Two-shifting: Coal units are being turned off as they dance around rooftop PV in “new normal” for the grid

Well, so much for “baseload” power.

Baseload can be thought of as the premise that a generating unit needs to be “always on”, and operating at or near full capacity to keep the lights on. Flexibility can be thought of as the ability to provide power “when needed”.

The political debate around Australia’s green energy transition is largely based around a misunderstanding, or a deliberate distortion, of those concepts, particularly by those insisting that coal or nuclear is necessary, because “baseload” means keeping the lights on.

New Coalition spokesman Dan Tehan is a case in point, although it is not entirely clear whether his confusion is accidental or acquired. See: Dan Tehan fails to grasp difference between baseload and firming as he sprouts nonsense on nuclear

The reality is that the grid is moving on. Baseload capacity remains in Australia’s main grid, at least for another decade, but the ageing machines are now being asked to do things that many engineers never thought possible – they are learning to dance.

As Renew Economy has reported, some coal generation companies are making an heroic effort to make their ageing generators more useful to the modern system, adapting them so they can “flex” up and down to as low as 20 per cent of their rated capacity, and now – in some cases – to switch off altogether.

This “switching off” is known as “two shifting”, and – as Renew Economy reported just over a year ago – AGL (the operator of the country’s biggest coal fleet) first tried out this ” groundbreaking technique with one of the units of its Bayswater coal generator in the Hunter Valley.

See: Coal generator switches off to make room for solar in significant boost to renewable switch

AGL CEO Damien Nicks has also flagged the likely development of “two shifting” in a recent interview with the weekly Energy Insiders podcast hosted by Renew Economy.

See: AGL may mothball coal units, or shut them down over weekends, to make way for solar, hints at wind contract

And AGL appears to have been doing just that on a regular basis in the last week to 10 days, in the middle of spring when demand is usually low to moderate, and wind and solar generation strong.

Geoff Eldridge, the keen energy market watcher from GPE NEMLog, notes that AGL has been quietly extending the practice through tests on Units 2 and 3, and now appears confident in applying two-shifting more routinely when market and demand conditions support it.

He says notable two-shift days included March 17, March 22, and April 26, all during the shoulder-season when daytime demand was low and solar output was high.

In recent weeks, the Bayswater No 2 unit has been cycled offer at 8am, and returned to service at around 3pm, on three occasions – On Saturday, September 27, and again this long weekend (Saturday October 4 and Sunday October 5).

As this graph above illustrates, the No 2 unit really can dance. On a daily basis it has been dialling down to around 20 per cent of its rated output, and on the weekend shut off completely.

“This is not a conventional outage,” Eldridge notes. “The boiler remains fired to minimise thermal movement of plant components. It is a strategy that can be overall cheaper than running through periods of very low or negative prices, while also creating headroom for renewables in the middle of the day.

“The implications are significant. Coal is no longer operating only as inflexible baseload — it is adapting, at least temporarily, into a more semi-flexible role.

“For the system, this reduces daytime oversupply and curtailment. For operators, it introduces new stresses and costs from cycling. And for the market, it shifts the timing of coal availability into the evening peak.”

An AGL spokesman confirmed in an email to Renew Economy that the “two-shifting” continues to be trialled. There was no comment on whether it would be extended to other units. It is not likely to be replicated in the ageing brown coal generators in Victoria’s Latrobe Valley, for instance.

Energy Australia has been canvassing its own version of “two-shifting” at the Mt Piper coal generator near Lithgow in NSW, although it is also thinking of longer “seasonal” shutdowns, presumably to avoid the wear and tear that the two-shifting causes.

And what will replace them? Flexibility, or dispatchable capacity, will come from technologies such as peaking gas generators, which can switch on when needed – and often for just a few hours a year (100 hours or so). Some have “capacity factors” measuring in the low single digits.

But these technologies – largely because of the cost of gas and the fact that they are one-trick ponies – are being challenged by technologies such as battery storage, where costs are falling rapidly, and which can provide multiple services all throughout the year.

That can include time-shifting the output of wind and solar (such as the big solar soakers in Western Australia), acting as giant “shock absorbers” to maximise the capacity of transmission lines (such as the country’s most powerful battery at Waratah), or just doing a host of energy arbitrage and other grid services.

Many also see the need for pumped hydro storage, although the fiasco at Snowy 2.0, and the soaring civil construction costs at afflict such projects, has been making the case for that technology more difficult.

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