There is a minor problem in the South Australian energy system, says SA Power Networks general manager strategy and transformation Mark Vincent. “What we have is the largest generator in the state that we can’t monitor or control – it does whatever it wants to do.”

He’s talking, of course, about the 1.5GW of rooftop solar PV connected to the SAPN network, which he reminds EcoGeneration is about equal to average demand in the state. “It’s a huge amount of PV on a state scale.”

The influx of exported solar around midday is causing voltage rises in substations around the network, Vincent says. Is it a worry? For those who don’t own solar life goes on as usual, but PV owners are seeing their systems trip out – switch off – in response to voltage rises. “We’ve seen levels of complaints increasing over the past few years.”

Vincent sees these grumblings among solar owners as the thin end of the wedge. As reverse flows increase, the network is starting to see thermal issues. If nothing’s done, things can only get worse. “There is so much energy going backwards through the network it’s actually exceeding what used to be going forwards – it’s exceeding the thermal ratings of equipment.”

Connected power

It’s not only homeowners who are affected. Because of its status as being somewhat at the vanguard of solar adoption, battery-makers and retailers have partnered to trial virtual power plants in the state. Adelaide is buzzing with VPP activity, Vincent says. The trouble some VPPs are finding is that when they want to dispatch into the National Electricity Market there may already be so much exported solar that they trip out and fall short of their dispatch targets.

As VPPs become more important in the energy mix, he says, operators will want to be sure their orchestrated systems can be controlled. The coordinated networks of privately-owned batteries can be a revenue source for participants, yes, but all energy users are meant to benefit from the stability that VPPs can help provide.

On a broader scale, minimum demand in South Australia is falling and falling, Vincent says, with a recent low around 200MW. It’s a trend and it’s deeply worrying. “You need to match supply and demand in a power system all the time,” he says. “The rooftop solar is gradually pushing out synchronous generation.”

It’s getting to the point, he says, where the SA-Victoria interconnector is needed in service to carry the surplus renewables away to ensure enough local synchronous generation is maintained. If that interconnector trips, however, the South Australian energy system is “highly challenged”.

Reach for the controls

The state government’s Smarter Home rule change, which mandates that PV systems installed from late September can be remotely disconnected by an approved agent if need be, is a move to float with the solar tide.

With the state energy minister and Australian Energy Market Operator on one side and consumers and PV owners on the other, the folk at SAPN might feel as though they’re caught in the jaws of change. But engineers love a challenge, right? “We’re kind of excited by it,” Vincent says, “which might sound bizarre but what’s happened in SA is a result of a whole range of circumstances. But we think we can play a really significant enabling role for our state to have low-cost, low-carbon reliable energy – which is actually a really exciting future.

“We could have a whole state powered by rooftop solar, and we think that’s pretty cool. That’s people power at its greatest.”

A few different tools are being deployed by SAPN to deal with the problem. Its Solar Sponge tariffs apply deep discounts to encourage all consumers to increase daytime load. At network level, it is dropping voltage levels at select substations during the daytime so the network can accommodate higher volumes of exports.

“We have much more sophisticated control systems in our substations,” he says. “If customers are feeding back to us we can drop the voltage in the substation much lower than we normally would so that pulls down the voltage at the customer end and keeps it within the target range.”

The hoped for result, he says, is that many more inverters will stay on, so there will be greater exports and far lower complaints. “It’s very much a good news story in terms of better performance most of the time,” says Vincent, who sees no reason why there shouldn’t be twice as much rooftop solar in South Australia, so long as the system is nimble enough to manage it.

“We’re on the solar industry’s side, trying to enable this future,” he says. “A shift towards distributed energy is a fundamental part of [SAPN’s] business direction.”

Last resort

Of course, the voltage dial can also be turned the other way. In the event of a panicked call from AEMO over a failure at the interconnector, SAPN can lift voltage levels to trip off local PV and push up net demand so that supply is stabilised. “We hope to never have to do that,” Vincent says. “It’s a last resort.”

Another method of managing whipsawing output from residential solar is battery storage, either at home or on networks at “community” scale. Vincent says SAPN is open-minded to the option of community batteries but not yet convinced. “We can’t get the numbers to work,” he says, “but it’s definitely on the radar.”

If you work out how much battery storage it would take to soak up 1.5GW of solar, the answer, he says, is “mind-bogglingly” large. “Billions upon billions of dollars of batteries.” What’s really needed is an interconnector with NSW. “That would release additional capacity for renewables, which would be a positive. It just so happens that energy would be used in NSW.”

Some in the solar industry have grumbled about a new regime of invisible masters commanding customers’ inverters but that hasn’t stopped orders for new systems, which are as high as ever – covid or no covid.

The network has also recently been awarded ARENA funding to trial a method of increasing export limits from 5kW per phase to 10kW per phase, with an ability to wind back this flexibility if the grid is stressed.

“It’s about turning that [rooftop solar] into a resource that can be managed,” he says. “It’s a good outcome for the community.”