South Australia has one of the world’s highest penetrations of rooftop solar. When South Australia’s grid was recently isolated by storms from the rest of the market, the grid operator ordered local authorities to switch off as much rooftop solar as they could, and encourage as much firm electricity use as possible, to create enough “load” to give it control of the grid that could spin out of control if struck by another major event. Recently, SA Power Networks has been trying to cut off as much rooftop solar as it can, by sending signals over Wi-Fi, tripping inverters through increased voltage, and sending out public pleas for customers to switch off their rooftop solar systems and create more load for firm electricity.
SA Power Networks, which owns the local poles and wires in South Australia, had boasted recently that rooftop solar had met all local demand for more than five hours in a row in the middle of a sunny Saturday. South Australia has the largest share of wind and solar of any utility-scale grid in the world – 66 percent of local demand in the last 12 months—and rooftop solar is a major component. Australia’s grid is rapidly changing from a centralized, fossil fuel-based system, capable of operating 24/7, to a renewable and distributed grid composed of intermittent solar and wind technologies. South Australia has some of the highest electricity prices in the world and offers a wide range of subsidies for solar power.
What Happened
When rooftop solar reached more than 100 percent of local demand in late October it was not a problem because the grid in South Australia was connected to Victoria and could send excess solar power to its neighbor. There was still enough “load” on the grid that the system operator could use natural gas generation for grid security, ensuring that it had enough firm capacity to deal with any unexpected events.
But, a storm hit South Australia, tearing down one transmission tower that triggered a trip in multiple circuits and “separated” the state grid from the rest of Australia’s National Electricity Market. With South Australia isolated from the rest of the grid, large amounts of rooftop solar threatened to become a liability because if rooftop solar can meet all or most of local demand, there is little or no firm capacity available for the system operator to use if another major incident affects the grid. As a result, the system operator asked major energy users (residential, commercial and industrial) to turn off their rooftop solar during the middle of the day when it could supply most of the load and turn on their electric appliances to create additional demand, and called on the utility and the state government to switch off their solar farms.
The system operator turned off all the recently installed rooftop solar systems that are fitted with new inverters (about 100 megawatts) that can be switched off by remote control. Voltage control from the utility company may have tripped other inverters removing another 300 megawatts. The remaining households (who have older inverters that cannot be controlled remotely) were asked to switch off their solar systems. Electric consumers were also asked to switch other things on, anything – pool pumps, vacuum cleaners, electric vehicle chargers, anything that could create new load and give the system operator room to switch other controllable generators on. This is ironic since South Australia offers solar owners premiums for their surplus electricity via a feed-in tariff system.
Future Fixes
The system operator is insisting on new inverter standards that will allow it to “orchestrate” rooftop solar, turning it into an asset that can be controlled. Some want measures to control legacy rooftop solar systems installed years ago. More transmission lines, such as the one that is being built between South Australia and New South Wales, will be required as the state moves to its unofficial target of 100 percent renewables within the next few years. More storage to store excess solar power will also be required to act as a “shock absorber” for any disturbances on the grid, and for new big loads such as hydrogen electrolyzers that can act as large batteries, absorbing excess power and switching off if needed.
The irony is that if this event occurred in the middle of Australia’s summer, the system operator would be happy to have rooftop solar injecting more supply into the grid, and might be more likely to send out instructions to consumers to reduce load rather than increase it. With summer’s heat, there would be plenty of load on the grid as air conditioners are switched on, which means that the system operator would have no problem finding generation assets it can control and use as levers if any unexpected events occur. The system operator is less worried about peak demand than minimum demand when rooftop solar generates all or most of domestic demand.
Over time, battery inverters are expected to handle these issues, but the technology is still being tested. In the meantime, system operators in Australia are working with several states to provide more flexibility over how they manage rooftop solar.
Conclusion
The recent problem in South Australia was that not enough solar was able to be dialed down, so the system operator had to resort to using other methods to protect grid stability and minimize the likelihood of a state-wide blackout. Because the state’s grid was isolated after the storm, the system operator was worried about “trip risk” – that is, if there is another big event that trips another transmission line, or another generator, then the effect could flow through to all the solar inverters the system operator had not been able to control. The system operator had to ask rooftop solar owners to shut off their rooftop solar systems and curtailed large scale wind and solar to ensure it had enough controllable assets to manage the grid and that “operational demand” was kept above a certain threshold.
The South Australia situation indicates the need for the system operator to have controllable assets at its disposal. Without proper planning, a reckless move into solar and wind power, particularly rooftop solar that is not controlled by the system operator, can cause blackouts and brownouts. California may be very vulnerable since all new houses in the state must have rooftop solar systems.
