A Maori trust that has taken a 25 per cent equity share in the country's newest geothermal power station says future returns could be worth more than $20 million a year.

The $430 million Nga Awa Purua Geothermal Power Station outside Taupo officially opens next week.

It is a joint venture between Mighty River Power and Tauhara North No 2 Trust.

It houses a geothermal turbine with a capacity of 140MW - enough to power 140,000 homes and supply up to 3 per cent of New Zealand's electricity needs.

The trust owns 326ha over the Rotokawa Reservoir, which the station draws off.

Trust chief executive Aroha Campbell said that in five years' time returns could be worth more than $20 million annually, before costs.

That was a sizeable return for the 785 owners who affiliate to Ngati Tahu, Campbell said.

"We have a very small block of land with a very valuable resource. Nga Awa Purua will give us a long-term and secure source of revenue bringing real benefits to our people."

The project is one of three power generation developments trustees are involved in - the 110MW Ngatamariki station is at resource consent stage while Rotokawa North, which will generate 34MW, is less advanced.

The trust also has an existing interest in the 34MW Rotokawa station receiving royalties of $1 million a year.

Collectively, those assets make it a power player in the regional economy.

Mighty River Power chief executive Doug Heffernan said the plant could bring in $100 million worth of revenue annually.

He emphasised the importance of a strong relationship between the two partners, based on shared values.

In terms of scale the project is one of the largest geothermal stations built worldwide in the last 10 years and has used cutting edge technology.

The custom-made 210 tonne turbine is fuelled by three different injected pressure streams - effectively giving the station "three bites at the cherry" to maximise the field's energy.

POWERING UP
Nga Awa Purua Geothermal Power Station:

* Capable of generating enough power for Taupo, Rotorua, Tauranga and Hamilton.
* The Rotokawa field generates temperatures of up to 320C. The hotter a geothermal field the more energy it can produce.
* 48,000 tonnes of fluid are extracted each day to fuel the station - most of this will be injected back into the geothermal system.