National Grid
Electricity from coal
Electricity is generated in a power station. A power station is a system for the making or generation of electricity. The general method for the generation of electricity at a power station is to rotate a turbine that in turn rotates a generator. In South Africa most of the electricity is generated in power stations that burn coal. Approximately three quarters of all the energy comes from coal. Most of the power stations in South Africa are in Mpumalanga.
How a coal power station works
1. Coal in a furnace is used to heat water in a boiler.
2. Steam is generated, which moves through pipes to the turbine.
3. The steam moves through the turbine that has wheels with blades like a fan. As the steam mves over the blades, the energy in the steam causes the turbine to rotate.
4.The turbine is connected to a drive shaft that causes a generator rotate. As the turbine rotates, the enrgy in the moving generator is converted into electrical energy (kinectic -electrical energy).
5. The electricity is changed into the correct voltage in a transformer.
6. Electricity is distributed by means of a large pylons and high tension cables into the national network to houses, schools, factories, etc.
Disadvantage of coal power station
Air pollution-when coal is burnt, small dust particles and poisonous gasses such as carbon dioxide (CO2), sulphur dioxide (SO2) and nitrogen dioxide (NO2) are released into the atmosphere - a power that is called ash remains after a coal fire. It is one of the greatest causes of air pollution in South Africa. Acid rain forms when carbon dioxide, sulphur dioxide and nitrogen dioide dissolves in moisture in the air. Contributes to greenhouse effect as a result of the release of posionous gasses. Contriutes to global warming as a result of the release of posionous gasses. Nonrenewable coal resources are being exhausted.
Electricity generation from alternative energy sources
Coal is not the only source of energy that can be used for the generation of electricity. Other sources that may be used for the generation of electricty, apart from coal, are wind, falling water (hydroelectricity), solar heating, the waves of the sea and nuclear energy.
Wind power
Giant wind turbines are used to turn electrical generators. An expiremental wind farm at Klipheuwel near Cape Town can generate 3,2MW. A single coal power station can generate between 200 and 600MW; therefore it will take hundreds of wind turbines to replace one single coal power station.
Advantages of wind power
Free, renewable energy source, clean, no waste products.
Disadvantages of wind power
Wind turbines are lage and expensive, with relatively low power delivery. Not sufficient wind in many regions.
Falling water-hydraulic electricity
Hydro-electricity is generated through the movement of falling water from a high to a lower level. Water is then stored in a dam, and released through pipes. The power of the falling water causes rotation in the generator.
Advantages of hydraulic electricity
Free, renewable energy source, clean, no waste products.
Dependable source:
-Flow of water can be controlled.
-Stored resources can be used.
-There is a constant supply.
Changes in water levels are beneficial:
-Recreational activities
-Enlarges habitat of fresh water animals and plant species.
Disadvantages of hydraulic electricity
Dams (infra structure) are expensive. Must also be used in other projects.
Environmental impact:
-Flooding of surrounding areas.
-Destruction of land ased ecosystems (insects to wild life)
-Destruction of agricultural land
-Displaces communities
-Cultural and historical buildings (e.g temples) may dissapear under water.
Solar power
Solar panels and solar cells are used to capture the radiation energy of the sun-usuall as heat.
Advantages of solar power
Free, renewable source of energy, clean, no waste products. No moving parts on solar panels (solar cells). Relatively simple to design. Little repair and maintenance. No air pollution.
Disadvantages of solar power
Needs uninterrupted sun light - sun does not shine all the time: for that reason, batteries have to be rechared. Only for parts of the world that are sunny. Does not work at night. Equipment is very expensive.
Wave power
The motion of waves is used to drive a turbine that generates electricity.
Advantages of wave power
Renewale source of energy, clean, no waste products. Constantly available in specific areas. Available day and night. Production can be predicted. More reliable than wind or solar energy. The energy is free-no fuel is necessary. Not expensive to operate and maintain. A large qauntity of energy can be produced.
Disadvantages of wave power
Variable: depends on the size of the waves. Must find suitable places where the waves are constantly powerful. Sound pollution is possible. Visual impact if it is developed above water or on the beach. Disturbs sea life. Can interfere with mooring and anchor ropes of boats during commercial or recreational fishing.
Nuclear energy
Radioactive materal naturally releases heat. The heat changes the water into steam and the steam drives a turbine that drives a generator to generate electricity.
Advantages of nuclear energy
Small amounts of nuclear fuel gives lage amounts of energy. Less pollution if managed responsibly. It is perpetual. Effective electricity supply. Safe if safety measures are not relaxed.
Disadvantages of nuclear energy
Nuclear radiation is extremely dangerous. High safety standards required. Waste from power stations stay radioactive for thousands of years. Limited dumping sites. Dangers in dumping radioactive waste.
Nuclear power in south africa
South Africa has only one commercial nuclear power station, the Koeberg nuclear power station near Cape Town. The Koeberg nuclear power station supplies approximately 5% of South Africa's electricity requirements, and is the only one of it kind in Africa.
Nuclear energy
A large amount of energy is contained in the nucleus of an atom. This nuclear energy is in all sorts of atoms, but the technology for the release of this energy is only available for the atoms of a few elements. The element that is most often used, is uranium. Nuclear energy is released when the nucleus of an uranium atom is split (broken up) during a process that is called nuclear fission. Most of the nuclear energy that is released is in the form of heat; other energy that is being released, is in the form of extremely dangerous radioactive radiation. For this reason the reactions should take place in a nuclear reactor that is built with walls of lead and concrete. Nuclear reactors in nuclear power stations produce nuclear energy that is then used for the generation of electricity. The nuclear energy that is used for the generation of electricity is called nuclear power. Nuclear power stations generate electricity more efficiently than coal driven power stations, and they also do not cause air pollution.
Nuclear power station
Nuclear power stations use uranium as fuel. Uranium is a mineral that is being exploited in mines, but it is not very stable and breaks up easily. When the nucleus of an uranium atom is split (broken up), large amounts of energy is released in the form of heat. This energy is then used to boil water in order to produce steam. The turines are rotated by the steam that in turn rotates the generator. The generator produces electricity. The electricity is then sent to the national electricity network. Many power stations are built along the coast, such as the one at Koeerg in South Africa, where it uses sea water for the cooling of the steam so that it can "condensate" to form water. These nuclear power stations do not have gaint cooling towers.
Nuclear power and safety
Nuclear power stations produce dangerous radioactive waste materials. Radioactive waste has to be buried deep under the surface of the earth. It takes hundreds of years for the waste to degrade and become less dangerous.
The national electricity network
The national electricty network is a network of electricity cables and power masts throughout South Africa.
1.Generation(where electricity is generated, the voltage increased and the current decreased) At the power station electricity is generated at a voltage that varies between 11 000V and 24 000V (11kV to 24kV) which is then changed at at the power station to 132kV or to as high as 765kV by means of as step-up transformer before it enters the national transmission lines. Transported safely and efficiently over long distanves at a high voltage and a low current. This is beause the cable will overheat or even melt if the current is too high, and if the voltage is too low sufficient electricity will not be transmitted. Step-up transformer is used to increase the voltage and decrease the current.
2. Transmission (the electricity flows to the transmission lines of the national network and is distributed from there). Transmission lines (power lines) send electricity through thick aluminium and copper cables into the national network.
3. Distribution (electricity is being distributed to the sub-stations of different towns and regions, and the voltage lowered and the current increased. When the electricity reaches a power station to e locally distributed, there is a step-down transformer that lowers the voltage (11kV in large factories and 400 to 240 V in shops and in our houses), and the current increases. Low voltage electricity is sent through smaller power line systems to houses, schools and businesses.
4.Consumers(where the electricity is being transferred to usable enrgy outputs).
Power surge
If the current in the network is increased, power surges occur. A power surge then also creates a rise in the electrical current that flows to the wall plugs in your house. Sharp rise occurs over a very short period, normally less than a thousandth of a second, but it may cause serious damage to your house and appliances. Lighting strikes close to transmission lines may cause a power surge. Power surges include faulty wiring of household appliances and devices, such as lifts, air conditioners and geysers. Circuit breakers and shorts in the wiring system may also lead to a power surge.
Network overload
When the demand for electricity exceeds the available supply, we say the network is 'overloaded'. This demand for electricity therefore causes a network overload, which means that sometimes there is not sufficient electricity available in the network. It happens mainly during winter when people put their lights on earlier and use electric heaters. Network overloading results in power failures and load (power) shedding comes into operation, which means that the electricity supply to certain areas is cut off during peak periods. A message is shown on television every night asking consumers to switch off nonessential appliances and devices.