Rocking on with hot rocks geothermal energy

Rocking on with hot rocks geothermal energy

This topic is sponsored by the Australian Geothermal Energy Association and the Australian Government Department of Resources, Energy and Tourism.

You will get more from this topic if you have mastered the basics of The structure of the Earth – these links will take you to an annotated list of sites with helpful background information.

The world is getting hotter. This is because of the increasing concentration of greenhouse gases in the atmosphere, due mainly to our excessive burning of fossil fuels. We burn them for the energy that is needed increasingly in our daily life – to drive to school, cool ourselves on hot summer days, blow-dry our hair and listen to our music. The resulting greenhouse gases trap radiation from the sun, preventing it from escaping back into space, causing the planet’s temperature to rise. But not all of the planet’s heat comes from the Sun; some of it is within the Earth; and rather than causing global warming it could help to wean us off fossil fuels.

This heat, geothermal energy, lies in abundance beneath our feet. If the energy stored in hot rocks inside the Earth could be tapped and used instead of fossil fuels, it could help to reduce the threat of climate change.  

There seems to be enough geothermal energy to keep us all ‘rocking’. The Earth’s total heat content has been calculated at 12.6 x 10²⁴ megajoules, which would meet the world’s current energy needs for several billion years. Unfortunately, most of this is inaccessible; but tapping just a fraction of it would make a substantial contribution in terms of reducing greenhouse gas emissions. Geothermal enthusiasts talk about an ‘almost limitless’ supply of energy. The challenge is tapping into it in a cost-effective way.

What is geothermal energy?

The deeper you go into the Earth the hotter it gets (Box 1: Layers of the Earth). Part of the heat is left over from the creation of the Earth, which started off as a hot cloud of gas and dust and has been cooling over time. The outer layers of the Earth have cooled most quickly, forming the crust; heat from the core continues to radiate outwards along what is known as a geothermal gradient. Heat flows from hot to cold – the inner core of the Earth is hotter than 5,000°C, while the surface is generally less than 30°C and outer space is close to absolute zero.

Geothermal energy has an even more important source: radioactive decay. Radioactive elements break down into more stable atoms by emitting radiation and nuclear particles. Naturally occurring uranium, thorium and potassium decay over very long periods of time. The radiation they emit as they decay heats the rocks in which they sit, adding to the geothermal resource. This creation of new heat by radioactive decay and the continuous flow of heat towards the Earth’s surface are reasons geothermal energy is considered a renewable resource.

Using geothermal energy

Geothermal resources vary in character and in the ways in which they can be used. Globally the main accessible resources are in hydrothermal and hot rock systems. High temperature geothermal systems can be used for electricity generation, cooler systems can be used for direct-use applications, and shallow ground source heat pumps can be used in a wide variety of geographical locations.

Hydrothermal systems contain naturally occurring groundwater that has been heated by either heat-producing rocks or by magma that has intruded into the Earth’s crust.

Ergon Energy's hydrothermal power generation system at Birdsville (Image: Ergon Energy)

Hot rock systems such as the one being developed in the Cooper Basin in South Australia, do not contain naturally circulating water. In Australia they generally consist of rocks with higher than normal amounts of heat-generating radioactive elements, insulated by a ‘blanket’ of sedimentary rock. To transfer the heat to the surface, water needs to be sent down to the hot rocks via drill holes. The hot rocks, often granites, also need to be fractured to create a reservoir in which the water can be heated. This can be done by pumping water into the hot rocks under very high pressure using a technique called hydrofracturing; it creates a network of tiny cracks that provides sufficient space for a water-heating reservoir. The heated water is then returned to the surface for use via one or more production or extraction wells. Such systems are sometimes called engineered or enhanced geothermal systems (EGS), hot dry rock or hot fractured rock.

Related site:How geothermal energy works (streaming video) A video describing how energy is extracted from hot rock systems. (Geodynamics limited, Australia)

A simplified hot rock geothermal system: water is pumped underground at high pressure to create a reservoir (Image courtesy of Geodynamics Limited)

Australia’s resources
Hot rocks are the most abundant geothermal resource in Australia and hold promise as a major contributor to Australia’s future energy supplies. But Australia’s geothermal resources are only now starting to be understood. Data on rock temperatures down to a depth of about five kilometres are available from nearly 6,000 bore holes drilled during exploration for petroleum and minerals. These bore holes are distributed unevenly across the continent and many are shallower than five kilometres, so the geothermal resource is better known in some areas than others. Data on heat flow including thermal gradient and thermal conductivity, which are better suited to assessing the suitability of a resource for energy production, are much rarer. Their collection involves both field survey and the testing, in laboratories, of the thermal properties of rock samples.

Despite the need for more data, it is clear that Australia has massive geothermal resources. This is partly because of the presence of large quantities of heat-producing granites in the upper crust enriched by higher than normal concentrations of radioactive elements. The Cooper and Eromanga basins in South Australia and Queensland contain geothermal resources that reach temperatures of up to 250°C at 4.5 kilometres below the surface, putting them among the world’s hottest rocks at this depth (excluding volcanic systems).

The geological characteristics of many of the Australian hot rock sites, such as horizontal layers of granite, should make it relatively easy to create reservoirs of an optimal shape and connectivity for heat extraction. According to some estimates, Australia has enough geothermal energy within reach to supply the country’s energy needs (at current rates) for 20,000 years or more. This figure ignores the fact that geothermal energy is renewable – it is not a resource that will be depleted, unlike fossil fuels.

Direct uses

Geothermal resources can be tapped directly for their energy. The heat can be used, for example, to dry harvested crops and food. In Iceland, geothermal energy is used to heat greenhouses that produce year-round fruit and vegetables in an otherwise inhospitable environment. Geothermal heat can be used in a similar way to warm swimming pools, spas and buildings. Geothermal heat pumps are already being used to heat buildings around Australia including the Geoscience Australia building in Canberra and Antarctic Tasmania in Hobart. Given the prolonged droughts occurring across parts of Australia, the use of geothermal heat to desalinate seawater could also become important.

Indirect uses – electricity generation

In Australia, however, perhaps the most exciting potential application of geothermal energy is its indirect use to generate electricity. Most electricity today is generated using heat. In a coal-fired power station, for example, coal is burnt to heat water, which turns to steam, which is used to spin turbines, which generates electricity (Box 2: Electricity generation).

Geothermal heat can be converted into electrical energy in much the same way using dry steam, flash, or binary generation systems (Box 3: Geothermal electricity generation systems). Some countries are already producing electricity from their geothermal resources: the United States, for example, is generating about 16,000 gigawatt-hours per year, equivalent to around 10 million barrels of oil. Electricity was first generated in this way at Lardarello, Italy, in 1903.

Benefits of geothermal energy

Abundant and renewable: Geothermal energy has a great deal of appeal as an energy source for Australia’s future. It is abundant and it is renewable. While the heat of a hot rock reservoir tapped for its energy can be depleted, it will eventually be replaced. If managed carefully, by controlling the flow rate and/or rotating between a number of reservoirs, geothermal resources can be used sustainably.

Environmentally friendly: In almost every aspect of its development, geothermal energy is environmentally benign. Relative to its capacity for electricity generation and availability, it has a small footprint. Once the plant is established, geothermal energy production generates few greenhouse gas emissions or other forms of pollution. Its widespread use could make a substantial contribution to efforts to combat climate change.

Baseload and price: A drawback of many renewable energy options, such as solar and wind energy, is that, without storage systems, they are only available when the sun shines or the wind blows. Geothermal energy, in contrast, is available 24 hours a day and can therefore provide baseload power. With the introduction of carbon emission reduction schemes, geothermal’s low emission status should also make it price competitive compared to major greenhouse gas polluters such as coal-fired power stations. There are no on-going fuel costs, and it is a renewable energy source.

Issues

Given its benefits, why isn’t geothermal energy already being used commercially in Australia?

Technical challenges: One reason is that the techniques for tapping hot rock resources are only now being developed. Work at the Cooper Basin Innamincka site has shown encouraging results, but how the properties of hot rock reservoirs might change over time is unknown; such changes might also differ between locations. The combination of the high pressure and temperature of Australian hot rocks might also cause problems with drilling and well design.

Start-up costs: Given the lack of existing technologies and the costs of drilling, the start-up costs of hot rock geothermal operations are very high. To some extent these are offset by assistance from federal and state governments in Australia, but geothermal ventures still require investors willing to risk their money in technology that is developing.

Infrastructure: As for renewables including wind and solar, distance from population centres can be a problem. Some of the best-known geothermal resources are a long way from cities or even decent roads. Apart from the problems this remoteness creates for personnel, it also means that very long power transmission lines might need to be built, which would decrease efficiencies and increase costs. However, rather than erect long powerlines, some industries (for example, large computer data centres) may locate adjacent to large geothermal resources. Also, having the generation centre some distance from populated areas should reduce concerns over competing land use or other community objections to development.

In many of the geothermal resource-rich areas of Australia, the availability of water for hot rock operations might also be a considerable challenge. Once there, the water will be recycled through the system and losses are expected to be minimal.

Contaminants: In some systems, the hot geothermal fluids contain dissolved minerals and gases. Some of these might have commercial value, but there might also be a risk of groundwater contamination and the release of greenhouse gases to the atmosphere. Practises used in the petroleum extraction industry to minimise potential contamination will be adapted and adopted by geothermal operators. The very small amounts of radioactive substances that occur naturally in rocks are believed to be too low to be of concern. For example the level of uranium in high heat-producing granite is 100 to 1000 times lower than in a naturally occurring uranium ore body and about the same as Australian coal.

Careful management of the fluids and gases from a geothermal system is required. The use of closed systems like the one being developed at Innamincka overcomes many of these issues. 

Seismic effects: The hydrofracturing process employed in the creation of hot rock reservoirs can induce seismic activity – or mini earthquakes. Hydrofracturing experiments in the Cooper Basin, for example, have induced more than 27,000 small earthquakes, although few could be felt at the surface and none were sufficiently strong to cause any damage to nearby infrastructure. Geologists are learning more about the potential risks associated with hydrofracturing and developing strategies to minimise them.

The future

Rocking on with hot rocks geothermal energy

Box 1 | Layers of the Earth

The Earth is made up of three main layers: the relatively thin crust, the mantle and the core. Immediately beneath our feet is the crust, which ranges in depth from five to 70 kilometres (it is thinnest below the oceans). Below the crust the mantle is 2,900 kilometres deep and makes up 84 per cent of the Earth by volume. Below the mantle is the outer core, then the inner core at Earth’s centre.

These layers are distinguished by their composition, density and temperature; both density and temperature increase towards the centre of the Earth. The inner core, which is slightly smaller in diameter than the moon, is thought to consist mostly of a nickel-iron alloy. Surprisingly even though its temperature is around 5,000°C, it is solid due to the intense pressure at these depths below Earth’s surface. The outer core, although cooler than the inner core, is liquid because it is under less pressure. The deepest part of the mantle reaches temperatures close to 4,000°C but it is less than 1,000°C at its outer edge.
The movement of heat from the ultra-hot core, through the mantle to the crust and then into space is an essential part of the creation and maintenance of many geothermal energy resources. When heated sufficiently, rock melts to form magma; because magma is less dense than the surrounding rock it rises towards the surface. In some places, such as along the boundaries of tectonic plates, magma appears at the surface in the form of lava during a volcanic eruption. In other places, magma is unable to reach the surface and remains in the crust heating the rocks around it. Most of the geothermal energy below Australian soils is generated by radioactive decay, but heat coming from the centre of the Earth also contributes to our geothermal resources.

Related sites

• Layers of the Earth (Volcano World, USA)
  http://volcano.oregonstate.edu/vwdocs/vwlessons/plate_tectonics/part1.html

• This dynamic Earth: Inside the Earth (US Geological Survey)
  http://pubs.usgs.gov/gip/dynamic/inside.html

• Plate tectonics  (Nova: Science in the news, Australian Academy of Science)
  http://www.science.org.au/nova/027/027box02.htm

Rocking on with hot rocks geothermal energy

Box 2 | Electricity generation

Most electricity today is generated using heat. In a coal-fired power station, for example, coal is burnt to heat water, which turns to steam, which is used to spin turbines, which generates electricity. A geothermal power plant operates in a similar way to power plants that use uranium, coal, natural gas or oil. These systems all rely on the use of steam or another gas to turn the blades of a turbine (wind and hydro power also work by turning turbines). As the steam or other gas hits the blades of the turbine, it causes a central shaft on the turbine to rotate.

(© Oncor Corp. 2001)

The shaft of the turbine is attached to a device for producing electricity called a generator; it consists of large magnets attached to the shaft inside a coil of copper wire. The rotating turbine turns the generator shaft and its attached magnets; as they rotate the magnets cause a flow of electrons – an electrical current – in the wire coil by a process known as electromagnetic induction. Electrical current can also be produced if, instead of moving the magnets in the coil, the coil is rotated inside large magnets.
The coil is connected at both ends to an electrical circuit; the electrical current flows from the generator coil through the electricity grid to light and heat our houses, work our appliances and run factories.

Related sites

• Generating electricity: Using high temperature geothermal and other resources (Geothermal Education Office, USA)
  http://www.bpa.gov/Corporate/KR/ed/geothermal/homepage.htm

• How generators work (Wisconsin Valley Improvement Company, USA)
  http://new.wvic.com/index.php?option=com_content&task=view&id=9&Itemid=46

Rocking on with hot rocks geothermal energy

Box 3 | Geothermal electricity generation systems

Three systems currently exist for converting geothermal energy to electricity: dry steam, flash, and binary cycle power plants. The latter holds most promise for Australia’s hot rock resources.

Dry steam power plants use steam from geothermal reservoirs directly. Hot steam is tapped by bore holes and used at the surface to turn a turbine to generate electricity (Box 2: Electricity generation). Dry steam systems have been used for more than a hundred years and are effective for hydrothermal resources where the water is at temperatures of 150°C or more. It is employed, for example, at The Geysers in northern California as well as in Italy, Japan, Indonesia and Mexico. Dry steam systems are unlikely to find much use in Australia, however, because of a lack of sufficiently hot geothermal fluid.

(Image: US Department of Energy)

Flash steam power plants are the most common geothermal systems in use today. They are suitable for resources that are in liquid form at relatively high temperatures (180°C or more). The high-pressure water extracted from underground, enters a tank at the surface that is at a much lower pressure, causing the water to rapidly change to steam, or ‘flash’. The steam is used to drive a turbine and generate electricity. In some systems, left-over vapour can be fed into a second flash tank, enabling more energy to be captured, thus increasing the efficiency of the system.

(Image: US Department of Energy)

Binary cycle power plants, which are thermal power plants capable of utilising relatively low-temperature water, hold most promise in Australia. Heated water, for example from a hot rock system, flows under pressure into a binary cycle power plant. Heat is transferred from the water through a heat exchanger to another liquid with a lower boiling point than water. The vapour that forms from this secondary liquid is used to drive a turbine, which generates electricity. The cooled water is piped back underground into the geothermal system, where it is reheated and reused. The water and any dissolved substances in binary systems are in a closed loop so never come into contact with the other liquid or, more importantly, with the atmosphere. Recycling water also helps to maintain the heat and pressure of the geothermal reservoir.

 
(Image: US Department of Energy)

Related sites

• Geothermal: Electricity generation technologies (Research Institute for Sustainable Energy, Australia)
  http://www.rise.org.au/info/Tech/geo/index.html#gen

• Hydrothermal Power Systems (US Department of Energy)
  http://www1.eere.energy.gov/geothermal/powerplants.html

Activities | Rocking on with hot rocks geothermal energy
1. Putting on your thinking hat to evaluate geothermal energy

Other activities

• Geothermal Education Office (USA)
• Geothermal energy curriculum – looks at different sources of energy with a focus on geothermal energy: its geology, history and uses. Includes a range of student activities including making a model geothermal steam engine, porosity of soil and rocks, generating electricity and modelling the layers of the Earth.
  http://www.bpa.gov/Corporate/KR/ed/geothermal/homepage.htm

• Energy for keeps: Electricity from renewable energy (The California Study Inc., USA)
• Chapter 2 - Going for a spin and Getting current – students make a model steam turbine and investigate how different energy sources can be used to rotate it. They then use a magnet to generate electricity.
  http://www.energyforkeeps.org/book_chapters/ch2_activities.pdf

• Chapter 3 - Watt's my line? – students demonstrate their understanding of different energy resources (including geothermal) for electricity generation through presentations and pantomime (note: resources need to be provided for student research).
  http://www.energyforkeeps.org/book_chapters/ch3_activity.pdf

• US Department of Energy (USA)
• Geothermal energy – provides background information on geothermal technology and five related classroom activities on heat transfer, boiling points, geothermal emissions and turbine design.
  http://apps1.eere.energy.gov/education/lessonplans/pdfs/geothermal_energy.pdf

• Science upd8 (UK)
• Hot rocks – students look at the relationship between geology and geothermal energy, and how geothermal power stations might affect local communities.
  http://www.upd8.org.uk/activity/131/Hot-Rocks.html

Activity 1 | Rocking on with hot rocks geothermal energy
Putting on your thinking hat to evaluate geothermal energy

Note: this activity may be conducted in small groups or as a class.

De Bono’s 6 thinking hats is a tool for thinking about an issue effectively. By putting on a different metaphorical or symbolic ‘hat’, the group thinks about the issue from six different perspectives. For more information see:

Six thinking hats (Department of Education, Tasmania)

Evaluating with de Bono’s 6 thinking hats (Bendigo Senior Secondary College, Australia)

The task
You work for an organisation that provides funding for alternative energy projects in Australia (mostly solar, wind, biomass and wave power). Your team is responsible for evaluating incoming projects. A company has approached your organisation for funding to develop a new geothermal energy plant in the Cooper Basin. From initial exploration of the area they have found an area with geothermal resources of similar temperatures but at a greater depth than the existing Innamincka geothermal plant in the same basin.

Should your organisation consider providing funds for the new geothermal energy plant?

• Copy the 6 thinking hats guide below onto a piece of A3 or butcher’s paper.
• Use the information in Rocking on with hot rocks geothermal energy to evaluate the project as a team. Fill in the 6 thinking hats guide to help with your team’s evaluation of the proposal.
• Consider the project by comparing geothermal energy to other sources of energy, as well as by comparing the project to the existing Innamincka geothermal energy site.
• Present your team’s final findings and recommendations in either a Word document (less than 400 words) or a PowerPoint presentation.

De Bono’s 6 thinking hats guide

Further reading | Rocking on with hot rocks geothermal energy

About the house
September 2007, pages 28-31
The heat is on (by Andrew Dawson)
Looks at the development of hot rock technology in the Cooper Basin, Australia.
http://www.aph.gov.au/house/house_news/magazine/ATH32_Heat.pdf

ATSE Focus
October 2008, pages 17-19
Hot rock energy a likely source of baseload power (by Martin Albrecht and Doone Wyborn)
Explores geothermal energy production in the Cooper Basin, Australia.
http://www.atse.org.au/index.php?sectionid=1232

September 2007
Australia a hot prospect for geothermal (by Mike Etheridge)
Describes the prospects and issues with geothermal energy production in Australia.
http://www.atse.org.au/index.php?sectionid=1232

AUSGEO news
September 2007, pages 6-10
In search of the next hotspot (by Anthony Budd, Fiona Holgate, Edward Gerner and Bridget Ayling)
Explains the activities of the Geothermal Energy Project including mapping Australian geothermal resources.
http://www.ga.gov.au/ausgeonews/ausgeonews200709/geothermal.jsp

Australasian Science
August 2008, pages 25-27
Hot southern land (by Sandra McLaren)
Describes hot rock resources in Australia and their role in the evolution of the continent.
http://www.control.com.au/bi2008/297McLaren.pdf

Cosmos
August/September 2008, page 96
The heat beneath our feet (by Sandra McLaren)
Comments on the potential of hot rock geothermal resources in Australia.
http://www.cosmosmagazine.com/node/2147/full

Ecos
No. 145, page 6
Government and Google get behind geothermal
Reports on financial support for geothermal energy development in Australia.
http://www.ecosmagazine.com/?act=view_file&file_id=EC145p6b.pdf

Nature
17 December 2009, pages 848-849
Geothermal quake risks must be faced (by Domenico Giardini)
Calls for open discussion and evaluation of earthquake risk of geothermal energy systems.

14 August 2008, pages 816-823
Electricity without carbon (by Quirin Schiermeier, Jeff Tollefson, Tony Scully, Alexandra Witze and Oliver Morton)
Evaluates a range of alternative energy sources, including geothermal energy, in terms of cost, capacity, advantages and disadvantages.
http://www.nature.com/news/2008/080813/pdf/454816a.pdf

New Scientist
8 October 2008, pages 37-40
Renewable energy: Power beneath our feet (by Julian Smith)
Describes recent international developments in harnessing geothermal energy from hot rocks.
http://environment.newscientist.com/channel/earth/mg20026771.900-renewable-energy-power-beneath-our-feet.html

17 July 2008, pages 24-25
Who needs coal when you can mine deep heat? (by Rachel Nowak)
Reports on international projects to harness hot rock energy with a focus on the Cooper Basin, Australia.
http://www.newscientist.com/article/mg19926656.500-who-needs-coal-when-you-can-mine-earths-deep-heat.html

8 November 2006
Geothermal power plants could also consume CO₂ (by Tom Simonite)
Proposes that carbon dioxide could replace water in geothermal power plants as a means of extracting heat from rocks.
http://www.newscientist.com/article/dn10478-geothermal-power-plants-could-also-consume-co2.html

Research*eu
September 2008, pages 40-42
The geothermal revolution (Julie Van Rossom)
Explores a hot rock power plant developed in Alsace, France that uses an existing natural water reservoir.
http://ec.europa.eu/research/research-eu/earth/article_earth40_en.html

Scientific American
2 March 2009
Can geothermal power compete with coal on price? (by Christopher Mims)
Compares production costs of geothermal energy with other sources of energy.
http://www.sciam.com/article.cfm?id=can-geothermal-power-compete-with-coal-on-price&print=true

October 2007, pages 80-81
Heating up (by Mark Fischetti)
Provides a brief overview and clear diagrams of different technologies for extracting geothermal energy.

23 January 2007,
Hot rocks: Tapping an underutilized renewable resource (by David Biello)   
Describes a Massachusetts Institute of Technology report on the potential of enhanced geothermal systems in the USA.
http://www.sciam.com/article.cfm?id=hot-rocks-tapping-an-unde

Useful sites | Rocking on with hot rocks geothermal energy

Geothermal Energy Project (Geoscience Australia)

Provides details of the Australian Government Geothermal Energy Project. The outreach and education section provides the following fact sheets: Electricity generation from geothermal energy in Australia, Induced seismicity and geothermal power development in Australia and Direct-use of geothermal energy: opportunities for Australia
http://www.ga.gov.au/minerals/research/national/geothermal/index.jsp

Research Institute for Sustainable Energy (Murdoch University, Australia)

• Geothermal energy
  Discusses types of geothermal resources from an Australian perspective.
  www.rise.org.au/info/Res/geothermal/index.html
  

• Geothermal
  Covers international use of geothermal energy, electricity generation technologies and geothermal projects in Australia and New Zealand.
  http://www.rise.org.au/info/Tech/geo/index.html
  

Australian Government Department of Resources, Energy and Tourism

• Australian geothermal industry technology roadmap
  A technical document that examines in detail the research and development requirements for large scale geothermal energy use in Australia.
  http://www.ret.gov.au/energy/clean_energy_technologies/energy_technology_framework_and_roadmaps/hydrogen_technology_roadmap/Documents/GEOTHERMAL%20ROADMAP.pdf

• Australian geothermal industry development framework
  Identifies and discusses strategies for the development of the geothermal industry in Australia.
  http://www.ret.gov.au/energy/clean_energy_technologies/energy_technology_framework_and_roadmaps/hydrogen_technology_roadmap/Documents/GEOTHERMAL%20FRAMEWORK.pdf

Australian Geothermal Energy Association

• Members
  Lists and provides links to the websites of companies that are members of the Australian Geothermal Energy Association, a national body representing the Australian geothermal energy industry.
  http://www.agea.org.au/membership/members/
  

• About geothermal
  Provides answers to a series of frequently asked questions about geothermal energy.
  http://www.agea.org.au/information/about-geothermal/

AGEG (Australian Geothermal Energy Group)

Provides information on geothermal energy in Australia including research, licence activity, legislation and government programs. AGEG was formed in 2006 to provide support for Australia's membership in the International Energy Agency's Geothermal Implementing Agreement.
http://www.pir.sa.gov.au/geothermal/ageg

Education room (Geodynamics Limited, Australia)

Presents a range of clear information on geothermal energy in the form of fact sheets, videos, animations and diagrams.
http://www.geodynamics.com.au/IRM/content/educationroom.html

Australian Academy of Science

• Geothermal energy
  Transcript and slides from a public lecture series presentation on geothermal energy as an alternative energy source in Australia.
  http://www.science.org.au/events/publiclectures/re/budd.htm

• Generating new ideas for meeting future energy needs (Nova: Science in the news)
  Provides information on hydrogen, hot dry rocks and wave power as alternative energy sources. Classroom activities are included.
  http://www.science.org.au/nova/046/046key.htm

Note: the following information relates mostly to  volcanic geothermal resources.

Geothermal Education Office (USA)

• Geothermal energy facts
  Covers Earth’s heat, geothermal reservoirs, electricity generation, direct use of geothermal resources, sustainability, technology and the future of geothermal energy.
  http://geothermal.marin.org/geoenergy.html

• Renewable energy source: Geothermal
  Excerpt from a book on resources for electricity generation. This chapter clearly covers geothermal resources, power plants and issues with geothermal energy.
  http://geothermal.marin.org/geo_fmat/geo_excerpt_4_07.pdf

• Introduction to geothermal energy slide show
  A series of 122 presentation slides on geothermal energy: its geology and use for electricity generation, heat pumps and direct uses.
  http://geothermal.marin.org/GEOpresentation/index.htm

US Department of Energy

• Geothermal energy – energy from the Earth's core
  Aimed at a younger audience, this site provides a good overview of geothermal energy.
  http://www.eia.doe.gov/kids/energyfacts/sources/renewable/geothermal.html

• Geothermal Technologies Program
  Examines geothermal energy technologies, issues, enhanced geothermal systems and uses of geothermal energy.
  http://www1.eere.energy.gov/geothermal/

Geothermal energy (The University of Utah, USA)
Covers heat from the Earth, resources, uses of geothermal energy and benefits and challenges of geothermal energy.
http://www.geothermal.org/GeoEnergy.pdf

Glossary | Rocking on with hot rocks geothermal energy

alloy. A substance made of two or more metals, or a metal and one or more non-metals, that has mostly metallic properties. Alloys are often created to improve the properties of metals such as strength, resistance to corrosion and hardness. For example, steel is an alloy of iron with up to two per cent carbon and often small amounts of other elements. The properties of steel such as strength, malleability and machinability can be changed by adjusting the amounts of its component elements.

artesian. Describes a source of groundwater or aquifer that is under pressure. If an artesian aquifer is tapped by a well, water rises above the surface of the aquifer without the need for pumping. The Great Artesian Basin in Australia is one of the largest artesian basins in the world lying under 22 per cent of the country.  

carbon emission reduction scheme. A method such as a carbon tax or carbon trading scheme that reduces emissions of carbon (and often other greenhouse gases). A carbon tax is a tax imposed on the production or use of fossil fuels based on the carbon content of those fossil fuels. Trading schemes set a limit to the amount of greenhouse gases that can be released. Permits are then allocated to organisations for their carbon emissions; those reducing emissions below their quota can trade the excess to other organisations. For more information see Carbon currency – the credits and debits of carbon emissions trading (Nova: Science in the news).

electromagnetic induction. The production of electrical current in a conductor due to a changing magnetic field (moving magnet) or to the movement of a conductor through a magnetic field. For more information see electromagnetic induction (Florida State University, USA).

geothermal gradient. The rate of increase in temperature per unit depth in the Earth. For more information see Geothermal gradient (Absolute astronomy, USA).

granite. A hard, coarse grained, rock that is often used in building materials. Granite is an intrusive, igneous rock ie. it forms from magma underground. Like most other rocks, granite contains low levels of radioactive elements.

heat pump. By circulating water underground, a geothermal heat pump uses the relatively constant heat of the earth to alter the temperature of the circulated water. This water can then be used to heat or cool buildings. Heat pumps can extract heat from the earth for heating buildings in winter and deliver heat from buildings to the earth in summer.

hydrothermal. Describes geothermal systems with naturally occurring groundwater that has been heated by either heat-producing rocks or nearby volcanic activity.

impermeable. A substance that cannot be penetrated. A rock or material that stops the movement of water or other liquids through it.

megajoule. The unit of energy is the joule (J). It is defined as the work done, or energy expended, by a force of one newton moving one metre in the direction of the force. When we consider power generation, we use larger units. A megajoule is 1,000,000 joules.

radiogenic. Produced by radioactive decay, eg, the heat and isotopes produced as a result of the decay of uranium in the Earth’s crust are radiogenic.

Ring of Fire.  A region around the Pacific Ocean where volcanoes and earthquakes frequently occur, corresponding to the edge of the Pacific tectonic plate. For a map see Ring of Fire (US Geological Survey).

sedimentary. A class of rocks that are formed from sediments eg, sandstone or from precipitation of chemicals from solution eg, limestone.

tectonic plate. The Earth’s crust is broken up into a series of large areas or tectonic plates. These plates move slowly on top of the currents in the semi-liquid mantle below them. Volcanoes, earthquakes, geysers and hot springs frequently occur where plates are either colliding or pulling apart from each other. For more information see Plate tectonics (Nova: Science in the news).