A Morning of Electricity Generation in the NEM

In this post I show the sources of electricity in the Australian NEM region for one particular morning, that of the 28th April 2016. Tasmania was (and currently still is) disconnected from the NEM, and is not included. The morning of 28th April was chosen for analysis due to the power outage at the electric railway system in Adelaide at around 7:30 am, though this post is mainly about which generators did load-following.

The following figure shows the total electricity generated in the NEM at 5-minute intervals (the black curve), together with the amount generated in each state:


Note that the curves are offset vertically for display purposes, the main purpose of the figure above is to show the overall shape of the electricity generation, in particular the peak demand in early evening and the steep rise in demand in the morning.

In the morning around 6 GW of electricity supply was added to the nightime level over a period of around 3 hours. If wind power is falling over this early morning rise in demand then the dispatchable generators have to change their output by more than 6 GW.

To understand where the extra 6 GW of power came from I looked at the individual generators of electricity in each state, shown in the series of figures below., starting with Queensland:



In Queensland coal power fluctuated relatively rapidly (indicating its use for controlling frequency?), but rose only modestly over the morning. Most of the rise in demand was met by OCGT generators, i.e. they were used for load-following, not just for meeting demand peaks. There was a temporary drop in coal power (around 100 MW) at around 7:30 am, giving a similar drop in electricity export to NSW, is this related to the power outage of the Adelaide railway? To answer that question we need to look at what happened in NSW:



In NSW coal power did more load following than in QLD, but was helped initially by Hydro generation, and then by a very rapid rise in OCGT generation. The combination of hydro and OCGT has a very large temporary drop (around 300 MW) at around 7:20 am, requiring a spike in import to sustain the still rising consumption in the state. Note that the sharp rise in OCGT power dealt with the drop in QLD coal power at 7:30 am, as the NET IMPORT in NSW is normal at that time. The spike in NSW import must have come from Victoria, shown in the following figure:



In Victoria it was only Loy Yang coal power that did any significant load following, helped by OCGT generators and by HYDRO (blue curve). Note also that some of the rising demand in VIC between 6:00 and 7:00 am was met by a fall in NET EXPORT of around 250 MW, which was effectively caused by Torrens Power Station in South Australia (see below). The sharp rise in HYDRO output is reflected in a spike in NET EXPORT at around 7:20 am, corresponding in time to the spike in NET IMPORT in NSW.

Finally we get to South Australia, with its unusual dip in consumption at 7:30 am:



In South Australia most load following comes from Torrens Power Station (CCGT), with some help from OCGT generators. As noted above Torrens also provided some of the rise in demand in Victoria from 6:00 am, and it appears to have responded to demand variations from that state throughout the morning.

The next post will look in more detail at what was being generated and imported/exported around 7:30 am, roughly the time of the power outage at the Adelaide electric railway.

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