Energy sources

GEOTHERMAL

What is it?

The centre of the earth is hot enough to melt rock. Even at relatively shallow depths of a few kilometres, the temperature can be well over 250 degrees Celsius! That's 10 times as hot as a nice, sunny day! Also, in volcanic areas, melted rock can come up to or very close to the surface itself.

Heat energy from the earth is known as geothermal energy. This energy has been used for thousands of years in some countries for hot water, cooking and heating. Geothermal energy can also generate electricity using steam produced from heat found beneath the surface of the earth.

How does it work?

Generally, the main form of geothermal power occurs when bodies of water, either above or below the earth's surface are converted to steam by the earth's heat, much like when the water in a boiling kettle steams. The steam is collected, and used to power a turbo-generator just like in a regular coal fired power station.

The other form is called hot rock geothermal energy. It is where water is pumped below the surface to areas of hot rock. This water turns to steam, and is brought back up to the surface to drive a turbogenerator.

The temperature of the earth's core is estimated to be 6000 degrees Celsius.

Advantages

Geothermal energy is renewable and it does not produce greenhouse gases. Unlike coal energy, it does not take up very much land and it does not spoil the landscape as it comes from the land itself.

Disadvantages

Although geothermal energy in general is renewable, individual sites can 'run out of steam' - for decades. Another problem is that hazardous minerals may be produced which are difficult to safely dispose of. Also it may be difficult to find and use suitable reserves of geothermal energy.

Use in Australia and throughout the world

Australia produces a very small amount of electricity from geothermal energy, with one facility being Ergon Energy's geothermal power station at Birdsville in outback Queensland. Currently, trials are being carried out in South Australia and New South Wales to make Australia's first hot rock (geothermal) power station a standard service, much like other power stations that use more recognised types of energy.

The United States has the most geothermal power production in the world - currently around 2700 Megawatts. This is about 1.6% of the total electricity generation in the United States.