Energy Resources: Geothermal power

Introduction

The centre of the Earth is around 6000 degrees Celsius - easily hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius if the Earth's crust is thin. In general, the temperature rises one degree Celsius for every 30 - 50 metres you go down, but this does vary depending on location

In volcanic areas, molten rock can be very close to the surface. Sometimes we can use that heat.

Geothermal energy has been used for thousands of years in some countries for cooking and heating.

The name "geothermal" comes from two Greek words: "geo" means "Earth" and "thermal" means "heat".

Geothermal energy is an important resource in volcanically active places such as Iceland and New Zealand.

How useful it is depends on how hot the water gets. This depends on how hot the rocks were to start with, and how much water we pump down to them.

Water is pumped down an "injection well", filters through the cracks in the rocks in the hot region, and comes back up the "recovery well" under pressure. It "flashes" into steam when it reaches the surface.

The steam may be used to drive a turbogenerator, or passed through a heat exchanger to heat water to warm houses. A town in Iceland is heated this way.

The steam must be purified before it is used to drive a turbine, or the turbine blades will get "furred up" like your kettle and be ruined.

Video clip: How geothermal energy works

See Also:

A diagram showing a geothermal project http://www.geothermal.marin.org/GEOpresentation/sld037.htm

Types of geothermal power plants: www1.eere.energy.gov/geothermal/powerplants.html

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.

Is it renewable?

Geothermal energy is renewable.
The energy keeps on coming, as long as we don't pump too much cold water down and cool the rocks too much.