Energy Resources (Oxford AQA IGCSE Combined Science Double Award): Revision Note
Energy Resources
There are a range of energy sources available for use on a national and global scale
The use of each one has implications for society in terms of:
Extraction methods
Pollution & global warming
Safety & efficiency
Fossil fuels
Fossil fuels are formed underground and under sea beds from the remains of plants and animals over millions of years
There are three fossil fuels
Coal
Oil
Natural gas (methane)
The three fossil fuels
Extraction methods
Fossil fuels are extracted from underground which usually results in damage to the environment
Oil is drilled for under the sea
Coal is mined by digging into the ground
Natural gas is extracted through a process known as 'fracking' where rocks are fractured by drilling, and then water is pumped into the fissure forcing out the gas which can then be collected
Pollution and global warming
Burning fossil fuels releases carbon dioxide into the atmosphere
Carbon dioxide is a greenhouse gas (along with methane and water vapour) that contributes to global warming
Sulphur dioxide is also released from burning oil (and products made from oil like petrol and diesel) and coal
Sulphur dioxide is acidic when dissolved in water in the atmosphere producing acid rain
Of the three fossil fuels, natural gas is the cleanest and coal is the most polluting
There is a global push to move away from fossil fuels due to their impact on global warming
Safety and efficiency
Fossil fuel power stations use the energy released in the combustion of fuel to heat water to produce steam to turn turbines which generate electricity
Fossil fuel power stations:
are extremely reliable and are already well-established in most countries
are responsive (can be turned on and off easily) to meet the changing demands of a nation
are expensive to build and decommission
are relatively safe
produce an average output power of 500 MW
Nuclear fuels
The nuclear fuels are uranium-235 and plutonium-239
Extraction methods
These isotopes are found in rocks called ores which are mined from the ground
Uranium and plutonium are then extracted from the rock
Pollution and global warming
Nuclear fission releases no pollutants into the atmosphere
Nuclear reactors do produce radioactive waste that can remain radioactive for thousands of years
Radioactive waste is packaged and buried underground
Burial sites must remain undisturbed and uninhabited
Safety and efficiency
Nuclear power stations use the energy released in fission reactions to heat water to produce steam to turn turbines to generate electricity
Nuclear power stations:
are extremely reliable and well-established in some countries
are very responsive as the output can be easily controlled
are very expensive to build to decommission later
are potentially dangerous in the event of an accident
produce an average output power of 1 GW
This is twice the output power of a fossil fuel power station
Bio-fuels
Bio-fuels are made from plant matter
Extraction methods
Crops are grown to produce bio-fuels which uses farmland that could otherwise be used to grow food
Ethanol or methane can be produced and used in place of fossil fuels
However, they have only half the energy density of fossil fuels
Pollution and global warming
Burning biofuels releases carbon dioxide into the atmosphere
However, growing the crops removes carbon dioxide from the atmosphere in the process of photosynthesis
Therefore, bio-fuels are considered to be carbon neutral but this opinion is controversial
If the land had been used to grow crops for food, the same amount of carbon would have been taken out of the atmosphere and much less carbon would have been returned
Cycle of carbon in biofuel use
Safety and efficiency
Not many vehicles can run on biofuel alone
However, all petrol and diesel sold in the UK have a percentage of biofuel mixed in to reduce the volume of pollutants released in combustion
Biofuels have only half the energy density of fossil fuels
So twice the mass would be needed to produce the same power output
Hydroelectric dams
When water is stored above ground level it has energy in its gravitational potential store
This energy can be transferred to kinetic energy if the water is allowed to flow down the slope
Flowing water turns the turbine to generate electricity
A hydroelectric dam
Valleys are flooded to build hydroelectric dams which destroys habitats, towns and villages
Pumping systems are sometimes used to return the water to the dam
The pumping systems use fossil fuels and therefore release large amounts of greenhouse gases into the atmosphere
Hydroelectric dams:
are reliable and established in most countries
are responsive because they can be turned on and off easily
are expensive to build but cheap to run
produce an average output power of 200 MW
The rise and fall of waves or the tide can be used to turn a turbine and generate electricity
Tide and wave power
Wave power uses underwater turbines to generate electricity
The waves move the water which causes the turbines to turn
Turbines using wave power
Tidal power uses underwater turbines placed between a river and the sea to generate electricity
Water is stored at a height on the ocean side of the barrage at high tide
The gate is opened and water flows from the ocean side to the riverside
The flowing water turns a turbine
Water is stored at a height on the river side of the barrage at low tide
The gate is opened and water flows from the riverside to the oceanside
The flowing water turns a turbine
Turbines using tidal power
Tidal barrages are built in estuaries so there are not many suitable locations
The presence of turbines in the water can interfere with shipping routes and cause damage to habitats
The technology for wave and tidal power is not advanced enough for large-scale electricity generation
No fuels are used so there is no pollution
Smaller systems are useful for small islands
Wave and tidal power stations:
are inexpensive to build and very cheap to run
have a long construction time compared to other power station types
are very efficient (around 80%)
produce an average output power of 16 kW
Geothermal energy
Tectonic activity causes areas where the rocks below ground become heated
Water can be poured into shafts below the Earth's surface which is heated by the rocks and returned via another shaft as steam or hot water
Steam can be used to turn a turbine and generate electricity, and hot water can be used to heat homes
Power station using geothermal energy
Geothermal energy depends on tectonic activity so there are few suitable locations on Earth
Methane (natural gas) is found within spaces between rocks so this can be forced out when water is injected into the rocks
Methane is a greenhouse gas which contributes to global warming
Geothermal power:
plants are expensive to build and small compared to other power station types
is reliable
are not very efficient (around 12%)
produces an average output power of 300 MW
Wind power
Wind turbines are regularly placed in coastal, or hilly, areas with windy conditions
A group of wind turbines creates a wind farm
These are used to power nearby towns and cities
Wind is used to turn the turbine which generates electricity
Wind turbines
Wind power is not reliable because the wind does not blow constantly
Turbines are built facing a specific direction so they only work when the wind is blowing in that specific direction
Some people think that wind farms spoil the landscape so there may be local resistance to the construction of wind farms in some towns and cities
Wind farms:
are inexpensive to build and cheap to run
have a relatively high efficiency of 50%
produce an average power output of 500 MW
Solar cells
Solar cells transfer energy from sunlight electrically producing a current, and therefore generating electricity
Solar cells, sometimes called photovoltaic cells, are made of semiconducting materials
Several cells connected can supply electricity to homes, small-scale businesses, communication devices and satellites
Energy generated from solar cells can be stored in batteries for later use
Solar farm
In many places on Earth sunlight is a reliable energy resource where the sun shines most of the time
However, in the UK sunlight is not reliable
Solar farms produce no greenhouse gases or pollution
Solar energy can be generated in remote places where they don't have electricity
For example to power solar street signs in rural areas
Solar farms need to be large-scale to produce large amounts of electricity
People often don't like the appearance of large solar farms, this is known as visual pollution
Solar farms:
are relatively cheap to set up and run
are relatively quick to construct compared to other types of power stations
are the least efficient of all the electricity generation methods (20% efficiency)
produce an average power output of 5 MW
Renewable & Non-Renewable Energy Resources
Renewable energy resources
There are two types of energy resources:
Renewable
Non-renewable
Renewable energy resources are defined as:
An energy source that is replenished at a faster rate than it is being used
This means that renewable energy resources will not run out
Examples of renewable energy technologies are:
Hydroelectric
Wind power
Wave power
Tidal power
Solar power
Biofuels (including animal waste, wood, and fast-growing crops)
Geothermal
Non-renewable energy resources
Non-renewable energy resources are defined as
An energy source that is not replenished at a faster rate than it is being used
This means that non-renewable energy resources are finite and will eventually run out
Examples of non-renewable energy technologies are:
Fossil fuels
Coal
Oil
Natural gas (methane)
Nuclear
As the availability of non-renewables decreases and the demand remains the same, this drives up the prices
There are many global initiatives in place to reduce our dependence on non-renewable resources, particularly fossil fuels
This is partly to do with lowering demand as availability decreases
But is mostly to do with the more urgent need to reduce carbon emissions which contribute to global warming
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