Power stations
Electricity has to be generated. This means changing energy in
one form, for example chemical energy, into electrical energy. The
chemical energy locked up in fossil fuels is changed into electrical
energy in power stations. But that’s just the first part of the job.
Once generated, the electricity must be taken to where it’s needed
- factories, offices, houses, hospitals and so on. This is done through
the National Grid.
Releasing locked-up energy
Fossil fuels (coal, oil and natural gas) are primary resources of energy. It is stored as
chemical energy. In a power station this chemical energy is changed into electrical
energy. Here is an energy transfer diagram for a power station:
fossil fuels are burned
to heat water and
make steam
fossil fuels heat the
steam more until it’s
very hot
energy input
energy output
Chemical energy changes
into heat energy
chemical energy
electrical energy
Transfer takes place in the power station
The diagram simplifies the processes. So, what’s going on in the power station?
• When fossil fuels are burned their chemical energy is changed into heat energy.
Carbon dioxide and water (in the form of steam) are made.
Answer
Question 1
Write a word equation to represent the reaction when a fossil fuel is burned.
• This heat is used in power stations to boil water and produce steam.
• Further heating increases the steam's pressure.
• High pressure steam turns the blades of steam turbines. This is similar to the wind
turning the sails of a windmill. The turbine blades turn at high speeds.
• The blades are attached to a shaft which also turns.
• The turbine shaft turns the electricity generator.
• This produces electricity.
Answer
Question 2
What form of energy is there in:
(a) a fossil fuel
(b) a spinning turbine blade?
52 | gcse applied science | the revision guide
the steam is released
into a turbine
the force of the steam
makes the blades turn
Heat energy changes into
kinetic energy
the turbine shaft
drives the generator
electricity is generated
Kinetic energy changes
into electrical energy.
electricity is
distributed via the
National Grid
steam condenses (forms water) and
is fed back to the boiler
Making it and
getting it
The generator
With the exception of solar power, turbines are
the key to electricity generation.
Whether by wind, steam or running water, turbine
blades are made to turn.
• These turbines are linked to a coil of metal wire.
• Their movement causes the coil to rotate.
• The coil is in a large magnet.
• As the coil of wire spins in the magnet an electric current is produced.
Q. What fossil fuels are used in
power stations?
A. Coal and natural gas. Only small
amounts of oil are used. The relative
amount of coal, gas and oil vary.
For example:
Power station efficiency
electrical energy to National Grid
coal
gas
0
40
20
percentage (%)
60
A. Of course it varies from power
station to power station. Longannet
power station in Scotland is the
second largest coal-fired power
station in the UK. It’s capable of
producing 10 000 000 000 kilowatt
hours of electrical energy each year enough to meet the needs of
two million people.
Answer
Why does the output from a power
station depend on the time of year?
oil
station produce?
wasted heat energy
Question 4
2005
2003
nuclear
Q. How much energy does a power
Answer
chemical
energy in
fossil fuel
Question 3
(a) What happens to the carbon dioxide
that's produced?
(b) What law tells you that the chemical
energy in the fossil fuel equals the
sum of the electrical energy and heat
energy produced in a power station?
Energy resource
Power stations aren’t very efficient.
Only one-third of a fossil fuel’s chemical
energy is changed into electrical energy.
The rest is wasted, mainly as heat.
Electricity generated by main energy resources
Complete this crossword ...
Across
2
1
Q. What is 'the National Grid'?
A. It’s the network of cables carrying
3
1 _____ energy is stored in a fossil fuel.
5 _____ energy is produced when a
fossil fuel burns.
7 A _____ shaft turns the electricity
generator.
Down
4
1 _____ dioxide is formed when fossil
fuels are burned.
2 Wasted heat energy means power
stations are not very _____.
5
6
6 Electricity is distributed through the
National _____.
Q. Does all the electricity distributed
through the National Grid come from
fossil fuel power stations?
3 _____is a fossil fuel burned in many
power stations.
4 Pylons support overhead _____.
electricity from the power stations to
homes, offices, factories and other
places where it's needed. It consists of
4,500 miles of high-voltage overhead
line and 400 miles of underground
cable. The electricity transmitted
across England and Wales each year is
equivalent to the energy needed to
put 100 000 space shuttles into orbit.
7
A. No. Nuclear fuel and renewable
sources provide 25% of the energy
used to generate electricity.
gcse applied science | the revision guide | 53