The Australian Energy Market Operator has warned Victoria solar farms that they face further restrictions on their output because of system strength concerns in western Victoria, and has told other developers that new connections are not feasible without major investment.
The system strength issues, and the lack of network infrastructure in other parts of western Victoria, now risks a contagion effect on projects that are already operating, are waiting to be commissioned, are under construction, or just in the planning stage.
The delays that could result to projects both planned and under construction, and the growing restrictions on existing wind and solar plants,  could also pose challenges for the Victoria government to meet its medium  term renewable energy targets, such as the 40 per cent target set down for 2025. (It has legislated to lift that level to 50 per cent by 2030).
As RenewEconomy reported exclusively last year, AEMO wrote a letter to participants in December warning that the grid “was balanced on a knife edge” because of system strength issues that it said were unique in the world.
These “system strength issues” were discovered after new modelling revealed that solar plants in the West Murray area will likely “oscillate” – and undermine the stability of the grid – should what AEMO calls a “credible” contingency occur, such as the loss of a nearby transmission line.
In response, AEMO ordered four solar farms in Victoria and one in NSW to restrict their output by half until a short-term solution – such as reprogramming the inverters – could be found.
The issue, however, has dragged on longer than expected. And in a follow-up notice to market participants in late December, AEMO says new modelling conducted in late November and early December confirms the system strength problems, and it flags further cuts to the allowed output of five already restricted solar farms.
“It may be necessary for a larger number of online inverters to remain disconnected to maintain system security,” it warns. “Presently 50% of the inverters are permitted to remain online.”
AEMO also confirmed that the problem was likely to impact projects that were largely complete and awaiting commissioning, and other projects in the construction phase.
“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. Â 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.
“Even if performance standards have been, or can be, agreed under the National Electricity Rules for new grid-scale projects, it is unlikely that those performance standards could feasibly be achieved under all relevant system conditions, meaning generator registration requirements could not be met,” it writes.
“Generators may also identify the need for plant modification in order to meet performance standards on an ongoing basis. Thermal and stability limits mean it will not be possible for many of these projects to connect or generate at full output ahead of significant investment in network infrastructure.”
