Under the mountain: NZ’s secret underground power station

NZ Herald

18 Dec, 2022 04:00 PM2 mins to read

The Rangipō Power Station is 650 metres along an underground tunnel. Photo / Phibbs Visuals

It looks like the set of a James Bond movie, but it’s actually a hydro power station, buried deep underground.

Genesis Energy’s Rangipō Power Station turns 40 in 2023, and powers about 78,000 households a year, but many New Zealanders wouldn’t know it existed. 30 kilometres south of Tūrangi, 5km inside the Kaimanawa Forest Park, you enter through a door in a hill. Drive 650 metres down a 5m-wide tunnel and you arrive at the cavernous generation house containing two 60-megawatt turbines, 63m underground.

While Genesis staff visit for checks and maintenance, the upstairs control room is now empty – the company’s eight hydro power stations across the country are now operated from its Tokaanu Power Station down the road.

For nearly 40 years the Rangipo power station has pumped power to the people from half a kilometre underground. Photos / Phibbs Visuals

Rangipō is one of three hydro stations in Genesis’ Tongariro Power Scheme, which captures water from a 2600 square kilometre catchment in the central plateau through a complex series of pipes, lakes, canals and tunnels.

Tūrangi was home to the scheme’s tunnellers - some brought over from Italy - for more than 13 years through the 1970s and early 1980s. About 560,000 cubic metres of earth was dug out to create the Rangipō powerhouse, which was then lined with 81,000 cubic metres of concrete, reinforced by 5700 tonnes of steel. It is 36m high to allow for equipment to be lifted out of the turbine and generator housings for maintenance.

Inside the Rangipo Power Station. Photo / Brett Phibbs / PhibbsVisuals

Climb through a series of ladders and walkways and you enter the enclosed ‘surge chamber’, where water is dispelled from the turbines to release its energy before being piped back up to the Tongariro River. The combined length of the powerhouse and surge chamber is about 110m, as long as a rugby field. This footprint required the station to be built underground to preserve the forest park above it.

Once back in the Tongariro River, some water is diverted into a canal which takes it on to Tokaanu Power Station for more generation, before it’s finally released into Lake Taupō. The entire Tongariro scheme provides enough electricity to power 160,000 households a year.