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Frequently Asked Questions

Q. What is geothermal energy?

The earth is constantly generating naturally occurring energy.  This heat is known as geothermal heat and can be used to produce electricity.  Electricity produced from geothermal energy is environmentally friendly and a renewable form of energy.

Q. What are geothermal energy resources?

Heat is a form of energy and geothermal energy is literally the heat contained within the earth. There are different types of geothermal energy resources trapped underground. Geothermal energy is produced from hot geothermal water already in the ground or water which becomes hot after it is pumped underground. The first type occurs where water has naturally percolated, become heated by the Earth’s heat and become trapped underground in reservoir rocks which hold the geothermal water in natural voids, cavities or fractures in the rocks which are permeable. Permeable means the ability of water to flow through the natural or engineered cavities or fractures in the rocks. The other type of geothermal resource is where underground rocks themselves are very hot but are dry either because of lack of natural voids, cavities or fractures in the rocks which can hold water or lack of water (“Hot Dry Rocks”) in the rocks. The permeability of these rocks has to be engineered and water pumped through the hot dry rocks to collect the heat. 

Q. What is conventional geothermal energy?

Conventional geothermal energy is extracted from water that has seeped over time into fractured, or porous hot rocks. The rocks are usually hot because they are in regions of the earth that are geologically active, such as active volcanic areas. The hot water and/or steam is forced to the surface under its own pressure and fed directly to a turbine in a power plant to produce electricity.

Q. What are the three sources of geothermal resources?

Volcanic Systems, such as in New Zealand's North Island.  These are usually small (less than 50 km²) but are well developed around the World for electricity generation.  They are not found in Australia.

Sedimentary Geothermal - naturally occuring sandstone or limestone rocks containing water.  Well known examples in Australia are the Otway and Gippsland Basins in Victoria and the Great Artesian Basin in Queensland and South Australia.

Hot Rocks allow for Engineered Geothermal Systems (EGS) whereby developers artificially create a reservoir for water to flow through hot granite rocks.  In Australia, suitable sites are located in South Australia and Queensland.

Q. How is geothermal heat produced?

Geothermal heat comes from the slow decay of radioactive elements deep within the earth's core.  The heat is transferred or conducted torwards shallower rocks near the surface.

Q. What does Engineered Geothermal System (EGS) mean?

An Engineered Geothermal System is where the hot rocks, which contain the geothermal energy, do not have a naturally water saturated permeable reservoir. In an EGS the permeable reservoir has to be engineered. This is done either by:

• hydraulic fracture stimulation to open up natural fractures or zones of weakness in the rock via injection of water under high pressure into the rock; or
  
• injection of acid in the rock to dissolve minerals to enhance the rock permeability along existing fracture zones which have soluble minerals. Water then can flow or be pumped through these fractures and zones to collect the heat from the hot rocks.
  

An EGS system is also known as Hot Fractured Rocks (“HFR”). This is sometimes used where hydraulic fracture stimulation is used to enhance the permeability in hot dry rocks with no open fractures or in rocks which have open fractures which are water saturated.

Q. How is EGS different from Volcanic and Sedimentary geothermal resources?

All three make use of naturally occurring heat to produce power.  Volcanic and Sedimentary resources usually have natural occuring cracks and fractures (reservoir) which allow water to flow into wells and bring hot fluids to the surface.  In EGS, developers have to create this reservoir.

Q. How is the geothermal reservoir established in EGS?

EGS developers use a process known as hydraulic stimulation, where water is pumped into wells at high pressure slowly over a period of a few days or weeks.  This process opens up existing narrow fractures and joints making the geothermal reservoir.

Q. Is this experimental technology?

The technologies used to drill the deep wells and engineer a permeable reservoir in the hot rocks, the two principal keys to success, are not new. Power plants used in conventional geothermal projects are reliable, commercially available and used extensively around the World.

The principle EGS project is Soultz in France where a small power plant is operating.  While there are no large scale commercial EGS projects in operation, various projects are being pursued in Europe (Czech Republic, France, Germany, Switzerland) and in the USA. Australia has outstanding potential resources, which have been estimated at 7,500 times its total current annual energy consumption. 

Q. Will geothermal heat ever be used up?

Geothermal energy is constantly being generated by the earth over geological time.  However, EGS sites, where water is circulated through the same geothermal reservoir, will find temperatures are reduced over time.  To combat this, a project may develop multiple reservoirs which are used on a rotational basis.  The dormant reservoir will naturally regain temperature and then be available for use again.

Q. Is geothermal energy environmentally friendly?

Geothermal energy is virtually free of carbon dioxide and other emissions.  The equivalent of a 100 MW geothermal power plant could save 20 million tonnes of CO₂ each year (3% of Australia's current greenhouse gas emissions), by replacing a coal fired power plant.

Q. What are the avantages of geothermal generation over other forms of renewable power?

Geothermal energy produces no greenhouse gases or other pollutants.  Production plants have a very small “footprint” and, unlike natural energy from wind, wave and solar sources, where production fluctuates, energy is generated on a 24/7 basis. This continuous generation is known as “base load” electricity. Geothermal energy is classified as a renewable energy source and accordingly obtains the benefit of carbon credits.

Q. Where is geothermal energy being developed in Australia?

Two main locations in South Australia and Tasmania have to date been identified, where deeper granite basement rocks are suitable for an Engineered Geothermal System (EGS) style developments.  Sedimentary style geothermal resources have been identified by earlier oil and gas drilling in the Perth Basin of Western Australia and near the western Victorian coastline stretching into South Australia.

Q. Has geothermal energy been used commercially in Australia?

Yes, there have been two small scale examples in Australia.  The small town of Birdsville uses geothermal electricity sourced from hot water from the Great Artesian Basin.  At Portland, the town used a geothermal district heating scheme for about twenty years, using hot water from the Otway Basin resource.  Several companies within Australia are now developing both Engineered Geothermal Systems (EGS) and Sedimentary Geothermal Systems with most companies expecting to develop proof-of-concept projects before full scale commercial deployment.

Q. Why is geothermal energy being explored in Australia?

Australia is amongst the highest emitters of carbon dioxide per capita in the World, due in part to our reliance on coal and gas fired electricity generation.  Geothermal generation can provide a much cleaner substitute.  In addition, the cost of coal and gas for these fossil-fired generators is rising due to global demand for these fuels.  This means that geothermal electricity will become increasingly cost competitive.

Q. Is geothermal energy a "renewable resource"?

The answer depends on the time scale used.  While the temperature of the reservoir rocks will decline as heat is extracted from them over peiods calculated to be not less than 15 to 20 years, the heat will be replenished after production ceases by heat conducted from the surrounding hot rocks.  Current modeling suggests that HDR-driven generators in Australia will still be producing electricity at full load when the World's know oil resources have been exhausted.  This can be accomplished by drilling new wells, or sidetracking from, or deepening existing wells into the adjacent hot rocks.

Q. Is electricity produced by geothermal energy price competitive?

Our modeling of a 400 MWe power plant at Olympic Dam indicates it would be competitive with alternative electricity power sources.