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Hydro Tasmania has recently completed construction and is currently commissioning a substantial upgrade to the power station control system. The new control system employs a large resistive load which can be varied rapidly in order to absorb excess wind generation rather than spill it through shutting down or throttling back wind turbines. Instead of reducing output, the wind turbines are be allowed to produce as much power as possible, with the excess generation to be absorbed by the resistor. As the resistor can be adjusted rapidly, this will effectively convert spilled wind into spinning reserve that can be used to supplement diesel generation. Maintaining the power balance between generation and demand in this way will allow the resistor to maintain system frequency.

Shifting system reserve requirements away from the diesels enables the control system to reduce diesel output to minimum levels, reducing fuel use. Whilst this can occur only during periods of wind spill, a further increase in renewable energy generation will increase the amount of time that the system experiences spill, and thus increase the time that diesels can be run at minimum loading. This will in turn reduce the amount of overall energy contribution from the diesel generators.

The resistor frequency control will enable the running diesel generators to remain on minimum loading whenever the island’s load is less than the combined solar and wind output. Modelling of the King Island energy demand compared with historic wind data and expected solar output indicates that this will occur for about half of the year – resulting in significant diesel fuel and thus GHG emission savings.

RAPS has contributed to this project by working closely with Hydro Tasmania to design, construct and commission the containerised switch gear and control modules used in the project.