Can a sponge soak up SA’s rooftop solar problem?

Hello, my name is South Australia and I have a rooftop solar problem.

In the world’s biggest renewable electricity laboratory, otherwise known as the state of South Australia, rooftop solar PV is bigger than the Beatles. Around 36 per cent of South Australian households have installed solar panels: More than 282,000 installations producing more than 1300MW of solar generation capacity.

In practical terms this translates to a rooftop solar PV generation peak of around 600MW on sunny days, in an electricity market which typically cycles from around 1200MW to 2400MW of demand each day. More rooftop solar PV is driving down the level of operational demand, falling as low as 450MW on spring weekend weekends, which is around the minimum of power station supply needed to keep the grid stable.

Rooftop solar generation is a major power station in the size of the grid, tuning on during sunny days and delivering around a third of the state’s supply and then powering down before the evening demand peak spikes. And nobody is able to control it.

This is a big problem both technically and politically. Governments and retailers are reluctant to stand between a South Australian and their next solar panel. Yet continued uncontrolled expansion of this system is making the South Australian grid increasingly difficult to manage.

South Australia already has more than 2500MW of large scale wind and solar, which is also cycling in and out of supply as the wind and sunshine change through each day. These generators can be controlled by the Australian Energy Market Operator (AEM) so can be better integrated with gas generators, transmission and batteries to balance the grid.

AEMO has now been allowed by the South Australian Government to begin requiring technology to control new rooftop solar PV installations.

One practical solution is to find ways of increasing demand during the middle of the day to soak up the surplus solar electrons. The SA network provider SA Power Networks (SAPN) has included a “solar sponge” network tariff for the 2020-25 regulatory period, to try and encourage more South Australians to use more power during the middle of the day.

SAPN is particularly exposed to this problem because over-generation during the day spikes network voltages in those Adelaide suburbs with high penetration rates of rooftop solar. The network is required to keep voltages – the electricity pressure in the network – within a safe range around the standard of 230volts.

With lots of solar pushing power back into the grid  voltages in some suburbs are regularly pushing above 255volts, requiring either expensive capital works to manage this or cheaper demand based solutions.

The networks can set their own tariffs, but these are passed to electricity retailers who decide how consumers will actually be charged. They are not exposed to the costs of managing voltage, but are exposed to the competitive pressures of other retailers offering deals to try and take their customers.

SAPN’s new time of used network charges only reflect around 30 per cent of the total bill. Major retailers have a history of smoothing such changes out, not because they don’t agree with their intent, but because it doesn’t go down well with customers. To them the SAPN tariff changes is like having a noisy back seat driver.

The SA Government and SAPN would like retailers to pass these costs on, but so far retailers are resisting because solar sponge might be what the grid wants, but it’s not what customers want.