South Australia curtailed nearly as much wind and solar on Sunday as it used

South Australia produced nearly twice as much wind and solar as it could use at times on Sunday, forcing renewable plant operators to massively curtail their output. The total amount of curtailed at one point nearly equalled total demand.

South Australia leads the world in the share of wind and solar in its grid, but it wasn’t the only state affected by a big surplus of wind and solar over the weekend, with curtailment records falling across the grid.

According to Geoff Eldridge, a data analyst who provides the NEMLog service, the levels of curtailment hit instantaneous records in both South Australia and Victoria, and daily average records across the main grid.

The simple reason is that supply exceeded demand.

And whereas this is not unusual – the capacity of coal and gas plants has always far exceeded average demand (and many gas plants operate at less than 2 per cent of their capacity) – curtailment of technologies with zero marginal cost (the sun and the wind) does seem a bit of a waste.

There is probably no better case for added storage, or to use the excess for technologies such as green hydrogen, but the latter is a few year’s away at least from a rollout of significant scale, and storage capacity remains minimal.

South Australia has just three big batteries totalling just over 200MW (252MWh) that could have mopped up only a fraction of the excess on Sunday – even if their primary focus wasn’t elsewhere on services such as frequency control.

And, as we wrote on Friday, the handful of pumped hydro projects proposed for the state have barely advanced, even as it heads towards the state government’s interim target of 100 per cent renewables by 2030 and its longer term ambition of 500 per cent renewables (assuming green hydrogen exports).

Indeed, only one pumped hydro project remains of the six proposed just a few years ago, and storage projects in general are suffering from a lack of clarity over market rules and the fate of major transmission links – and other big wind and solar projects – that could affect the economics of their projects.

Even the new Project EnergyConnect, a new link to NSW with 800MW of export capacity, would not have been enough to absorb the excess power on Sunday.

As for the details of the weekend records, Eldridge says curtailment peaked at 4,897MW at 12pm on Sunday and totalled  39,875MWh for the day. The previous maximums were 3,981.6MW on August 15.

The peak NEM curtailment share of native demand was also a record of 20.69% at 12pm.

In South Australia, curtailment peaked at 1,306.7MW at 1.55pm, representing a record 93.73% share of SA native demand. Victoria curtailment was also a record max of 2,180.6MW at 1.35pm.

Most of the curtailment was from wind energy, although all the big three solar farms in South Australia were all switched off at various times too dodge negative prices. In many instances, they are required to do so as part of their contracts.

Most of the curtailment also happens at times when rooftop solar is producing the most. See also this analysis: Solar curtailment: You ain’t seen nothing yet

Curtailment in Queensland was exacerbate by a multi day outage of the Liddell to Tamworth 330 kV Line for upgrade work. That meant the excess wind and solar could not find a market elsewhere, such as NSW and had to be curtailed as priced went negative, and coal plants bid low for the right to be dispatched.