“Until new operating parameters are verified, approved and implemented by the solar plants, AEMO believes the only prudent course is to postpone final approvals for new generators due for commissioning or registration in the impacted area.

“Where practical, and on a prioritised basis, AEMO will continue to progress studies and address any independent outstanding issues, pending re-establishment of a stable base case on which to conduct final assessments.”

Solar and wind farm developers contacted by RenewEconomy say they have been told that AEMO has now bundled affected projects into three distinct groups.

The first are those that have already had their maximum output cut in half – the Wemen, Gannawarra, Bannerton and Karadoc solar farms in Victoria, and the Broken Hill solar farm in NSW. Some of these solar farms had been operating for a year or more without issue. This has taken 170MW of capacity from well established solar projects off the grid.

Another five projects – ready for commissioning – have been told that they had been placed in a queue which would not be advanced until the issues with the first group had been resolved. They would also only be allowed to connect one at a time. Delays to otherwise ready projects could last months, or even a year, developers fear.

Another group of projects under construction have also been warned of further delays. RenewEconomy understands the projects potentially affected include the Murra Warra and Bulgana wind projects, the Yatpool, Kiamal and Cohuna solar farms in Victoria, and other projects in NSW, including Limondale and Darlington Point solar projects.

On top of that, further constraints could be placed on other projects, including those on the line between Horsham and Ballarat, where a limit of 600MW will be applied. This could impact the Waubra, Crowlands, Ararat and the soon-to-be completed Bulgana wind farms.

AEMO’s latest letter warns that it could be years until the issues in the region are finally resolved. Apart from the potential short-term fix of changing the inverter settings, one medium term option is to install “synchronous condensers” in the region to maintain that system strength.

AEMO has hinted that it may need three of these machines – which are also being installed in South Australia by the transmission group ElectraNet, and on a much-criticised ad-hoc basis in NSW – or a total of more than 300MVA. AEMO has given itself until early 2021 to work out the best approach.

One option could be a large syncon being installed at the near complete Kiamal solar farm, but it is not clear where this fits into AEMO plans.

The longer term fix is upgraded network capacity – via the already announced renewable energy integration project – and possibly a new link to NSW. But this could take five years to complete.

In the meantime, AEMO is giving a bleak outlook for a region that has 1,200 MW of committed inverter-based generation projects and about 3,000 MW in the application phase. It says the currently identified maximum thermal network limit for the West Murray region is 1,700MW.