On November 12th a series of storms passed through South Australia that had the potential to black out the whole state, as had previously happened in 2016. Whilst parts of South Australia did lose power, it was far less dramatic than the last weather event due to a significant amount of work that has been undertaken by AEMO to build a more secure grid since the 2016 blackouts.
In 2017 AEMO released a review of the events that had blacked out the state; the main cause was of course the extreme weather that had knocked over transmission lines as well as some wind farms not meeting protection standards. Similar to 2016, it was destructive storms that passed through South Australia and damaged the network on the 12th November. At 4:59 PM, the market was notified of a significant power system event due to the tripping of multiple transmission lines. Both elements on the Tailem Bend – Southeast 275kV transmission line had tripped. Some transmission towers were damaged and had fallen over, resulting in the South Australian grid being disconnected from the NEM. On Saturday at 6:03 PM, AEMO notified the market that South Australia had been reconnected to the NEM after the 275kV transmission line at Tailem Bend was returned to service.
During events like this AEMO invokes its power to manage system security; however, this time, it went a step further and constrained off-rooftop PV to maintain a secure level of Distributed PV (DPV) generation. AEMO switched off as many rooftop PV installations as possible during the middle of the day, a rare occurrence known as “islanding” of the state grid to maintain stability, designed to keep the DPV below the secure threshold. PV generation is not as easily controlled as other sources. At times South Australia can meet all domestic demand for power via rooftop solar and sends surplus to Victoria but this cannot be managed in an islanded state, therefore requiring the curtailment of the rooftop PV allowing AEMO to manage scheduled and semi-scheduled generation assets to maintain system security.
Smart metering is required to enable the shutting down of rooftop PV systems, however not all South Australian PV systems can be controlled remotely as they have older inverters. This resulted in only 50% of systems being curtailed. Over time as more rooftop PV systems are installed using smart inverters, there will be more control of their output. Currently, AEMO can control 100MW of PV generation, but during the recent event, it also used voltage control to trip off a further 300MW of rooftop PV out of approximately 1,000MW of installed capacity.
The South Australian network has now been re-synchronised to the NEM, and electricity is flowing between South Australia and the other states of the NEM as before. While South Australia was isolated from the NEM for a week, South Australia was powered by wind and solar for up to two-thirds of its electricity demand, with gas providing the difference. System stability is a delicate balance between the supply of electricity, the types of generators providing the electricity and the electricity demand from end users. This time, part of the solution was to encourage end users to consume more electricity, enabling a higher generation level. Before the curtailment, South Australia was supplied by over two-thirds of its demand via renewable generation.
While high levels of renewable generation are good for keeping electricity costs down, the savings can be eroded by high-frequency control costs and the need for a more expensive gas-fired generation to fill the gap when the sun is not shining, and the wind is not blowing.
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