Now it was established in previous two posts that the Hornsdale Power Reserve did surprisingly little to avert a frequency drop caused by a 560 MW capacity loss (contrary to what was suggested in the RenewEconomy article), the focus of this post will be on how the message was brought. Knowing how little the battery actually did, then how on earth could Giles Parkinson paint it as if something extraordinary had happened? This post will explain how this is done.
Let’s start with the title:
Tesla big battery outsmarts lumbering coal units after Loy Yang trips
There are several elements of the story in this title. First, there are the three players that are involved in the story: a Tesla battery (the Hornsdale Power Reserve), coal units and the Loy Yang unit (this is a also a coal fired power unit in Victoria). Then there is the tripping event of the Loy Yang unit that led to the Hornsdale battery “outsmarting” coal units.
It is interesting how two of the players are characterized. The battery is described as “big” and the coal units as “lumbering”. I didn’t encounter the word “lumbering” in such context before, it seems that “lumbering” is also used to describe moving in a slow, awkward way or with a rumbling sound.
Now it makes more sense. On the one hand there is the “big” battery (suggesting powerful) and on the other side there are those “lumbering” coal units (suggesting not very stable, maybe even having difficulties keeping up).
The first paragraph builds on this characterization (my emphasis):
The Tesla big battery is having a big impact on Australia’s electricity market, far beyond the South Australia grid where it was expected to time shift a small amount of wind energy and provide network services and emergency back-up in case of a major problem.
This confirms the “big” from the title. The battery is having a big impact (as in already), even reaching far beyond the state border. The statement that one of the battery’s task is to be “emergency back-up in case of a major problem” follows the same line.
We also get the information that the big battery is underrated. The expectation was that it would only have local impact, yet it is suggested that it could handle an event that happened far beyond the South Australia grid.
The next paragraph contains some factual information about the tripping event. It specifies that it was the Loy Yang A3 unit that tripped, also when it happened (1:59 am) and how much the capacity loss was (560 MW).
Then the story develops further (my emphasis):
What happened next has stunned electricity industry insiders and given food for thought over the near to medium term future of the grid, such was the rapid response of the Tesla big battery to an event that happened nearly 1,000km away.
The Hornsdale battery surprised the insiders because of its response to an event happening 1,000 km away, confirming the “big impact far beyond the state border” statement from the first paragraph.
This is how it is described what the battery did (my emphasis):
Even before the Loy Yang A unit had finished tripping, the 100MW/129MWh had responded, injecting 7.3MW into the network to help arrest a slump in frequency that had fallen below 49.80Hertz.
This paragraph praises the speed with which the battery responded (before the tripping event was finished). We also get to know that the battery injected 7.3 MW of its 100 MW capacity into the grid and, according to the author, this was enough to help arrest the frequency drop.
Then follow some informative paragraphs that were the subject of the first post on this RenewEconomy article, among which this paragraph (my emphasis):
Importantly, by the time that the contracted Gladstone coal unit had gotten out of bed and put its socks on so it can inject more into the grid – it is paid to respond in six seconds – the fall in frequency had already been arrested and was being reversed.
This is why the battery “outsmarts” the lumbering coal units. The Gladstone generator is a coal unit that is contracted to help in the case a major problem arises, like a tripping coal unit.
The battery was faster to responded than the Gladstone generator and that 7.3 MW didn’t just help stopping the frequency drop as we seen earlier, the frequency drop was already reversed before the Gladstone had the chance to step in…
Then that “lumbering” Gladstone generator finally stepped in (my emphasis):
Gladstone injected more than Tesla did back into the grid, and took the frequency back up to its normal levels of 50Hz, but by then Tesla had already put its gun back in its holster and had wandered into the bar for a glass of milk.
By that time the battery already made the difference and retreated, letting the Gladstone finish the job that it started.
It also became clear that it was not the Hornsdale battery that was contracted to respond to such events. Then why did the battery respond anyway (my emphasis):
So why did the Tesla big battery respond when not contracted?
One reason is because it can, and so it did.
Looking at it that way, it seems logical that readers would come to the conclusion that the response of the battery was exceptional, maybe even crucial in the recovery process of the event that happened 1,000 km away.
A quick summary:
- The Hornsdale Power Reserve is a big battery
- It is underrated: it was expected that it only would have a local impact, it however has a big impact, even over the state borders
- It is capable of providing emergency back-up in case of a major problem
- There was such a major event (a tripping coal unit, 1000 km away) and its response stunned the insiders
- It “outsmarted” the “lumbering” coal units and initially took over the task that was in fact contracted to the Gladstone coal generator.
That is very impressive, but is it also true?
Looking at the numbers and what actually happened, not in the slightest:
- Although its capacity of 100 MW/129 MWh is big for a battery, it is small potatoes in a grid the size of South Australia
- A battery with that capacity can only handle small fluctuations on the grid, it would come woefully short in case of a “major problem”, as the tripping event showed
- The insiders were surprised about its speedy response, not the amount of power discharged
- The battery may have responded insanely quick (when it got the signal that the frequency dropped below the 49.8 Hz threshold), but its response came just seconds before the capacity of the Loy Yang A3 unit would have reached zero anyway
- During the time that it would have made the difference, it injected at a capacity of 7.3 MW, that is an incredibly tiny capacity being used to respond to a frequency drop caused by the unexpected capacity loss of 560 MW in less than 30 seconds…
No meaningful contribution is expected when seeing those numbers. That should also be clear from the graph shown in previous post:
The response of that battery (blue) was downright pathetic when it comes to the scale of that capacity loss (brown). There is no way that discharging at this capacity would have made a significant contribution in arresting and reversing the frequency drop caused by this capacity loss.
But then, if the numbers tell a different story, why is Giles Parkinson so convinced that the Hornsdale battery made the difference? His reasoning became clear in the comment section below the article. There he responded to a comment of a reader who (rightfully) stated that this 7.3 MW would have no measurable effect on the frequency, that it basically is a rounding error and as effective as “a gnat peeing on a fire” (I wish I came up with that expression) and this is his revealing answer (my emphasis):
You may wish to think that, but the AEMO data is unequivocal. The frequency drop hit its nadir after Tesla response and before Gladstone got out of bed.
Now it becomes clear. The frequency drop was indeed arrested and reversed in the time frame after the Hornsdale battery discharged its (underwhelming) load to the grid and Giles Parkinson limited the necessary response to the Gladstone coal generator. Meaning, if it is the Gladstone generator that was supposed to respond to the frequency drop and the Hornsdale battery responded 4 seconds earlier, then that frequency uptick can easily be used as proof that the battery had a significant contribution to the stopping and the reversing of that drop…
My objection in the first post I wrote about this article was that the time frame of the uptick was also the time frame that the Gladstone coal generator stepped in. I was also not convinced that only the Gladstone generator would be triggered by such a frequency drop.
In the meanwhile I found an article of the Australian Energy Council that made an analysis of the December 14 event, similar to what I did in previous two posts (including the exercise of giving the secondary y-axis the same scale as the primary y-axis). It also had a graphic that confirmed that the Gladstone generator was not the only generator that was triggered to come to the aid:
There were 16 (!) generators other than the Gladstone generator responding to this event. The Gladstone generator response became prominent after the frequency drop was halted, but the other generators were already filling in the gap at that moment. The meager contribution of the Hornsdale battery would very likely made not much of a difference. It would certainly have “helped” arresting and reversing the drop, but in the same way as the proverbial gnat would reduce the temperature of the fire by peeing on it…
Correlation is not necessarily causation. It is not because the frequency reversed after the Hornsdale battery injected its (underwhelming) load to the grid, that it was the one that actually arrested and reversed the frequency drop. A lot of other power generators worked in unison here.
The author surely told a compelling story that readers could relate to. The story was widely shared uncritically and it is used, until this day (two years later), as evidence that the Hornsdale battery prevented a potential blackout by tackling a problem that occurred in a neighboring state.
Giles Parkinson is certainly a gifted story teller. He told the story of two characters in a Western setting. One probably young and vital, the other old and lumbering. Then an emergency happened and the young man responded immediately. Before the old guy got out of bed, the young guy had already averted the emergency and then he left it to the old guy to finish the job, putting its gun in its holster and wandering away into the bar for a glass of milk…
That is surely a captivating story, but it is not exactly in line with what happened in reality.
I can tell a story too, so just let me try to correct this so it fits reality better.
An old man trips and falls to the ground. A young boy noticed the fall, runs quickly to the man, but nevertheless arrives mere seconds before the old man would hit the ground. Not that it would be much of avail, the young boy wouldn’t have the strength to prevent the man from falling anyway. Some other old men saw their colleague falling and came huffing and puffing to his aid. They managed to catch him before he hit the ground and while they were busy getting the fallen old man back upright, the young boy went already home to his mammy for a glass of milk, hoping to do better when he grows older…