The NGA electricity factor for a Western Australian site depends on which grid supplies it. Unlike most states, Western Australia has more than one grid, and the NGA Factors publish a separate location-based factor for each.
Key points
- NGA Factors list SWIS and NWIS separately
- NGER defines the SWIS as Western Australia's main grid
- Main-grid electricity uses Method A1, other networks Method A2 with the supplier's factor
- On-site generation is Scope 1 for the operator of the power station
- Map each site to its real supply before applying a factor
The Western Australian rows
The NGA Factors electricity table includes rows for the South West Interconnected System (SWIS) and the North Western Interconnected System (NWIS). Each has its own Scope 2 and Scope 3 factor, reflecting a different generation mix. The table also lists the Darwin-Katherine Interconnected System in the Northern Territory and a national average.
How NGER treats Western Australia
For NGER reporting, section 7.2 of the NGER (Measurement) Determination 2008 defines the main electricity grid for Western Australia as the South West Interconnected System. Electricity drawn from the main grid is estimated with Method A1. For other networks, section 7.3 sets Method A2, which uses the emission factor provided by the electricity supplier or, if that is not available, the Northern Territory factor in Schedule 1. NGER reports must use the Determination’s factors for the reporting year, not the NGA Factors.
Off-grid and on-site generation
Many mining operations generate their own power from gas or diesel. That generation is Scope 1 for the facility that operates the power station, estimated from the fuel it burns. A site that buys electricity from a third party’s power station reports Scope 2 for it, and should not apply the SWIS or NWIS factor unless it is actually connected to that grid.
Practical checks
- Map every site to its actual grid or supply arrangement before applying any factor.
- Use the NGA row for voluntary and AASB S2 estimates, and the Determination for NGER.
- Record the factor source and edition against each site and year.
Why it matters
Applying the SWIS factor to a site on the NWIS, or a grid factor to a site on its own power station, misstates Scope 2 in a way an auditor will pick up quickly. For portfolios spread across Western Australia, the grid mapping is one of the first things to verify.
References & sources
Primary regulatory documents and authoritative references underpinning this answer.