Natural Science & Technology: Grade 6
Energy and Change: Mains Electricity
MAINS ELECTRICITY
Fossil Fuels and Electricity
A fuel is a material which can be burnt to produce heat, light and movement. Fuels are
therefore used as a source of energy.
Around 80% of the world’s energy is made from fossil fuels – coal, oil and gas. They are
known as fossil fuels because, like fossils, they have been formed over millions of years from
the remains of living things, like dead plants and animals.
Coal is a solid, oil is in liquid form, and natural gas is a gas.
Coal
Oil
Gas
Our electricity supply comes from power stations and is known as ‘mains electricity’. The
source of energy used to produce electricity in power stations comes mainly from fossil fuels.
Fossil fuels need to be mined in order to use them. Coal is mined by digging out coal deposits
and gas and oil are mined by drilling deep into the ocean bed and extracting it through the
drill hole.
Coal Stockpile at a Coal Mine
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Drilling for Oil / Gas
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Energy and Change: Mains Electricity
Fossil fuels are non-renewable energy sources which cannot be replaced when they are used
up. Coal is made from the remains of plants and oil and gas are made from dead sea
creatures. Over millions of years, these remains changed into fossil fuels. The energy stored
in fossil fuels originally came from the Sun.
Nuclear energy is another non-renewable energy source. Nuclear power is made from
splitting atoms to produce heat energy, which is turned into electricity. Nuclear power creates
toxic waste which can accidently be released into the atmosphere.
Nuclear Power Station
Fossil fuels contain high percentages of carbon and when they are burned, they release
carbon dioxide into the atmosphere. Carbon dioxide is a greenhouse gas that contributes to
global warming.
Pollution
Coal is a sedimentary rock found in layers called coal beds or coal seams.
Coal Seams
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Coal
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Coal is formed from dead plant matter in forests, which were found in low lying wetland
areas. Over millions of years, these forests flooded and became buried under water. The dead
vegetation was covered with sand and silt. New plants grew on the surface and the process
was repeated over time, so layer upon layer of plant material, called ‘peat’ was formed. Peat
is not really coal, but is used as a fuel in some places, where it is burnt for heat and cooking.
As the dead organic matter sank deeper and deeper, it was compressed and subjected to high
pressure and high temperature. So under high pressure and high temperature, the dead
organic material slowly turned into coal.
Coal is the largest source of energy in the world and is burned to produce electricity in a coalpowered power station.
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Energy and Change: Mains Electricity
In South Africa, coal is the most commonly used fuel in power stations. Coal power stations
use thermal (heat) energy to make electricity. In this process, the coal is burned to boil water
and create super-heated and very high pressure steam. The steam, in turn, causes a
mechanical turbine to rotate at very high speed, which rotates a generator to produce
electricity.
The electricity produced can be changed to other forms of energy such as heat, light and
movement energy for appliances in our homes and machinery in industry.
Eskom operates 24 power stations in South Africa, with a generating capacity of 43,969 MW
(mega watts). There are fourteen thermal (coal) power stations which generate 37,600 M, of
which three were ‘retired’ and had to be refurbished and brought back into service in 2010.
These three return-to-service power stations can generate 3,650 MW of electricity. There is
one nuclear power station in the Western Cape, which can generate 1,940 MW. Four hydroelectric power stations generate 2,000 MW, as well as four gas turbine power stations which
generate 2,426 MW. In addition, one wind farm currently generates 3 MW.
Eskom are currently building two new thermal power stations, Medupi and Kusile, which
when commissioned, will generate 9,588 MW, one hydro-electric pumped storage facility,
Ingula, will generate 1,332 MW and one additional wind farm which will generate 100 MW.
A concentrating solar energy factory is also being built.
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Natural Science & Technology: Grade 6
Energy and Change: Mains Electricity
Click on the link below for a map of the location of Eskom’s power stations:
http://www.eskom.co.za/Whatweredoing/ElectricityGeneration/PowerStations/Pages/M
ap_Of_Eskom_Power_Stations.aspx
Coal Power Station
Thermal power stations which burn coal to produce heat energy, produce about 90% of South
Africa’s electricity and are mainly found in Mpumalanga, as coal is mined there.
A thermal power station can be recognised by its high cooling towers where the steam is
cooled and the condensation, which is in fact water droplets, can be seen rising above the
towers, like smoke.
Arnot Power Station, Middleberg
Wikipedia Creative Commons
Attribution Share-Alike: Gerhard Roux
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Energy and Change: Mains Electricity
The diagram below shows how electricity is made from coal, once it has been mined.
1. The coal is burned and heats the water, causing it to boil. This results in a build up of
steam, which creates pressure.
2. The steam pressure builds up and is directed through pipes onto the blades of the
turbine wheel. The turbine turns at very high speed and turns the output shaft.
3. The output shaft is connected to a generator which turns and produces the electricity.
The generator has a coil of copper wire encased in magnets, attached to the shaft. The
electricity is made by the coil turning the magnets.
4. The electricity is transferred by overhead cables or wires to substations where it is
changed to high voltage and then through overhead power lines, to distribute the
electricity to homes and industries.
5. Some steam goes into a cooling tower. This steam cools, condenses and drips down
as water. The water is recycled back to the boiler.
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Energy and Change: Mains Electricity
The Cost of Electricity
Electricity is an expensive resource and prices are continuing to rise. From 2007 to 2015,
electricity tariffs in South Africa have increased by 300%.
The cost of electricity is calculated to include the following:



Capital costs for the infrastructure of coal mines, power stations, transport, pylons,
wiring and substations.
Maintenance and running costs of the above.
Fuel costs – the cost of coal and other energy sources.
Electricity from the mains supply passes through a meter before it enters your household. The
meter shows the electricity consumption (usage). Eskom or the local municipality bills for the
amount of electricity used every month. Pre-paid meters are installed in some homes, so the
electricity has to be paid for before it is used.
Three-Phase Electrical Supply
Electricity Meter
The power of an electrical appliance is measured in watts (W) and kilowatts (kW).
1 kW = 1000W.
The amount of electrical energy that an appliance uses depends on:


how long the appliance is switched on and
the rate at which it transforms energy, i.e. how much power it uses.
Appliances have a label that shows their power rating, for example, a 2400W iron.
Power Rating on an Iron
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Energy and Change: Mains Electricity
Some electrical appliances use more energy than others. It is usually the appliances that
transfer electrical energy into heat energy that use the most watts and therefore consume the
most energy, for example, a hairdryer, an oven, an iron, a kettle, a toaster etc. A stove, for
example, uses more electricity than a TV. The higher the value of the watts of an appliance,
the more energy it uses.
We can work out the cost of using an appliance by calculating the amount of electricity that it
uses. This is measured by the length of time the appliance is used for and is called the
kilowatt-hour (kWh) and is the amount of energy used by a 1 kW appliance running for 1
hour and equals 1kWh.
Cost of Electricity is Measured in kWh
The current cost of electricity in South Africa (2016/7 rates) per kilowatt-hour (kWh) is:
Less than 600kWh
R0,999
More than 600kWh
R1,5379
Source: Eskom – April 2016
The two different rates in the table above are used depending on the usage in the household
and show that the more electricity that is used, the more expensive it becomes.
The basic minimum household requirements consume up to 350kWh per month. However,
the majority of households use electricity at much higher rates.
The price of a unit of electricity can vary from place to place.
To work out the number of kilowatt-hours transferred to an appliance, use the formula below:
Energy transferred (kWh) = power of appliance (kW) x time (h)
The cost of this energy transfer can then be calculated by multiplying the number of units
used by the cost per unit in the table above.
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Energy and Change: Mains Electricity
Example
To work out the cost of using a 600W washing machine for 4 hours, at a rate of R1,5379/
kWh.
600W = 0,6kW
Energy transferred = 0,6kW x 4 hours
= 2,4 kWh
Cost = number of units x cost per unit
= 2,4kWh x R1,5379
= R4,66 to use a 600W washing machine for 4 hours.
The more electricity we use, the more coal is used up, and the more
we pay. As electricity is such an expensive and precious resource,
we should try to reduce power usage in order to save energy and
reduce our electricity bill. This will also reduce the pollution caused
by burning fossil fuels in coal powered stations.
There are many ways to save energy, including switching off
applicances when not in use, using energy-saving light bulbs,
insulating your home and using solar energy to heat water.
Energy-Saving Light Bulb
For more information on saving energy, go to the following links:
Save Your Planet – The Energy Crisis:
https://mycyberwall.co.za/save-your-planet/resource-depletion/energy-crisis
NS Grade 7 – Insulation and Energy Saving:
https://mycyberwall.co.za/get-smart/science/grade-7/insulation-and-energy-saving
NS Grade 7 – The National Electricity Supply System:
https://mycyberwall.co.za/get-smart/science/grade-7/national-electricity-supply-system
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Natural Science & Technology: Grade 6
Energy and Change: Mains Electricity
Illegal Connections
By law, only a qualified electrician can connect mains electricity as it
has 220 volts, which is enough energy to kill, if incorrectly handled.
An illegal connection is the draining or diverting of power from the
mains supply and includes the following:


Direct connection to the mains supply. This involves running a
cable from the Eskom pylon, or cutting through cables to divert
electricity directly to the property.
Illegal Connections
are Dangerous
Bypassing or tampering with the electric meter to avoid paying for electricity usage.
People make illegal connections to avoid paying for electricity. These illegal connections are
extremely dangerous and cause serious accidents and even death. They are one of the main
causes of electrical accidents in South Africa.
Illegal connections are often made with non-insulated wiring, so if the wires (which are
conductors) are exposed and a metal object, such as a gate or fence comes into contact with
these bare wires, they will conduct electricity at 220 volts. If a fault occurs in the illegal
circuit, the protective devices will not trip and the faulty circuit continues to supply power,
until the wires overheat and cause a fire.
Illegal Connections Can Cause a Fire
Illegal connections can cause:




Overloading of transformers and power lines, leading to a poor electricity supply and
power outages, thereby adding to the energy crisis.
Damage to electrical appliances.
An increase in the cost of electricity to others.
Fires and explosions.
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Energy and Change: Mains Electricity
Illegal connections are considered as a form of theft and making or using these connections is
therefore a criminal offence.
What to do in an Emergency
If you or another person gets an electrical shock, follow these
steps:



If the person is still connected to the circuit, do not
touch them as you can also get electrocuted.
Turn off the electricity at the mains switch.
If the person is not visibly connected to the mains, get
help immediately.
Electrical Shock
Turn off Electricity at Mains
Renewable Energy Sources
Our supplies of fossil fuels are being used up much faster than they can be made (remember
they take millions of years to make). Therefore alternative sources of renewable energy are
being looked at.
Renewable source means that they can be replaced (not re-used) and will not run out. These
sources can be replenished or made again in a short period of time.
The race is on to find ways to harness the energy from renewable resources which will not
run out, such as the Sun, wind, water, plant and organic materials.
Examples of renewable energy sources include:
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Energy and Change: Mains Electricity
Biomass
This type of energy comes from living things, such as plants and other organic materials. The
energy that is stored in living organisms comes originally from the Sun.
Biomass – Elephant Dung
Biomass is a form of energy that uses the material of living things such as animals, plants,
droppings, as well as decayed matter which produce methane gas (known as biogas) that can
be burnt to provide heat and electricity. It is burned in the same way as natural gas.
Dried elephant dung is an ideal fuel for burning at a low, constant temperature and can be
used as cooking fuel. Chicken droppings are another source of biomass.
Wind Power
This is energy from moving air. Wind power can be harnessed through wind turbines, in the
same way that windmills have been used for thousands of years. The turbine harnesses the
energy in wind into electrical energy. However, wind turbines are unsightly and can be
expensive. They only work in very windy areas.
Wind Turbines
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Energy and Change: Mains Electricity
Water Power
Water that moves can also be made into electricity in the following ways:

Hydroelectric power uses the potential of storing water in a dam and releasing this
water through large pipes, where it flows down to the base of the dam and causes
large turbines to turn. This type of power is a renewable source of energy which does
not pollute or use up any resources. Norway is one country that produces 99% of its
electricity through hydroelectric power. Tidal barrages are also a form of
hydroelectric power and are built in the mouths of rivers, so that when the tide turns,
the energy is harnessed.

Wave energy can be harnessed to produce electricity through tidal flows. This type of
energy can only be made for 6 – 12 hours a day when the tide is flowing the fastest.
Hydroelectric Power
Wave Energy can be Harnessed
Geothermal Power
Geothermal energy is made from heat inside the surface of the Earth. At the surface of the
Earth, the average temperature is 15°C and for every 100 metres we drill down, the
temperature increases by 2°C. At the Earth’s core, the temperature is more than 5 000°C.
Drilling for Geothermal Power
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Natural Science & Technology: Grade 6
Energy and Change: Mains Electricity
Solar Power
Solar power is energy from the Sun and works through solar panels made of silicone, which
soak up the sun and turn it into electricity. This method of converting solar energy into
electricity is known as photovoltaics (PV). Photovoltaics converts the light from the Sun into
electrical energy.
Solar Panels
As the world’s energy consumption is increasing every year, most countries are looking at
using more and more renewable energy sources.
Solar Powered Street Light
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