In a turbine there is a shaft, connected to this shaft are various blades, this is known as a rotor. The rotor is then put inside sealed casing. At the bottom of the turbine lie lots of nozzles that let through high-pressured jets of steam, and depending on the type of turbine water. These jets impact on the turbine’s blades to drive the rotor’s shaft to speeds between 10’000 and 100’000 rpm.
This shaft is connected to a generator. The shaft drives a rotating coil of wire through a magnetic field. As the wire moves through the magnetic field the electrons that are free to move will experience a force along the length of the wire. As these electrons move from one end of the wire to the other, each end is left with a net excess of electrons or neutrons, this leads to the production of an electromotive force or EMF across the ends of the wire. From this current can flow in an external circuit. This relates to Faraday’s Law, which is:
After the hot steam rises to the top of the turbine it is cooled, condensed and flows back down a much longer pipe which takes the water closer down to the hot dry rock where the same process is continuously repeated to generate more electricity.
The efficiency of these power stations depends on which type you look at. For instance the ORC or Organic Rankine Cycle engine is used in many geothermal sites around the world, however when one was used in Mulka in South Australia in bad times (when hot weather was experienced) the output of the ORC engine was limited and the capacity became a mere 10kW at any one time in the year of 1994. Gross conversion efficiency was only 8% with a net of 6% when parasitic loads were taken into account. The factors taken into account that decide this efficiency rate include the temperatures of the water in the bores and the temperatures outside on the surface. If the temperatures are very hot inside the efficiency rating will be very high, whereas if the temperatures outside are very hot the generator slows down.
The 10kW capacity of the ORC engine is very small compared with 1,100mW, as was the capacity of a geothermal power plant in San Francisco in the year 1994. In 1996 the power plant produced 4.5 million megawatt-hours of electricity, which is enough to provide all of California with electricity. An estimate of the potential size of this energy source comes from the above value of 4.5 million megawatt-hours of electricity, which as can be seen below converts into 16,200 Giga-Joules at the Geothermal Power Plant in San Francisco. Once again this potential size is affected by the core temperatures and the temperatures on the surface.
At the end of the 21st century it is estimated that one third of America's power will be generated through geothermal power stations.
Some advantages of geothermal energy production include the fact that it is a reliable and renewable source in terms of the heat of the rocks and the water levels. Another main advantage that should spur on entrepreneurs is that it has a very good case history; this can be seen in the geothermal power station at Birdsville, and also in the success in America and New Zealand. Geothermal energy does not use fossil fuels or other bad fuels that emit large amounts of bad gases such as carbon dioxide. The energy acquired through geothermal energy is taken from naturally occurring heat leftover from the earth’s creation; therefore we are not taking away anything from the planet that will be needed in the future. It is relatively simple technology and the generation of energy will not be disturbed by change in weather, as may be the case with solar power or wind power. Probably the largest advantage is that the potential number of sites in Australia is almost endless.
There are only two main disadvantages to generating geothermal energy. The first is that sometimes the process may take too much water without replacing it. When this happens there is a need to re-inject water or liquid back into the production wells to keep the process running. If water is not re-injected then as a result there may be landslides, land may shrink or sink and there may be an increase in seismic activity. The other disadvantage is that when the drilling has been completed sometimes small levels of underground gases can escape. These gases include small levels of carbon dioxide, ozone gas and radon gas, all of these gases pose a potential threat however in small amounts they can easily be handled without anyone being hurt.
There is little environmental impact in the production of geothermal energy. The only negative environmental impact might be that at ground level ozone gas is a pollutant along with radon gas, which might escape when the holes are initially drilled at a new site.
In conclusion geothermal power is effective and efficient, as can be seen in the case history of geothermal power plants and the relatively simple processes involved. It is a large potential energy source, which one-day could be powering our homes and workplaces. A key point is that it is a renewable source of energy with a large amount of potential in Australia. And one of the most important things it is an alternative energy source, meaning that it is not going to fill our world with pollutants that will harm the world, which God has provided us with.
Bibliography
-
Bassett, A (1999) Geothermal Power is it Reliable? (Internet) Utah: Institute of Technology in Utah. Available from: (Accessed 15 October 2003)
-
Burns et al. (2000) Status of the Geothermal Industry in Australia. (Internet) Barcaldine: Ergon Energy. Available from: (Accessed 12 October 2003)
-
Graham, I. (1998) Energy Forever? Geothermal and Bio-Energy. East Sussex: Wayland Publishers Ltd.
-
Snelling, R (2001) Geothermal Energy Around the World. (Internet) Wikipedia: New Zealand Government. Available from: (Accessed 16 October 2003)
-
Walding et al. (1999) New Century Senior Physics. South Melbourne: Oxford University Press.
By: Phillip Ridgway 11E -
