Hydroelectric

A hydroelectric power plant generates electricity from falling water. As water falls, it gains kinetic energy (energy of movement). This kinetic energy is converted to electrical energy in a hydroelectric plant.

The falling water pushes against turbine blades causing them to spin. As the turbine spins it turns a generator that produces electricity.



Hydroelectric power in Australia

The most famous source of hydroelectric power is the Snowy Mountains Hydro-Electric Scheme. Built over a 25 year period from 1949 to 1974, it diverts water for irrigation west to the Murray and Murrumbidgee river systems and produces hydro electricity through infrastructure which includes sixteen major dams, seven power stations, 145km of interconnected tunnels and 80km of aqueducts.

Each year the Snowy Scheme produces on average 4500 gigawatt hours of energy, and is the largest contributor to renewable energy in the National Electricity Market (Nemco). 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. 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:

• Barron Gorge power station near Cairns
• Kareeya power station at Tully Falls in Cairns region
• Somerset Dam power station on the Brisbane River
• Wivenhoe Dam power station on the Brisbane River 30 km north of Ipswich

Barron Gorge Hydro is located in the wet tropics world heritage area on the Barron River, 20 kilometres north of Cairns. The 60 megawatt (MW) station, which is now remotely operated, was first commissioned in September 1963.



1. Kuranda Weir

Barron Gorge Hydro owns Kuranda Weir, which has a capacity of 1500 million litres (ML), is situated on the river above the Barron Falls. From here, the water passes through a reinforced concrete intake structure that has four channels. Headrace

From the intake structure the water flows along the 2.9 metre diameter, concrete lined, horizontal tunnel - or headrace - for a distance of about 1.6 kilometres. In the headrace there are three slit or sand traps with flushing valves. These prevent the water from carrying debris, which could damage the turbine, into the power station.

2. Headrace surge tank

The headrace surge tank is a large cylindrical chamber with its base opening into the horizontal tunnel and its top connected by a ventilation shaft to the surface. It minimises the effects of water hammer (pressure surges), which could occur with the closing of the butterfly valve or abrupt changes in flow through the water turbines.

3. Butterfly valve

An underground valve chamber is located at the end of the horizontal tunnel. In the valve chamber, between the horizontal and inclined pressure tunnel, there is a butterfly valve 2.7 metres in diameter. The valve is designed to close automatically if there is a failure in the inclined tunnel or an equipment malfunction in the power station.

4. Inclined tunnel

The water descends 286 metres though a steel-lined tunnel, (inclined at 39o to the horizontal) to pass through the turbines located in the underground machine hall. At the lower end of the inclined tunnel there is a y-piece that divides the flow into two distributing pipes, which lead to the 1.2 metre diameter main inlet valve of a turbine.

5. Turbogenerators

Two 30 MW generator sets are installed at the station. Each consists of a turbine and generator. Water flowing through the turbine turns the generator shaft that is attached to an electrical rotor. This spins inside the stator windings to produce electricity at 11,000 volts. The rotor spins at 600 revolutions per minute. At full capacity the two turbines each require a flow of 25 000 litres (25 cubic metres) of water per second. When both turbines are operating, enough water flows through them to fill a backyard swimming pool every second.

Learn more about generators

6. Tailrace

Both water turbines discharge into a flooded tailrace that returns the water to the Barron River downstream of the falls.

7. Transformers

The electricity is stepped up to 132,000 volts by transformers located in an outdoor substation. From there it is linked into the state-wide electricity grid

Advantages and disadvantages of hydroelectricity

Advantages:

• Hydroelectricity is a renewable energy resource.
• Hydroelectricity is one of the most efficient energy sources because most of the kinetic energy of the water is converted to electrical energy.
• No greenhouse gases or other dangerous gases are produced so there is no damage of this kind to the environment.
• No fuel is needed, therefore the price of hydroelectricity will not change if the price of fuel increases.
• Hydroelectric plants are generally less expensive to run than other generating plants.
• Electricity can be generated almost straight away compared to coal-fired power stations which take several hours to start.
• Electricity can be stored for later use by using excess production to pump water to a higher altitude facility until it is released again to generate electricity.
• Hydroelectric plants only need a turbine and generator where as coal-fired stations need a furnace, boiler, condenser, cooling towers etc.

Disadvantages:

• The construction of hydroelectric plants is expensive.
• Hydroelectric plants are site specific. In other words you can't build them just anywhere.
• Hydroelectric plants can have a detrimental effect on the river flow and water supply. The construction of hydroelectric plants usually means that areas of land will be flooded. This means that habitats for animals and plants are lost. People living in the area may also lose their land.

Hydroelectric power stations and the environment

Hydroelectric power plants are the most efficient electricity generators. They produce no greenhouse gases and are an ideal way to store electricity. However, building hydroelectric plants can have serious consequences for both the environment and people. Damming a watercourse normally results in the flooding of the surrounding area with the consequent loss of flora and fauna. People living in the area can be displaced for the same reason.

Even though a hydroelectric plant produces no greenhouse gases they can have an impact on the greenhouse effect. The carbon on the flooded land has to be considered. It has been proposed that as the size of the lake associated with the flooding due to a hydroelectric scheme increases, so does the amount of CO2 equivalent emissions. The amount of the carbon (contained in biological material) that is converted to methane increases with the size of the lake. However, this decreases as the output of the hydro-scheme and its lifetime increases. Over a period of a hundred years, methane has a warming effect twenty-one times that of CO2. More research into this aspect of hydroelectric plants is required.