The site

Coral Bay is a small, remote community on the northwest coast of Western Australia not connected to the main electricity network. It now has a new wind-diesel system comprising of three wind turbines and a low load diesel (LLD®) power station operated by Verve Energy. The new power station replaces three previous privately owned and operated diesel power stations. The new power station and the wind turbines are located approximately 1 km south of the Coral Bay settlement.

Technology

The Coral Bay Power System is a high-penetration wind-diesel system that combines three Vergnet 275 kilowatt (kW) wind turbines with seven 320 kW LLD.

The three wind turbines are horizontal axis, two-blade, pitch controlled, two speed induction generator turbines, which can be lowered in case of cyclones. Because Vergnet turbines cannot be accurately power limited, they are combined with a 500 kW short-term energy storage system provided through a flywheel – PowerStore by Powercorp – to smooth, control and maximise the output from the turbines. The flywheel rapidly absorbs power surges from the wind turbines or supplies power when the wind suddenly drops off. This grid stabilisation function is achieved through Australian designed and built computer control technology installed at the power station.

Powercorp’s LLD technology is based on standard diesel generator technology but is altered to run for sustained periods at loads as low as 5 per cent. Typically, diesel generators used for stationary power generation are not taken below approximately 40 per cent loading for long periods because they would suffer damage. The low loading characteristic is achieved through changes to the operational characteristics of the machine and additional equipment. In the wind diesel system, the LLD technology allows the wind turbines to supply up to the full system load at any time, thereby achieving significantly better fuel savings compared with a standard wind-diesel system. LLD generators online also provide spinning reserve coverage and voltage and frequency regulation, resulting in a reliable and quality power supply.

Operational tests have demonstrated that the electrical characteristics of the wind turbines in combination with the PowerStore allow a load to be supplied even if there are no diesel generators on-line. Although the system is not currently operated in this way, Verve Energy and Powercorp are refining the control system to exploit this characteristic in future.

The merits of the technology implemented at Coral Bay were recognised when Verve Energy won a 2006 WA Engineering Excellence Award (Environment Category).

Energy purchase and supply

The wind turbines are expected to produce approximately up to 2.5 gigawatt hours (GWh) of electricity per annum. Unlike a grid connected wind farm, where wind availability determines the production, the production from the wind turbines at Coral Bay depends on wind availability and load conditions.

Verve Energy purchases diesel fuel and sells the wind and diesel-fuelled electricity to Horizon Power under a long-term power purchase agreement. The wind farm is registered as an accredited generator under the Mandatory Renewable Energy Target and the Green Power Scheme. The power station is connected to the Coral Bay 22 kilovolt (kV) distribution system, owned by Horizon Power.

Environmental Impact

The wind turbines are expected to supply more than 40 per cent of the town’s annual electricity requirement. Over the 20 year life of the plant, this will save 500,000 litres of diesel fuel per year and avoids the production of 1,300 tonnes of greenhouse gas per annum (the equivalent of 302 cars off the road).

Success of the project to date

The Coral Bay system has proven to be a highly reliable, high penetration wind diesel system.

Coral Bay Power Station was fully commissioned on 17 August 2007 after passing Horizon Power’s network fault-ride-through tests. The tests confirmed that the power station would be able to withstand three-phase and phase-to-earth faults for the specified duration.

The overall wind penetration for the period August to December 2007 was 64 per cent. The three wind turbines generated 618 megawatt hours (MWh) of energy and saved approximately 140,000 litres of diesel fuel.

An issue with high penetration wind systems is the control of wind turbine output in response to load, whilst meeting power quality requirements. This is achieved through a combination of dynamically adjusting the wind farm power setpoint – pitch control on the wind turbines – and absorbing or exporting power from the flywheel energy storage. There have been some initial issues on the wind turbine pitch systems, but these issues are being addressed and will be monitored. Other opportunities to install this wind-diesel technology are being pursued.

Funding arrangements and acknowledgements

The project received a grant from the Australian Government through the Renewable Remote Power Generation Program. The Western Australian Sustainable Energy Development Office implements the Program. Separately, the Renewable Energy Development Initiative also contributed to aspects of the installation of new wind turbine hardware and software to improve wind energy penetration into the electrical system.