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The movement of water can be used to generate electricity. Water is the most commonly used source of renewable energy. There are a number of technologies which harness this energy.
The power of the rise and fall of the ocean, or tidal power, can be harnessed to generate electricity. A tidal power station is part of a dam or barrage, built across a narrow bay or river mouth. As the tide flows in and out, it creates uneven water levels on opposite sides of the barrage. Water flows from the high side to the low side through turbines to generate electricity.
Waves and water motion below the ocean’s surface can be used drive generators to produce electricity. A great variety of ways to capture the energy from waves have been proposed and a number are in the production or near-production stage.
Ocean thermal energy extracts energy from the temperature difference between the ocean’s warm surface waters and deeper colder layers of the ocean. Thermal energy conversion plants use the water to make steam and then pass the steam through a turbine generator to make electricity. This has been a challenging technology and we are yet to see a commercial deployment.
Hydroelectricity uses the kinetic energy of flowing water to drive a turbine to produce electricity. The amount of electricity generated depends on the height that the water falls and the quantity of water flowing.
Big hydroelectric power stations need dams to store the water. These dams are often built for irrigation or drinking water, and the power station is included in the project to ensure maximum value is extracted from the water.
Hydroelectricity can provide both base load and peak load electricity; and some hydro generators can start up and supply maximum power within 90 seconds.
Smaller hydro power stations harness flowing river water.
Pumped storage hydroelectricity
Some hydroelectric schemes are designed so that the turbines can run backwards, becoming pumps. During off-peak times when electricity is cheaper, water is pumped from a low reservoir to a high reservoir. When peak electricity demand occurs, the flow of water is reversed, flowing from the upper to the lower storage and driving the turbine generator to generate electricity.
Hydro produces most of Australia’s renewable energy. There are more than 100 hydroelectricity stations totalling over 8,000 megawatts of capacity which produced around 5.5 per cent of the nation's total electricity output in a year. The Snowy Mountains hydroelectric power scheme in NSW is the largest hydro electric system in Australia; it has seven power stations, 16 dams and a generating capacity of nearly 3,800 MW.
The world’s leading hydroelectricity producers are China, Canada, Brazil, USA, Russia, Norway, India, Venezuela and Japan.
Geothermal energy is extracted from the hot rocks deep below the Earth's surface. Wells are drilled down to the rocks and water is pumped down where it is heated to a temperature of up to 300°C before it returns to the surface via another well as steam. This steam is used to drive a turbine and produce electricity. The steam is captured in condensers and recycled.
It has zero greenhouse gas emissions in use. One megawatt hour of geothermal-derived electricity offsets about one tonne of CO2.
Geothermal generators could operate 24 hours a day, providing a critical base-load power supply.
Australia has vast geothermal assets. Although probably the least known renewable option for Australia, there are some major projects underway. More than 50 companies are currently working on geothermal exploration in Australia and several are expected to have geothermal generators working within the next 2-5 years.
Worldwide, 24 countries are currently generating geothermal energy including USA, Iceland, Italy, New Zealand and Japan, most from hot springs associated with volcanic activity.