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16 November 2022

Australia seeks further power to curtail rooftop solar

South Australia’s grid has the highest rate of solar penetration in the world, with over 2 GW serving only 1.8 million citizens, and each summer, which Australia is currently entering, there is a longer string of middays through which over 100% of grid demand is met by solar. The excess has to be exported to other states, stored in batteries or curtailed.

Transmission lines connecting this region to other Australia states are long, therefore expensive and have limited capacity. On Saturday 12th  November thunderstorms again disrupted one of those thin connections, with the 650 MW Heywood interconnector to the more populated state of Victoria disabled. Extensive parts of the state’s grid were also disabled with 100 kilometer and hour winds and 50mm rain bursts resulting in hundreds of thousands left without power.

In response the Australian Energy market Operator (AEMO) and SA Power networks have been curtailing rooftop solar, to the tune of around 400 MW on Sunday and less since, in part using powers granted to it in the past few years. One curtailment-enabling reform was the August 2020 South Australian requirement for new inverters to have internet and remote switch-off capability. This time around the main tool has been the rather crude approach of voltage control, with some citizens complaining that they’re rendered unable to run their panels even just to power their own house, never mind for grid export.

A more elegant solution would be retroactively including rooftop capacity into VPPs, which would have the know-how to react to signals including negative power pricing. Certainly South Australia and Western Australia are pursuing that kind of distributed data and market-driven approach in the long term, using modern smart inverters and new software. Total curtailment in the state on Sunday peaked at over 1.6 GW from all causes including centrally imposed rooftop switch-offs and price-driven utility-scale projects curtailing themselves.

In contrast, at the start of this month Energy Queensland announced that all new solar and battery systems over 10 kW would be fitted with generation signaling devices, called ripple control, which would allow network operators to remotely disable them. As one might expect the industry has decried the measure as adding expense and as antiquated.

If that paints a picture of a powerful grid operator that can switch people’s solar installations off on a whim, it clearly hasn’t panned out entirely yet. AEMO says it is seeking market solutions and on Sunday SA Power Networks, the sole electricity distributor in the state, put out SMS and Facebook messages requesting that customers switch off their solar panels.

Australia’s negative pricing is disproportionately prevalent in South Australia state, but grew rapidly through 2020 and 2021 across the whole country. Through September and October 2021 wholesale electricity prices were negative 40% of the time, for most of the daylight hours, with battery installations being rewarded for the power they were taking from the grid, and some solar farms allowed to shut off thanks to “no negative price” PPA clauses. The 150 MW Hornsdale Battery Reserve and 25 MW Lake Bonney grid battery projects together earned a net of $400,000 AUD from power intakes alone in the course of the two months.

The South Australian electricity price averaged an unremarkable $92 AUD per MWh in the couple of days after the storms knocked out various transmission lines, with periods of negative pricing playing a part.

In 2020 South Australia suffered a much longer separation from the National Electricity Market (NEM), from 31st January to 17th February.