Clarifying Notes about the Data

NEM Time

First things first - it is essential to understand that the NEM is operated on Australian Eastern Standard time (GMT + 10 hours) - which means no daylight savings. All data published by AEMO (and hence updated by NEM-Review) is stamped on this basis.

NEM Time Intervals

It is important that you are aware that, in real-time, the NEM has operated in two different intervals:

5-minute Intervals

AEMO dispatches the market on a five-minute basis.

In doing so, AEMO takes generator's bids to supply, and assumes what the demand in each region will be at the end of the current five-minute (dispatch) interval to determine:

  • what each generator should be producing at the end of the five minute interval, and hence
  • the dispatch price.

It should be understood that the dispatch data is data derived from the dispatch algorithm for the end of each dispatch interval. Specifically in terms of generator production, regional demand, and interconnector flow:

  • the data is an instantaneous value (i.e. MW rather than MWh); and
  • the data is not actual metered data, but rather derived from calculations.

As of October 1st 2021, the market is also settled on a 5-minute basis - where previously, settlement (and hence 'trading') occured on 30-minute intervals. The change has meant that what comes under the banner of 'trading data' will have different meanings depending on which point in time you are analysing. Please read the section below about 30-minute intervals.

30-minute Intervals

Up until October 1st 2021, even though the dispatch process was operated on a 5-minute basis, commercially the NEM operated on a half-hour (trading) basis.

The 30-minute trading interval data published by AEMO was just the time-weighted average of the 6 x five-minute dispatch data points within a given trading interval. Hence, it was not until just after 25 minutes into a trading interval that the trading data for that interval was known with certainty.

The generators were paid the variable trading price for net production in the half hour, and wholesale market customers (and hence indirectly the energy users) paid the variable trading price for energy consumed in each given half hour.

On October 1st 2021, '5 Minute Settlement' came into full effect, hence trading data was no longer applicable to these 30-minute intervals. However, some other data sets will remain to be publshed on 30-minute intervals.

Please keep this information in mind when analsysing a data set relating to 'trading' with dates before, during or after October 1st, 2021.