1. Natural Sciences Grade 7
Term 3: Energy and Change
Sources of energy

2. Topic 1 Sources of Energy
Renewable energy
Natural Sciences - Grade 7

3. Natural Sciences - Grade 7
What is renewable energy?
This is energy that can be replaced and restored as it replenishes.
It is free and cheap, because it comes from nature.
It is expensive to change the energy from renewable sources to a useful form , e.g. electricity and heat.
Natural Sciences - Grade 7

4. Natural Sciences - Grade 7
What is renewable energy?
Plants, hydropower (falling water), wind, biofuel (wood) and sunlight are renewable energy sources.
It causes little pollution of the atmosphere.
Natural Sciences - Grade 7

5. Types of renewable energy
1. Hydro power- Energy from falling water [PART 1]
Hydro means water.
Hydropower uses the energy in moving water to make electricity.
Hydro-electric power stations are built next to dams or in the mountains where there are large waterfalls.
Natural Sciences - Grade 7

6. Types of renewable energy
It is used in wetter climates and where the water supply is fast running. [Lesotho Highlands Scheme [picture 1] and Cahora Bassa in Mozambique [picture 2].
A turbine can be made in order to turn when water runs through on the other side of it.
Water stored in a dam can run through a channel where it turns a turbine which then turns a generator to produce electricity.
Natural Sciences - Grade 7

7. Types of renewable energy
Hydropower- Hydro-electricity [PART 2]
One of our country’s sources of hydro-electricity
There are not many rivers in South Africa that are large enough to power a hydropower plant.
Most of South Africa’s rivers dry up during the dry season.
One source of hydro-electricity for South Africa is the Cahora Bassa Dam [292 km long, 38 km wide, 157 m maximum depth] on the Zambezi River in Mozambique.
Natural Sciences - Grade 7

8. Types of renewable energy
Electricity is exported from this large hydro- electric power station. [Dam produces MW of electricity]
A view of the Cahora Bassa dam
Natural Sciences - Grade 7

9. Types of renewable energy
Hydropower- Hydro-electricity [PART 3]
South Africa has three hydro- electric power stations:
Vanderkloof Dam [Northern Cape]
Second biggest dam in South Africa.
The highest dam wall is 108 metres.
It has a span of 765 metres.
When the dam is full, the shoreline is 100 km long.
Natural Sciences - Grade 7

10. Types of renewable energy
Hydropower- Hydro-electricity [PART 4]
Tugela – Vaal Scheme [Northern Drakensberg]
Problems of future water supply for commercial, domestic and industrial use in the Gauteng area were becoming increasingly serious.
Transferring water from the Tugela River catchment area into the Vaal River catchment was the solution.
It was completed and served as a pumping station for water that was built mostly underground to transfer water over the Drakensberg from the Tugela River into the Vaal River as well as a pumped storage scheme.
Natural Sciences - Grade 7

11. Types of renewable energy
It generated electricity for 10 hours per day.
It is constructed underground and the shaft buildings, a dam wall and transmission lines are visible at the surface.
Sterkfontein Dam [picture 1] is situated in the very upper reaches of the Vaal River. This reservoir forms the upper storage reservoir for the Tugela- Vaal pumped storage scheme - Campsite [picture 2] ; scenery [picture 3].
Natural Sciences - Grade 7

12. Types of renewable energy
Hydropower- Hydro-electricity [PART 5]
3. Gariep Dam [Free State]
Electricity from Gariep Dam is fed into the Eskom network at the Hydra Distribution Station near De Aar.
Natural Sciences - Grade 7

13. Natural Sciences - Grade 7
Wave and tidal energy
In some parts of the world the rise and fall of tides or the movement of waves is used to generate electricity.
South Africa does not have suitable tidal conditions for this, because our waves are usually too strong.
Natural Sciences - Grade 7

14. Natural Sciences - Grade 7
Wind energy
South Africa’s climate is suitable for using wind energy to generate electricity.
Wind [air currents] move different objects [clothes hanging on a washing line; windsurfers; windmill blades that pump water; sailing ships; kite surfers; dead leaves; etc.].
The pictures below shows a wind farm near Darling in the Western Cape.
People have been using wind as a source of energy for a long time. [windmills on farms are used to pump groundwater].
Natural Sciences - Grade 7

15. Natural Sciences - Grade 7
Wind energy
A wind turbine is similar to a propeller which turns when wind blows through it. It can be connected to a generator to produce electricity.
Wind energy will help reduce our dependence on imported fossil fuels; decarbonise our energy supply and increase our energy security.
Natural Sciences - Grade 7

16. Natural Sciences - Grade 7
Solar energy
The Sun is our most important source of energy.
Energy coming from the Sun, is called solar energy.
The main use of solar energy in South Africa is for heating water.
Most home owners with a low income, have Solar panels installed freely.
Natural Sciences - Grade 7

17. Natural Sciences - Grade 7
Solar energy
This is the government’s attempt to increase the use of solar energy and to reduce people’s electricity costs of heating water.
Sunlight shining onto the solar panels [pictures 1-4 are a few examples] provides energy to push electricity to charge from one part of the panel to another.
Natural Sciences - Grade 7

18. Natural Sciences - Grade 7
How solar energy works
Natural Sciences - Grade 7

19. Natural Sciences - Grade 7
Biofuel
Energy from the sun is stored in all plant matter, but mainly in wood [it releases heat when it burns]. Wood is cheap and easily accessible. More trees can be planted.
Biofuels are fuels made from plants [sugar cane, maize, wood, soybeans, algae] and waste material produced by humans [gives off biogas as it breaks down].
We can also get energy from animal dung.
Natural Sciences - Grade 7

20. Natural Sciences - Grade 7
Ethanol
It is a fuel that can be used on its own or added to petrol.
It is made from sugar cane in KwaZulu-Natal, but can also be made from maize, for example.
Brazil produces ethanol from sugar cane as well as cassava [similar to sweet potatoes].
The first engines designed to run on ethanol as fuel, were designed in Brazil.
Ethanol is a renewable, domestically produced alcohol fuel made from plant material, such as corn, sugar cane or grasses.
Natural Sciences - Grade 7