GRADE 7
Name:
Renewable resources Renewable resources are those that can be replenished or replaced continually and easily. The supply of these resources will not be used up no matter how high the demand for them will be.
Water power Hydro-electric power stations use moving water to create energy. Water is considered a renewable resource as it is continually being replaced through the water cycle. Hydro-electric power stations are often built across a river, forming a dam. The water flows through the sluice-gates in the dam and out into the “other side” of the river. As the water flows through the dam, it turns giant turbines which is connected to the generator which makes electricity. In some countries, the waves and tidal action of the ocean are used to generate electricity in a similar way.
Wind power Wind farms are areas where huge windmills are erected in rows and as the wind blows through them, they turn. This turning motion is the same as that of the turbine in the hydro-electric power station; it is connected to a generator which generates electricity. In South Africa, there are wind farms in the Eastern Cape. This form of energy has great potential for a country. Wind is considered a renewable resource because wind energy cannot be used up. In areas that have a consistently high levels of wind, this is a sustainable, inexpensive energy source. For more information about wind farms in South Africa, visit this website: http://jeffreysbaywindfarm.co.za/ © e-classroom 2014
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Grade 7 Term 3 Natural Science: Energy and Change: Sources of Energy: Renewable energy
Renewable energy
GRADE 7
Energy from the sun is called solar energy. It is considered a renewable resource, because the sun will not burn out until billions of years have passed. South Africa has mostly sunny days throughout the year which makes this source of energy ideal to use. Solar energy is mainly used on a small scale, powering solar geysers and appliances or lighting equipment. There are however, solarthermal power stations. Solar panels contain photocells which absorb the sunlight and transfer the solar energy into electrical energy. This energy can be used or stored in a battery and used at times when there is no sunlight. In solar geysers, the solar energy is transferred into heat energy and this heats the water as it flows into the geyser. This hot water is stored in the geyser until it is used. Solar-thermal power stations use a similar technology. Mirrors on a panel reflect the sunlight onto a “power tower”. This tower contains a type of salt which is heated up by the solar energy. The molten salt heats up water which produces steam. The steam then turns the turbines which cause the generator to generate electricity.
Biofuel Biofuel can be found as a solid, liquid or gas. Solid biofuels include wood and animal dung (such as from cows). Both of these substances are burned to release energy that can be used for heat. Liquid biofuel is formed when crops like maize and soybeans are fermented. The sugars in these crops turn into Ethanol in the fermentation process and this alcohol can be used as a fuel for cars, or it can be mixed with petrol and diesel. Biogas (biofuel in gaseous form) is formed when waste in landfill sites decomposes. If a landfill site is correctly designed, the gases, such as methane gas produced as the waste breaks down, can be collected and used similarly to natural gas. Biofuels are considered renewable for the following reasons: wood and crops can be replaced by planting new trees and crops. Animal dung will always be available as long as one has animals. Finally, as long as there are humans on the Earth, there will be waste dumped at landfill sites. © e-classroom 2014
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Grade 7 Term 3 Natural Science: Energy and Change: Sources of Energy: Renewable energy
Solar power
GRADE 7
Answer the following questions: 1) Explain what is meant by “renewable resources”. _______________________________________________________________ _______________________________________________________________ 2) List the renewable resources you have learnt about. _______________________________________________________________ _______________________________________________________________ _______________________________________________________________ 3) Why is biofuel considered a renewable resource? ______________________________________________________________ ______________________________________________________________ 4) How does the wind produce electrical energy? ______________________________________________________________ ______________________________________________________________ 5) Do you think there are any negative effects to using these renewable resources? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Class Discussion Activity Discuss whether you think firewood is really a renewable resource?
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Grade 7 Term 3 Natural Science: Energy and Change: Sources of Energy: Renewable energy
Activity
GRADE 7
Activity Answer the following questions in your book: 1) Explain what is meant by “renewable resources”. Renewable resources are those that can be replaced continually and easily. Their supply is not limited and will not run out. 2) List the renewable resources you have learnt about. Water, Wind, Sun, Biofuel. 3) Why is biofuel considered a renewable resource? It comes from resources that can easily and continually be replaced. Wood – new trees can be planted. Crops – new crops can be planted. Animal dung – will always be available as long as there are animals. Waste – will always be available as long as humans dispose of it. 4) How does the wind produce electrical energy? The wind turns the turbines which are connected to a generator. The generator generates electricity. 5) Do you think there are any negative effects to using these renewable resources? There are definitely negative effects to using renewable resources. Resources that have to be replaced – trees and crops can be replanted, but they take time to grow. If this is not managed correctly, the supplies of trees and crops can be exhausted (used up). Cost – the setting up and maintenance of power stations, such as the hydro- electric powerstation, solar-thermal power station and the wind power stations is expensive. (However, in the long run, they work out cheaper for people paying for the electricity.) Certain things have to be in place for such power station to be built. A hydro- electric power station must be constructed over a river that flows throughout the year; a solar power station has to be placed in an area that has lots of access to sunlight throughout the day. A wind power station must built in an area that is consistently windy. © e-classroom 2014
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Grade 7 Term 3 Natural Science: Energy and Change: Sources of Energy: Renewable energy
Answer Sheet
(This said, in the long term they are the cleanest and least expensive source of energy. They do not contribute to global warming and air pollution and the other negative negative effects mining, etc. has on ecosystems.)
Class Discussion Activity Do you think firewood is really a renewable resource? Yes – Firewood comes from trees. When the wood is used, the tree dies, but a new tree can be planted and thus the tree can be replaced. Renewable resources are those that can be replaced. No – Once the tree is used (lets presume it is an “adult” tree), it is dead and a new one must be replanted. This new tree will take a long time to grow into an “adult” to be used for firewood. It is possible that the demand for firewood can outweigh the supply and that the supply of firewood in an area could decrease during the period that new trees are growing. The ultimate answer is YES, as long as the planting-and-harvesting process is mangaged correctly. If it is not managed properly, the supply will be depleted and eventually exhausted because the demand is so high and there are not enough trees to meet the demands. In South Africa, rural communities have a great need of natural resources such as firewood. Managing their resources effectively ensures that future generations will also have access to these resources.
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GRADE 7 Grade 7 Term 3 Natural Science: Energy and Change: Sources of Energy: Renewable energy
Many of these powerstations have a significant impact on ecosystems in their area.
