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A resource for New Zealand Science and Physics students.
New
pipelines carrying steam from a well head. The fencing prevents sheep
from warming themselves in cold weather and ruining their wool - Image:
Heurisko Ltd.
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Before the 1950's the Wairakei Geothermal Field
had about 20 geysers, springs, mud pools and
fumaroles which produced about 30 000 tonnes
of hot water each day, which flowed into the
Waikato River. Since then considerable development
has occurred.
In the 1950's the NZ Government
started development in the Wairakei area by drilling
20 wells to investigate the production of steam for electricity generation.
The reasons for the development were:
- two successive dry years resulting in
poor hydro electric generation and nation-wide
power shortages.
- a limited hydro generation potential in
the North Island for future growth.
- coal fired thermal stations could supply
the electricity but government wanted to
vary the generation sources - partly due
to militant unions at the time.
- the supply of hot water and steam for
geothermal power is not affected by rainfall.
- the 'unused' area of land was already
Government owned.
- the land was flat and accessible.
- the Waikato
River was nearby and therefore large volumes
of cold water were available for the important
step of cooling the steam in condensers.
New
uses for waste hot water have also been found such as farming these
prawns in 38°C water - Image: Heurisko Ltd.
When power generation commenced on 15 November
1958, Wairakei was only the second geothermal
power plant in the world.
Development of the field
continued until the installation of the last
turbine in 1963.
By the 1980's the extraction
of steam and hot water had resulted in measurable
changes in the geothermal system:
- production had caused the geothermal systems
pressure to drop considerably
- this pressure
drop allowed cool water to enter the underground
resource, which in turn lowered its temperature
from about 250°C to 200 - 230°C in some parts of the field. This was of concern
because it is the temperature that determines
the amount of steam available to drive the
turbines.
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