Hydro Power

The most commonly used form of renewable energy is from water. It has been used as a source of power for more than two thousand years to turn waterwheels for the operation of simple machines.

Today, water is used to generate electricity. Electric power using the energy of moving water to drive generators is called hydroelectricity. Around 19% of the world electricity is generated this way and in 2005, accounted for more than 63% of the total electricity generated from renewable sources.

Hydroelectric energy is a term generally associated with large dams, which use the potential energy of the dammed water to drive turbines and generators in a hydroelectric power station to generate electricity.

The amount of electrical power generated is dependable on the height that the water falls and the quantity of water flowing. The greater the height, or ‘head’ of the water above the turbine, the more pressure the water can impart to spin the turbine, which drives the generator to produce the electrical power.

There are three types of hydroelectric turbines – Pelton wheels, Francis turbines and Kaplan propeller-type turbines. Each type can be mounted horizontally or vertically.

The Pelton wheel is used where a small flow of water with a large head is available. The wheel has small trough around its rim and is similar to the water wheels on the early water mills. The water shoots through nozzles at a high speed, hits the troughs and pushes the wheel around.

The Francis turbine is used where there is a large flow with a high or medium head of water. The wheel is called a runner and looks like a spinning wheel with fixed blades between the rims. Guide vanes around the runner control the amount of water driving the turbine.

The Kaplan turbine is used where there is a small head. It resembles a ship’s propeller. It can be mounted at any angle and the pitch of the blades can be altered to suit the available flow of the water.

Small Hydro-electric plants can feed electricity into the grid or supply electricity to isolated communities. There are also Mini-and Micro-hydro systems depending on the ratings of the power units. Some hydro systems use the kinetic energy from the flow of the water in rivers rather than building dams. These are called ‘run-of-the-river’ hydroelectric plants.

Pumped Storage hydroelectricity is utilised by some hydro plants for load balancing. Energy is stored in the form of water pumped from a lower reservoir. During times of peak load when there is a demand on electricity supplies, the stored water is released through turbines. In some cases, off-peak electricity is used for the pumping process and does make such plants consumers of energy. However, this is counteracted by the electricity the plant generates in periods of peak demand when electricity prices are highest.

Wivenhoe Power Station is an example of a pumped storage system. It is near Ipswich in South East Queensland and is situated between Splityard Creek Dam and Lake Wivenhoe, which is around 100 metres below the Splityard Creek Dam. Lake Wivenhoe is the body of water formed by Wivenhoe Dam and is the lower storage for the pumped-storage 500 MW hydroelectric power station. The power station uses Francis turbines and is owned and remotely-operated by Tarong Energy Corporation. Wivenhoe Dam is owned and managed by SEQ Water.

A second small hydro-electric generating plant at Wivenhoe Dam was commissioned in 2003. It was installed by Stanwell Corporation and is positioned beneath one of the dam’s five spillway slots. It operates 24 hours a day, every day of the week. The water passes through an inlet valve into a horizontal 4.5 MW Francis turbine.

The installed hydro capacity in Australia is 7,600 MW. The largest hydroelectric power scheme in Australia is the Snowy Mountains with seven power stations, 145 km of tunnels and 16 dams. The scheme generates around 50% of Australia’s hydroelectric power. The second largest scheme is operated by the Tasmanian Hydroelectric Corporation and generates around 30% of Australia’s hydroelectric power. The world’s largest single hydro-electric generating company is Hydro-Québec with a total installed capacity in 2005 of 31,512 MW. China produces the highest annual hydroelectric energy output at 486.7 TWh (Terra Watts per hour) from its installed capacity of 145.26 GW (Giga Watts). The next in order are Canada, Brazil, USA, Russia, Norway, India and Japan.

Renewables Global Status Report, 2006 Update published 2007, cited in Wikipedia ‘Hydroelctricity’.

Electricity Fact Sheet

Hydro Power