The Australian Energy Market Operator has formally recognised that an innovative technology solution based around solar inverters has resolved one of the most vexing problems of the transition to a grid dominated by wind and solar – how to provide “system strength.”
The breakthrough has occurred in north Queensland, where the fine tuning of inverters at four solar farms and one wind farm has allowed AEMO to declare that a shortfall of “system strength” in the region has been resolved.
It is a significant development, because it points to the ability of inverter-based technologies to not just produce and store enough electricity to meet grid demand, but also to deliver the same key grid services that have traditionally been supplied by synchronous generators, such as coal and gas.
Over the last few years, AEMO had raised concerns about system strength issues across the grid, and these have often translated into heavy constraints on wind and solar farms in certain regions, or a requirement to install expensive spinning machines known as synchronous condensers.
One of these regions was at the Ross node in north Queensland, at the heart of the one of the biggest solar provinces in the country. The shortfall meant that under certain conditions, up to 10 solar and wind farms had to dial down their output to maintain grid security.
As AEMO says:
System strength is a critical requirement for a stable and secure power system. A minimum level of system strength is required for the power system to remain stable under normal conditions and to return to a steady state condition following a system disturbance.
System strength relates to the ability to maintain and control the voltage waveform and, among other things, can impact the stability and dynamics of control systems used in inverter-based resources.
Last year, inverter supplier SMA – whose technology was installed at the Daydream, Hayman, Whitsunday, and Hamilton solar farms – started working on a potential solution to “fine tune” the inverters so that they could deliver the system strength deemed necessary by AEMO.
A lot of the learnings came from SMA’s experience in the West Murray region a year earlier, where five big solar farms in Victoria and NSW had their output cut in half for nine months because of the risk of uncontrolled “oscillations” in certain circumstances, a situation blamed on the lack of system strength in the region.
As RenewEconomy reported exclusively in March, the early success of the fine-tuning in north Queensland meant that the issues had been resolved at a fraction of the cost of “traditional” responses using spinning machines.
At the time of that article, final testing had not been concluded at two of the solar farms, but AEMO said on Monday that the change of control settings at the Mt Emerald wind farm and the retuning of inverters at the four solar farms had been successfully concluded.
“Following the implementation of these solutions in North Queensland, AEMO no longer considers there to be a fault level shortfall at Ross,” it said in a report.
SMA’s Josh Birmingham said the company has worked closely with AEMO, transmission company Powerlink and solar farm developer Edify Energy to implement firmware upgrades at the Daydream, Hayman, Whitsunday, and Hamilton solar farms.
“It is fantastic to see the solution developed for the West Murray now providing positive outcomes in other parts of the network,” Birmingham told RenewEconomy.
“Generally, what has been achieved here is a bit of a harbinger for the industry, not just in Australia but globally, as we transition to away from fossil fuel synchronous generation, the grid will rely more and more on inverters to maintain and improve system strength.
“The outcomes in Ross and West Murray are early examples of what can be achieved through innovation and a collaborative approach.”
He also said it was significant in the light of events such as the recent explosion at the Callide C coal generator in Queensland.
“As we move forward, there are further gains to be had with grid forming inverters operating to provide system strength and respond to network events like Callide C.
“Due to the nature of the Australian grid and the high level of renewable penetration at particular times of the day we are going face into these challenges before anyone else in the world.”
Battery based inverter technology have already proven adept at delivering frequency control services to the grid – via the Hornsdale Power Reserve and the other five big batteries on the main grid.
Hornsdale is now trialling – successfully already after the Callide incident – the delivery of “synthetic inertia”, helping to slow down the ripple effect of major events such as the Callide explosion.
Soon, a new big battery at Wallgrove will test out “grid forming” inverters, similar to that already trialled at Dalrymple North and Mt Newman in Western Australia, which means inverters can set the signal for grid frequency rather than just following. It enables a grid to operate on wind, solar and battery storage only.
Regulators are also catching up with the multiple talents of battery storage and inverter based technologies, flagging a new market for “fast frequency control” that uses inverters to respond to grid disturbances at a fraction of the time that it takes coal and gas and hydro generators to respond.
The main rule maker has also dumped its controversial “do no harm” rule that required many wind and solar farms to invest tens of millions of dollars in synchronous condensers that often doubled up at the same location and even threatened to weaken rather than strengthen the grid, according to transmission companies.
AEMO is expected to publish a new paper in coming weeks that will outline the potential of these new inverter technologies in a grid expected to transition rapidly to renewables over the next 10 to 20 years.
And RenewEconomy’s new map of large scale solar projects in Australia: Large Scale Solar Farm Map of Australia