By Phil Kreveld
Dunkel, German for ‘dark’, and Flaute, a mariner’s term for ‘no wind’ make up the combined word ‘Dunkelflaute’—a dark lull.
No sun for solar farms and no wind for wind turbines. Writing in The Australian weekend edition of November 29/30, Chris Uhlmann mentions a report by consultant Global Power Energy, which questions minimum wind conditions forecast by the Australian Energy Market Operator as too optimistic, based on measured minimum wind conditions by the consultant.
Uhlmann quotes the consultant regarding gas turbines: “Building three to four times more renewables to cover this gap [in gas and diesel fuel supply] does not seem logical. That’s just building more generation, we won’t have any fuel for”. In other words, gas turbine generated electricity would provide energy during dark, cold, windless days.
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AEMO CEO Daniel Westerman, in an ABC News bulletin on December 1, is mentioned as wanting to increase the reach of Emergency Backstop, the measure which allows distribution companies to switch off rooftop solar systems so as to prevent grid instability in high-voltage transmission lines.
The Australian Financial Review of December 1 carried an article “AEMO warns of blackouts if coal plant closes”. The following is a quote from the article:
“Origin Energy’s giant Eraring coal power plant cannot close in 2027 without risking blackouts in NSW, the Australian Energy Market Operator has advised, warning that equipment [synchronous condensers] needed to keep the grid secure will not be installed in time. The threat to power supply from shutting down Eraring is not because of a lack of electricity to replace the 2880 megawatt generator—the country’s biggest—but because of a lack of system strength services for the power grid, according to the market operator.”
Nordic countries, e.g. Denmark and Germany might well be more prone to dunkelflaute than Australia, but its occurrence here cannot be ruled out. As Uhlmann points out, if the weather event lasts long enough, batteries will have been discharged, there will be no energy to recharge them and fuel supplies might have been exhausted. Separately, the Energy Council of Australia has proposed that annual unserved energy be doubled from the current .002%. But is this just playing with numbers? An engineering view is that the grid is already imperilled. And unserved energy projections would appear to be of little or no value.
We have very long AC high-voltage transmission lines, one (EnergyConnect) approaching an electrical length of 0.15 of wavelength (design standards indicate a practical maximum of 0.18). The south eastern grid is 5,000km long (AC wavelength is 6,000km approx.). Obviously, such a length destroys synchronicity between the extreme ends of South Australia and Queensland, but this is saved by synchronous generation at intermediate busbars.
The continental USA has an east to west coast distance of approximately 4,500km but rather than attempting a contiguous synchronous grid, it has two separate synchronous grids for the eastern and western region that are linked via DC transmission for energy exchange. Only western Europe, with the highest population density by comparison to the USA, has a contiguous, meshed AC transmission system. Such a system makes for a much healthier renewables climate as the meshing provides for more grid strength than we can provide because of our long radial grid topology.
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Our electricity system is overly-stretched distance-wise, it could be argued. Although our renewable integration process is an object of study by the USA and Europe, we will have to make it all work. Our geography and high density, but widely separated population centres indicate local, self-sustaining grids, starting with generation facilities at terminal stations.
Grid strength problems would disappear, and large-scale renewables would connect at medium voltage, avoiding calamities like the Waratah Super Battery high voltage transformer mishap. We wouldn’t need to invoke Emergency Backstop, which is really an outcome of long transmission lines carrying too little power (shades of the Iberian grid collapse of April 28).
But will such a scenario come about? Of course not, because we living the ‘no transition without transmission’ strategy. Even so, it is not too late to re-evaluate projects like VNI-west. In sum, we could do with a wholistic engineering review subject to open, public discussion by the engineering community.
