Each of the four original generating units, which are capable of burning either coal or gas, installed in stages between 1973 and 1985, is capable of generating 250 MW of electricity, giving a historical generating capacity of 1000 MW. Its chimneys are 150 metres high and each chimney has two flues that are 7 metres in diameter. The plant uses a reheat steam cycle, with C A Parsons turbines and Combustion Engineering boilers. In 2004 the power station was upgraded with the addition of a 50 MW gas turbine plant, and in 2007 the combined cycle gas turbine plant was commissioned. This plant increased the total generating capacity of Huntly by 403 MW. The new turbine represented an investment of NZ$520 million and it increased the total installed capacity to 1453 MW. In 2007, Huntly operated at a load factor of 85% and was providing a large amount of the baseload energy needs of the northern North Island. In 2007, the plant was mainly gas-fired, but a dry winter in 2008 prompted more coal thermal generation. In December 2012, Genesis Energy placed one of the four Huntly Power Station 250 MW units into long-term storage. The second coal-fired 250 MW unit was permanently retired in June 2015 after being placed in storage in 2013.
Fuel and coolant
The four 250 MW units were constructed as dual fuel, able to operate on natural gas from Taranaki or coal from the nearby Rotowaro coal mine. A 10 km conveyor belt was constructed to carry coal from the mine to the power station. Previous to the substitution of coal, Huntly used gas from the fields to power the generation of the main units as well, but these were switched in the 1990s because of dwindling resources. Natural gas to power units 5 and 6 comes from several gas fields in Taranaki. The gas is transmitted along the 307 km, 750 mm diameter Maui gas pipeline from Oaonui production station near Opunake, which was commissioned in 1979 to supply the station. The station uses water from the Waikato River for cooling. However, in order to protect aquatic life, conditions are imposed by the resource consent, specifying the quantity of water that can be removed by the station along with the maximum temperature of the water when returned to the river. These conditions mean that on very hot summer days the station cannot operate at maximum capacity, and has sometimes effectively been shut down. A new cooling tower has been built as part of expansion works at the site, which allows one 250 MW unit to run at full load even during such times.
The majority of the energy generated at Huntly Power Station is transmitted through the national grid to Auckland, New Zealand'slargest city, which lies to the north of the station. Huntly is connected to the rest of the national grid via a large substation switchyard and six 220 kV transmission circuits carried on three high capacity transmission lines. These transmission lines are:
a double circuit line to Otahuhu substation in Auckland, via Drury and Takanini
a double circuit line to the Ohinewai switching station, where it connects with the Otahuhu to Whakamaru C line
The Huntly switchyard also includes a grid exit point for supply to the local distribution network in the Huntly area.
Future
The plant, as the biggest carbon dioxidegreenhouse gas generators of the country, contributing over half of New Zealand's emissions of greenhouse gases from electricity generation, has repeatedly drawn the ire of environmentalists and has been the focus of associated protests. A 2006 government report outlining future climate change mitigation and energy policies was seen by the operator as a sign that the plant might have to be closed by 2015 under these plans, with around 10 years of design life still remaining. It was also noted that, apart from being difficult to replace as a source of power, such a decision would also be uneconomical for the foreseeable future, even if coal prices were to rise. In May 2012, resource consent was granted by the Waikato Regional Council to continue running the gas and coal units for a period of 25 years. This shows that the Huntly Power Station can continue to have a strategic long term role in New Zealand energy generation. In April 2016, Genesis Energy announced that the Huntly Power Station would continue operation of its two remaining coal / gas burning units until December 2022. The two gas turbine generators would continue to operate into the future. Company chief executive Marc England has stated "By 2025, Genesis will only use coal in its thermal units in abnormal market conditions, and it is our intent to remove coal completely by 2030".
In popular culture
In the online game , run by Genesis Energy, coal-fired power stations take the form of Huntly. The Huntly Power Station features in the video for the Purple Pilgrims' song 'Two World's Apart'.
