OEC4, the 31.5MW geothermal power station to the north of the Ngāwhā Springs Settlement, was commissioned at the end of 2020 – six months earlier than planned.

OEC4

The OEC4 power plant is built on a large engineered platform at the centre of the construction site to the north of the Ngāwhā Springs settlement.

It is independent of Ngāwhā Generation’s existing power stations and has its own separator plant, turbine and generator, air-cooled condensers, feed pumps and controls.

A new control room and office building was built at the same time to control all the power stations at Ngāwhā. This building is located next to the main access way into OEC4 off Ngāwhā Springs Road.

A new substation and 4.8 kilometres of 110 kilovolt overhead transmission line transmits the electricity generated to the power grid at Kaikohe. The substation is located to the south of the power station and the transmission line route runs to the north west.

Earthworks

Civil works saw the construction of platforms for the production and injection wells, the preparation of the power station platform, storm water ponds and internal roadways across the site.

Nearly 1 million cubic metres of material was excavated from over a working area of 36 hectares.

These works were undertaken by Whangarei based United Civil Construction with a largely locally based workforce.

Well drilling

Drilling and testing of the three production and three injection wells required to provide geothermal fluid to OEC4, was wrapped up at the end of January 2019.

The wells range between 1,350 and 1,750 metres deep and are one metre in diameter at the surface and 22.5 centimetres at their deepest point. Each well has taken around 30-40 days of continuous 24/7 activity to drill, with additional time required to move the drilling rig between well sites.

Iceland Drilling, with decades of experience in the field of geothermal drilling, including the Ngatamariki geothermal power station near Taupo, based a specialist team in Northland for the 10 months it took to complete the work.

Power station construction

Construction started in September 2019 and the first shipment of power station equipment arrived on site in October 2019. This equipment was pre-fabricated offsite to facilitate its relatively quick assembly on site.

Israeli geothermal plant construction experts ORMAT were contracted to design, build and supply the power station. ORMAT has a long history with the operations at Ngāwhā supplying the original 10 megawatt power station, which was commissioned in June 1998 and then expanded to 25 megawatts in 2008.

Pipeline construction

In October 2019, Whangarei based Culham Engineering began installing the above ground pipelines required to bring the hot geothermal fluid from the production wells to the power station and the cooled fluid from the power station to the injection wells. They completed the work in August 2020.

Project timeline

  • JUL 2017 – Final resource consents for the expansion granted
  • OCT 2017 – Major transaction approval granted by Top Energy Consumer Trust and Top Energy Board. United Civil begin enabling works onsite.

  • DEC 2017 – United Civil awarded contract to construct drilling pads and foundations for power station. Contracts awarded to Iceland Drilling and geothermal plant construction experts ORMAT.

  • JAN-APR 2018 – Construction of drilling pad (production well), water storage pond and settlement ponds completed. First stage of construction of the power station platform completed.
  • APR-MAY 2018 – Iceland Drilling sets up the camp for its crew, the HH-220 Drillmec rig is transported to site and drilling begins.
  • SEP-OCT 2018 – Viability of geothermal resource determined.

  • JAN-FEB 2019 – Drilling wraps up and Icelandic Drilling dismantles drilling rig and decamps site.
  • APR-SEPT 2019 – Formation of a hardstand platform for construction of the power station completed. Construction of the new control room and office, substation and new transmission line begin. Culham Engineering awarded the geothermal pipeline contract.
  • OCT 2019 – ORMAT begins assembling power station on site. Culham begins pipeline installation.

  • DEC 2019 – Ngāwhā Generation’s operating team move into the new control room.
  • OCT 2019-AUG 2020 – Construction of the power station, pipelines and transmission system occurs on multiple fronts using many local tradespeople.

  • AUG 2020 – All major power station equipment installed on site and construction finishes on the 110kV lines from Ngāwhā out to Kaikohe.

  • OCT 2020 – Commissioning and testing of the power station begins.

  • DEC 2020 – Power station OEC4 to be commissioned.