Wivenhoe Mini Hydro

Grid-connected, distributed generation, renewable
Location: Wivenhoe, NSW

The site

The Wivenhoe Dam consists of an earth and rock embankment 2.3 kilometres long and 59 metres high, with a concrete spillway section on which fi ve steel gates are installed. These gates,12 metres wide and 16.6 metres high,are among the largest of their type in the world.During a fl ood situation,the dam is designed to hold back 1.45 million megalitres (ML)as well as its normal storage capacity of 1.16 million ML. This facility is evidence of the value of Wivenhoe to the Brisbane and Ipswich areas in fl ood control.

Technology

The Wivenhoe Mini Hydro Project harnesses the energy of water released through the spillway of Wivenhoe Dam.This water fl ows through the existing outlet pipe (which is 3.6 m in diameter), before passing through a butterfl y-type turbine inlet valve into the 4.5 MW Francis turbine designed by GE Energy Australia.

The turbine is a horizontal shaft "Francis" type, meaning that the runner (the part that converts the energy of the water into rotational power)has fi xed-pitch blades attached between two rims. A Francis turbine is used in situations where the water pressure upstream of the turbine is relatively low compared to the flow rate. In some hydroelectric facilities, flywheels or surge tanks are used to minimise the effects of pressure surges. At Wivenhoe Mini Hydro, surge protection devices are not necessary because the "penstock" (the area into which water is diverted before passing through the turbine) is relatively short, and has a large diameter.

The flow rate through the turbine will generally be between four and 15 cubic metres of water per second.The shaft will rotate at a speed of 300 revolutions per minute.

Energy purchase and supply

The plant is expected to produce 22.5 GWh of electricity per annum (enough for about 3500 homes). The electricity produced at the generator is stepped up to 33,000 volts via an on-site transformer and fed into the State-wide electricity grid.The plant is connected to the Energex 33kV distribution system.

Power generated from the project is sold to Energy Australia under a long-term agreement. The generator operates 24 hours,7 days, at an output determined by the required release rate of water from the dam. The generator is registered as a non-scheduled market generator.

Environmental impact

The project is expected to save more than 20,000 tonnes per annum of greenhouse gas emissions. The hydro plant uses existing water release as a part of the Brisbane water supply scheme and therefore has none of the impacts associated with dedicated hydro power generation schemes.