The National Energy Market (NEM) is run by Australian Energy Market Operator (AEMO). Western Australia and Northern Territory are not included and the ACT is considered part of NSW.
The grid supplies the power to satisfy the demand of consumers. In a grid the supply must always equal demand. If the demand increases suddenly, the grid frequency will reduce slightly causing the demand to be slightly lowered and indicating that the online generators should increase power to restore the frequency.
Variation of Demand
The demand changes throughout the day and through the seasons.
The generators that are actually used depends on the wind and prices amongst other factor. Here is the breakup by fuel class on a very windy day and for a calm day.
Generator Classes and Types
The generators that use the same fuel may differ in technology.
Interconnectors between states
The State grids export and import power via Interconnectors. This site treats the forward and reverse directions as separate Interconnections. The interconnectors are not of unlimited capacity so the market may sometimes be fragmented and this may contribute to differences in price between states.
National Energy Market
The grid is managed as a market with companies bidding their generators and prices fluctuating. Occasionally the prices are quite stable and uniform across the whole grid, usually otherwise. Prices are an area for further investigation.