Wairakei Geothermal Power Station.
The power station at Wairākei, the second oldest geothermal power station in the world, is set to close.
Contact Energy wants to invest in new power stations in the Wairākei Geothermal Field, move operations closer to the steam source, and has an environmental goal to have zero discharge to any water body from its operations.
It has named the project GeoFuture and resource consents have been lodged with Waikato Regional Council.
There are a few firsts associated with Wairākei Power Station. It was the first in the world to use wet steam technology and today New Zealand is considered to be a world leader in geothermal power generation, with much of the human resource concentrated in Taupō.
The world's first geothermal power station opened in Larderello, Italy in 1913. Wairākei Geothermal Power Station was the world's second and opened in 1958, generating 125 megawatts (MW). By the early 1960s it was at its highest generating capacity, generating 192 MW.
Currently, Wairākei A & B and the binary plant (built in 2004) can operate at 132MW, but Contact Energy general manager geothermal resources Mike Dunstall says it is not normally run at that capacity.
Also running off the Wairākei Geothermal Field steam supply are Te Mihi Power Station and Poihipi Power Station. In 2007, Contact came to the conclusion that the core generation development on the Wairākei Geothermal Field should occur at Te Mihi.
It is proposed to develop new, more efficient power stations at Te Mihi to replace the existing Wairākei A & B Power Stations by 2031 at the latest, and 2026 at the earliest. It is also possible a smaller, more efficient power station will be built beside Wairākei A & B to produce less than 40MW.
Mike says it has not yet been decided if Wairākei A & B will be pulled down.
"Some people say they are really proud of the history of Wairākei Power Station and the buildings are iconic, and could be repurposed. Others say geothermal power is so clean if you could just pull down the ugly power station by the river."
More steam in the Te Mihi part of the geothermal field is a driver to invest in more power stations at Te Mihi, and the resource consent application seeks to expand to a new steam field at Te Mihi. Mike says in modern times the underground steam source has been more fully explored and also 64 years into geothermal power generation, they have a much greater knowledge about steam fields.
"When they built Wairākei Power Station in the 1950s they didn't fully understand that it was more efficient to have power stations closer to the steam source. Their focus back then was on being close to the river so they would have access to water to cool the power plant."
Twenty years ago, Contact Energy linked all parts of the field together so the steam could go to either Wairakei, Poihipi or Te Mihi power stations.
An objective of GeoFuture is to make more renewable electricity, more efficiently. The idea is that a similar amount of geothermal water will be taken from the ground, but from an operating point of view, none will need to be discharged into any watercourse, making the operation more environmentally friendly. Currently, water is used to cool Wairākei A & B and then the used but still hot steam is mixed with water and then discharged into the Waikato River.
GeoFuture also includes two downstream users of the geothermal water, Wairākei Terraces and Huka Prawn Farm, and Mike says Contact Energy is committed to maintaining a supply of water to these two tourism operators and so they are proposing to increase their discharge into the Te Kiri-o-Hinekai Stream from 500 tonnes per day to 600 tonnes per day.
As part of mitigation, Contact is addressing a future problem they foresee with the popular swimming spot at Spa Park, at the confluence of the Otumuheke Stream with the Waikato River. Monitoring shows the Otumuheke Stream tributaries are drying up at the source and the result is swimmers at Spa Park are experiencing a cooler geothermal spa experience.
"Swimming in natural hot water in the Central Plateau is an iconic thing to do," Mike says.
He says the water temperature of the Otumuheke Stream has varied over time, being quite cool in the 1940s, peaking in the 1980s, and now declining.
It is proposed to send up to 4800 tonnes per day of river water mixed with geothermal water into the Otumuheke Stream from the Te Huka Binary Plant located off Centennial Drive.
"At present, we wouldn't put the full amount in, but this volume gives us the ability over decades to top the stream up as required."
An application has been made to alter then renew existing resource consents to provide certainty before investment. Consents are in place until June 2026 and Contact expects a hearing for the new consents to take place in the middle of this year.
Power generation happening at Wairākei Geothermal Field currently includes the Wairakei Binary, generates 15MW, geothermal power from Wairakei A & B, generates 125MW, geothermal power from the Poihipi and Te Mihi power stations together generates 205MW. The proposed consent changes would see generation increase to 400MW.
The resource consents will provide Contact Energy with some flexibility before it makes the decision to invest hundreds of millions of dollars into geothermal generation at Te Mihi.
"There are many choices yet to be made. The new consents will allow us to make use of the choices we have and progress on with the engineering required to make these decisions."
If the new power station at Te Mihi is to be built by 2026 then an investment decision needs to be taken by late 2023, and this includes beginning construction contract tendering and negotiations with key contractors by late-2022.
Find out more about GeoFuture at https://contact.co.nz/aboutus/our-story/our-projects/geofuture. Make a submission by March 25, 2022 at www.waikatoregion.govt.nz/community/whats-happening/have-your-say/rc-applications/geofuture/
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