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Energy

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Sources of energy

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The sources of the energy put to work by humans fall into two categories:

  1. Non-renewable or finite energy resources are sources of power that cannot be replaced once they are used, because the energy source has taken millions of years to form (eg coal and oil).
  2. Renewable or infinite energy resources are sources of power that quickly replenish themselves and can be used again and again.

Some resources can be thought of as both renewable and non-renewable.

  • Wood can be used for fuel and is renewable if trees are replanted.
  • Biomass, which is material from living things, can be renewable if plants are replanted.

Over the last 200 years an ever-increasing proportion of our energy has come from non-renewable sources such as oil and coal.

The advantages and disadvantages of non-renewable energy resources.

Type of fuelWhere it is fromAdvantagesDisadvantages

Coal (fossil fuel)

  • Formed from fossilised plants and consisting of carbon with various organic and some inorganic compounds.
  • Must be mined from seams of coal, which are found sandwiched between layers of rock in the earth.
  • Burnt to provide heat or electricity.
  • Coal is a ready-made fuel.
  • It is relatively cheap to mine and to convert into energy.
  • Coal supplies will last longer than oil or gas.
  • When burnt coal gives off atmospheric pollutants, including greenhouse gases.

Oil (fossil fuel)

  • A carbon-based liquid formed from fossilised animals.
  • Lakes of oil are found under land or sea, sandwiched between seams of rock in the earth.
  • Pipes are sunk down to the reservoirs to pump the oil out.
  • Used a lot in industry and transport.
  • Oil is a ready-made fuel.
  • Relatively cheap to mine and to convert into energy.
  • Only a limited supply.
  • When burnt, it gives off atmospheric pollutants, including greenhouse gases.

Natural gas (fossil fuel)

  • Methane and some other gases trapped between seams of rock under the earth's surface.
  • Pipes are sunk into the ground to release the gas.
  • Often used in houses for heating and cooking.
  • Gas is a ready-made fuel.
  • It is a relatively cheap form of energy.
  • It's a slightly cleaner fuel than coal and oil.
  • Only limited supply of gas.
  • When burnt, it gives off atmospheric pollutants, including greenhouse gases.

Nuclear

  • Radioactive minerals such as uranium are obtained by mining.
  • Electricity is generated from the energy that is released when the atoms of these minerals are split (fission) or joined together (fusion) in nuclear reactors.
  • A small amount of radioactive material produces a lot of energy.
  • Raw materials are relatively cheap and can last quite a long time.
  • It doesn't give off atmospheric pollutants.
  • Nuclear reactors are expensive to run.
  • Nuclear waste is highly toxic, and needs to be safely stored for 100s or 1000s of years (extremely expensive)
  • Accidental leakage of nuclear materials can have a devastating impact on people and the environment. The worst nuclear reactor accident was at Chernobyl, Ukraine in 1986.

Biomass

  • Biomass energy can be generated from decaying plant or animal waste.
  • It can also be an organic material which is burnt to provide energy, eg heat, or electricity.
  • An example of biomass energy is oilseed rape (the fields of yellow flowers you see in the UK in summer), which produces oil.
  • After treatment with chemicals it can be used as a fuel in diesel engines.
  • It is a cheap and readily available source of energy.
  • If the crops are replaced, biomass can be a long-term, sustainable energy source.
  • When burnt, it gives off atmospheric pollutants, including greenhouse gases. If crops are not replanted, biomass is a non-renewable resource.

Wood

  • Obtained from felling trees, burnt to generate heat and light.
  • A cheap and readily available source of energy.
  • If the trees are replaced, wood burning can be a long-term, sustainable energy source.
  • When burnt it gives off atmospheric pollutants, including greenhouse gases.
  • If trees are not replanted wood is a non-renewable resource.

How long will fossil fuels last?

Estimates from international organisations suggest that if the world's demand for energy from fossil fuels continues at the present rate that oil and gas reserves may run out within some of our lifetimes. Coal is expected to last longer.

Estimated length of time left for fossil fuels

Fossil fuelTime left

Oil

50 years

Natural gas

70 years

Coal

250 years

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