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Energy Resources (Higher) 
Generating Electricity | Non-renewable energy resources | Renewable energy resources
 
Generating Electricity

Electricity is a very convenient and widely used energy source, but it has to be generated using other energy resources in power stations. This is why it is called a secondary energy source.
 

Most power stations use a fuel to heat water.

Steam is produced which turns turbines .

The turbines then derive generators, which produce electricity.

The energy transfers for a power station that burns fossil fuels would be:

Chemical energy     arrow2     heat energy     arrow2    kinetic energy     arrow2    electrical energy
     in the fuel                        in the boiler                    in the steam                   produced by the
                                                                                   and turbines                   generators

A lot of energy is wasted as heat in waste gases, steam and due to friction in the turbines and generators.

In nuclear power stations the fuel used to release heat to boil the water is usually uranium or plutonium.
Non-renewable energy resources

Non-renewable energy resources are those which will eventually run out and cannot be replaced.

Power stations that use fuels can produce electricity at any time of the day or year. They are reliable energy sources.

The time it takes to start them up varies:

Longest start up time ---------------------------------------------------------arrow2 shortest start up time
          nuclear                          coal                                oil                                natural gas

Fuels are also concentrated sources of energy.

There are several disadvantages of using fuels to generate electricity.

  • Fossil fuels and uranium are non-renewable.
  • Oil is a very useful raw material that we should conserve for other purposes.
  • Burning fossil fuels releases carbon dioxide gas which increases the greenhouse effect and global warming.
    For the same amount of energy released coal produces more carbon dioxide than oil, and oil produces more than natural gas.
  • Burning coal and oil also releases sulphur dioxide gas that causes acid rain.
    The sulphur can be removed from the fuel before burning, or the sulphur dioxide can be removed from the waste gases before they enter the atmosphere. This increases the cost of the electricity generated.
  • Although nuclear fuels do not produce carbon dioxide or sulphur dioxide gases, and they emit very little radiation or radioactive materials into the surroundings when running normally, there is always the risk of an accident.
    Large amounts of very dangerous radioactive material may then be released over a wide area.
  • Nuclear power stations produce waste which stays dangerously radioactive for thousands of years. This has to be stored safely, or could increase the incidence of cancers in the population.
  • Fuel costs for nuclear power stations are low, but initial building costs and de-commissioning costs at the end of their useful life, is high.

Renewable energy resources

Renewable energy resources are those which can be replaced, so they will not run out.

Energy from renewable resources can be used to drive turbines directly.

Although there are no fuel costs, the energy is dilute so the capital cost of the generating equipment is high.

They do not release pollutant gases into the atmosphere but may have other disadvantages.

Renewable energy resource Disadvantages
Wind
Giant wind turbines turn generators.
  • Unreliable because the strength of the wind varies considerably.
  • Wind farms are usually sited on hills or coasts and are considered unsightly by some people.
  • Cause noise pollution for people who live nearby.
  • Costly to build.
Tides
A lake fills behind a barrage built across an estuary at high tide and empties at low tide.
The fast flowing water turns generators.
  • Unreliable because the time and height of tides varies on a monthly and yearly cycle.
  • Tidal barrages built across estuaries destroy the habitat of wading birds and mud living organisms.
  • Expensive to set up and few areas are suitable.
Hydroelectric energy
A reservoir behind a dam at the top of a hill fills with water. When the water is released it turns turbines.
Generally very reliable and can be started quickly to meet sudden demands for electricity.
Can be operated in reverse to use surplus electricity from other power stations to pump water from a low reservoir to a higher one. Most of the energy from the surplus electricity is therefore stored instead of being wasted.
  • Flooding upland river valleys destroys habitats and land that may previously have been used for farming or forestry.
  • Few areas are suitable.
Geothermal energy
Decay of radioactive elements within the Earth releases heat.
In some volcanic areas hot water and steam rise to the surface. The steam can be used to drive turbines.
  • Deep drilling is required which is difficult and expensive.
Solar energy
Electricity can be produced directly from the Sun’s radiation using solar cells.
This is often the best energy source for producing electricity in remote places, e.g. on satellites, or when only small amounts of electricity are needed, e.g. for watches or calculators.
  • Unreliable as light intensity from the Sun varies.
  • Very expensive – only non-rechargeable batteries have a higher cost per Unit of electricity produced over their lifetime.