Big cold front gives a glimpse of the energy future

A big cold front passing through south-eastern Australia overnight has provided a useful glimpse into how Australia will manage more renewable generation in the future and some of the challenges that lay ahead in the transition.

Strong south-easterly winds from made landfall yesterday afternoon, powering more than 5000 megawatts of wind generation spread across South Australia, Victoria and Tasmania.

That resulted in a big surge of extra generation into relatively soft market across the NEM. Demand was lower due to the time of year, day of the week and global crisis: a mild autumn Sunday afternoon in the middle of a global pandemic.

South Australia has had a number of 100 per cent renewable generation events in recent years, with AEMO now ordering gas turbines to remain on overnight to provide key ancillary services (system strength, frequency control). This will continue until synchronous condensers are brought on line later this year.

The surplus generation would normally be sent into Victoria, but the transmission line had been constrained  due to system and weather conditions. As a result of this oversupply, some of the wind generation has been constrained by AEMO.

South Australia: generation from 19 to 20 April 2020: source OpenNEM

In Victoria the wind turbines cranked up about seven hours later as the front passed through. At first the wind displaced gas generation (as it often does) while Victoria’s brown coal generators ramped down slowly (they cannot change output quickly). This meant wind and coal generation in Victoria was bigger than demand, with the surplus being sent across the Basslink undersea cable to Tasmania and into NSW.

Victorian generation 19 to 20 Aril 2020 source Open NEM

Tasmania’s generation is mainly hydro and wind, and its wind farms increased output around the same time as Victoria, while imports of surplus electricity meant that Tasmania’s dams reduced output by nearly two-thirds overnight. Hydro is flexible and can turn on and off quickly, which is a real advantage in situations like these.

Tasmania generation 19 and 20 April 2020 Source OpenNEM

NSW has less wind relative to the size of its system than the three southern states, and it is less directly affected by increased wind speeds from south-westerly cold fronts. Wind generation increased slightly overnight, while black coal generators ramped down to make room for about two-thirds of Victoria’s surplus generation (Tasmania wasn’t nearly big enough to take it all).

NSW generation 19 to 20 aril 2020 Source: Open NEM

Even Queensland was affected by the big cold front. Its black coal generators didn’t vary output by much, but the state’s gas generators shut right down so that NSW had room to import extra power from Victoria (it normally imports from Queensland). Queensland has more flexibility to reduce supply overnight. Its bigger challenge is what to do with its growing solar PV generation every day.

Queensland generation 19 to 20 April 2020 source: OpenNEM

The big cold front required a response from every state in the NEM to manage the surge in supply. South Australia found itself in oversupply because of transmission constraints, otherwise the response from the east coast states would have needed to be bigger. The response shows home much more flexible hydro is than coal, highlighting the basic shortage of hydro in an increasingly renewable grid.

The other problem this data doesn’t show is what happens when the wind stops blowing. Winds are forecast to drop quickly this afternoon, and extra generation has been brought on line in South Australia ready to jump in when this happens.

The NEM is evolving to respond to these types of weather events, which are a normal part of the changing seasons (except the pandemic bit) but are creating increasingly challenging conditions as renewable generation increases.