AEMO to fast-track “grid forming inverters” to help transition to 100% renewables

In the electricity world, it’s about as significant as the transition from analogue to digital, and Australia’s market operator has now openly admitted that the key to the country’s “once in a lifetime” energy transition will be found in advanced grid-scale inverters.

The Australian Energy Market Operator on Thursday published a “white paper” on the subject that it hopes will help fast track the deployment of big batteries with grid forming inverters, to support what is say is the “undeniable” transition to a grid with little or no synchronous generation, such as coal-fired generation.

“The NEM (National Electricity Market) is undergoing a once-in-a-lifetime transition from synchronous generation, such as thermal and hydro, to variable inverter-based renewable generation,” says Chris  Davies, the head of AEMO’s Future Energy Systems.

“When offline or decommissioned, synchronous generators can no longer provide the critical system stability capabilities that the grid relies on, requiring these capabilities be provided by different technologies.”

Davies says that AEMO has been working with  stakeholders to understand the potential of so-called grid-forming inverters to address many of the challenges facing the future power system.

As mentioned at the top of this article, this is as profound as the switch from analogue to digital, with the added complexity that AEMO needs to try and manage the transition from incumbent to new technologies and keep the lights on at the same time.

Inverters are used in large wind and solar farms, and rooftop solar and battery storage, and while they can deliver key grid services such as frequency response and inertia, they are largely “grid following”, meaning that they respond to the dominant signals on the grid.

Grid forming inverters, also known as “virtual synchronous machines” when paired with sophisticated software, are used in off-grid situations, and are increasingly used in bigger networks (such as the Pilbara) and more recently on the country’s main grids.

As AEMO notes, the terminology around them is still not defined. Broadly, though, grid forming inverters can set their own internal voltage waveform reference, and can either synchronise with the grid or operate independently of other generation.

The response from AEMO and the country’s biggest network operators to the renewables transition to date has been to use old spinning machines known as “synchronous condensers”, which seek to mimic coal and gas generators without actually burning any fuel.

But these machines are cumbersome and expensive, and in the past year or two inverter technologies have been used to find a much cheaper, quicker and more flexible solution to some of the key problems emerging in the grid, particularly as the best wind and solar resources are often found where the grid is weak.

The transition is happening very fast. Just five years ago, AEMO predicted that the biggest battery inverter that would likely be seen on the grid was around 1 megawatt.

A year later, the rapid construction of the then 100MW/150MWh “Tesla big battery” at Hornsdale and its multiple successful interventions in the markets, including keeping the lights on in at several key moments, changed the way many engineers thought about the grid.

AEMO says its new white paper, called the Application of Advanced Grid-scale Inverters in the NEM outlines how the shift from synchronous generation towards inverter-based resources (IBR) is changing the way the industry must plan for the future.

This includes running the grid at 100 per cent instantaneous penetration of renewable energy, including grid-scale solar, wind, hydro, biomass and rooftop PV, the target that has now been fast-tracked to 2025 by new AEMO boss Daniel Westerman.

Davies says the plan is to secure funding and permissions to allow for more grid-forming projects to join the grid, and to show how they can work at scale.

The second part of the plan is fill in the void on specifications to make it easier for developers to specify their requirements to design inverter offerings. That’s a process that is likely to continually evolve.

Davies wants to get as many new grid-scale battery deployments as possible to incorporate grid-forming capabilities, which will be needed to support the transition to 100 per cent instantaneous renewables by the new target of 2025.