Four wind farm operators are being taken to court by the Australian Energy Regulator (AER) over a statewide blackout in South Australia during a major storm in September 2016.

Subsidiaries of AGL, Neoen, Pacific Hydro and Tilt Renewables are accused of failing to comply with performance requirements to “ride through” major disruptions and disturbances, in breach of national electricity rules, and now face financial penalties, if found guilty.

“The AER has brought these proceedings to send a strong signal to all energy businesses about the importance of compliance with performance standards to promote system security and reliability," AER chair Paula Conboy said in a statement.

"These alleged failures contributed to the black system event [BSE], and meant that AEMO [Australian Energy Market Operator] was not fully informed when responding to system-wide failures in South Australia in September 2016.”

Conboy added that the regulator would seek declarations, penalties, compliance program orders and costs.

On 28 September 2016, a major storm, which included two tornadoes, knocked down transmission lines in the mid-north of the state. The AER argues that the blackout — which affected 850,000 customers and in some areas lasted for days — was then triggered by a loss of generation from the accused companies’ wind farms (see below).

This contradicts the results of a previous AER investigation last December into the blackout, which stated that although there had been some instances of non-compliance with obligations, these “did not contribute to the state going black”.

The regulator’s explanation for this discrepancy is that: “The AER’s [December] investigation into the BSE involved four components — pre-event period, system restoration and market suspension and the event. This announcement relates only to the event component.”

AGL says it did "not accept the AER's conclusions" and would "strongly defend these proceedings". Tilt has declared that it had "acted in good faith and in accordance with the applicable National Electricity Rules".

An earlier 2017 report by the Australian Energy Market Operator found that the blackout had been caused by extreme weather, including the two tornadoes, which saw wind speeds of 190-260km/h. It said that the wind farms initially rode out grid disturbances caused by a damaged transmission line, but that a protection mechanism in the turbines then triggered the loss of about 450MW of capacity within seven seconds. This led to a sudden influx of imported energy from the neighbouring state of Victoria, which then caused the blackout.

The charges brought by the AER will be highly controversial as the argument about the South Australia blackout has been raging for years, inflaming the debate around the country’s energy policy. This culminated in then-Treasurer (and now prime minister) Scott Morrison brandishing a lump of coal in Parliament in February 2017, saying: “This is coal. Don’t be afraid. Don’t be scared.”

The wind farms that allegedly caused the blackout are: Hallett 1 (Hallett), Hallett 2 (Hallett Hill), Hallett 4 (North Brown Hill) and Hallett 5 (The Bluff) (AGL); Hornsdale, which now hosts the world’s largest lithium-ion battery, Tesla’s 100MW/129MWh facility (Neoen); Clements Gap (Pacific Hydro); and Snowtown 2 (Tilt Renewables).