Solar switch-off a must for all states, says AEMO, to control “seven Erarings” of rooftop PV

Australian Energy Market Operator chief Daniel Westerman says emergency rooftop solar switch-off mechanisms must be set up across the national electricity market, to better control “more than seven Eraring power stations” worth of consumer installed PV.

In a speech on Monday, Westerman said Australian households and businesses have collectively installed around 3.5 million solar systems, representing about 20GW of potential generation capacity.

“That’s more than seven Eraring power stations at full output, and capable of meeting almost half [48%] of our energy demand when the sun is shining at its brightest,” Westerman told the AFR Energy and Climate Summit. AEMO forecasts that rooftop solar capacity could jump to 50GW by 2040.

Westerman said currently the market can’t dispatch power from solar rooftops like it can from solar and wind farm.

“And having so much generation that doesn’t respond to market signals or operational signals, can sometimes be a challenge.”

This challenge is now presenting itself on an almost daily basis in the shape of the infamous solar duck, where uncontrolled generation of excess PV floods the grid during the middle of the day. Demand then spikes at sunset, requiring ageing fossil fuel generators to be rapidly ramped up to replace the solar.

At the end of last month, the share of rooftop solar supplied more than half of all generation on the National Electricity Market on the Sunday of the AFL Grand Final weekend, sending the output of coal and grid demand to new lows.

At the time, AEMO said, rooftop solar was supplying 51 per cent of total demand. It noted records were also broken in Queensland and South Australia, where rooftop solar met 99.7 per cent of total demand from 1pm to 1.30pm. (Rooftop solar has since exceeded 100 per cent in South Australian on a five minute dispatch basis).

The market operator’s main concern on days like these, says Westerman, is that an oversupply of energy from rooftop solar – particularly when the back-up is clunky and slow to respond coal plants – can threaten grid stability.

“An oversupply of energy from solar rooftops – when supply of electricity becomes greater than demand – can cause the grid to lose balance and lead to serious consequences,” Westerman told the conference.

“That’s why an emergency solar curtailment mechanism is needed across the NEM.”

Already, in two of Australia’s most rooftop solar heavy states – South Australia and Western Australia – AEMO has the ability to order residential rooftop solar systems to be switched off remotely as an emergency measure to keep the grid stable.

For the industry and consumers, this means all new or upgraded solar systems (with inverter capacity 5kW and below) installed on the grid in these states must have the capability to be remotely switched off, and back on again. The owner of the rooftop system must also nominate an “agent” who can control it via those inverter settings.

These sorts of control protocols are also expected to be used to remotely manage other “consumer energy resources” in the future, ranging from pool pumps to electric vehicle charging stations, hot water systems and even air conditioners.

Westerman says the other major concern for the market operator around rooftop solar systems is their susceptibility to grid disturbances, like a lightning strike.

“Consumers expect our power system must be resilient. The power system has small disturbances all the time, from lightning strikes to small faults that propagate through the system,” he said on Monday.

“If our rooftop solar systems can’t ride through these disturbances like other generators do … this can also cause significant issues. That’s why appropriate standards and compliance for these systems is important.”

Another rule change that requires all new inverters to have “ride-through capabilities” will eventually come into force all across the main grid, but has already been put in place in South Australia.