When Victoria basks in mostly sunny spring weather this weekend, energy authorities will be monitoring how far electricity demand ebbs. If needed, they’ll turn off rooftop solar systems to ensure stability for the grid.
Such minimum system load events, as they are called, have emerged as a new challenge as households across Australia take advantage of plunging prices for solar panels to shield themselves from rising power bills and cut carbon emissions.
The Australian Energy Market Operator issued two such alerts for Victoria during the AFL grand final weekend a fortnight ago, and warned of two for this Saturday and Sunday.
Prior to this cluster, the state’s only previous warning was last 31 December.
The public has become inured to annual alerts to possible power shortfalls during summer heatwaves or extended cold snaps during winter.
It won’t be long before the obverse – a grid strained by too little demand – is common during mild, sunny spring and autumn days, when the need for cooling or heating abates, experts say.
“It’s all going to be uncomfortably interesting for energy system people,” said Tennant Reed, director of climate change and energy at the Ai Group, noting there are “emerging rules to keep the show on the road”.
While Sunday, too, has another minimum system load alert for Victoria. (The fourth in 15 days.) (Via@AEMO_Energy ) pic.twitter.com/HPyqE2QoJS
— @phannam@mastodon.green (@p_hannam) October 11, 2024
Having a grid that is supplied entirely by renewable energy is something Aemo and state and federal governments have anticipated as they step up support for so-called consumer energy resources. Australian households have already embraced rooftop solar at a pace unmatched anywhere, with more than a third generating power at home.
Many options are available to source extra demand, such as encouraging people to use more of their generation at peak sunny periods, renewable advocates say.
Hot water heaters, now often operating at night, could be switched on during the day, while certain industrial users could be given incentives to increase production, much like they are now rewarded to power down during summer heatwaves.
Still, the looming challenges aren’t small, particularly as coal-fired power plants shut.
The grid’s system strength is “projected to decline sharply over the next decade”, Aemo said in its latest 2024 Electricity Statement of Opportunities report.
From October to December is likely to be when demand sinks to its lowest for most parts of the national electricity market. (The national electricity market or Nem serves all regions except Western Australia and the Northern Territory.)
Windy, sunny spring days – much like the coming weekend in Victoria – also mean an elevated supply of renewable energy in a season of minimal heating or cooling need.
A year ago, on 29 October, Nem grid demand hit a record minimum of about 11 gigawatts for 30 minutes. Small-scale solar, most of it on residential roofs, met 52% of underlying demand.
As more homes install solar, the Nem’s minimum demand may continue to shrink at the present rate of 1.2GW each year, Aemo said.
The Nem needs at least 4.3GW of electricity moving across its transmission network. If there are “unplanned network or unit outages”, the threshold rises to about 7GW – a level that may be breached as soon as next spring, Aemo said.
“While these periods of very high distributed PV levels relative to underlying demand are currently not frequent, they will increase over time and could occur during unusual events and outage conditions,” it said.
“A credible disturbance could lead to reliance on emergency frequency control schemes which are known to be compromised in such low operational demand periods, escalating risks of system collapse and blackouts.”
However, the market has a sizeable toolkit to address those risks. South Australia, where about half the homes have solar panels, already has coped with two minimum system load events of level 3 – the most serious – on 11 October 2020 and 14 March 2021.
For the latter, SA Power Networks, a company part-owned by the Hong Kong-based conglomerate Cheung Kong Infrastructure, was ordered to turn off 71 megawatts of photovoltaic systems. It was the first such intervention by Aemo.
So-called solar curtailment is now a feature of SA’s operating system even if such an intervention is meant to be a “last resort”, the network group said.
Before such action, large-scale solar and wind farms will be turned off, as will big solar systems on shopping centres and factories. Exports of surplus solar power from homes will also be halted before the systems themselves are turned off.
According to WattClarity, a leading energy data website, SA had at least eight such rooftop solar curtailments in 2022 and 2o23.
Victoria, which introduced similar “backstop” rules on 1 October this year, says consumers can do their bit. Solar curtailment should be authorities’ last move.
“We encourage households with solar panels to make the most of their clean energy and save on bills by using their solar power during the day – whether it’s charging electric vehicles, doing laundry or running dishwashers,” a Victorian government spokesperson said.
For Victoria, the backstop mechanism won’t affect a household’s ability to consume their own solar generation. Large batteries are part of the toolkit from this spring, with storage on standby to create additional demand by charging up.
New South Wales and Queensland are expected to face similar challenges in coming years. NSW, though, is yet to start public consultation on restrictions of solar exports, with minimum load issues not forecast until late 2025 or beyond.
The sun shining on family rooftop solar systems was powering more than half of total energy demand in QLD & NSW this weekend. QLD set a new record of 3,091MW at 10:30am (AEST) on Saturday, with NSW setting a new record of 3,479MW at 1pm (AEST) on Sunday.https://t.co/i3OBExGJXL pic.twitter.com/6o5H3dqgQq
— AEMO (@AEMO_Energy) October 7, 2024
Wayne Smith, the acting CEO of Smart Energy Council, said the best way to solve the issue would be to encourage more adoption of home batteries, not restraining rooftop solar. (About one in five new solar system includes a battery, consultancy SunWiz says.)
“The abundance of rooftop solar is a gift from Australian households who’ve forked out their own money to produce energy from their own homes,” Smith said.
“Too often, governments and regulators see solar as a problem that needs to be managed, rather than an opportunity that should be harnessed.”
Peter Hannam is Guardian Australia’s economics correspondent
