Spring is barely two weeks old and the sun had yet to pass the spring equinox (September 23), but already South Australia has set a new record low for electricity demand from the grid, thanks to its increasing supply of rooftop solar PV.

The record low demand – 786MW – was reached around 2pm on Sunday and was cited by Australian Energy Market Operator chief executive Audrey Zibelman as an example of how the grid is transforming.

At the time, rooftop solar accounted for 36 per cent (445MW) of electricity demand in the state. There is 761MW of small-scale rooftop solar on homes and businesses in South Australia, as at the end of August, according to industry statistician SunWiz.

The new record is notable for two reasons: firstly, it confirms that record low demand has shifted from the night to the middle of the day; and second, it did not occur in summer, as had been forecast by AEMO, but in early spring.

According to an AEMO analysis released in July, the previous record low of grid demand in South Australia occurred on November 6, 2016, with 800MW.

(We should point out that this is not total demand, but grid demand. It means much of the demand is delivered by rooftop solar and is not seen by the grid).

AEMO has predicted that by 2019, record low demand may fall to just 354MW, and within 10 years the grid demand may fall to zero because of the increasing amount of rooftop solar, particularly as South Australia has high grid prices, due to its historic legacy of an elongated network and the lack of competition in wholesale market.

“Minimum demand generally happens in summer,” it suggested. Not this time, though, because it occurred just 11 days after the end of winter.

South Australia is the first region where rooftop solar PV has caused a shift in minimum demand from night time to the middle of the day (most states still have electric hot water being switched on at night, when it would make sense to use the “solar sponge” as Queensland has suggested).

A similar prediction of zero minimum demand is made for Western Australia, which also has excellent solar resources, and is adding rooftop solar at a record rate and has overtaken South Australia with 771MW.

This is despite the price of electricity being subsidised (up to one-third of the true cost) by the state government, which owns all the infrastructure but now finds itself unable to balance the budget because of it.

Zibelman told a Melbourne public forum on “2017 energy sector strategic priorities” on Tuesday that she had “spent the weekend” watching the load curve in South Australia, “the lowest curve we’ve ever seen, because of all the solar.”

She used this to explain how the grid was changing because of these new technologies. “This is not a bad thing,” she said, but it required a different approach to the grid and improved management.

One option was to store this excess power and export it to other states, or as ARENA and the state government are suggesting, using excess renewables to export energy to other countries.

As we note in our updated story about prime minister Malcolm Turnbull’s rooftop solar and battery storage system in his Point Piper mansion, AEMO predicts that around 40 per cent of Australia’s supply could come from “distributed generation”, which effectively means rooftop solar and storage.

Using this resource would be critical for AEMO in managing a grid that has decreasing amounts of “baseload” generators and needs more flexible and reliable “disptachable generation”.

This is where demand response mechanisms come in – but Zibelman insists that this does not mean that people would have the lights and their fridges switched off at random.

“It’s about managing demand more efficiently, using our resources better, to create a more efficient system.”