Hot rocks underground heat water to produce steam.
We drill holes down to the hot region, steam comes up, is purified and used to drive turbines, which drive electric generators.
There may be natural "groundwater" in the hot rocks anyway, or we may need to drill more holes and pump water down to them.
The first geothermal power station was built at Landrello, in Italy, and the second was at Wairekei in New Zealand. Others are in Iceland, Japan, the Philippines and the United States.
In Iceland, geothermal heat is used to heat houses as well as for generating electricity.
If the rocks aren't hot enough to produce steam we can sometimes still use the energy - the Civic Centre in Southampton, England, is partly heated this way as part of a district heating scheme with thousands of customers..
One method used to extract thermal energy from the Earth is referred to as hydrothermal. Hydrothermal energy is manifested in two general ways:
1. As hot springs and geysers.
2. As dry steam.
2. As dry steam.
From deep in the Earth, thousand of meters in to the crust, water reservoirs are heated by the hot mantle or, in some cases, seeping magma. The highly pressurized water seeks passage through fissures in the crust to finally come out at the surface. Hot water hydrothermal sources are generally used in direct heating applications such as homes, fishponds, and various buildings. A great example of this is found in Reykjavik where hot water hydrothermal energy is used to directly heat the homes of approximately 100 000 people.
Underground, hot water reservoirs are more common than Geysers, but the energy in hot water is a bit more difficult to use than the energy in dry steam, that the geysers provide. If the water reservoir contains Higher-temperature hot water (175° C or more), the water can be flashed to steam in a separator (flash tank) to drive a turbine at a flash plant.
To use reservoirs containing Lower-temperature hot water (100° C - 175° C) a binary plant is required. At a binary plant the hot water is used to boil a working fluid, a binary liquid which is usually an organic compound with a low boiling point such as isopentane. This is done in a heat exchanger. This working fluid is then used to rotate a turbine. After the vaporized binary liquid has gone through the turbine it is condensed and can therefore be reused over and over again.
Around the world there are Geysers, which is an underground steam reservoir. Having access to a Geyser means that you can pipe the steam directly to the turbines.
Dry steam is produced when the hot mantle or magma superheats water trapped deep in the Earth. High-pressure steam forces its way upward and is released at the surface as an extremely hot gas having little or no liquid content. Dry steam sources are generally used to directly drive a steam turbine with a generator for the production of electricity. The largest dry-steam hydrothermal electricity generating plants are located northeast of San Francisco and have a total capacity of more than 1400 MW.
Dry steam is produced when the hot mantle or magma superheats water trapped deep in the Earth. High-pressure steam forces its way upward and is released at the surface as an extremely hot gas having little or no liquid content. Dry steam sources are generally used to directly drive a steam turbine with a generator for the production of electricity. The largest dry-steam hydrothermal electricity generating plants are located northeast of San Francisco and have a total capacity of more than 1400 MW.
Advantages :
- Geothermal energy does not produce any pollution, and does not contribute to the greenhouse effect.
- The power stations do not take up much room, so there is not much impact on the environment.
- No fuel is needed.
- Once you've built a geothermal power station, the energy is almost free.
It may need a little energy to run a pump, but this can be taken from the energy being generated.
Disadvantages :
- The big problem is that there are not many places where you can build a geothermal power station.
You need hot rocks of a suitable type, at a depth where we can drill down to them.
The type of rock above is also important, it must be of a type that we can easily drill through.
- Sometimes a geothermal site may "run out of steam", perhaps for decades.
- Hazardous gases and minerals may come up from underground, and can be difficult to safely dispose of.
Geothermal Power: It's Hot! ( video )
How geothermal energy works ( video )
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