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Fossil fuels
Coal, Oil and Gas are called "fossil fuels" because they have been formed from the fossilized remains of prehistoric plants and animals. They provide around 66% of the world's electrical power, and 95% of the world's total energy demands (including heating, transport, electricity generation and other uses).
Coal is crushed to a fine dust and burnt. Oil and gas can be burnt directly. Coal provides around 28% of our energy, and oil provides 40%.
Burn fuel → heat water to make → steam burns turbines →
turbines turn generators → electrical power sent around country
Burning coal produces sulphur dioxide, an acidic gas that contributes to the formation of acid rain. This can be largely avoided using "flue gas desulphurization" to clean up the gases before they are released into the atmosphere. This method uses limestone, and produces gypsum for the building industry as a by-product. However, it uses a lot of limestone.
Crude oil (called "petroleum") is easier to get out of the ground than coal, as it can flow along pipes. This also makes it cheaper to transport.
Natural gas provides around 20% of the world's consumption of energy, and as well as being burnt in power stations, is used by many people to heat their homes.
It is easy to transport along pipes, and gas power stations produce comparatively little pollution.
Other fossil fuels are being investigated, such as bituminous sands and oil shale.
The difficulty is that they need expensive processing before we can use them.
The steam that has passed through the power station's turbines has to be cooled, to condense it back into water before it can be pumped round again. This is what happens in the huge "cooling towers" seen at power stations.
Some power stations are built on the coast, so they can use sea water to cool the steam instead. However, this warms the sea and can affect the environment.
Advantages
- Very large amounts of electricity can be generated in one place using coal, fairly cheaply.
- Transporting oil and gas to the power stations is easy.
- Gas-fired power stations are very efficient.
- A fossil-fuelled power station can be built almost anywhere, so long as you can get large quantities of fuel to it. Didcot power station, in Oxfordshire, has its own rail link to supply its coal.
Disadvantages
- Basically, the main drawback of fossil fuels is pollution. Burning any fossil fuel produces carbon dioxide, which contributes to the "greenhouse effect", warming the Earth.
- Burning coal produces more carbon dioxide than burning oil or gas.
It also produces sulphur dioxide, a gas that contributes to acid rain. Mining coal can be difficult and dangerous. Strip mining destroys large areas of the landscape.
- Coal-fired power stations need huge amounts of fuel, which means train-loads of coal almost constantly. In order to cope with changing demands for power, the station needs reserves.
- This means covering a large area of countryside next to the power station with piles of coal.
Fossil fuels are not a renewable energy source.
Once we've burned them all, there isn't any more, and our consumption of fossil fuels has nearly doubled every 20 years since 1900.
This is a particular problem for Oil, because we also use it to make plastics and many other products.