Negative demand: The new grid reality in a state where half of all homes have rooftop solar

ElectraNet, the transmission company that runs the backbone to the grid in South Australia, says the demand profile of the local grid has been fundamentally altered by the massive uptake of rooftop solar.

The company say more than half of all homes in South Australia now have rooftop solar, and it is now seeing events on the grid that it could barely imagine just a few years ago, let alone witness.

Before 2022-23, ElectraNet says, South Australia had never experienced a day when minimum demand had fallen below 100 megawatts. In fact, minimum demand levels up to 2015 were usually more than 1,000 MW.

In 2022-23, there were three days when demand fell below 100 MW, but that number jumped to 21 in 2023-24, and already in 2024-25 it has totalled 27 days.

And it’s not just happening on weekends, when demand and industrial activity is usually low, it is also occurring on mild weekdays (grey shaded columns in graph above).

Even more remarkably, over the last six months, Electranet has reported eight days when demand was negative and power flows were flowing back into its transmission network from rooftop solar on distributed networks.

One of those occasions – on February 16 this year – occurred just four days after the state experienced record high demand, highlighting the extraordinary changes that can occur at rapid speed, and which underline the need for flexible and fast responding technologies, such as battery storage and demand response.

Electranet says the minimum demand on February 16 fell to minus 54 MW – which it regards as the record low because other days when demand fell even further, to minus 214 MW, were affected by outages when industrial loads were cut off by grid disruptions.

“This minimum was recorded only four days after the maximum demand recorded during the summer period, further reflecting the significant extremes in demand experienced by the transmission network as a result of the mass adoption of solar PV,” it says.

“At times, and more frequently, ElectraNet is even seeing demand become negative, where rooftop solar generates more electricity than the state requires. In fact, 90% of transmission connection points to the SA Power Networks distribution network have experienced times when this has occurred.”

Which, of course, points to the need for big battery storage, and the state will have more than a dozen big batteries by the end of next financial year as a raft of new projects are built and commissioned.

The state also has nearly 50,000 household batteries, and expects this to jump significantly in coming years with the help of the federal government’s household battery rebate, and demand in the middle of the day will also likely be lifted by the uptake of electric vehicles, and the big new loads seeking a grid dominated by renewables.

ElectraNet says South Australia already operates with an annual average share of 74 per cent wind and solar – a world-leading share – and says the state is well on track to meet its target of 100 per cent net renewables by 2027.

For that reason, ElectraaNet says, it is seeing huge interest from industries in establishing business activities in South Australia, with 37 different business organisations representing 50 different proposals totalling more than 15 gigawatts making enquiries about grid connection.

That 15 GW is five times the average peak load in the state, and 10 times the average load.

See also: Dozens of big industries want to plug in to Australia’s first 100 pct net renewable (wind and solar) grid

And: “Unimaginable a few years ago:” It seems everyone wants to plug in to Australia’s most renewable grid