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Fact Sheet 9HYDRO POWERSome of the heat from solar radiation converts water to water vapour, or steam, that rises in the atmosphere to form clouds. When this water precipitates as rain or snow in upland areas, the waters stored in rivers above sea level are like a storage of potential energy. This potential energy changes to kinetic energy when the stored water is channelled to turn the blades of a turbine to generate electricity. Electric power generated in this way is called hydro power. For centuries water wheels have been used to convert the kinetic energy of moving water into mechanical energy, used in flour mills and other machinery. The water was usually taken from a fast-flowing river. Sometimes dams were constructed to store water, or control the flow rate to the mill. The two basic kinds of water wheel are the undershot wheel and the overshot wheel. The overshot wheel produces much more power. The first hydroelectric power stations were small and were placed at waterfalls near towns because transmitting electrical energy over long distances was not economical. The best places to generate hydroelectricity are in mountainous regions where few people live. Today, electric power can be transmitted inexpensively over long distances to make hydro power inexpensive. Transmission over long distances is carried out by means of transmission lines that can transmit large quantities of electricity cheaply and efficiently. Unlike coal-fired power stations, hydroelectric power stations can begin generating electricity very quickly. They can respond to sudden increases in demand for electricity. Regular time for high demand for electricity is called ‘peak demand’, for example when people wake up and cook breakfast; when businesses and factories start work; and when people cook their evening meal. Hydro stations need only small staffs to operate and maintain them, and no fuel is needed. A hydroelectric power plant uses a renewable source of energy that does not pollute the environment. However, the construction of dams to enable hydroelectric generation may cause significant environmental damage. Also, water used to drive the power plant could have other uses at other times, for example, for irrigation or town water supply. The amount of electrical energy that can be generated depends on the height that the water falls and the quantity of water flowing. So, hydroelectric power stations are placed where they can use the greatest fall of a large quantity of water, or near the base of a dam. Water can be stored in the dam above the power station for use when it is required. Some dams create large reservoirs to store water, but others divert water down to the power station through pipelines. All water turbines used for electricity generation work in a similar way. Blades are attached to a shaft that turns a generator. Water moving past the blades turns the shaft and the generator. The water that has given up its energy to the turbine is discharged through the ‘tail race’ of the power station. A hydroelectric generating unit is simpler in operation than a coal-fired power station because it does not need a boiler, or to burn fuel. The energy available from water depends on both the quantity of water available and its pressure at the turbine. The pressure is referred to as the ‘head’, and is measured as the height of the surface of the water above the turbine. The greater the height (or head) of the water above the turbine, the more energy each cubic metre of water can impart to spin a turbine – which, in turn, drives a generator. The greater the quantity of water, the greater the number and size of turbines that may be spun, and the greater the power output of the generators. Water for a hydroelectric power turbine can come from a specially constructed dam set high up in a mountain range, or from a river close to ground level. As water sources vary, water turbines have been designed to suit different locations. The design used depends on the head and quantity of water available at that site. The three main types are Pelton wheels, Francis turbines and Kaplan or propeller-type turbines. Each can be mounted vertically or horizontally. The Pelton wheel is used where a small flow of water with a large head is available. It resembles the waterwheels used at water mills in the past. The Pelton wheel has small buckets around its rim. Water from the dam is fed through nozzles at very high speed, hitting the buckets and pushing the wheel around. The Francis turbine is used where a large flow and a high or medium head of water is involved. It is also similar to a waterwheel in that it looks like a spinning wheel with fixed blades between two rims. This wheel is called a runner. A circle of guide vanes surrounds the runner and controls how much water drives the turbine. Water is fed to the runner from all sides by these vanes, causing it to spin. The Kaplan turbine can be mounted at almost any angle, and is designed to operate where a small head of water is involved. It resembles ships’ propellers. The angle of the propeller blade to the flow of the water and the pitch of the blades can be altered to suit the water flow. This alteration is called variable pitch and it allows the machine to operate efficiently with different heads and different water levels in the storage dam. The installed hydro power capacity in Australia is 7,600MW. The largest hydroelectric power scheme in Australia is the Snowy Mountains Scheme that generates about 50 per cent of Australia’s hydroelectric power. It has seven power stations, (two underground), 145 km of tunnels and 16 large dams. The largest dam, Lake Eucumbene, holds nine times the water volume of Sydney Harbour. The second largest hydro power scheme, run by the Tasmanian Hydroelectric Corporation, generates about 30 per cent. Some people are opposed to any more large hydroelectric schemes being developed in Australia because of the high cost, the loss of valley land which could be farmed, the loss of natural scenery and the effect on the number and spread of native species (biodiversity). They support other forms of renewable energy, including small scale hydro power stations. Some new hydroelectric projects are the pumped storage type, for example the Wivenhoe Dam in Queensland. This type of power station stores the water that has passed through it in a dam below the station. During off-peak times this water is pumped back to a storage dam above the power station, using power from fossil fuel power stations. In some countries nuclear power is used for off-peak pumping. The use of pumped storage increases the peak power generation capacity of the power station. This increase is not renewable energy because the pumps use non-renewable energy to raise the water. However, pumped storage allows excess electrical energy to be stored as the potential energy of water raised to the height of the storage dam. Small scale hydro power systems are usually not connected to the electricity grid. The smallest systems, called micro-systems, may operate by diverting part of a river flow through a pipe (or penstock) and a turbine, which drives a generator to produce electricity. The water then flows back into the river, allowing the river flow to continue. No storage dams are used so seasonal river flow patterns downstream are not affected and there is no flooding of valleys upstream. However, there may not be enough water to operate the power station in the dry season and excess power generated may be wasted in the wet season. Micro-hydro systems are suitable as remote area power supplies for rural and isolated communities, as an economical alternative to extending the electricity grid. The systems provide a source of cheap, independent and continuous power, without degrading the environment. One micro-system in Tasmania has an effective head of 142 m and a flow rate of 46 litres/second. The 52kW generator provides power for refrigeration, lighting, instant heating, hot water and small power requirements. However, suitable locations for such micro-systems are rare in Australia. Another kind of system using stream flow is the hydraulic ram. It uses the downward movement of water from a height to pump up a smaller volume of water to a greater height. Some hydroelectric sources using turbine technology in Queensland are:
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