Many countries have recognised the threat caused by climate change. Geothermal power has been a consideration for some time and many countries us it as a source of clean energy.
Geothermal energy is heat energy that exists in dry rock formations deep below the surface (four to 10 kilometres) or in seismically active regions. These “hot rocks” occur in geologically unstable areas or at places where the Earth’s crust is thin enough to permit heat to move to the surface. This heat energy can be used directly for industry, agriculture and heating and cooling or indirectly to heat the water used in steam turbine engines to generate electricity. Another source of geothermal energy is through radioactive decay. This occurs naturally when radioactive elements in low concentrations of uranium, thorium and potassium below the Earth’s surface, break down into more stable elements and, in doing so, emit small amounts of radiation. The decay occurs over very long periods of time. The emitted radiation heats the rocks in which they are contained, creating a localised increase in temperature and a continuous flow of heat, resulting in a consistent and stable supply of renewable, clean energy.
Geothermal energy has been the subject of much research and development since the mid-1950s when the first steam-driven system entered into operation in California. Since then, innovation and technological advancements in regulating heat distribution and the supply of water for steam and power plant design and operation have resulted in geothermal production plants being established in many parts of the world.
According to the 2013 Annual Global and US Thermal Energy Report, the extent of power generation from geothermal sources in operation globally, was more than 12,000 megawatts (MW) of large utility-scale geothermal capacity was, with another 30,000 MW capacity in the planning stages. Combined, these geothermal facilities are intended to produce approximately 68 billion kilowatt-hours of electricity which is enough to meet the annual needs of more than six million typical US households. Similarly, in Iceland and El Salvador, energy derived from geothermal plants in these countries account for more than 25 per cent of electricity production. Internationally, the Philippines, Mexico, New Zealand, Germany, Kenya, Ethiopia, Costa Rica and Turkey have existing plants or are in the process of developing their geothermal power infrastructure.
The supply of geothermal energy in Australia is currently limited to several, mining-related ‘demonstration’ plants and a single small commercial plant established near Birdsville in Queensland. Notwithstanding the potential benefits of moving to geothermal energy production in Australia is significant. Estimates suggest that drawing only one per cent of the geothermal energy sourced at shallower than five kilometres, and hotter than 150°C, could supply all of our national energy requirements for 26,000 years. For that reason, through an Australian government-funded Onshore Energy Security Program, work is ongoing to enable researchers to better understand the location of hot spots and their potential capacity, in all states and the Northern Territory. With a focus on WA, NT and Queensland, Geoscience Australia data indicates, with a high degree of confidence, the existence of vast areas in the NT, Kimberley and in northern Queensland, where temperatures are expected to reach 235oC at a depth of five kilometers.
The development of geothermal energy in Australia will be controversial, resulting in much debate and argument to identify and implement measures to mitigate many social and environmental risks. These will include surrounding groundwater use, induced seismic events from drilling, competing use of resources as geothermal resources can be located near coal seam gas, groundwater and sites for CO2 sequestration. There will also be financial risks given the large scale, relatively high capital costs and high number of uncertainties. Further, exploration and research into geothermal energy is costly and there are considerable technological challenges involved in drilling boreholes used to gather the data needed to measure the occurrence and distribution flow of heat. Limitations in drilling technology and engineering currently restrict bore-hole depths to around five kilometres. At greater depths, rock density and geology, as well as heat, combines to inhibit cooling of the drill shaft and the supply of surface-delivered lubrication.
Though the costs can be high, geothermal energy has the potential to provide Australia with reliable and clean renewable energy for millennia. The technology presents the potential opportunity for Australia to play a significant role in moving the world towards a cleaner, more sustainable system of clean-energy supply.