Geothermal energy
Geothermal energy is heat energy available from the earth. Geothermal energy has been used for thousands of years in the form of hot springs for bathing, heating, cooking and medicinal reasons.
Geothermal energy is considered a sustainable resource in that the heat generated in the earth will still be around for millions of years. Heat is conducted from the earth’s core, which has a temperature of about 6000 degree Celsius. Some of the heat in the earth comes from the sun which will also continue to burn for billions of years.
Today, geothermal energy is used around the world for heating and electrical generation. To produce electricity, the geothermal resource must be concentrated and easy to access.
Geothermal: How Does it Work?
The main form of geothermal power is where bodies of water, either above or below the earth's surface, are converted to steam by the earth's heat. The steam is collected, and used to power a turbogenerator just like in a regular coal fired power station.
The other form is called hot rock geothermal energy. It is where water is pumped below the surface to areas of hot rock. The water turns to steam, and is brought back to the surface to drive a turbogenerator.
It is debatable whether geothermal energy is a renewable source. If the rate of extraction of geothermal energy is less than or equal to the rate of resource creation, it may be considered to be sustainable.
Geothermal: Use throughout the world and in Australia
The United States has the most geothermal power production in the world - currently around 2700 Megawatts. This is about 1.6% of the total US electricity generation.
A hydrothermal power station called The Geysers in California has been producing low cost electricity for many years. Steam or water is released from the geysers at a high pressure and used in a turbine to generate power. Similar resources are available in New Zealand and Australia.
Australia produces a very small amount of electricity from geothermal energy, with one facility being Ergon Energy's geothermal power station at Birdsville in outback Queensland. In addition, trials are being carried out in South Australia and New South Wales to commercialise Australia's first hot rock (geothermal) power station.
Most of Australia's hydrothermal resources are water-dominated sources found in the Great Artesian Basin which stretches from the far north of South Australia through western Queensland to the Gulf of Carpentaria.
There are also a number of potential hot dry rock sites in the north of South Australia and in the Hunter Valley, New South Wales.
The Birdsville geothermal power station is one of the few low-temperature geothermal power stations in the world. The plant derives its energy from the near-boiling (980C) water taken from the Great Artesian Basin (at a depth of 1230m) that provides a water supply for the town.
The power station provides the town of Birdsville in western Queensland with energy. Operation of the geothermal power station reduces diesel consumption by about 160,000 litres per year, saves $135,000 in fuel costs, reduces emissions of 430 tonnes of greenhouse gases, and allows relatively noise-free operation.
The photograph of an exploration bore is courtesy of http://www.abc.net.au exploration (article reporters Pat Hession & Chrissy Arthur and photographer Mike Chuk).
A close-up view of a well at Innamincka, South Australia, where the 'hot rocks' technology is being developed.
The Cooper Basin Project
A significant geothermal resource has been known of for some time in the Cooper Basin area of north-eastern South Australia. This basin is an important source of gas and petroleum and many boreholes have been drilled in the process of exploration and production from the field. The majority of these boreholes have had temperature measurements made in them. As a result, the very high temperatures that characterise the sub-surface near the town of Innamincka are both well known and well understood.
The first borehole to be drilled in the Cooper Basin has been named Habanero 1 (after what is reputedly the world's hottest variety of chilli). It is now the hottest borehole ever drilled in Australia with a temperature at 4300 metre depth of >250°C.
Considering that well costs depend on the power plant size, well depth, and rock type, it is clear that the temperature of the resource has a significant effect on geothermal fuel cost. The capital cost of a geothermal power plant is affected by such factors as:
- nature and temperature of the resource
- plant output capacity
- energy conversion process
- chemical composition and gas content
- geothermal fluid conditions
- site conditions and environmental factors
Advantages
- Geothermal energy is renewabl
- It does not produce greenhouse gases
- Limited land is necessary for mining structures
- Limited impact on landscape
Disadvantages
- Though geothermal energy in general is renewable, individual sites can run out of heat for significant periods of time (decades).
- Hazardous minerals may be produced which are difficult to safely dispose of.
- Suitable reserves of geothermal energy can be difficult to find and use.
