera Downs wind farm in Southland, and the Kaiwaikawe wind farm in Northland."
The Ngā Tamariki geothermal station is owned by Mercury. However, the resource has been developed in partnership with Tauhara North 2 Trust and with mana whenua Ngāti Tahu Ngāti Whaoa.
The trust jointly owns the resource consents, receives a revenue stream from the station, and holds options to take an equity stake.
Investigations into geothermal development at Ngā Tamariki date back to 1986, with the power station first commissioned in 2013.
