AEMO has called for an expansion of its power to switch off rooftop solar to maintain system stability. Residential batteries are ideally placed to provide a solution for the grid and consumers alike.

The past 10 days has seen a lot of public debate about the electricity market operator’s call to expand its power to remotely switch off solar, to cope with what it describes as “minimum load.” It’s pretty safe to say that householders generally don’t like the idea of having their solar shut down remotely. And it’s hardly surprising: no-one wants their perfectly good solar going to waste while they have to use expensive and often dirty electricity from the grid.

There are legitimate concerns in the community that while the Australian Electricity Market Operator (AEMO) has no worries about households adding new electricity loads, solar production could be throttled in service of grid stability. But it is increasingly the reality around the country, with AEMO continuing to advocate for an expanded ability to do just this – even if the idea is the remote shutdown capability be used as a last resort or “backstop” capability. 

For homes with solar, the move is another sign that adding a battery system can protect them from their solar being switched off, and even be a part of the grid solution. Batteries can charge during the hours of peak production delivering value for homeowners and the electricity network.

Through the integration into a virtual power plant (VPP), batteries can also provide some of the grid services that are in short supply when solar is the dominant generation source on the network. While distributed PV can be seen as a problem, distributed batteries are clearly a solution.

AEMO’s latest move has come with an effort to increase its transparency into how it is managing the challenge of the ever-growing amounts of rooftop PV. It published a factsheet on minimum grid load as a part of its latest communication effort. The report provides more detail into how AEMO intends to manage rooftop solar, and the discussion it has spurred brings into focus the importance of developing and deploying a wide range of strategies to accommodate Australia’s ever-growing distributed PV fleet.

Rarely used

It is important to recognise that AEMO says it would only use remote shutdown powers in “rare circumstances,” namely when rooftop solar production is causing very low levels of electricity demand from the grid – potentially resulting in system instability. Also important is that this latest move is only an expansion of existing powers to New South Wales (and potentially the territories and Tasmania). The remote shutdown capability has already been granted most recently in Victoria, along with Queensland, SA, and WA.

“AEMO does not want to directly control people’s rooftop solar,” said executive general manager of operations Michael Gatt, looking to reassure solar homeowners. The agency reports that since being granted the capability to remotely shut off rooftop solar in South Australia in 2020, it has only been deployed three times: March 2021, November 2022, and February 2024.

Inside “minimum load”

Referred to by AEMO as “minimum load,” the dynamic can cause challenges in terms of maintaining grid stability. In particular, it can leave the system vulnerable to disturbances like transmission failures or unplanned generator outages – an ever-increasing occurrence due to Australia’s ageing coal generators.

It is particularly prevalent on sunny days that are not excessively hot. In such conditions, solar produces at its peak, while air conditioners are not fully ramped resulting in PV production going unused.

One description of the challenge posed by minimum demand is that it is like balancing on a bike when speed is decreased or the bike is stopped. While moving forward quickly, the equivalent being the electricity network operating with lots of grid demand and coal and gas generators firing, then maintaining stability is easy. Once speed is decreased, grid demand sags and generators switch off, stability becomes a challenge.

To extend the metaphor, this lack of stability is particularly problematic when the cyclist hits a bump in the road. For the grid that could be an outage on a transmission line or a coal or gas generator going offline unexpectedly. When speed is up, such a bump can be handled by the system. At low speed, during a minimum demand occurrence, the cyclist can topple over.

Of course, that polluting generators are being squeezed out of the market is a good thing. That millions of Aussie households have invested their own money in rooftop solar and need less power from the grid is a major positive. And it seems only fitting that the next wave of investment into batteries take centre stage as a big part of the solution for the grid.

AEMO notes that at present there are times when solar is meeting more than 50% of the total demand on the National Electricity Market. In some states, in particular WA and SA, it can far exceed that.

“As the market operator, we’re aware that high contributions of rooftop solar coinciding with certain system conditions needs to be carefully managed to ensure electricity reliability and grid security while managing power system risks,” said AEMO’s Gatt.

Batteries ideally placed

Referring to the shutdown as an “emergency backstop” capability, the regulator is keen to emphasise that it would only be deployed when other strategies to either reduce electricity being fed into the grid or increase demand have been deployed. Which is precisely why residential batteries, with their ability to absorb solar at the point of production, are such an ideal tool.

While there has been some recognition of the role that residential batteries can play in the form of limited state-based subsidies, their economics have dramatically improved. Home battery systems are also safer and more efficient than ever before. Homeowners should be encouraged to make the move to adopt batteries today, rather than wait for subsidies to arrive or for their solar to switched off.