Relief for five constrained solar farms as new inverter “firmware” passes test

The owners and operators of five solar farms in Victoria and NSW that have had their output cut in half for the last seven months have breathed a sigh of relief as new inverter “firmware” designed to avoid uncontrollable “oscillations” successfully passed a week-long series of testing, leading to a lifting of constraints.

The five solar farms affected – Broken Hill in NSW, and the Karadoc, Bannerton, Gannawarra and Wemen solar farms in Victoria – were told in September last year that they had to switch off half of their inverters because of concerns provoked by new, detailed modelling that uncovered the potential of “uncontrolled oscillations” if a major transmission line was lost.

That event has not actually occurred, and many of the solar farms had been operating without incident for many years. The decision took 170MW of solar capacity out of the system, and hobbled the output of four of the five large scale solar farms in Victoria.

Initially, the owners and operators of the five solar farms were told that the constraint would last only weeks, but the issue proved harder to solve than first thought, and it has had a contagion effect on the industry by causing delays to commissioning and connection approvals for more than a dozen other large scale wind and solar projects.

This week, however, new “world-first” technology from SMA – whose inverters are, coincidentally, common to all five affected solar farms – was used in a series of tests where a major line – in this case the MurrayLink from Victoria to South Australia – was deliberately “opened” (confusing network talk for being taken out of operation) and the solar farms gradually ramped up to full capacity.

The final test – at 100 per cent of inverters – was conducted on Friday, allowing the five solar farms to produce at full potential (weather conditions permitting) for the first time since early September. Broken Hill went first – just before noon (orange in the graph above)- and was followed by others soon after 1pm.

The initial assessment was so good that the solar farms – according to the data on various energy apps – continued to operate with all their inverters into the afternoon (the graph above was taken at 3pm), even though a formal removal of the constraints may not be confirmed until early next week.

AEMO later confirmed that the constraints had been lifted, saying the removal would be “provisional” pending further monitoring.

“The scale and pace  of inverter based solar and wind generation connected in remote and electrically weak areas of the National Electricity Market, like the West Murray Zone, is presenting grid performance and stability issues,” AEMO head of engineering Alex Wonhas said.

SMA’s Scott Partlin, who has been leading the team seeking to find a solution to the problem, told RenewEconomy earlier this week that it was the first time this new “firmware” had been used anywhere in the world, and there was much interest in its success.

One grid operator in the US, which he did not identify, was considering its application to deal with potential issues with a big new solar farm.

“This has been developed to address this unique problem of low system strength,” Partlin says. “It’s the same hardware, but with new functionality and different code.”

And the fact that it could be adjusted by code, and remotely, pointed to the changing nature of the country’s, and the world’s energy systems. “Imagine if this was an issue with a coal fired generation. You’d have to build something, install it, commissioning. We’re solving a problem with 2- to 30 people across the globe login in with computers. It’s a sign of the new world to come.”

On Friday, Partlin said the SMA teams in the utility service team in Australia and the R&D engineers in Germany deserved great credit.

“This week has seen the culmination of a lot of hard work … this week had opportunities everywhere for things to go wrong. But the team has put it a lot of work planning and getting sites ready, all while under the increased difficulty of COVID-19 and being forced to do it all remotely, and they didn’t miss a beat.

“The Generators and their consultants have been through some very stressful and long work weeks these past months trying to satisfy what is necessary under our regulatory process.

But even that would not have been possible without the collaborative approach AEMO has taken in recent months, working with Powercor, with SMA, with the Generators and their consultants. What SMA is most hopeful of after the dust has settled on this, is coming back together with AEMO and other stakeholders to look at how we can learn from this as an industry.

“There are plenty of lessons to be learned which could go a long way to bringing a lot more investment confidence back to the large scale renewable energy industry. It shows what can be achieved when all the parties are working together to deliver a power system with is delivering low cost energy, is secure and reliable, and is seeing ever increasing amounts of renewable generation connect.”

System strength issues have also been detected in other parts of the grid, most recently in north Queensland where two solar farms and one wind farm have been told their output would be constrained to zero in certain conditions.

AEMO and network operators are looking to solve these solutions with a mix of short and long term solutions, including the upgrade of inverter technology, such as in the West Murray region, medium term grid solutions that could include synchronous condensers, and longer term solutions such as additional grid capacity and links.

The resolution of the West Murray issues should now allow other projects – many near complete – to finish their commissioning process, although they have been warned that this may happen “one by one”, to ensure that there are no further congestion issues.