Electricity transmission networks could soon be required to invest in big batteries, or other heavy duty equipment to help stabilise the nation's increasingly fragile power grid.

The national body responsible for setting rules in the national electricity market, the Australian Energy Market Commission (AEMC) said the system had been weakened by the rapid take-up of wind and solar generation and the retirement of thermal generators.

It has called for public submissions on a new plan to strengthen power system security, which includes plans for a new market that would allow wind farms, solar arrays and batteries to provide security services.

What's going wrong?

The transition to a lower emissions power system is presenting a few different challenges for the electricity grid — not least the problem of system security

The AEMC said the take-up of non-synchronous, intermittent generation such as wind and solar was continuing at speed in response to mechanisms such as the federal large-scale renewable energy target (RET).

The transition is being accelerated by the closure of old synchronous power stations, like Victoria's Hazelwood coal-fired plant, which closes next week, and Port Augusta's Northern and Playford coal-fired plants, which closed last year.

South Australia has a high proportion of wind farms and rooftop solar. ( Supplied: timo29570 )

"A power system with increasing non-synchronous generation has less inertia," the AEMC said.

"Falling inertia means the system has less time to recover from sudden equipment failure before widespread blackouts."

These challenges were all too apparent in South Australia last September, when the entire state was blacked out.

With a high proportion of wind farms and rooftop solar, its coal generators closed and some gas generators mothballed, South Australia has become increasingly reliant on an interconnector across the Victorian border to stabilise its grid.

When the interconnector failed in September, there was not enough synchronous generation turned on within SA's borders to arrest the rate of change of frequency.

Wait, what is 'frequency' and what does 'synchronous' mean?

Power grids are complex machines, dependent on the laws of physics.

The national grid, which supplies power from Cape York Peninsula in Queensland to Eyre Peninsula in South Australia, is designed to operate at a consistent frequency of 50 Hertz, or 50 cycles a second.

Traditional coal, gas and hydro power stations are considered "synchronous" because they use turbines or spinning wheels to produce electricity.

Those spinning parts need to stay close to 50Hz to help keep the grid in synch.

The AEMC said "an electricity system that operates outside of these strict physical parameters may become unstable, jeopardise the safety of individuals, risk damage to equipment, and lead to the possibility of blackouts".

The gas power station at Torrens Island in Adelaide is considered 'synchronous'. ( ABC News: Dean Faulkner )

With the right technology, wind turbines can be synchronous, but most of Australia's installed wind and solar systems are not considered to be.

That's because they use inverters to connect to the grid, rather than spinning wheels.

It's up to the Australian Energy Market Operator (AEMO) to keep an eye on frequency across the grid by constantly trying to keep supply and demand in balance.

If too much power is fed in relative to demand, the frequency will increase. If demand outstrips supply, the frequency drops.

Regulators rely on a suite of factors to help keep the grid frequency close to 50Hz. These include:

Inertia: More on this in a minute.

More on this in a minute. Frequency control and ancillary services: This is a market that operates in addition to the electricity market. Some power stations agree to keep a portion of generation in reserve, and AEMO can send signals to generators to "raise" or "lower" their output to correct frequency deviations .

This is a market that operates in addition to the electricity market. Some power stations agree to keep a portion of generation in reserve, and AEMO can send signals to generators to "raise" or "lower" their output to correct frequency deviations Emergency frequency control schemes: When unexpected problems happen, like a big generator suddenly breaking down, an automatic system of load shedding kicks in. This very quickly blacks out groups of electricity customers to try and rebalance frequency

What's inertia?

Imagine a big children's playground, with a series of merry-go-rounds linked together by belt-drive.

If you've got a few big merry-go-rounds, with lots of kids to help you spin them, it might take a while to get this contraption up to speed — for arguments sake, let's say 50 spins per minute.

But once your new playground machine is up and running at 50 revs a minute, it's quite hard to stop. Even if one or two kids get a bit tired, and unexpectedly stop pushing, or even if one crazy kid jumps on board and gets dizzy.

But in the kitty-go-round that is the Australian Energy Market, the biggest merry-go-rounds are being closed down.

It's possible to keep the system going with the remaining ones, but if one kid goes wild and jumps on board for a rest, the whole system slows down much more easily.

What's the proposed solution?

The AEMC is proposing some short-term and longer term measures to address the problems.

These include:

Requiring each state's transmission network to provide and maintain a defined level of inertia at all times. In states with low inertia, such as South Australia, the transmission companies may need to install new equipment, like synchronous condensers, to meet the minimum inertia levels.

Requiring each state's transmission network to provide and maintain a defined level of inertia at all times. In states with low inertia, such as South Australia, the transmission companies may need to install new equipment, like synchronous condensers, to meet the minimum inertia levels. As an interim measure, transmission networks would be allowed to buy fast frequency response services. These services, which could be provided by large-scale, grid connected batteries, are capable of providing a much faster response than traditional frequency control services. In effect, batteries could act as a form of synthetic inertia.

As an interim measure, transmission networks would be allowed to buy fast frequency response services. These services, which could be provided by large-scale, grid connected batteries, are capable of providing a much faster response than traditional frequency control services. In effect, batteries could act as a form of synthetic inertia. All new non-synchronous generators (wind and solar farms) would be required to have the capability to provide fast frequency response services.

The AEMC expects the provision of inertia and fast-frequency control services will, in time, move to a market mechanism.

"One of the things that the transition to these new technologies has brought about is the need for frequency control over much shorter time periods. We're talking fractions of a second," AEMC Chairman John Pierce said.

"We currently don't have a market for frequency control or rather a market that rewards appropriately frequency control over those sorts of time periods."

He said part of the problem is that in the past, grid stability was provided as a by-product of building new generators.

"In the future we want to create an environment where people can invest in these technologies that provide these system services independently of the need to produce energy."

The AEMC hopes to have its new rules in place later this year.

Could South Australia be first?

The South Australian Government has already announced plans to build "Australia's biggest battery" as part of its $550 million energy plan.

In reality, that pledge is to pay one or more battery operators a "capacity payment" to have the right to tap energy off the battery in times of critical need.

Outside those times of emergency, the battery operator(s) would be able to earn revenues from the market, by either supplying energy or frequency control services.

The emergency of new inertia and "fast-frequency response" markets would make the business case for large grid-scale batteries much more attractive.

Several companies have already worked up plans to build batteries in South Australia and have expressed interest in tendering to meet the South Australian Government's requirements.