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Pushing the limits of wind diesel penetration

Several novel features of a new wind-diesel system being developed in Western Australia could bring the technology to a point where the good economics of using wind plant to save diesel fuel in remote power systems are no longer in doubt.

The penetration of wind systems in remote diesel based mini-grids will be substantially increased with the installation this month of a 230 kW Enercon E-30 turbine near the town of Denham in the state of Western Australia (WA). Up to 80% of Denham's electricity could be supplied by wind, according to the project's co-ordinator, Paul Ebert of utility Western Power. Denham is one of the state's 23 diesel based mini-grids and costs A$0.25-0.35/kWh to run, says Ebert. But under WA's uniform tariff structure, this means a considerable running loss as the town's 800 consumers are only charged A$0.10-0.15/kWh. The wind turbine is intended to help straighten out the poor economics.

With three years of monitoring data showing the site had an average wind speed above 8 m/s at a height of 50 metres, the economics for the turbine stacked up reasonably well, says Ebert, although he declines to be specific about the cost of the wind power. He notes, however, that the A$950,000 project is a purely commercial operation that would save about 175,000 litres of diesel fuel each year and supply, on average, 20% of the town's electricity.

Western Power hopes to attain penetrations of wind as high as 80% based on its substantial experience with the Esperance and Ten Mile Lagoon wind farms on the state's far southern coast -- both of which operate in a diesel based mini-grid. The wind farms use constant speed induction generators which limit the penetration of wind on the grid to about 40%, says Ebert. The Denham project, however, will use a variable speed turbine that can better adjust the output through such techniques as blade pitching to coexist with the town's four diesel generators.

The E-30 turbine also has an inverter connected via a radio link to the Denham power station. The inverter is able to control the power factor, which is very important in small systems, according to Ebert. Another advantage is that the E-30 does not need to draw reactive power from the grid in order to operate, unlike machines with induction generators which need capacitors to limit the need for reactive power. "Using the actual turbine to control the power factor is something we haven't tried but its in the back of our minds," he adds.

Ebert says the system at Denham is really a wind turbine plus control system which will completely automate the power station. Initially, the control system algorithm will be simply to start and stop generators to meet load and control the input from the wind turbine. If the loading on the diesels gets below a certain limit, then the control system will tell the wind turbine to back off.

A more advanced control system, however, will be under development with the assistance of the Australian Centre for Renewable Energy (ACRE). The research team will be trying to optimise the contribution from wind power -- and hence the economics of the system. The control system is also being developed by Powercorp, a private company specialising in renewable-diesel generation with expertise in the integration of wind into diesel systems.

As Denham is in a cyclone area, one of the critical factors was a tower design that could withstand a one-in-1000 year wind gust of 64 m/s over three seconds. The design team had to evaluate the economics of greater output at a higher height versus survivability in severe weather such as cyclones.

Ebert believes the project's many specialities make it unique and the largest of its type in the world in mini-grids the size of Denham's grid. "The wind-diesel system is hard to crack and we are really pushing it with this one," he says. Western Power, says Ebert, is eventually planning to market its expertise internationally.

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