Taylor’s projections assume rooftop solar will be shut down for two months a year

But it says so much rooftop solar will pose challenges to the grid. “To ensure an operable and secure system, and taking precedent from actions in South Australia, the projections include curtailment of rooftop generation during periods of low minimum demand in the system,” the report says.

Let’s just pause around that number – 6,000GWh of curtailment. It does not appear to be a mistake, because – as the report says – this is equivalent to around 3 per cent of annual demand in Australia’s National Electricity Market and the number is repeated several times. And it is not “by” 2030, it is “in” 2030.

Think about what that means for rooftop solar. Australia’s current capacity of around 12GW of behind the meter rooftop solar produces around 12,000GWh a year, or six per cent of annual demand. With around 36GW of capacity, rooftop solar could be producing around 36,000GWh a year, or 18 per cent of NEM demand.

So the predicted curtailment of 6,000GWh represents one half of the current output of rooftop solar and one sixth of the normal annual output from the rooftop solar capacity predicted for 2030. That’s the equivalent of assuming that rooftop solar will be shut down for an average of two months a year.

It’s true that the Australian Energy Market Operator (AEMO), with the support of the South Australia government, has required new inverter standards and protocols to be introduced in that state that allow it to instruct rooftop solar systems to be shut down when needed.

This will happen from this summer in South Australia, but will only impact new rooftop solar installed, or updated, since September this year. But AEMO and the South Australian government insist that these rooftop solar shutdowns will only happen on very rare occasions, and for very short periods.

Those standards and protocols are likely to be rolled out in other states. But because the “off switch” can only be applied to new systems with the right inverters and agreed protocols, and are difficult to retrofit, the government report would likely mean that it would be only newly installed systems that would be switched off.

That means an even more astonishing prospect – these new systems would be shut down for at least one quarter of the time, or three months a year, or even more, according to the government forecasts.

Frankly, it doesn’t make any sense, and would be truly shocking if it came true.

The report does suggest that longer-term trends in storage, demand response and other balancing or system managing technologies may result in a different and potentially lower outcome for rooftop generation curtailment outside the projections period.

It notes that the “Energy Security Board (ESB) is undertaking a post 2025 Project to take a holistic look at what needs to change to ensure the NEM can meet the needs of consumers in a future of diverse energy sources including distributed energy participation.”

But is 6,000GWh of curtailment really going to happen? The assumption of the massive curtailment is yet another astonishing conclusion in a report that Ketan Joshi writes is already “weird” enough because of the many strange assumptions that it makes.

RenewEconomy reached out early today to the department and Taylor’s office to check the numbers and learn more about the basis of their assumptions, and also to AEMO to ask if they had provided any such advice, or done any such modelling. We didn’t hear back from either organisation by the time of publication.