The role of ageing gas-fired generators may have been part of the problem in the events leading up to the state-wide blackout in South Australia in September, which experts say could have been avoided if the gas generators had been replaced by inverter linked renewables and storage.
A new study by international renewable energy and storage firm RES and engineering group Lloyds Register has modelled the events leading to the September 28 blackout, and suggested that if inverter controlled solar and storage had been in place instead of gas generators, then the blackout may have been avoided.
That’s because new smart and fast reacting technology can respond much quicker to unexpected events than the ageing portfolio of gas and diesel generators. The inverters and storage that go with such systems could have smoothed out the changes in output and voltage, and not made them worse as the gas-fired generators did.
It’s ironic, because the blackout in South Australia has been used by the Coalition government, the fossil fuel lobby and critics of renewable energy as proof that such technologies are not reliable and endanger the grid. The findings also challenge the idea that the situation can be resolved with more expensive transmission lines and more gas generation.
The blackout was caused when huge storms, with winds of up 260km/h, brought down three major transmission lines, in turn causing changes in output and frequency that caused the link to Victoria to separate and the grid to go “system black”.
The fall in output from six wind farms, because they were not programmed to ride through multiple voltage changes, were blamed in some quarters. However, most energy experts say the blackout was inevitable no matter what generation was operating in the state.
Questions have also been raised about why the Australian Energy Market Operator took no pre-emptive action, despite clear warnings of the approaching storm. Its latest report on the blackout is due for release on Monday.
The new study from RES and Lloyds Register suggests the problem may have been in the way that the gas-generators responded to the changes in the network. The sudden changes in output from the gas-fired generators may have made the situation worse, as they did in a previous outage in November, 2015.
Using precise computer models of the South Australian system obtained from AEMO, RES and Lloyds Register looked to see if the system may have performed any differently if the remaining gas generation in South Australia was replaced with inverter connected batteries and solar power.
This is an excerpt from their report:
“The simulation shows the behaviour of the wind generators, gas generators and interconnectors with Victoria in the lead up to the disconnection of the Heywood Interconnector. It starts at 16:17:30 AEST, approximately 45 seconds prior to disconnection of the Heywood Interconnector.
Notice the how the gas units swing up and down, causing rapid loading of the interconnection after the faults at 68 seconds and 74 sections. At the 76 second mark the system voltage collapses. The simulation is stopped at this point, as the models provided by AEMO do not include the very fast equipment protection systems that disconnected the Heywood interconnector (ref 2 p.16) at this point.
So, would the system have behaved any differently if the gas power stations were replaced with inverter connected solar and storage power stations?
To find out, the modellers repeated the simulation with the same fault sequence, and in this case the inverter generators smoothly resume power after the fault, flows on the interconnection remain stable and the system survives.
The “wobbles” in the output from the gas generators disappear, and the system remains stable.
And it should be pointed out that this occurs even with the wind farms losing output from the setting of their fault-ride through mechanisms, which in most cases have since been fixed.
What does this mean?
It shows that inverter controlled solar, wind and storage generation is offering the opportunity to provide much smarter and more stable controls than the previous combination of gas and coal-fired plants. And remember, most of South Australia’s gas plants operating on the day of the blackout are 40 years old.
“While there is much discussion around the challenges of integrating renewable power into the grid, technology is advancing at a rapid pace,” the report says.
“So perhaps a fully secure and sustainable future for electricity is not so far away.”
To illustrate their findings, RES Australia and Lloyd Register are progressing plans for a 100MW lithium-ion battery storage plant in South Australia, in a location that is yet to be revealed. They hope to use this to illustrate the savings that could be achieved from avoiding construction of more transmission lines or more gas plants.
The findings of the study – which are consistent with observations made by the likes of Reposit Power, network operator ElectraNet and even AGL (pointing to benefits of renewables based micro grids), point to the rapid change in energy systems, as dramatic as the switch from internal combustion engines to electric vehicles.
Andrew Jones, from Lloyds Register, says the gas market wobbles are the natural result of a system focusing on “inertia” and “synchronous” generation. Gas plants are like giant flywheels – if the output is blocked, it will suddenly speed up, much like a car might do if you apply the clutch and keep your foot on the accelerator.
Then it tries to back off. In each case, it overheats, leading to the sort of output “wobbles” highlighted by the AEMO data.
“Because the system was on edge, this would have helped push it over,” Jones says. “We are still waiting for data from AEMO, who have said the interconnector was “out of sync” but haven’t explained what they mean by that.”
“But what we do see here is that the inverter connected generation rides through the event.”
Jeremy Moon, from RES-Australia, adds: “There is a lot of talk about power system security. Inertia is seen as key in traditional power systems, but we think we should start to use the battery storage system and want to get that conversation started.”