How electricity is generated
Over the centuries we have harnessed the energy of the wind (for sailing ships), and falling water (flour mills) and used wood to heat water to generate steam (for trains and cotton mills).
Power in the form of electricity today is mostly sourced from the chemical energy of fuel - whether it's natural gas, coal or oil. This chemical energy is first converted to heat energy, then to mechanical energy and finally to electrical energy. The intermediate steps are carried out by means of boilers, turbines and generators.
There are several different forms of electrical generation - hydroelectric, nuclear, wind and solar. Each has unique aspects, but they all operate on the similar principle of converting some form of fuel into heat energy, then mechanical energy and finally electrical energy.
Fuel is burned in a boiler and the heat is used to produce steam under pressure. The steam is collected in a cylinder at the top of the boiler. From the boiler steam is led through heat-insulated pipes to the steam turbine.
A turbine is a machine powered by gas or steam. A steam turbine contains a horizontal shaft fitted with a number of wheels, each carrying many blades. The steam passes through these blades, making the shaft rotate at high speed, just as the wind turns the blades of a windmill. When the steam has given up its energy to the turbine shaft, it is condensed back into water in a 'condenser' and returned to the boiler to repeat the cycle. A gas turbine works much the same way, except hot air replaces the steam.
The turbine shaft turns the electromagnet of the generator, changing the mechanical energy from the turbine into electrical energy. This electric energy takes the form of Alternating Current (AC) and Direct Current (DC).
A powerful electromagnet (rotor) is mounted on a shaft which rotates inside a cylindrical iron shell (stator) containing slots through which the conductors are wound. The current flows momentarily in one direction through the conductors and then reverses. This is called 'Alternating Current' (AC).
The AC used throughout South Australia flows alternately in each direction 50 times each second. In technical terms this frequency of change of direction is measured in hertz (Hz).
A current which continuously flows in one direction is called a 'Direct Current' (DC).
Hydro Electric Power
The energy produced by the flow of water can be transformed into electricity by a hydroelectric power scheme. The Snowy Mountains hydroelectric scheme is the best known Australian example of hydroelectric generation.
Dams are used to create big reservoirs of water, either by raising the levels of natural lakes or rivers.
Tunnels, canals, channels and pipelines convey the water from the reservoir to the turbines in the power stations. The power stations are situated where they can take advantage of the greatest fall of water, such as at the bottom of a deep and steep-sided valley or gorge.
The water flows through a turbine, which drives an electric generator.
Nuclear power unlocks the enormous energy contained in every atom. The fuel used in nuclear reactors is an element called Uranium. The Uranium produces huge quantities of heat in a process called nuclear fission, which takes place in the nuclear reactor. This heat travels through a heat exchanger, which serves as a boiler for rapidly heating up water and creating steam. This steam is used to power an ordinary steam turbine and generator to produce electrical energy.
Wind power has been grinding grain and lifting water for centuries. Now it is also used to generate electricity by using large wind-powered turbines. A typical 300kw turbine has a large (30 metre diameter), three-bladed rotor rotating. Turbines generally are grouped together in wind farms.
While energy from the sun is free, the cost of devices to convert it has been high, and the conversion from light to electricity has been relatively inefficient, though it is improving. Some methods include:
Solar Cells (sometimes called photovoltaic cells), which are semi-conductors activated by light. Their power is determined by the intensity of light falling onto the cell. Many cells are joined together to provide sufficient electricity to do useful work. Photovoltaic panels are seen on remote telephones, the roofs of solar cars and on the roofs of houses.
Heliostats or sun-tracking mirrors produce high temperatures that can be used to power traditional steam turbine generators.
Solar Ponds of salt water that use special low-temperature generators.
Solar Collectors that capture heat from the sun and use it to directly heat water for homes.