Excellent Prospects for Geothermal Power in Australia, America and Worldwide
Geothermal power is generated from the heat inside the Earth and it can be utilized to develop electrical power by using two major kinds of geothermal resources.
There is a need for additional research about geothermal sources, new methods for deep drilling and power conversion at the surface, as well as dealing with the risks of inducing earth quake. But the basics understanding or what is required is already known are and there are several plants already operating throughout the world.
The potential resources in Australia and America are huge (Figs 1 and 2). The basic concept is shown in Figure 3.
If high pressurized water is not available, then water can be injected deep below ground where it permeates through fissures and absorbs heat from the surrounding rock. The fluid that comes back to the surface is very hot and has high pressure and this heat is extracted to produce electricity (Figs 4 and 5). The cooled water is then re-injected below ground to complete the cycle.
The process produces virtually no emissions and is completely renewable. or some applications there is a net loss of water and water availability may be an issue in some locations. There are three basic types of power generation systems:
- Hydrothermal water-based systems use naturally-occurring hot water or pressurized steam available in through permeable hot rock beds (Figs 2and 3);
- Hot Rock systems that generate super-heated water or vapour by artificially pumping circulating fluid through the rock (Figs 4 and 5).
- In binary power plants (Figure 6), a heat exchanger is utilised to transfer heat energy from the rock-heated fluid to another internal fluid (called the ‘working fluid’, for example ammonia or iso-pentane) that has a lower boiling point and higher vapour pressure than water at the same temperature. This allow units to operate below the boiling point of water (100 degrees C). The internal working fluid passes through the heat exchanger and is vaporised, and then directed through a turbine to develop electricity. It is then cooled and condensed to start the cycle afresh (Figure 3). Advances in binary plant technology have enabled lower temperature geothermal water and rock resources to be exploited (with temperatures as low as 85°C). However these plants have much lower energy conversion efficiencies than higher temperature plants (only 5 to 10% for resources less than 100°C) and the requirement for much larger heat-exchangers, make these plants more costly and expensive to develop and run.
Currently, the United States leads the world in terms of existing geothermal electrical power output with a total capacity of 3,086 MW of power available from more than 77 power plants. The biggest cluster of geothermal power plants worldwide is located at a renowned Californian geothermal area, called `The Geysers`. The Philippines boasts the second largest capability at 1,904 MW, contributing about 20% of the country's total electric power.
In the past most Geothermal electric power stations were situated close to the borders of tectonic plates where high temperature rock and water exist close to the surface. The development of binary cycle power plants (see diagram) and improvements in deep drilling and power extraction technologies have allowed potential geothermal systems to be considered over a much larger geographical range, including deeper resources. Demonstration plants utilising this expertise are already in operation in Soultz-sous-Forets, France, and in Landau-Pfalz in Germany. Other demonstration plants are being built in Australia, the United Kingdom, and America.
Electric power generation from geothermal energy plants in Australia is confined to a single 80kW power unit located near Birdsville in south west Queensland. However the future is very bright and many more Hot Rock Power Plants are being built and planned. The localities with promise for geothermal power in America and Australia are shown in the figures.
The potential benefits of Geothermal Power Generation are:
- Suitable for provision of baseload and peak-elecricity demands: Geothermal power-plants can produce power continuously 24 hours a day, 365 days a year and are unaffected by climatic factors (unlike solar and wind power), with the level of power generated capable of being increased or decreased to meet peak power loads.
- Virtually zero CO2 emissions and low other emissions such as or oxides of nitrogen and sulphur.
- High availability factors: as binary power plants can generally produce electricity for more than 95% of the time.
- Low pollution and ecological impacts and low land requirements and visual amenity issues are generally minor ( no smoke stacks). The hot water can also be used for other purposes such as heating homes of businesses.
- Low cost and increased security of power supply
Geothermal Power Generation Systems in Australia
The only geothermal power plant operating in Australia is a tiny, 80kW binary-cycle plant located near the famous outback town of Birdsville, located in south west Queensland. This power unit consists of low-temperature hydrothermal-type generator, using a 98°C groundwater resource from a 1,200 m deep artesian bore that draws water from a confined naturally hot water aquifer in the renowned Great Artesian Basin in Central Australia. The Great Artesian Basin covers about 25% of interior of Australia continent and has groundwater with temperatures that range from about 30°C to 100°C at the well heads. The water is pressurized and no pumping is needs and the water is used for other purposes.
Large-scale power output from Geothermal plants is probably about 10 years away and will need improvements in the existing technologies to make it viable.
© 2010 Dr. John Anderson
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