Sources of electricity are everywhere in the world. Worldwide, there is a range of energy resources available to generate electricity. These energy resources fall into two main categories, often called renewable and non-renewable energy resources. Each of these resources can be used as a source to generate electricity, which is a very useful way of transferring energy from one place to another such as to the home or to industry.
Non-renewable sources of energy can be divided into two types: fossil fuels and nuclear fuel.
Sources of electricity include fossil fuels are found within the rocks of the Earth's surface. They are called fossil fuels because they are thought to have been formed many millions of years ago by geological processes acting on dead animals and plants, just like fossils.
Coal, oil and natural gas are fossil fuels. Because they took millions of years to form, once they are used up they cannot be replaced.
Oil and natural gas
Sources of electricity include oil and gas are chemicals made from molecules containing just carbon and hydrogen. All living things are made of complex molecules of long strings of carbon atoms. Connected to these carbon atoms are others such as hydrogen and oxygen. A simple molecule, called methane (CH4), is the main component of natural gas.
Crude oil (oil obtained from the ground) is a sticky, gooey black stuff. It contains many different molecules, but all are made of carbon and hydrogen atoms.
How were they formed?
Gas and oil were formed from the remains of small sea creatures and plants that died and fell to the bottom of seas. Over many millions of years, layers of mud or other sediments built up on top of these dead animals and plants. The pressure from these layers and heat from below the Earth's crust gradually changed the once-living material into oil and natural gas.
Over time, the layers of rocks in the Earth's crust move and may become squashed and folded. Gas and oil may move through porous rocks and may even come to the surface. In some places, pockets of oil and gas can be found, because non-porous rocks have trapped them.
Natural gas and crude oil can be found in many places around the world, such as the Middle East (about 70 per cent of the world's known resources of oil), the USA and under the North Sea off the coast of the UK.
When gas and oil burn they produce mainly carbon dioxide and water, releasing the energy they contain. Crude oil is a mixture of different chemicals and is usually separated out into fuels such as petrol, paraffin, kerosene and heavy fuel oils.
The oil-based fuels provide less energy per kilogram than natural gas. Both oil and natural gas produce carbon dioxide, which is a greenhouse gas.
How long will they last?
Oil and gas are non-renewable: they will not last forever. New sources of oil and gas are constantly being sought. It is thought that the current resources under the North Sea will last about another 20 years and the world resources will last for about 70 years.
Estimates vary, however, because we do not know where all the resources are and we do know how quickly we will use them. It is thought that with new discoveries these fossil fuels will last well into the next century.
These sources of energy are relatively cheap and most are easy to get and can be used to generate electricity.
When these fuels are burned they produce the gas carbon dioxide, which is a greenhouse gas and is a major contributor to global warming. Transporting oil around the world can produce oil slicks, pollute beaches and harm wildlife.
Sources of electricity can include coal, which mainly consists of carbon atoms that come from plant material from ancient swamp forests. It is a black solid that is reasonably soft. You can scratch it with a fingernail. It is not as soft as charcoal, however, and is quite strong. It can be carved into shapes. There are different types of coal. Some contain impurities such as sulphur that pollute the atmosphere further when they burn, contributing to acid rain.
How was it formed?
Millions of years ago, trees and other plants grew rapidly in a tropical climate, and when they died they fell into swamps. The water in the swamps prevented the plant material from decaying completely and peat was formed.
As time passed, layer upon layer of peat built up. The pressure from these layers and heat from below the Earth's crust gradually changed the material into coal.
Coal can be found in parts of the world that were once covered with swampy forests, such as the UK about 250 million years ago. There are large deposits in China, USA, Europe and Russia. South Africa also has relatively large deposits.
When coal burns it produces mainly carbon dioxide, some carbon monoxide and soot (which is unburned carbon). Many coals when burned produce smoky flames.
Their energy content weight for weight is not as great as oil. When coal burns it produces more carbon dioxide than oil.
How long will the supply of coal last?
The world has relatively large reserves of coal, more so than oil and gas. Estimates vary, but suggestions are that supplies will last well into the next century.
Coal is relatively cheap, with large deposits left that are reasonably easy to obtain, some coal being close to the surface. It is relatively easy to transport because it is a solid.
Some sources of coal are deep below the ground, as in the UK. They can be difficult, costly and dangerous to mine.
Burning coal without first purifying it contributes to global warming, as well as to the production of smog (smoke and fog), which is harmful to health. It is a finite resource and will eventually run out.