Two solar farms and one wind farm in north Queensland face major constraints due to newly discovered “system strength” issues and their output could be curtailed to zero under certain conditions.
The generators affected are the Haughton and Sun Metals solar farm near Townsville, and the newly commissioned Mt Emerald wind farm, according to a market notice issued by the Australian Energy Market Operator.
The system strength issues are similar to those that have seen the output of five solar farms in Victoria and NSW cut in half, and many other projects in that area warned of significant delays to connections and commissioning.
Both situations have emerged after new and detailed modelling which found that in certain “contingencies” i.e. when a major network link failed, there was a risk of uncontrolled “oscillations” caused by the nature of the inverter technology.
The situation seems to be caused by the fact that most inverters installed in Australia are “grid following”, and what AEMO is now looking for is more “grid forming” inverters, which can correct frequency and voltage issues. Trials, including at the newly expanded Tesla big battery in South Australia, and Dalrymple North, will help inform the grid operator how these perform in contingency situations.
The issue in north Queensland has been identified by the new modelling conducted by the transmission company Powerlink and AEMO, although the situation is not considered as dire as the West Murray region of Victoria and NSW because there is not a big queue of new projects to join the grid.
Nevertheless, the three solar and wind projects face significant cuts to their output. Sun Metals is a 125MW solar farm owned by the Korean-owned zinc refinery of the same name, and accounts for one third of its power needs. It has been operating for two years.
Haughton is a 100MW solar plant owned by Pacific Hydro, and has been operating for six months and has plans to grow to up to 500MW, while Mt Emerald is a newly commissioned 180MW wind farm owned by Ratch Australia.
Indeed, without the Barron Gorge and Kareela hydro plants in operation – both of which are now owned and operated by the newly created state-owned Cleanco renewable energy generator the three projects face major cuts to their output.
An advisory issued by AEMO says that the three projects can run at full capacity only if Kareeya and Barron Gorge are operating all their units, and flow is less than 300MW from central to north Queensland, and a certain amount of coal generation in the centre of the state such as Gladstone, Stanwell and Callide.
If one unit at Barron Gorge is not running, the allowed output for the three affected wind and solar projects falls to 80 per cent, and to 70 per cent if Kareeya also halts production at two of its units. However, if the 5 approved combinations outlined by AEMO are not met, then the output of the three renewable generators will be slashed to zero.
Alex Wonhas, the head of system design at AEMO, told RenewEconomy that the system strength issues had been identified by new and detailed modelling, and while there are many solar farms in the region, these three projects were impacted because of their specific location.
“We are in a much better position in north Queensland than we are in West Murray,” Wonhas told RenewEconomy. “That’s because of Cleanco – and the hydro plants in Barron Gorge and Kareeya which can provide local synchronous generation.
“There are circumstances when we can get all the power (from the three affected generartors) away.”
Wonhas indicated that some of the affected generators will work on their own system strength issues – possibly with the addition of synchronous condensers, while the two hydro plants operate by CleanCo could also operate in “syncon” mode.
Wonhas says he was confident that other further modelling in other regions will not expose similar problems. “I hope we don’t see any more of those surprises,” he said.
CleanCo is expected shortly to announce the winners of the long delayed (more than two years) of its RE400 tender, which will seek the combination of renewables and storage facilities, although it is not clear whether this will address the issue at hand.
Another major hydro generator, the Kidston pumped hydro project, has been delayed because of a decision by EnergyAustralia to renegotiate the terms of a contract with the owner and developers Genex. A decision on that development is expected later this year.
(Updating story to clarify role of inverters and flows from central Queensland).