National Electricity Market

What the NEM is

The National Electricity Market is the wholesale electricity trading market and physical grid connecting the eastern and southern states. It came into operation in 1998 when the previously separate state-owned electricity systems were interconnected and a single dispatch mechanism was introduced.

“Market” here refers specifically to the spot market where generators bid to supply electricity and are dispatched by AEMO every five minutes at the current spot price. That price varies from near-zero (or even negative, when there’s excess renewable generation) to the market price cap of $17,500/MWh during acute supply shortages.

The physical grid spans approximately 5,000 km from Port Douglas in Queensland to Port Lincoln in South Australia - genuinely one of the longest AC interconnected systems on the planet.

Who’s in and who’s out

In the NEM:

• Queensland
• New South Wales (including ACT)
• Victoria
• South Australia
• Tasmania (connected via the Basslink HVDC undersea cable)

Not in the NEM:

• Western Australia (operated by AEMO separately as the South West Interconnected System, or SWIS)
• Northern Territory (managed by Power and Water Corporation - a separate much smaller system)

This matters for residents because some federal policies (like certain grid service schemes) apply only to NEM states. SA, VIC, and NSW have been at the forefront of rooftop solar and battery uptake partly because of NEM dynamics - high penetration solar creates volatile spot prices that make storage and export timing more valuable.

Why it matters for solar and battery owners

The NEM’s spot price volatility is what creates value in battery storage, flexible load, and VPP participation. Feed-in tariffs offered by retailers are partly hedges against wholesale price spikes - retailers buy your export at 5–10¢/kWh and on-sell it when the spot price might be $200–$500/MWh during a hot afternoon.

As renewable penetration has grown, the NEM has experienced more frequent price events at both extremes - very low or negative prices during sunny midday periods, very high prices during evening peaks. A home battery that discharges during the 5–8 pm peak and charges on cheap overnight or midday power captures part of that spread, whether or not the owner is explicitly trading the market.