Brown coal generators must now dance to the tune of rooftop solar

Victoria’s ageing brown coal generators are being forced to learn new tricks in the latter stages of their lives – dancing around the huge changes in grid demand caused by rooftop solar. And it’s not a skill that comes naturally.

The state of Victoria began its first weekend of spring by setting a new record low for grid demand – 2,713MW according to data from Dylan McConnell at the Climate and Energy College.

That beat the previous low of 2,967MW set in 2017 – but the important new factor with the latest record is that it occurred in the middle of the day (2pm), rather than at night (4am for the previous record), when minimum demand used to occur.

Such records are tipped to fall regularly this coming spring and in coming years, and it’s going to prove difficult for the three remaining brown coal generators in the state – Loy Yang A, Loy Yang B and Yallourn – to manage, mainly because they don’t like ramping up and down, and doing so on a regular basis may stress equipment and accelerate their exit from the grid.

This is particularly true of EnergyAustralia’s Yallourn, the oldest remaining brown coal generator, which was forced to put on its dancing shoes on the weekend, regularly winding back output to minimal levels. In Victoria, there is now more than 2.3GW of small scale rooftop solar on nearly 450,000 different household and business rooftops.

It’s part of a radical re-shaping of the grid that is causing regulators to re-write the rules of the market, and key institutions are also looking at new ways of shifting demand back from the night time (where it was moved decades ago to keep coal generators amused) to the day-time, including hot water systems and storage.

The Australian Energy Market Operator is also looking to rush through change to inverter standards and other protocols that will give them greater visibility and control over the growing share of rooftop solar, including the ability to control their exports and disconnect them from the grid if needed.

Rooftop solar was the big swing factor in Victoria over the weekend. As the graph above illustrates, rooftop solar on Saturday and Sunday (and to a lesser extent on Friday) led to a dramatic reduction in the output of brown coal, dropping back more than 1GW on Sunday in just a few hours. Rooftop solar was delivering 31 per cent of overall demand – or 1,431MW – at its peak around 1230pm

Yallourn’s generators appear to have borne the brunt of those reductions (in brown in graph above), with capacity at its units quickly winding back from around 350MW to 50MW. This trend is becoming more intense, as this graph below illustrates, showing the average increased ramping rates over the last three years.

The latest minimum demand records come just a week after a new minimum demand record was posted in Western Australia and two “winter demand” record lows were posted for Victoria and South Australia.

It was also accompanied by low prices, with prices going negative for many trading periods in the middle of the day in both Victoria and South Australia, and prices across the main grid also hitting zero at one stage early on Monday.