Nga Awa Purua Geothermal Power Station Hero

Nga Awa Purua Geothermal Power Station: helping to secure New Zealand’s long-term electricity supply

Geothermal power in New Zealand provides approximately 13% of this country’s electricity. It’s been described as our most reliable energy source above wind, solar and hydroelectricity, due to its lack of dependence on the weather.

Following the success of the Kawerau geothermal power station project, the Hawkins Infrastructure / Sumitomo Corporation / Fuji Electric Systems partnership was retained for the delivery of the Nga Awa Purua geothermal power station at Rotokawa; a joint venture between Mighty river Power and the Tauhara North No 2 Trust, who represent about 800 owners affiliated to Ngai Tahu.

What we did:

Hawkins Infrastructure acted as the ‘on-shore' partner responsible for the design and construction of the civil, structural, architectural and building services elements of the $430M, 140 MW facility. The scope of work and services supplied was within the context of an E.P.C. contract that comprised planning, design, manufacture, procurement, transportation, construction, installation and commissioning of all facilities within the boundary of the power station.

This was the second major geothermal power station to be built by Hawkins and the fourth New Zealand geothermal project to have major input from Hawkins Group.

Initial earthworks for the 22-month project began in May 2008, with building excavations getting underway a month later.

All project participants took part in a continuous improvement process to increase implementation efficiency. Based on the team's previous project experience at Kawerau, numerous efficiencies and innovations were applied on the Nga Awa Purua project. These included:

  • Changing the electrical annex from the two storeys at Kawerau to a flat single-storey building in order to improve construction and operational access
  • The Nga Awa Purua site terrain is hilly compared to that of Kawerau. Whereas brine bumps were located in a 4 metre deep pit at Kawerau to retain suction head from the LP Separator, the separators at Nga Awa Purua were located at a higher elevation, which removed the need for a brine pump pit.
  • Arranging the first and second stage stream jet ejectors horizontally, rather than the vertical system used at Kawerau.

Unique challenges:

Particular challenges on the site included the demanding and varied gradient of the site, weak volcanic soils, aggressive groundwater, high temperatures, and susceptibility to liquefaction. This meant 30m deep bored piles were required to support the plant structures that included the generator, turbine and turbine casing (the largest triple flash geothermal turbine in the world, weighing a combined 325 tonnes) and the turbine hall itself. The use of cutting-edge, pre-cast and post-tensioning systems accelerated the project timeframe significantly.

The outcome:

The project was completed and handed over to the power station on 4 April 2010, 39 days ahead of programme.

Nga Awa Purua is New Zealand's second largest geothermal power station and the steam turbine is the largest geothermal turbine in the world.

The power station is making a valuable contribution to New Zealand’s long-term security of electricity supply, producing enough energy to power around 140,000 homes.