www.csiro.au What is Geothermal Energy? Geothermal energy is simply the heat in the Earth, and is a renewable energy source. Geothermal energy 1MW (megawatt) Geothermal energy is simply the heat in the Earth, and is a renewable energy source. The application of geothermal energy ranges from domesticscale, ground source heat pumps used for heating and cooling homes, direct use applications such as heating large swimming pools through to hundreds of MW-scale power plants. Around the world geothermal energy provides over 10,000MW of electricity generation capacity, and 55,000MW of direct use and ground source heat pump applications. Geothermal resources have been used for millennia in the form of hot springs and bath houses, and commercially for over 100 years in areas such as: • Lardarello field in Italy since 1913, • Wairakei field in New Zealand since 1958, • The Geysers field in California since 1960, and • Unterhaching in Germany since 2007. Powers 1,000 homes, or is the power produced by two V8 supercars. 1.8MW (megawatt) Runs the lights at the MCG. The city of Sydney needs about 10,000MW. Types of geothermal resources Most geothermal resources used for power generation globally are associated with volcanic activity, e.g. the west coast of the USA, New Zealand and Indonesia. There are no significant volcanic resources in Australia, however the Australian geothermal industry is targeting two geothermal concepts that are also the subject of global activities. 1.Hot Sedimentary Aquifers (HSA) consist of hot water in layers of rock (called aquifers), typically in sedimentary basins, that easily allow the water to flow through them. The heat energy is used by pumping the water out of a well, extracting the heat through a heat exchanger, and then returning the water underground. These resources are typically found at depths between 500m and 4.5km. See our fact sheet on HSA for more information. 2.Enhanced Geothermal Systems (EGS) have hot rocks that do not contain enough water or have the permeability needed to allow the water to flow through the rock. These resources need to be enhanced either by adding water, increasing the permeability of the rock, or both. The heat can then be extracted in the same way as HSA reservoirs. These resources are typically targeted at depths of more than 3km. Surface temp 14°C Plate mantle boundary 1330°C Core mantle boundary 4500°C Where does the heat come from? The heat comes from the Earth which, when first formed, was very hot. The Earth has been slowly cooling ever since but a lot of heat still exists deep below the surface. The Earth also generates heat, i.e. the heat released as the Earth’s outer core solidifies and the heat produced from decay of naturally occurring radioactive elements (low concentrations of potassium, uranium and thorium) and other geological processes. This heat flows from the hot interior of the Earth to the surface which is relatively cool. This internal heat engine drives geological processes like plate tectonics, earthquakes and volcanoes. When searching for the best resources, geothermal explorers seek out areas where high temperatures are close to the surface. Crust 0-70km Solid Mantle 70-2891km Solid Outer Core 2391-5150km Liquid Inner Core 5150-6731km Solid What is a geothermal energy resource? How is geothermal energy used? Geothermal energy for everyone Geothermal resources require three things: The heat extracted from geothermal resources can be used to generate electricity or in any process that uses heat. Geothermal energy is also available at a scale that can be used by everyone. Ground source heat pumps use the Earth’s thermal mass, typically at depths of less than 100m, as a heat source for heating and cooling buildings, including homes. The heat pump enhances the flow of heat from warm to cool, e.g. from the ground into a house during winter, or the opposite during summer. • Heat: The Earth gets hotter with increasing depth. Some areas are hotter than others due to a range of geological factors. • Fluid: Fluid in the form of water or steam is required to move the heat to the surface. The fluid can be naturally occurring or added as part of the extraction process. • Permeability: This describes the ability of fluid to flow through spaces in the rock. Permeability is very important; the greater the permeability the easier it is to extract the fluid. Benefits and challenges of geothermal energy ELECTRICITY GENERATION Heat is brought to the surface (in steam or hot water) and used to drive steam turbines that spin a generator to produce electricity. The electricity generated can be either used directly or put into an electricity grid. Electricity generation needs resource temperatures over about 130°C. In Australia, geothermal power stations are likely to use binary systems where the heat is extracted from the geothermal fluid through a heat exchanger so that none of the geothermal fluid is lost. Turbine Electricity to the grid Generator Hot sedimentary aquifers Cooling or waste heat recovery BENEFITS Low to zero emissions The Geoscience Australia building located in Canberra uses one of the largest geothermal heat pump systems in the southern hemisphere (see www.ga.gov.au). The system uses the very stable nature of the Earth’s temperature at depth which remains at around 17°C throughout the year, and has projected energy savings of over $1 million over the anticipated 25-year life of the plant. Ground source heat pumps Condensor Sandstone Shale Heat exchanger Always available (not intermittent) Direct use HSA resource Low environmental impact EGS resource Large resource, if EGS can work Direct use applications can displace electricity generation Enhanced geothermal systems No resource, no insulating layers to trap heat 150 °C Insulating coal and mudstone Fault assisted HSA power resource Sandstone HSA power resource EGS resource Electricity generation from geothermal heat. 200 °C Renewable over relatively short time scales Small surface footprint relative to other energy generation technologies CHALLENGES EGS and HSA are not proven at a large scale; economic viability is a challenge High upfront costs due to requirement for deep drilling in most cases Difficulty in achieving required flow rates from HSA and EGS reservoirs Costs of developing EGS have proven to be high Possible social and environmental impacts; while these impacts are expected to be small, they will still need to be managed. Ergon Energy’s geothermal power station in Birdsville, about 1,600km west of Brisbane on the edge of the Simpson Desert, is one of the few low-temperature geothermal power stations in the world. The power station is not connected to the national electricity grid but its geothermal power provides approximately 30% of the annual electricity needs of Birdsville. DIRECT USE This involves using the geothermal heat to heat or cool (using industrial chillers) buildings, swimming pools, and processes used within industry, agriculture and aquaculture, and domestically – without needing to convert it to electricity. This is a very efficient way of using geothermal resources with lower temperatures, i.e. under 130°C. St Hilda’s Anglican School for Girls, located in Western Australia, has an eight-lane, 50m pool heated to 28°C by a geothermal bore. Shale Heat producing granite Different geothermal resources can be used for a variety of energy applications. CSIRO and geothermal energy CSIRO is working to enable lower cost and lower risk energy options for Australia’s future. We are actively developing and demonstrating new energy technologies, and enabling improved access to and understanding of new energy resources. Our geothermal energy research is a part of these activities. We work with the geothermal industry, government and other research institutions addressing a range of challenges facing the development of geothermal energy in Australia, including: - developing a geothermal systems analysis approach and workflows for the evaluation of geothermal energy resources, from exploration through to development; - working on engineering methods and technologies needed to extract energy from geothermal reservoirs; and - improving the understanding of the impacts of geothermal energy on society, the environment and the economy. Visit www.csiro.au/geothermal CONTACT US FOR FURTHER INFORMATION t e w CSIRO geothermal energy www.csiro.au/geothermal 1300 363 400 +61 3 9545 2176 [email protected] www.csiro.au YOUR CSIRO Australia is founding its future on science and innovation. Its national science agency, CSIRO, is a powerhouse of ideas, technologies and skills for building prosperity, growth, health and sustainability. It serves governments, industries, business and communities across the nation. CONTACT Geothermal Energy Stream Leader Dr Cameron Huddlestone-Holmes t +61 7 3327 4672 [email protected]