Grid Export vs Demand Trend Report Data Difference

  • Last post 14 March 2019
LJHS posted this 12 March 2019


I've been examining the demand data available through from the Demand Trend Report and the Grid Export data. Comparing the data from 2009 to 2016, there is a difference from 700 to 1200 GWh between the annual totals, with Demand Trends being greater than the Grid Export data. I've attached a rough image with time series plots of:

  • Left: NI and SI data 
  • Middle: The difference between the Demand Trends and Grid Export
  • Right: Demand Trends divided by Grid Export data

The time resolution is 1/2 hour.

I assume the difference is due to Embedded Generation? Is that correct? Or are other adjustments involved with the Demand Trends data?

Thank you in advance.




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LJHS posted this 12 March 2019

Sorry about the image size, did not realise it would not allow it to be opened in a separate window in full resolution. My mistake!

PDF version is attached

Attached files

Matthew Keir posted this 13 March 2019


Yes, essentially you are correct.

Assuming you had the demand trend report set to reconciled demand. Reconciled demand is total demand including the impact of network losses but excluding transmission losses (transmission losses are taken into account in wholesale pricing engine SPD). Reconciled demand is what purchasers must pay for in the wholesale market and is available on a monthly basis. To say that another way it’s all the end consumption or offtake (within networks etc) grossed up to the impact or demand it imposes on the electricity system at the grid level.

Demand can be supplied by embedded generation or from offtake from the grid. However, the grid export is only a measure of offtake from the grid.

Over time both small and, in some cases, quite large generation has been embedded within networks. At the locations with large embedded generation, the output can often exceed local demand. This results in the excess being injected into the grid. Clearly, this injected energy from embedded generation is then used to satisfy demand at other GXPs. Hence it is not correct to assume grid offtake is supplied solely from grid-connected plant.

There are a couple of small exceptions to the above but I won’t complicate this post with these at this time. We are working on some new datasets that we hope to publish sometime this year which will improve the quality of information available in this space.

I hope that helps. If you haven't already you can click the demand tag for further discussion on demand.



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LJHS posted this 14 March 2019

Hi Matthew,

Thank you very much for your response.