The Quest of the Ring: Will the Sydney Ring of Power unlock commercial viability of renewables?

With the development of Renewable Energy Zones (REZs), the need for transmission augmentation arises to unlock the transfer of energy from Renewable Energy Zones to major load centres. This may subsequently increase the commercial viability of renewable generators within the Renewable Energy Zones, for example, by reducing plants’ technical curtailments due to network constraints and improving Marginal Loss Factors (MLF). In this Chart of the week, we investigate the impact of transmission augmentations on the loss factors in surrounding areas using our in-house Power System Analysis model.

In this case study, we focus on the Sydney Ring transmission upgrade to reinforce supply to Sydney, Newcastle, and Wollongong as the major load centres accounting for about three-quarters of the NSW demand. With the future retirement of the power stations at Vales Point and Eraring, the load is expected to be met by the generation outside the load area. Sydney Ring is proposed to increase the transmission capacity from regional NSW to the major load centres, which is expected to positively impact the MLF of the Variable Renewable Energy (VRE) generators (i.e., solar and wind) within the surrounding Renewable Energy Zones. In this study, we consider the following 500 kV network development of the Sydney Ring:[1]

  • The Hunter Transmission Project (i.e., Sydney Northern Ring), a double circuit 500kV line between the Upper Hunter and Central Coast areas
  • A double circuit 500 kV line between Bannaby and Sydney (i.e., Sydney Southern Ring)

The analysis of the loss factors is carried out for the following Renewable Energy Zones:

  • Central-West Orana Renewable Energy Zone, which is centred around Dubbo and Dunedoo;
  • New England Renewable Energy Zone, which is centred around Armidale; and
  • Hunter-Central Coast Renewable Energy Zone, which incorporates Newcastle and the Hunter and Central Coast regions.

For each location, the loss factors, i.e., the incremental increase in total losses that occurred between the location and Regional Reference Node (RRN) due to incremental injection of electricity into the power system, are calculated for each half-hour interval for the full year using our in-house Power System Analysis Model. The changes in the loss factors due to Sydney Ring are shown in the box and whisker plot in Figure 1.

A positive number of the change in the loss factor represents an improvement in the loss factor, i.e., decreases in losses, and vice versa. After introducing Sydney Ring, general improvement in the loss factors is observed across all three Renewable Energy Zones. Median loss factor increases of around 1pp (percentage point) are observed in Central-West Orana Renewable Energy Zone and New England Renewable Energy Zone, while median increases of around 0.5pp are shown for the Hunter-Central Coast Renewable Energy Zone. The Sydney Northern Ring, i.e., the Hunter Transmission Project, has a major impact on the loss factors in the New England Renewable Energy Zone and Hunter-Central Coast Renewable Energy Zone, both located north of Sydney. The Central-West Orana Renewable Energy Zone, which is located west of Sydney, receives benefits from both Sydney Northern Ring and Sydney Southern Ring.

It is expected that the MLF, which is the annual generation-weighted loss factor, for the VRE within these Renewable Energy Zones, may be lifted to some degree. Since MLF can have a significant impact on the profitability of the generators, this improvement may boost the commercial viability of the VRE within the Renewable Energy Zones. Furthermore, transmission augmentations may also reduce the technical curtailment of the VRE in the affected locations by relaxing certain network constraints, thus further unlocking their commercial viability.

Our in-house Power System Analysis and Market Modelling provides MLF forecasting based on sound engineering techniques and assumptions based on our vast experience, comprehensive research and independent view of relevant areas. For more information on Power System Analysis or other modelling products, please contact

[1] “Transmission Annual Planning Report 2022”, TransGrid,

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