Geothermal energy is an important contributor to New Zealand’s electricity supply. But extracting geothermal energy affects the geothermal features and the surrounding environment. Reusing and reinjecting geothermal energy and fluid, and managing the geothermal system as an integrated whole to development helps to minimise the effects.
Primary energy – In 2011, New Zealand’s total primary energy supply was 818 petajoules (PJ). Twenty percent (159 PJ) of New Zealand’s primary energy came from geothermal sources 1.
Primary energy comes directly from natural sources such as the sun, gas and oil, wood, coal and geothermal energy:
Primary energy obtained from geothermal sources is forecast to increase to 30 per cent of the total by 20302. Estimates say we could extract between 30,000 and 57,000 PJ per year of geothermal energy using present technology3. But this could lead to irreversible effects, such as the destruction of geysers and other surface features, and land subsidence.
Electrical energy - In 2011, New Zealand’s total electrical energy supply was 155 PJ per year. Geothermal energy from the power stations in the Waikato region provides about 20 per cent of our national electricity supply.1.
Waikato region - The Waikato region provides 90 per cent of the primary geothermal energy extracted in New Zealand4. Of the geothermal energy extracted, only 15 per cent is converted to a useable form1. The rest is re-injected or disposed of into the environment as heat. In the Waikato region there are about 60 separate industries, accommodation facilities and tourist facilities that take small amounts of heat for direct uses. (Barns and Luketina 2011, Valuing uses of the Waikato Regional Geothermal Resource, 2011/ 15, Waikato Regional Council, Hamilton.)
New Zealand has thirteen geothermal power stations(external link). Nine are in the Waikato region. There are plans to build others and expand existing stations, in the Waikato, Bay of Plenty, and Northland regions. The table below lists the stations in our region.
Geothermal power stations
|Geothermal system||Site||Owner(s)||Productive output (MW)||Year built|
|1. Wairakei-Tauhara||Wairakei||Contact Energy||140||1958|
|Wairakei Binary||Contact Energy||14||2005|
|Poihipi Rd||Contact Energy||55||1997|
|Te Huka||Contact Energy||23||2010|
|2. Rotokawa||Rotokawa||Rotokawa Joint Venture||30||1998|
|Rotokawa B||Rotokawa Joint Venture||6||2003|
|Nga Awa Purua||Tauhara North No. 2 Trust||140||2010|
|3. Mokai||Mokai A||Tuaropaki Power Company||55||2000|
|Mokai B||Tuaropaki Power Company||37||2005|
|Mokai C||Tuaropaki Power Company||17||2007|
|4. Ngatamariki||Ngatamariki||Rotokawa Joint Venture||82||2013|
|5. Ohaaki||Ohaaki||Contact Energy||45||1988|
As well as these large power stations, about 60 commercial operations extract small or medium quantities of geothermal water and energy in the region. Most operations take the water from wells or springs, but others take water from hot streams such as the Onekeneke at Taupō. This heated water is used mainly for public baths or motel pools.
Geothermal systems extend under large areas of land. To find, develop and extract these economic sources of geothermal energy and fluid resources (sometimes as deep as five kilometres below the Earth’s surface) requires large capital investment and complex infrastructures.
Although only a fraction of geothermal energy is currently used, the environmental effects have been dramatic.
Since the 1950s, the number of geysers in the region has fallen because of heat and fluid extraction and the effects of overlying land uses. When water extraction prevents pressure from reaching the level necessary to fuel the geysers, they disappear. As a result, many sinter-depositing springs and geysers and their associated ecosystems were lost with the development of the Wairakei Geothermal Power Station.
The extraction of heat and fluid can cause land subsidence. For example, a marae near Ohaaki Geothermal Power Station is sinking and runs the risk of being inundated by the Waikato River, as the ground it sits on subsides.
Effects on other parts of the natural environment are summarised in the table below.
Environmental effects of geothermal contaminants5
|Contaminant||Adverse effects||Source of contaminant|
|Arsenic||Lethal at high levels. Lower doses cause a wide range of illnesses including cancer. Toxic to humans, fish and plants. Levels in the Waikato River from Wairakei to the sea exceed drinking water standards. Levels in water cress exceed food standards. The beds of some of the Waikato hydro lakes are identified as contaminated land because of high concentrations of arsenic in the sediment.||Natural geothermal discharges. Separated water from geothermal wells discharged into water.|
|Boron||Toxic to humans at high levels. Toxic to some crops at low levels.||Natural geothermal discharges. Separated water from geothermal wells discharged into water.|
|Heat||Elevated water temperatures may kill fish and aquatic life. Fish may avoid water if the temperature rises even slightly above their preferred level.||Separated water and condensed steam from geothermal wells discharged into water. Cooling water passed through geothermal power stations.|
|Hydrogen sulphide||The ‘rotten egg’ smell. This discharge can cause death if concentrations build to dangerous levels in enclosed areas and are inhaled. It can also cause corrosion. Toxic to fish.||Discharges to air from the de–gassing of geothermal fluid. Natural geothermal discharges.|
|Carbon dioxide||A greenhouse gas. This can kill if found in high concentrations in enclosed spaces, such as in power stations.||Released by geothermal powerstations at a rate of about 1/3 that of cas-fired powerstations6.|
|Mercury||A toxic element. Accumulates in the food chain. Mercury concentrations in some fish from the Waikato River exceed recommended levels for human consumption7.||Discharged into air from geothermal cooling towers and into water from geothermal wells.|
Find out more about the arsenic levels in the Waikato River.
In the past, once geothermal fluid extracted for electricity generation had been through the power station, any excess heat and fluid was discarded. Now increasingly, other industrial and domestic processes use the discarded heat and fluid before it is reinjected into the geothermal system. This means less of the energy extracted is wasted, and less heated water is produced as a by-product. For example:
Developers must obtain resource consents prior to developing geothermal areas. The resource consent process requires consultation with iwi and considers potential effects on waahi tapu and other significant sites. Significant adverse environmental effects must be avoided, remedied, or mitigated.
Each power station needs a set of about 15 resource consents to cover such activities as taking geothermal fluid and fresh water, and discharging steam and other gases to air, reinjection of geothermal fluid to ground or its discharge to land or water, drilling geothermal wells, and building and maintaining roads.
Find out about how the Mokai Geothermal System is being managed.