Tidal Energy
The generation of electricity from tides is very similar to hydroelectric generation, except that water is able to flow in both directions and this must be taken into account in the development of the generators. The simplest generating system for tidal plants, known as an ebb generating system, involves a dam, known as a barrage across an estuary. Sluice gates on the barrage allow the tidal basin to fill on the incoming high tides and to exit through the turbine system on the outgoing tide (known as the ebb tide). Alternatively, flood-generating systems, which generate power from the incoming tide are possible, but are less favoured than ebb generating systems.
Whilst tidal power generation can offer some advantages, including improved transportation due to the development of traffic or rail bridges across estuaries and reduced greenhouse gas emissions by utilising tidal power in place of fossil fuels, there are also some significant environmental disadvantages which make tidal power, particularly barrage systems less attractive than other forms of renewable energy.
Potentially the largest disadvantage of tidal power is the effect a tidal station has on the plants and animals which live within the estuary. As very few tidal barrages have been built, very little is understood about the full impact of tidal power systems on the local environment. What has been concluded is that the effect due to a tidal barrage is highly dependent upon the local geography and marine ecosystem.
Tidal Power in Australia
Tidal power has been proposed in the Kimberley region of Western Australia since the 1960s, when a study of the Derby region identified a tidal resource of over 3000 MW. In recent years a proposal to construct a 50 MW tidal plant in the Derby region has been developed by Derby Hydro Power. This project has received a $1 million grant through the Australian Greenhouse Office's Renewable Energy Commercialisation Program to further develop the project. Of more recent interest is Western Australia's tidal energy potential that has been actively promoted near the town of Derby, (situated at the head of two adjacent inlets off the King Sound). The inlets would be connected via an artificial channel. By damming each inlet, differences in water levels in each basin could be controlled which would enable flow via the connecting channel. Power take-off would be achieved from a bank of turbines housed in a structure built in this channel. The Derby tidal power project had been assessed by a consortium led by KPMG. The project's promoters submitted this scheme to an independent ministerial advisory committee. The committee compared the scheme with an alternative gas-fired power plant and decided in July 2000 not to proceed with the Derby tidal project. The committee compared the two bids on financial and technical grounds as well as community benefits and environmental impacts (World Energy Council, 2001).
