Illustration: Dionne Gain When unit 3 at Loy Yang shut down without warning on December 14 taking out 560 megawatts and imperilling the entire system, the new Tesla battery 1000 kilometres away in South Australia sprang into action ahead of the coal-fired power station that was contracted to restore stability. It proved to be "dispatchable" in a way coal-fired power stations are not. Age, heat and the steady encroachment of renewables are destroying the only advantages coal-fired power stations ever had. When Treasurer Scott Morrison stood up in Federal Parliament and waved around a lump of coal in a stunt unworthy of his office, he said coal was an important part of ensuring a "more certain" energy future. But he was speaking about the past.

One of the four giant units at Victoria's ageing Loy Yang A power station broke down on Tuesday night and early on Wednesday morning. Credit:Bloomberg Coal-fired power stations didn't used to get critically hot as often as they do now. The February 2017 heatwave that took out 2438 megawatts in one day in NSW might have once been a once-in-500-year event. Now it's a once-in-50-year event and perhaps soon a once-in-five-year event. The calculations are by the Australia Institute's Mark Ogge and Hannah Aulby in a study of the risks to energy security entitled Can't Stand the Heat. Ogge is the person who has been keeping a record of power station outages. When temperatures in control rooms get as high as 50 or 60 degrees the electronic control systems buckle and the boilers leak. Failures are inevitable, although unfortunately not predictable. When Treasurer Scott Morrison stood up in Parliament and waved around a lump of coal in a stunt unworthy of his office, he said coal was an important part of ensuring a "more certain" energy future. Credit:Alex Ellinghausen Wind power and solar power are in large part predictable. Yes, they are intermittent, but it is usually possible to tell a day or two ahead of time when and where the wind will blow and the sun will shine. There's time to put batteries, hydro and gas on standby.

But in summer it's becoming impossible to know when and where coal-fired power stations will blow. They are becoming unpredictably intermittent, all the more so each year they age. Output of Loy Yang A Power Station, December 26, 2017 Credit:Australia Institute And standby power is costly. Tony Wood of the Grattan Institute helped run Origin Energy for 14 years. He says the industry standard is to have as much back-up as the biggest independent unit, so that if it drops out it can be instantly replaced. But the biggest independent coal units are huge. They require big back-up. The biggest wind and solar farms are much smaller. While they require storage and gas peaking plants to fill in overnight and when the wind's not blowing, they don't need anything like as much back-up for when mechanical problems knock them out of service. Output of Tarong Power Station, December 28, 2017 Credit:Australia Institute

There are caveats. Independent turbines can stop blowing at once, and sometimes unpredictably. That's because most are located together in South Australia and Victoria, where the wind systems are synchronised. It would be better to have more wind farms in NSW, where the weather cycle is different. At times cloud cover is also unpredictable. A future without coal-fired power stations is inevitable, and entirely manageable. Wind accounts for 40 per cent of South Australia's electricity supply, 8.5 per cent of Victoria's supply, and 2.8 per cent of the NSW supply. One of the many reasons no new coal-fired power stations will be financed or built is they are not well-suited to filling in gaps. They are good at providing always-on baseload power, but that's not needed in the middle of the night when the wind is blowing a gale and providing all of a system's need for virtually nothing. They are not as good at turning on or ramping up quickly when the wind stops blowing. If they are used repeatedly to do that, they break down sooner. Loading The Turnbull government's proposed national energy guarantee would require retailers to ensure that a certain amount of the electricity they line up is dispatchable. Critics took this to be a code word for coal, but it can't be, not unless Turnbull wants to misuse the word. Battery storage, pumped hydro, molten salt solar plants that can fire up overnight, and gas peaking plants are far more dispatchable.

And they are more reliable. The more we move away from coal the more secure our power system becomes.