Coal output hits record low in Australia’s biggest state grid: Are wind farms more reliable?

The share of coal fired generation in the state with the biggest coal fleet in the country hit a record low this week, as new data shows that most of Tasmania’s operating wind farms proved more reliable in September than the ageing coal generators in NSW.

The new record low for the share of coal generation in NSW – of just 14.6 per cent – occurred at 11.35 am on Thursday, according to Geoff Eldridge of GPE NEMLog, and compared to a previous record low of 15.6 per cent reached in late August.

(Update: It was beaten again on Friday when the share of coal hit a new low of 13.9 per cent at 12.20pm).

According to Eldridge, there were a number of things going on. For a start, one third of the state’s 12 remaining coal units were offline – two at Eraring, one at Vales Point and another at Bayswater.

The second major factor was that renewable energy generation was very strong, reaching the third-highest daily maximum NSW renewable energy share of 91.2%, and rooftop solar PV were particularly active.

The coal units in NSW have had to learn how to dance around rooftop solar, adjusting their machines so they can ramp down to just 20 per cent of their rated capacity, which is what the two units at Mt Piper were doing at the time.

Normally, coal fired generators like to chug along at a steady rate, but the rise of rooftop PV has forced them to become flexible, where they can.

“These new lows remind us that the transition is no longer gradual averages, but sharp turning points where the mix can change in short periods of time,” Eldridge writes on LinkedIn.

“Each record shows both the opportunity of high renewable penetration and the challenge of managing reliability as coal retreats. The trend is clear — the floor keeps falling, and planning must adapt to a system that will lean more heavily on flexibility than ever before.”

But here is another interesting statistic. Renewables like wind and solar are often derided because of their low capacity factors, although this is not something remarkable given that it is reasonably well understood that the sun, for instance, sets every day, and doesn’t rise till morning.

But in the month of September, three wind farms in Tasmania returned higher capacity factors than all of the coal generators in NSW.

See: Renewables overtake coal for first time on monthly basis in Australia’s main grid

Cattle Hill, according to Rystad Energy, delivered a capacity factor of 67.9 per cent, followed by the Granville Harbour (64.0 per cent) and Musselroe (61.4 per cent) wind farms.

How did the NSW coal generators perform? According to Open Electricity, the Bayswater coal generator returned a capacity factor for the month of 61.6 per cent, behind the best two wind farms in Tasmania, while Mt Piper had a capacity factor of 59.1 per cent, Eraring 46.9 per cent and Vales Point just 36.0 per cent.

Some of this can be explained by outages for repairs and maintenance – some of them planned and some of them not. And by the significant ramping required to dance around rooftop solar PV.

But it’s just a little too easy, and wrong, to suggest – as many do – that wind and solar are not reliable. They are certainly variable, because of the weather, but mostly predictable.

And it’s not as though so called “baseload” is not threatened by weather, as the multiple outages of coal and gas generators due to “tube leaks” and other problems in the middle of heatwaves attests.

This includes the problems experienced in France with nuclear reactors forced to shut down because the rivers that are supposed to cool them are too hot, or their inlets have been swamped by swarming jellyfish attracted by warm waters.

As the Australian Energy Market Operator has made clear, it is not passing clouds or wind gusts or lulls that it fears most, but the sudden, surprising and unexpected loss of a big generator that is the biggest threat to grid reliability.