Rooftop solar pushes state’s entire local network into negative load for four hours

The South Australia grid has set what is undoubtedly another world first for a gigawatt scale grid – with the local distribution network reporting “negative demand” as a result of the output of rooftop solar for four hours on Sunday.

It’s not the first time that the local network – operated by SA Power Networks – has experienced negative net load, but it is the deepest and longest to date, and points to the rapid change of a one-way grid to a two-way network.

It’s important to clarify two points here. Earlier this week, the Australian Energy Market Operator announced a new “minimum demand” for the South Australia grid of 188MW, on the very same day.

But that calculation included both the distribution (or local) network, and the main transmission network in the state, operated by ElectraNet, which has direct customers such as BHP’s Olympic Dam and other big industrial users, which added to the overall load.

The SAPN experience reveals a great big solar duck curve (see graph above). The peak negative load was minus 69.4MW in the half hour ending 1.30pm local time (1pm grid, or eastern standard time)

It was the fourth time in the month of October that the local grid experienced negative load. It had happened for the first time in the previous weekend in late September. Normally, the SAPN network experiences average load of 1.5GW, and up to 3GW in the summer peaks.

“Rooftop solar is contributing to decarbonisation of our energy and to lower energy prices,” SAPN head of corporate affairs Paul Roberts said in an emailed statement.

“In the not too distant future, we expect to see South Australia’s energy needs (all of them) during the middle parts of the day regularly being supplied 100% from rooftop solar.” (AEMO has said this could occur this spring, when temperatures are mild and demand is still relatively moderate).

Roberts said one solution to create load, and relieve the tension created by negative demand was electric vehicles, which could charge during the day.

“Longer term, we hope to see a transport system where most vehicles will be fuelled by renewable-sourced electricity, including from solar rooftop PV,” he said.

“It is exciting to think that South Australia is leading the world in this transition and there is so much possibility for us as a State in making it happen as quickly as we can.”

It’s one of just a number of major landmarks achieved in the past few months in South Australia, which has averaged a world-leading 62 per cent of wind and solar (percentage of local demand) in the last 12 months.

In the month of October, South Australia reached a peak of 100 pct renewables in every day bar two days, and last week solar alone mets more than 100 per cent of local demand in South Australia for the second time.