1 gcse physics energy resources and energy transfer
TRANSCRIPT
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GCSE Physics
Energy resources and energy transfer
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This topic•During this topic we will learn about energy transfers in a range of different contexts and how insulation can reduce energy transfers,
•We will learn and use the formula: Work done = Force x Distance, we will also learn the formulas for kinetic and gravitational energy,
•We will learn about power as the rate of transfer of energy or the rate of doing work.
•We will learn about the advantages and disadvantages of methods of large-scale electricity production using a variety of renewable and non-renewable resources.
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Lesson 1 – Energy and transfersAims:
•To describe energy transfers involving the following forms of energy: thermal (heat), light, electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational),
•To understand that energy is conserved and to recall and use the relationship: efficiency = useful energy output / total energy output.
•To draw energy flow (sankey) diagrams for a variety of situations.
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Energy types
There are many different types of energy. All of these energies can be classified into three groups:
•Potential or stored energy,
•Kinetic or movement energy,
•Radiation.
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ClassificationPotential energy Kinetic energy Radiation
Gravitational (GPE)
Moving objects Radio waves
Chemical (CPE) Hot objects (thermal energy)
Micro waves
Elastic (EPE) Sound Infra red
Nuclear (NPE) Electricity Visible light
Ultra violet
X-rays
Gamma rays
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Energy is measured in Joules (J)
James Prescott Joule,
1818 - 1889
Joule was a brewer of beer by trade but had a passion for science. His experiments were famous for their attention to detail and the quality of his analysis.
He spent years trying to measure a temperature difference between water at the top and the bottom of a waterfall. He even took his thermometers when he went on his honeymoon!
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Energy transfer diagram
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Sankey diagrams
A sankey diagram can be used to show the different energy transfers that are taking place.
In all transfers some heat is lost to the surroundings. It is hard to get this heat back as it is randomly spread out.
Electric motor
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Toaster
Changing the bread into toast
The toaster gets hot
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DeviceInput
energyOutput energy
kettle
solar cell
catapult
coal fire
Complete the input and useful output energies for the devices in this table.
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This means that energy never just ‘disappears’.
The total amount of energy always stays the same,i.e. the total input energy = total output energy.
In most energy transfers, the energy is transferred to several different forms, which may be useful or not useful.
The energy that is transferred to unwanted forms of energy is wasted.
All energy transfers follow the law of conservation of energy:
Energy cannot be created or destroyed, just changed in form.
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The efficiency of a device can be calculated using this formula:
This means that efficiency does not have any units.
It is a number between 0 and 1 or a percentage.
Useful energy is measured in joules (J).
Total energy is measured in joules (J).
efficiency = useful energy out
total energy in
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Efficiency is a measure of how good a device is at changing energy from one form to another.
All devices waste energy, so the efficiency of a device is never 100%.
Energy efficient light bulbs are more efficient than normal light bulbs because they w____ less energy. More of the e_______ energy that they are supplied with is converted into l____ energy and not h___.
The more efficient a device is the less energy is wasted.
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Efficiency example 1What is the efficiency of a speaker that is supplied with 2530 J of energy and gives out 1010 J of sound energy?
Efficiency = Useful energy out Total energy in
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Efficiency example 2
What is the efficiency of a neon light bulb that that is supplied with 35 J of electrical energy and gives out 10 J of light energy?
Efficiency = Useful energy outTotal energy in
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Efficiency example 3A guitar amp is 45 % efficient. Work out the total energy in (energy input) if the electrical energy given out is 200J?
Efficiency = Useful energy out Energy input
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Efficiency Example 4
a) How much energy is wasted?
b) In what form is the energy wasted?
c) What is the efficiency of the bulb?
This filament bulb is supplied with 100 J of electrical energy which it converts to 45 J of light energy.
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a) How much energy is wasted?
b) In what form is the energy wasted?
c) What is the efficiency of the radio?
This radio is supplied with 300J of electrical energy which it converts to 96J of sound energy.
Efficiency Example 5
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a) What useful energy does a television produce?
b) How much useful energy is produced?
This television converts 2 000J of electrical energy into useful energy at an efficiency of 65%.
Efficiency Example 6
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Summary – Energy transfers
•An energy arrow diagram can show how energy is transferred from one type to another.
•When an energy arrow diagram is drawn to scale it is called a ‘Sankey diagram’.
•In all energy transfers the total amount of energy entering a system is equal to the total amount of energy leaving the system. This is called the Law of conservation of energy.
•Efficiency = Useful energy output / Total energy input.
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Lesson 3 – Work done
Aims:
•Understand that ‘work done’ is equal to energy transferred.
•Be able to rearrange and use the formula
Work done = Force × Distance
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Force and direction
F
xF
yF
When we calculate the work done by the person pushing the pram we are only interested in force Fx. The work done is the distance travelled multiplied by the force in the direction of the movement.
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Work done Example 1 A lady pushed a trolley with a force of 50 N and the trolley moved through a horizontal distance of 12 m. What is the work done by the lady?
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Work done Example 2
Can you calculate the work done?
Weightlifter =
Lawnmower =
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More examples• How much work does it take to lift a 200 N
weight 2 m off the floor?
Work done =• How much work does it take to hold a 200 N
weight 2 m off the floor?
Work done =• How much work is done if you drop a 2.5 N
text book 3 metres?
Work done =
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More examplesHow much force is required to move a box 4 m if 200 J of work is done?
Force = Work ÷ Distance
How far will a cart be pushed if a force of 45 N is used and 405 J of work are done?
Distance = Work ÷ Force
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Summary – Work done
•Sometimes when energy is transferred we use the term ‘work done’.
•Work is done when a force is applied and a distance travelled in the direction of this force.
•Be able to rearrange and use the formula
Work done = Force × Distance
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Lesson 4 – Kinetic energy
Aims:
•Understand that kinetic energy is a measure of the amount of energy of a moving object.
•Be able to rearrange and use the formula
KE = ½ m v2
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The greater the mass of a moving object, the greater its kinetic energy.
If the mass is doubled, the kinetic energy is doubled.
The greater the velocity of a moving object, the greater its kinetic energy.
If the velocity is doubled, the kinetic energy is quadrupled!
Kinetic energy is the energy an object has because it is moving.
So, if the velocity of a car is slightly above the speed limit, its kinetic energy is much greater than it would be at the speed limit. This means it is more difficult to stop the carand there is more chance of an accident.
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The kinetic energy (KE) of an object depends on its mass and its velocity.
The equation for calculating kinetic energy is:
kinetic energy = ½ x mass x velocity2
KE = ½mv2
What are the units of kinetic energy, mass and velocity?
Kinetic energy is measured in joules (J).
Mass is measured in kilograms (kg).
Velocity is measured in metres per second (ms-1).
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Sometimes it is necessary to rearrange the kinetic energy equation in order to calculate the mass or the velocity of a moving object.
KE = ½mv2
What are the rearranged versions of this equation for calculating mass and velocity?
TIP: If you do not think you can rearrange the KE formula during an exam, learn the rearranged formulae instead.
mass = 2KE
v2velocity = 2KE
m
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kinetic energy = ½ x mass x velocity2
A car has a mass of 1500 kg and is travelling at a velocity of 10 ms-1.
What is the kinetic energy of the car?
Kinetic energy - Example 1
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Kinetic energy – Example 2Calculate the kinetic energy of an apple thrown at 9.0 m/s.
Estimated mass of an apple = 100 g = 0.100 kg
KE = ½ m v2
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A train has a mass of 100 000 kg. If its kinetic energy is 3 MJ, what velocity is it travelling at?
3 MJ = 3 000 000 J
Kinetic energy - Example 3
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Kinetic energy – Example 4Calculate the mass of a balloon of water thrown at 10 m/s that has a kinetic energy of 50 J.
KE = ½ m v2
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Kinetic energy – Example 5Calculate the speed of a shot put with kinetic energy 90 J, if its mass is 5 kg.
KE = ½ m v2
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Summary – kinetic energy
•Kinetic energy is the energy of movement. Sound waves, moving objects and electricity can be thought of as kinetic energy.
•Kinetic energy can be calculated using the formula:
KE = ½ m v2
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Lesson 5 – GPE
Aims:
•Understand that Gravitational potential energy is the amount of energy of an object due to its height above the ground.
•Be able to rearrange and use the formula
GPE = m g h
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Potential energyPotential energy is sometimes called stored energy.
In chemistry we study the energy given out or taken in during a chemical reaction. Energy changes take place when there are changes to the chemical potential energies of the chemicals.
When we release a stretched elastic band it will fly across the room as its elastic potential energy is changed in kinetic energy.
Electricity is generated in a nuclear power station when nuclear fission releases the nuclear potential energy of uranium atoms.
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Any object in a gravitational field has gravitational potential energy due to its position in that field.
The Moon has gravitational potential energy due to the gravitational field of the Earth.
The Earth has gravitational potential energy due to the gravitational field of the Sun.
The gravitational potential energy depends on the distance between the two objects.
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When a bungee jumper starts to fall they start to lose gravitational potential energy.
As the elastic cord pulls the bungee jumper back up, they gain gravitational potential energy.
The gravitational potential energy of an object on Earth depends on its weight and its height above the Earth’s surface.
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The gravitational potential energy (GPE) of an object depends on its weight and its height.
The equation for calculating GPE is:
GPE = weight x height
GPE is measured in joules (J).
Weight is measured in newtons (N).
Height is measured in metres (m).
Calculating GPE
What are the units of GPE, weight and height?
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A seagull with a weight of 30 N flies at a height of 10 m above the ground.
How much gravitational potential energy does the seagull have?
GPE of seagull = weight x height
GPE – Example 1
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The weight of an object is its mass multiplied by the strength of the gravitational field acting on the object.
This can be substituted into the GPE equation to give:
GPE is measured in joules (J).
Mass is measured in kilograms (kg).
Gravitational field strength is measured in newtons per kilogram (Nkg-1).
GPE = weight x height
What are the units involved?
GPE = mass x x heightgravitational field strength
Height is measured in metres (m).
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GPE
m
h
If this mass m is held at a height h then it has gravitational potential energy. It is equal to its weight, mg, times its height above the ground:
GPE = m g h
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When an object falls or is raised, it is useful to calculate the change in gravitational potential energy (GPE).
To do this, the change in height is used in the GPE equation:
GPE = weight x height
change in GPE = weight x change in height
What are the units involved?
Change in GPE is measured in joules (J).
Weight is measured in newtons (N).
Change in height is measured in metres (m).
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A parachutist of weight 600 N jumps from a plane, which is 2000 m above the ground.
How much gravitational potential energy will the parachutist have lost when she reaches the ground?
GPE = weight x height
GPE – Example 2
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Increasing GPE
m
GPE = m g h m
As the object falls, gravitational potential energy is converted into kinetic energy.
If the object starts from rest, its initial kinetic energy is zero.
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Potential and Kinetic energy
G.P.E.
G.P.E+K.E.
K.E.
•When a body falls from a height, its gravitational potential energy is changed into kinetic energy during the fall.
•As the body gains speed, more and more of its gravitational potential energy is changed into kinetic energy.
•Just before the body strikes the ground, all its gravitational potential energy is changed into kinetic energy.
•The total amount of energy at the beginning and the end is the same.
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Michael Jordan does a vertical leap of 1.0 m and dunks successfully.
What was his original take-off velocity if all his kinetic energy was transferred to gravitational potential energy ?
m g h = ½ m v2
Jordan jumps
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What is the total energy of the boy (m = 50 kg) at the top of the hill? (gravitational field strength = 10 N / kg)
•GPE = m g h
Sledge example page 1
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What is the work done to pull the boy to the top of the hill?
•Work done = Change in energy
Sledge example page 2
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What is the total energy, gravitational potential and kinetic, on top of the 15 m bump?
Sledge example page 3
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What is the kinetic energy of the boy at the bottom of the hill?
Sledge example page 4
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What is the speed of the boy at the bottom of the hill?KE = ½ m v2
Sledge example page 5
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Summary - GPE•Gravitational potential energy is equal to the energy given to an object by lifting it away from the surface of the Earth.
•GPE can be calculated using the following formula:
GPE = m g h or GPE = Weight x height
•g is the gravitational field strength of the Earth and equal to 9.8 N/kg. It is also sometimes called the acceleration due to gravity and equal to 9.8 m/s/s.
•Your weight on the Earth is W = m g
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Lesson 6 – Power
Aims:
•Describe power as the rate of transfer of energy or the rate of doing work.
•Be able to rearrange and use the formula
Power = Work done / time
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The units of power are Watts
James Watt, 1736 - 1819
Inventor of the Steam Engine
Power is measured in Watts
1 Watt = 1 Joule/second
James Watt was born the son of a shopkeeper and carpenter in Scotland. Watt is best known for improving the steam engine. Crude steam engines were used before Watt’s time, but they used large amounts of coal and produced very little power. Watt designed a steam engine that was much better and more practical.
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Power example 1
What is the power of a machine that can do 640 J of work in 4.00 s?
Power = Work done Time
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Power example 2
How long does it take for a 150 W motor to do 1350 J of work?
Power = Work done Time
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Power example 3How much work is done by a 1500 W blender in 90 s?
Power = Work done Time
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Power example 4A 57 N force is exerted through a distance of 2.5 m for 3.0 s. How much work was done and how much power was used?
Work done = Force Distance
Power = Work done Time
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Power example 5A builder carried a pile of bricks of total mass 30 kg up a staircase of height 3 m. If he took 5 minutes to do the job, what is his power?
Change in GPE = Work Done
Power = Work done Time
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Summary - Power
•Power is the rate at which energy is transferred or the rate at which work is done.
•We can calculate the power of an object using the following formula’s:
•Power = Energy transferred / Time
•Power = Work Done / Time
•Power is measured in Watts, Watts have the symbol W.
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Lesson 7 – Electricity and fossil fuels
Aims:
•Be able to describe the advantages and disadvantages of methods of large-scale electricity production using a variety of renewable and non-renewable resources.
•Understand energy transfer chains illustrating the environmental implications of fossil fuels.
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Steam, heat and work•Power stations that use coal, oil, gas and nuclear fuels all rely on the properties of steam to generate electricity.
•When water turns to steam it increases its volume by approximately 1500 times.
•This increase in volume in an enclosed space creates a lot of pressure. It is this pressure that can be used to turn the turbine blades.
•The pressure of the steam can still be thought of as heat as the particles are moving randomly. The motion of the turbine is work as it has an ordered direction of rotation.
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TurbineThe turbine has many sets of blades at opposing angles to each other.
The blades must be able to withstand the 1000 C steam that passes through, most metals will melt.
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Turbine generator
Like all steam turbine generators, the force of steam is used to spin the turbine blades which spin the generator, producing electricity.
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Cooling towersThese are cooling
towers, steam turns back to water.
Cooling towers heat the atmosphere but do not cause pollution.
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Fossil fuel power stations
Fossil fuel power stations convert c______ energy into e______ energy.
Oil and coal fired power stations work in a very similar way. The fuel is burnt and the heat boils water to make high pressure superheated steam, which is used to turn a turbine.
Natural gas fired power stations do not use steam. The natural gas is burnt, which produces hot gases that turn the turbine directly.
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Power station energy transfers
Fossil fuels, like coal, are used to generate electricity in a power station.
Chemicalenergy in
fuel
Heatenergy
Kineticenergy
Electricalenergy
Burn
fuel
Turbine Generator
Coal is used to turn water into steam at high pressure. The steam can turn the blades of the turbine, like the wind turning the blades of a windmill. The turbine spins coils inside of magnets in the generator that creates the electricity for use in our homes.
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Fossil fuels
What is a fuel?
What is a fossil fuel?
Name three fossil fuels:1. ___________2. ___________3. ___________
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Fossil fuels
Today, coal provides 55% of the U.S. electricity supply and the U.S. imports more than half of the oil it consumes. The burning of fossil fuels cannot be sustained.
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How coal formed
Over millions of years, due to high temperatures and pressure…
…the trees became fossilized, forming coal.
Millions of years ago trees died and fell to the bottom of swamps.
Over time they became covered by mud and rock.
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Over millions of years, due to high temperatures and pressure…
…the plankton became oil and natural gas.
Millions of years ago plankton died and fell to the bottom of seas and oceans.
Over time they became covered by mud and rock.
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What damage ?
Damage to the environment can come in many forms including:
•The greenhouse effect,
•Acid rain,
•Depletion of resources,
•Mining and quarrying.
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Global Temperatures - 150 years
The year 2000 was the 6th warmest on record
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The big threeCO2 (Carbon Dioxide)
• 25 billion tons produced on earth each year.
• Earth can absorb 15 billion tons.
• 10 billion ton excess each year.
CH4 (methane)
• Has increased since 1977.
• In less amount than CO2 .
• 20 – 30 times better at trapping heat.
CFC’s (ChloroFloroCarbons) (also causes ozone hole)
• Smaller amount produced than others.
• Has increased since 1977.
• 20,000 times better at trapping heat.
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Carbon in, carbon out.
• The total amount of carbon on our planet remains quite stable. When coal was formed, over millions of years, trees were taking carbon from the air which ended up in coal, oil and gas after the trees had died.
• When we burn fossil fuels we release this carbon goes into the air.
• Carbon dioxide is a greenhouse gas that keeps our planet warm. Unfortunately when the amount of carbon increases the Earth becomes hotter, which may have severe effects on our environment.
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Acid Rain
The poisonous sulphur gases rise into the air and returns to earth as acid rain (sulphuric acid). This can damage trees as shown above, kill wildlife on both land and in lakes.
Coal is not a pure hydrocarbon it also contains small amounts of other substances. One of these is sulphur. Sulphur dioxide gas is given out when coal is burnt.
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The effect on buildings
Acid rain can have a devastating effect on historic building made from carbonate materials such as limestone. The picture on the left was taken in 1908, the one on the right was taken in 1968.
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Reducing acid rain
Acid rain is mostly caused by sulfur dioxide (which forms sulfuric acid), but carbon dioxide also contributes (by forming carbonic acid).
How can acid rain be reduced?
1. Burn fewer fossil fuels – generate electricity in other ways.
2. Remove sulfur from oil and natural gas before it is burnt.
3. Scrub waste gases to remove sulfur dioxide.
4. Use expensive coal that contains little sulfur.
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Production and consumption
Combustion (95%)
Mining, Transport & Handling (5%)
It is not only the burning of fuels that damages the environment. Energy is required to mine and quarry coal for power stations.
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Pros and cons of fossil fuels
Advantages Disadvantages
Although there are problems burning fossil fuels in power stations there are also advantages:
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Summary – Electricity and Fossil fuels•Fuel is burnt to produce heat,
•Water is turned to steam at high pressure,
•The steam drives a turbine,
•The turbine drives a generator to create electricity.
•Coal, oil and gas are fossil fuels formed over millions of years from dead plants and animals.
•Burning fossil fuels releases carbon dioxide and sulphur dioxide. Acid rain can damage forests, lakes and buildings. Carbon dioxide contributes to global warming that will cause widespread environmental change.
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Lesson 8 – Geothermal energy
Aims:
•Understand a range of energy transfer chains illustrating the environmental implications of generating electricity, including geothermal resources.
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Old faithful Geyser•Natural hot springs and geysers have been used by native people for thousands of years.
•Washing, bathing and cooking were common practises before the industrial revolution.
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What is Geothermal power ?
• Geothermal power is energy that is taken from the hot parts of the Earth’s crust. Geo = earth, Thermal = heat.
• In many cases water is pumped down into the Earth where it is heated and returns to the surface. Steam from this water can be used to drive turbines and generate electricity.
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Structure of the Earth
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Internal temperature of the Earth
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Geothermal reservoir
When the rising hot water and steam is trapped in permeable and porous rocks under a layer of impermeable rock, it can form a geothermal reservoir.
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A basic geothermal generator
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Geothermal emissions
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The largest geothermal power plant is in California and has an output of 750 megawatts.
California calling
© David Parsons/NREL
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Advantages of geothermal
• Geothermal energy will last for many thousands of years and can therefore be considered renewable.
• It is a relatively clean source of energy.– 1/10 of carbon dioxide compared with fossil
fuels.• Fewer environmental problems than fossil fuels.• Once operating the running costs are low
compared to other sources of energy.
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Disadvantages of geothermal
• Physical effects due to fluid withdrawal including possible volcanic activity and earthquakes.
• Some noise pollution.• Other chemicals, within the heated water, can come to the
surface of the Earth and cause pollution.• Many sites are found in reservoir areas and areas of natural
beauty.• Areas suitable for geothermal generation are often in tourist
areas.• Social impact on in small rural societies.
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Summary – Geothermal energy
•In some places of the Earth steam rises from the ground. In others water can be pumped down into the ground and returns as steam.
•The steam can be used to drive a turbine/generator and create electricity.
•Geothermal energy does not originate from the Sun. It does not contribute to global warming and does create significant amounts of pollution.
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Lesson 8 – Nuclear energy
Aims:
•Understand a range of energy transfer chains illustrating the environmental implications of generating electricity, including nuclear energy.
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Why nuclear ?•Why would anyone choose to use nuclear power to generate electricity?
Independence – Many countries do not not natural sources of coal, oil and gas and want to be independent.
Weapons – Nuclear power plants can be used to generate isotopes useful for creating weapons.
Efficiency – When first created it was thought that nuclear power would be very cheap.
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Nuclear reactor animation
Cold coolant in
Hot coolant out
Fuel rod
Control rod
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Generating electricity
•Controlled nuclear fission reactions produce heat in the form of the kinetic energy of the particles involved.
• Coolant fluid is passes around the fuel rods absorbing heat and reaching very high temperatures.
•The coolant fluid passes this energy to a separate source of water, which is turned into steam at very high pressure.
•This steam drives a turbine, which in turn drives a generator converting kinetic energy into electrical energy.
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Advantages of nuclear power
• Independent of fossil fuels.
• Less emissions of sulphur and nitrogen dioxide.
• Some reduction in carbon dioxide emissions.
•Independence of imported fuel prices.
•A source of weapons grade plutonium.
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Disadvantages of nuclear power
•A high cost of building and decommissioning the power plant.
• High running costs makes electricity expensive.
•Potential nuclear disasters are rare but possible.
•Storage of nuclear waste a very long term problem.
•The cost of safely storing nuclear waste is high. The US Congress has been told that radioactive cleanup and decontamination at military nuclear facilities in the US will cost over $200 billion.
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Nuclear waste•Nuclear waste comes in several forms.•The used fuel rods contain some uranium that has not decayed as well as other isotopes made from the uranium that are dangerous.•All the other components of the power station e.g. moderator, control rods and coolant fluid become contaminated.•Many other parts of a nuclear power station must be stored when it is dismantled.
•It has only been 3000 years since the Egyptian Empire.•Some high level radioactive waste will take over 20,000 years to decay.
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Nuclear fuel rod storageUsed nuclear fuel rods, called spent rods, are stored in water.
Water keeps the rods cool as the number of nuclear reactions gradually decreases.
After some time they can be cut up and processed.
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High level waste disposal
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Advantages Disadvantages
Expensive to buildExpensive to decommission
Radioactive waste
Cheap to runConserves fossil fuelsNo sulfur dioxideemissionsNo carbon dioxideemissionsSafe undernormal conditions
Links with cancer
Although there are problems in the use of nuclear power, there are also advantages:
Little fuel used meansless transport needed
Non-renewable
Risk of disaster
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Summary – Nuclear power
•The controlled fission of Uranium 236 can be used to generate electricity.
•The fission releases energy as heat that can be used to turn water in to steam.
•Nuclear waste products can remain radioactive for long periods of time. These waste products need to be carefully stored for long periods of time in a secure site.
•Accidents at nuclear power stations can cause wide spread death and contamination.
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Lesson 8 – Solar energy
Aims:
•Understand a range of energy transfer chains illustrating the environmental implications of generating electricity, including solar energy.
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Solar energy systems
There are two main types of solar energy, both of which are renewable sources of power.
The basic type is found in solar panels that absorb energy form the Sun to heat water that can be used for domestic use or to generate steam for electricity.
The second type consists of solar cells, sometimes called photovoltaic cells. These cells directly convert energy from the Sun in electrical energy.
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Solar panel cross section
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Some solar power stations use a series of mirrors called heliostats to reflect light onto a boiler.
© Sandia National Laboratory/NREL
This solar power station in California consists of about 1800 heliostats, with an electrical output of 10 megawatts.
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Solar furnace
•Water within the tower is turned to steam at high pressure.
The steam drives a turbine which in turn drives the generator and makes electricity.
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Solar power stations are most effectively located in areas with high light intensity.
This test design is located in Arizona where the sunlight is intense and the air temperature is high.
The mirrors must track the Sun as it moves across the sky to be efficient as possible,
© Bill Timmerman/NREL
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Solar cells (or photocells) turn light energy from the Sun directly into direct current electricity.
Manufacturing solar cells is very expensive and requires the use of highly toxic materials. However, once the solar cell is built it produces no pollution and requires little maintenance.
This makes solar cells ideal for use in remote locations where maintenance is difficult and other sources of electricity would be expensive.
© NASA/NREL
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Solar cells suffer from a low efficiency. This is because only light with enough energy causes an electron to be released which is only about 25% of all sunlight.
The amount of electricity a solar panel can produce depends on two factors: its surface area and the light intensity.
Producing enough electricity to power a town would require a very large area of solar panels but covering the roof of a house can meet the annual electricity needs of the household.
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One obvious problem with solar cells is that they do not produce electricity at night.
If more electricity is produced during the day than is used, the excess can be used to charge a battery which can then provide power during the night.
Scientists are working to develop improved solar cells which require less polluting chemicals in their manufacture, cost less to produce and are more efficient than the current technology.
© Warren Gretz/NREL
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Solar cells are very useful for remote locations where supplying mains electricity would be expensive.
This solar-powered street light is in a remote part of mid-Wales with no mains electricity supply close by.
The use of solar power in this way removes the need to lay electricity cables to the light, which is another benefit to the environment.
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Solar cells are very useful where the light intensity is highest.
These solar panels are in a remote part of Morocco where they are used by a local utility company.
Solar cells are also useful where low amounts of power are needed.
Calculators only require a small amount of electricity, so most calculators now use solar cellsin place of batteries .
© Courtesy of BP Solarex/NREL
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Advantages of solar cells
•Running costs are low.•No carbon dioxide emissions to add to the Greenhouse Effect•No sulphur dioxide emissions to cause acid rain.•A renewable and almost unlimited source of energy.•A good source of energy in extreme conditions i.e. space, deserts etc.
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Disadvantages of solar cells
•The initial cost of solar cells can be very high.•The output is dependent on weather conditions and the time of day.•Many solar panels are needed to produce that of a power station.•Large areas of land are required for large scale generation of electricity•A warm reliable biome would be needed.•Solar cells have relatively low efficiencies.
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Summary – Solar power
•Solar panels can be used to heat water that can be used as a cheap supply for home heating.
•Solar furnaces focus the Sun’s energy to turn water into steam and then to generate electricity.
•Solar cells can directly transfer the light energy from the Sun into electrical energy.
•Solar energy is renewable and does not create any significant pollution.
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Lesson 8 – Water energy
Aims:
•Understand a range of energy transfer chains illustrating the environmental implications of generating electricity, including water energy.
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Energy from water
•Energy from water is derived in one of two ways.
• Gravitational forces from the Moon and Sun cause the tides, this movement of water can be harnessed by using wave power generation.
• The Sun powers the water cycle which increases the gravitational potential energy of water.
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The power of flowing water has been used for hundreds of years to operate machinery. This power can also be used to generate electricity.
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Energy from the water cycle
•When moving along rivers the GPE of rain water can be harnessed by hydroelectric power stations. This form of water energy is the most common current form of alternative electricity generation.
•The heat of the Sun evaporates water which rises into the atmosphere. This water returns to higher parts of the Earth during rainfall.
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Hydroelectric power stations• Hydroelectric power stations provide 5 to 10% of
the worlds electricity.• The evaporation of water by the Sun increases the
GPE of the water droplets, this is the original source of energy for hydroelectric power stations.
• Big lagoons, lakes or reservoirs are necessary to provide a constant source of energy to be converted to electrical power.
• Hydroelectric power stations can only be found in certain areas where the rainfall, river flow and geographical regions are correct.
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Energy Transfers
GravitationalPotentialEnergy
KineticEnergy(water)
KineticEnergy
(turbine)
ElectricalEnergy
Stored water in the reservoir is used to generate electricity in a hydroelectric power station.
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• Water stored in the reservoir has a high gravitational potential energy.
• The water is allowed to fall under gravitational force.• The water’s gravitational potential energy is converted
into kinetic energy.• The kinetic energy drives the turbines of the power
station.• The turbine drives the generators.• Inside the generator kinetic energy is converted into
electrical energy.
How it works
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Advantages of hydroelectric•Hydroelectric power is a renewable source of energy, as long as the Sun evaporates water we will have a source of power.
•It is a relatively clean source of energy emitting almost no greenhouse gases and no contributions to other gas emissions.
•Once operating the running costs are low compared to other sources of energy.
•It is a reliable and quick response system of generating electricity.
•Excess power can be exported to other countries to generate wealth.
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Disadvantages of hydroelectric•A large area of land will need to be flooded when the dam is constructed leading to loss of plant and animal species.
•Any change to the flow of a large river causes problems to crops and fishing as well as increasing land erosion by the wind; waterfalls disappear.
•The initial cost of building a hydroelectric power station is high.
•Future problems if the reservoir fills up with silt and sand.
•The large area of land required makes their placement very difficult to change. Risky near volcanoes.
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The Roosevelt dam•Originally completed in 1911, although recent improvements have been made.
•It delivers 36 MW of power.
•Its reservoir covers 19200 acres.
•It is located 76 miles north east of Phoenix, Arizona.
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How has the use of water power changed over time?
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The rise and fall of waves is a renewable source of energy. Effective sites for harnessing wave energy need to have strong waves most of the time, to ensure that enough electricity will be produced.
The “Limpet” (land-installed marine-powered energy transformer) on Islay, Scotland, is the world’s first commercial wave energy device. Its low profile is designed so that it does not effect coastal views.
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Tidal power involves building a dam across a river estuary.
Water can only flow in and out of the estuary through turbines in the dam, which harness the tidal energy.
When a tidal barrage is built, it results in some of the estuary being flooded. This can mean the loss of important habits for wading birds.
Tidal Barrage
Tidal power is able to provide a lot of electricity, however building a tidal barrage is very expensive.
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Tidal powerA huge dam (called a "barrage") is built across a river estuary. When the tide goes in and out, the water flows through tunnels in the dam.
The ebb and flow of the tides can be used to turn a turbine. Large lock gates, like the ones used on canals, allow ships to pass.
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Tidal power provides a regular source of electricity. Exactly when this electricity will be produced is governed by the tides, which depend on the Moon.
The passage of ships past the tidal barrier and the effect on wildlife also complicate the construction of tidal barrage schemes.
Effective use of tidal power
Monthly variations in the tidal range will also affect how much electricity can be produced.
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Advantages of tidal power
•Once you've built the dam, tidal power is free.
•It produces no greenhouse gases or other waste.
•It needs no fuel.
•It produces electricity reliably.
•Not expensive to maintain.
•Tides are totally predictable.
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Disadvantages of tidal power
•Very expensive to build.
•Affects a very wide area - the environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed.
•Only provides power for around 10 hours each day, when the tide is actually moving in or out.
•There are very few suitable sites for tidal power stations.
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Summary – Water power
•The water cycle gives rain water gravitational potential energy that can be changed into electrical energy in hydroelectric power stations. It is renewable energy but does cause localised environmental damage when dams are constructed.
•Wave energy can be used to generate electricity but is not yet widely available.
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Lesson 8 – Wind energy
Aims:
•Understand a range of energy transfer chains illustrating the environmental implications of generating electricity, including wind energy.
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Energy from the wind•Wind is a renewable energy resource. •The Sun heats our atmosphere causing changes in temperature and pressure. The pressure differences cause the winds.•As long as the Sun heats our atmosphere we will have wind energy.
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An old science•Wind power has been used for thousands of years. Early farmers used windmills to grind corn.
•Since the industrial revolution steam engines, petrol engines and electricity have took over from wind.
•We can now generate electricity from the wind.
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Generation of electricity•The kinetic energy of the wind is converted into rotational work when the turbine blades spin.
•The moving turbine drives the generator. The generator converts kinetic energy into electrical energy.
•When the wind is strong the blades automatically twist a small amount to prevent damage to the turbine and generator.
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Palm Springs, California
A large number of wind turbines grouped together is called a wind farm. The turbines are arranged in special patterns.
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Advantages of wind power
•Wind power is renewable- it will last as long as the Sun shines.•Particularly useful in remote areas without an electricity supply.•Wind power is a clean source of energy – there are no emissions of carbon dioxide, sulphur dioxide and nitrogen oxides. •Government initiatives often provide funds to promote wind power.
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Disadvantages of wind power•A large land area is required to get sufficient energy to power a city. In many highly populated countries this land is expensive.
•Not all areas have a constant source of wind to generate electrical energy.
•Only approximately 5 MW of power is produced per turbine so many are needed to produce the same amount of energy as a power station.
•A large number of wind turbines can make sensitive environmental areas look unattractive.
•Turbines can be noisy stopping them being used in urban areas.
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Summary – Wind energy
•The winds are caused by the heating of the atmosphere by the Sun.
•The movement of the wind can be used to turn fan blades, this in turn can be used to generate electricity.
•Wind energy is renewable and does not create any wide spread pollution but can be an eye sore and is dependant on the weather.