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The Clyde Dam on Lake Dunstan is the largest concrete gravity dam in New Zealand. There is a million cubic metres of concrete in the dam with another 200,000 cubic metres in the powerhouse. The power station is capable of producing 432 megawatts (MW) of power from its four turbine generator units.
A great deal of landslide stabilisation work was carried out behind the dam before Lake Dunstan could be filled and the power station commissioned. More than 14 kilometres of tunnels were excavated into the hillsides to prevent water build-up that could destabilise the hillsides. Huge buttresses of compacted rock and gravel have been built to strengthen the hillsides and a total of 3,500 measuring and monitoring instruments have been installed around the lakeshore.
The first of Roxburgh's eight generators was commissioned over 50 years ago in 1956. Roxburgh is a concrete gravity dam, and with the powerhouse, contains about half a million cubic metres of concrete, weighing 1.5 million tonnes. The lake formed by the dam covers an area of nearly six square kilometres. The power station has a capacity of 320MW.
Commissioned in November 1958, the Wairakei power plant is situated above a large geothermal system containing water at temperatures up to 240°C. Currently, about 5,000 tonnes per hour of fluid is taken from the reservoir. This is separated into roughly 1,500 tonnes per hour of steam and 3,500 tonnes per hour of water at a temperature of about 130°C. Dry steam is also taken from shallow production wells (up to 500m depth) and piped directly to the turbines. The steam is directed towards the turbines through a network of pipes around the Wairakei steam field.
Once steam has passed through the turbines, it is condensed within 'direct contact' condensers. This cooling system uses water pumped from the adjacent Waikato River. After use, the cooling water and steam condensate is discharged back into the river. Gases found in the steam supply are pumped from the condenser and released to the air via gas stacks on the power station roof. The hot geothermal water is discharged into a system of drains leading to the Waikato River or it is injected back into the ground.
Wairakei, the first geothermal plant of its kind anywhere in the world, is an iconic symbol of New Zealand's electricity generation system. The Wairakei A and B stations have 10 steam turbines ranging in size from 4–30 megawatts (MW). The station generates on average 157MW.
The Ohaaki geothermal power station was commissioned in 1989. Production wells at Ohaaki are, on average, 1.2 km deep and reach water at temperatures up to 280°C. The most distinctive feature at Ohaaki is the 105 metre high cooling tower. Using natural convection, the tower cools the water used to condense the steam as it exits the power turbines.
The Poihipi Road power station was commissioned in 1997 and was bought by Contact in 2000. It is now operated as an integral part of the Geothermal and is supplied with steam from the Wairakei geothermal system. Poihipi currently generates 334 GWH per year and on average 38MW.
In 2005, Contact commissioned a new 14MW binary plant at Wairakei. This plant increases the generation yield by 10 per cent and utilises heat previously untapped by the existing plant. The binary plant capacity provides enough energy to supply approximately 14,000 homes.
Commissioned in 2010, Te Huka geothermal power station delivers around 23 megawatts to the grid. That's enough renewable energy to power around 23,000 homes. At Te Huka power station, electricity is generated through a binary (organic rankine cycle) process. It is the first power station to be built on the Tauhara geothermal steamfield.
The first four units of Otahuhu A were commissioned in 1968. It was the first large gas turbine power station in Australasia. Two of the three available units are currently operated to provide 'reactive power' for the electricity transmission system. This provides stability to the electrical system and helps minimise electricity transmission losses.
Otahuhu B was commissioned in January 2000. This 400MW power station is the largest of its kind in New Zealand and one of the most efficient in the world. The combined cycle technology produces significantly more electricity from the same amount of gas than conventional single cycle plants.
The Taranaki Combined Cycle Power Station (TCC) is a large, efficient and modern plant, producing 380MW of electricity. It has one of the best fuel efficiencies of all of New Zealand's thermal stations at 56.7 per cent. The heart of TCC is one of the largest gas turbines in the world housed in a single building. Constructed from special metals and featuring advanced cooling systems, the Alstom turbine burns gas at a temperature of 1,200 degrees celsius. The exhausts heat the steam boiler at temperatures around 640 degrees celsius. Within the turbine, two separate combustion sections allow the plant to produce very low emissions – a trademark of the Alstom gas turbine.
Contact Energy commissioned its 200MW gas-fired peaking power station in early 2011. The facility plays an important role in providing New Zealand with a secure supply of electricity, while enabling the country to increase the level of electricity generated from renewable sources. The two fast-start gas turbine peaking units supply enough electricity for 200,000 average homes and can go from a cold start to full load in just 10 minutes. The two units are high efficiency LMS-100 gas turbine generators, the most efficient fast start technology available in Australasia. The gas turbine peaking units have been installed on the site of Contact's former Stratford power station, adjacent to the company's existing Taranaki Combined Cycle (TCC) power station. Together, TCC and the two new peakers produce a total combined output of 580MW - that's 9 per cent of New Zealand's electricity during peak loads in winter.
The Te Rapa power station was commissioned in 1999 and is a cogeneration facility providing high quality steam and electricity to Fonterra's Te Rapa factory, one of the world's largest milk powder drying plants. Surplus electricity is directed back to the local area.
The Whirinaki peaker plant is a 150MW, diesel fired peaker plant located at Whirinaki in Hawkes Bay. Approximately four million litres of diesel can be stored on site at Whirinaki, enabling the plant to operate at full capacity for 92 hours. The plant consists of three fast-start, Twinpac units each consisting of 2 FT8 Pratt and Whitney open cycle gas turbines with a nominal capacity of 50 MW. The plant can reach full generating capacity from a cold start in between 20-30 minutes. The Whirinaki plant was originally built by Contact for the government in 2004 and Contact operated the plant under contract to the government. The Whirinaki Power Plantwas put up for sale by the government in 2010 and acquired by Contact after a closed tender process in 2011.