When I was a kid growing up in Yorkshire, wasting electricity was almost criminal. Coming from a place synonymous with frugality, I learned early that every kilowatt-hour was sacred. And fair enough: back in the 1970s, generating each kWh of electricity meant burning roughly a kilogram of coal mined by Arthur Scargill’s finest1.
Fast-forward to today and things couldn’t be more different. Solar and wind have free ‘fuel,’ and we often find ourselves with more electricity from wind and solar than we know what to do with.
The solution: curtailment, the practice of intentionally limiting renewable energy output when there’s too much.
Curtailment means we’re well on our way from energy scarcity to energy abundance. And counterintuitively it is not a sign to slow down or stop building more renewable generation.
Continuing to build more solar and wind capacity, which will only increase curtailment, isn’t wasteful; it’s strategic. It ensures our future electricity mix is cheap, clean, and abundant most of the time.
Renewables Are Already Dominant
To give this some substance, consider the work of renewables expert David Osmond, who runs simple weekly simulations2 of Australia’s main electricity grid using scaled-up amounts of solar and wind generation and real demand data. His findings show Australia can get close to 100% renewable electricity using 120GWh of storage (about 5 hours at average demand). His most recent results indicate that:
- Last week his simulation of Australia’s main electricity grid achieved 99.7% renewable electricity, despite demand being well above average, and wind being below average.
- Over the last 186 weeks, the simulated grid averaged 98.7% renewables, with about 16% of wind and solar generation regularly requiring curtailment.
David Osmond’s latest simulation of Australia’s main electricity grid.
How Curtailment Affects Homeowners
For homeowners with recently installed solar, curtailment can mean dealing with flexible exports, when your solar inverter’s exported power is remotely throttled to manage grid stability (but still producing enough solar to power your home).
I get it: it hurts seeing that beautiful solar curve squashed down on your monitoring app, not to mention losing out on feed-in tariffs (FiTs). But here’s the thing: if you crunch the numbers, at current FiT rates (~5 cents per kWh or less), the dollar loss is small relative to savings from self-consumption of solar.3
Some might still see curtailment as wasteful, but that’s old-school thinking. What really matters now is timing. A kilowatt-hour at 6pm on a cold, still winter evening is precious. But at midday on a spring day, electricity can be so plentiful some customers literally get paid to use it.
The challenge today is balancing abundant daytime energy with storage like batteries and pumped hydro, occasionally supported by gas peakers. This optimal mix lets us rely on renewables without fear during those tricky evening peaks.
Next time you hear complaints about curtailment being wasteful, remember it’s proof we’re on the right track, building enough renewable energy to make Australia’s energy mix plentiful, cheap, and clean. Curtailment isn’t just cool — it’s essential.
Footnotes
- I’m assuming 1970’s UK coal plants were half the efficiency of a modern Australian black coal plant ↩
- Yes – this is a very simplified model of the grid, and we’ll need more than just more generation and storage – but it is all doable if we are motivated ↩
- It would, however, take the sting out if more retailers offered higher FiTs in the late afternoon, rewarding savvy homeowners with big west-facing arrays who contribute power precisely when it’s most valuable. ↩
About Finn Peacock
RSS - Posts
It is OK to just switch off our connection to the grid, but cutting off our solar panels completely when we could be charging the car is really annoying.
Hi Mel,
It’s only very basic backstop control or critical emergency where inverters would be turned off completely.
SAPN are running flexible exports where a grid event would see *exports* throttled to zero at worst.
You can still use your own power.
Total curtailment in which our panels were completely switched off and we could not use the power at all occurred nearly every day in February this year. Feb 2,12, 13, 15, 16, 17, 20, 21, 23, 24, 26 and on March 3, 5, 9 and 14. This is not a seldom used practice.
Hi Mel,
Are you sure it’s network curtailment and not grid over voltage?
Your solar system monitoring should be able to graph what the supply voltage is.
National electricity rules should dictate the DNSP will fix the problem in any case, but you may have to raise a complaint with enough detail they can’t ignore.
Please let us know, the curtailment you’re seeing certainly isn’t cool.
We monitor our solar system with 3 apps: Solar Edge, Amber and Tesla. They log kilowatthours but I do not know that they log voltage levels. But the main reason I think the curtailment is being imposed centrally is that it begins and ends at precise times of each day. For example on the 3/3/25 power was cut off at 10.00 and came on again at 12.15; on 5/3/25 off at 12.00, on at 13.15; on 9/3/25 off at 12.30 on at 15.00, on 19/3/25 off at 12.30, on at 13.00.
Curtailment signalling from my experience is a grubby/messy implementation.
Energex in SEQ uses 50 year old ripple signalling (AFLIC) that really is past its use by date.
https://www.energex.com.au/our-services/connections/residential-and-commercial-connections/solar-connections-and-other-technologies/emergency-backstop-mechanism
AFLIC is a blunt instrument that broadcasts to all/many consumers. That might explain the fixed time experience. AFLIC is also used to switch other devices loke off-peak hot water on or off.
IF a frequency stting is incorrect the receiver could curtail incorrectly. Worth checking.
I also have 3 consumption monitoring systems. Two of them monitor power quality factors. Enphase + Smappee HEMS + myenergi Zappi with triple CT clamp inputs. They exhibit slight value and timing differences so “a man with two watches never knows the time”?
The AFLIC unit connects to Enphase internals and cuts feed-in. The BTM equipment still operates normally with PV input, EV charg
Curtailment means there is a lack of storage pumped hydro is probably the way to go for longer duration storage many many suitable sites and best of all pump’s generation equipment and also earth works can be done using Australian materials and labour helping balance of trade independence and national energy security.
…and/or lack of capacity to handle the PV supply level in the DNSP network.
Flow batteries, community batteries, pole batteries, solar soaking for EV charging etc. are all needed.
Try telling that to Potato Head Dutton.
Even in the nuclear space the man who wants to be leader is well off track.
The potential of pumped-hydro is enormous but don’t expect a man in the Gina Reinhart climate change denying camp to talk about it.
The Chinese have developed THORIUM nuclear technology which might make the rantings of Dutton even more out of step.
This link is well worth watching:-
Hi Howard,
Interesting video but it’s still vapourware at the moment.
I did find it entertaining that the comments about molten salts being highly corrosive was framed by footage of a steam locomotive.
As ever, nuclear is still just a complex and expensive way to turn a steam engine.
As a certified train nut I’d just like to point out that builder’s plate close-up, presumably to highlight Westinghouse, is on a steam-powered air compressor, to run the train’s brakes. AFAIK Westinghouse didn’t build steam locomotives, just braking equipment. (However today’s modern train braking systems the world over are still known as ‘the Westinghouse air brake system’.)
Hi Clive,
The main point is that brass plaques manufactured in London are 100+ years out of date… like steam engines generally.
Nuclear is just a helluva complex way to generate steam.
Good trainspotting though 😉
Renewables Curtailment currently isnt mostly due to lack of storage. Its because fossil fuel sycronous generators like coal and thermal gas can’t derate far enough or are expensive to derate so are a static part of energy mix. Thus renewables are massively curtailed because fossil fuel generators can’t
Curtailment, backstop, I’ve seen another term used in one state, but can’t recall that right now.
Yes, it will become more and more necessary to curtail more often, the more household PV, commercial / industrial rooftop, and large solar / wind farms, get more renewables into the grid.
Here in SA, SAPN have curtailed 2 or 3 times only since flexible exports began some years ago (2020 ?), and the annual test to make sure it’s working, for about an hour at most.
Their written policy is to curtail large solar / wind ops first, then larger commercial / industrial rooftop, then lastly residential rooftop.
“Curtailment means we’re well on our way from energy scarcity to energy abundance.”
Only of we can store it, and use it in non solar hours early morning and evening.
This is vital for residential, as it can make homes with suitable PV size and battery capacity totally independent for grid needs, and have enough to contribute to peak demand times . . . it needs to be a VPP type thing, with excess to a households need put back into the grid when needed in the peak demand, perhaps in exchange for subsidy contribution to get a battery and installation.
Commercial and industry rooftop can also be used if they don’t require battery power after normal business hours, as a VPP type arrangement almost all of their battery excess could be used similarly to assist peak demand times.
There’s a long way to go with that, but experimenting is taking place with trails like the SAPN / ARENA / AGL Solar Grid Savers plan starting May, and they have done a couple of these in the recent past few years here too.
I feel one issue is that some people think curtailment means the inverter is turned off, & their own requirements are fed from the grid. This is incorrect as modern inverters can be throttled back to reduce the grid feed, but self consumption of excess is allowed.
A better way to look at this is thinking of a variable feed in allowance. Many systems are already curtailed due to the Export limit (Rural NSW 3kw/phase in some areas, 5Kw/phase most common). If curtailment is merely seen as a temporary tightening of the export limit, it is less frightening. Also, the daytime grid voltage is often high, so the inverter cannot push much excess to the grid anyway.
Remember: Perception! Perception Perception!. The Media fear-mongering about curtailment is a far larger problem than the actual curtailment.
However, I think energy resellers should be asked to assist customers to better use their self consumption & batteries, if fitted. These retailers should get a report about curtailment, so can pass that information to the consumer.
The problem is that in WA I think this actually *IS* the case.
In a situation where there is so much power they are paying people to use it, they can remotely deactivate your inverter and force you to buy all your power from the grid at 36c /kWh. This is so incredibly offensive – not to mention I don’t know if they actually tell you about it – so unless you’re watching you monitors you don’t know.
In SA it’s all roses, they prevent exports – very reasonable – so yes, some people think the inverter is turned off, because that’s the case.
If this was oil and gas, lobbyists would have sorted it out and the gun lobby would be very vocal.
Pretty sure it is also the case for Queensland for those with systems large enough to require a “switch”, they shut off your inverter which means you cant use your own solar.
All the more reason to get a battery, if it’s benefit viable and one can afford the outlay.
When power is cut, your solar still charges your battery, and the battery can run whatever essential circuits you have decided to have covered.
Not in WA – they shut your inverter down – it’s not generating any power. So the best you might have is a battery to draw down on, unless it relies on your inverter.
Incorrect. The inverter is completely switched off and one can NOT charge the battery or your EV.
Absolutely agree, if you have a battery you can also make some real cash with a controller at the other end of the spectrum to help the grid when there is a lack of energy https://www.smartmotion.life/product/solar-and-battery-controller/
Your figures of 99.7% & 98.7% are misleading unless you include other information. 99.7% is not so impressive if it was for 5 mins at midday.
It’s a simulation or model based on last week’s demand, but if the supply was based on 24GW / 120 GWh of storage plus ~2.5x the solar and ~4x the wind we have now.
There’s more info from David if you click on the links in the article.
I find that very hard to believe, looking at the open electricity data for Queensland for last week, at no time did Coal drop below 40% of the power mix in use. It never does.
Hi Andrew,
Aside from rooftop solar, Queensland is a bit backward in renewables but they’re making progress.
Have you heard about South Australia recently?
Now running a rolling average of 70% renewable over the last 12 months. 80% over summer.
South Australia has just chalked up what is undoubtedly a world first – a run of more than 10 consecutive days over which the average production of wind and solar accounted for 100 per cent of local demand.
No other gigawatt scale grid in the world has come close to this amount of “variable renewable energy”, or for such a long time.
https://reneweconomy.com.au/south-australias-remarkable-100-per-cent-renewables-run-extends-to-over-10-days/
“South Australia set an impressive new renewable energy record in the final days of 2021, with the state’s solar and wind farms and rooftop solar systems supplying an average of just over 100% of local demand every day for a period of almost one week.
https://reneweconomy.com.au/south-australia-winds-up-2021-with-smashing-new-renewables-record/
Net exporting interstate via two interconnections (soon to be three) into Victoria two years running. The world’s first Gigawatt scale grid to have ever been run solely on rooftop solar.
https://reneweconomy.wpengine.com/wind-and-batteries-saved-the-day-when-storm-cut-south-australia-adrift-22060/
https://reneweconomy.com.au/world-first-south-australia-achieves-100pct-solar-and-lowest-prices-in-australia/
https://opennem.org.au/energy/sa1/?range=1y&interval=1M
Like Queensland, VIctoria is also nowhere near having enogh renewables to meet demand. Low prices and curtailment here require two things: lots of solar AND coal generation that cannot or will not turn off. When the coal goes, we will be able to use much more renewables.
David
If SA exports more renewable energy than the energy it buys in, and if renewable energy is supposed to be the cheapest source of electricity, can anyone explain why we have the highest power prices in Australia?
Clearly we need to use more of that power ourselves, so why do we pay higher controlled load prices too???
Hi Tim,
SA has always had expensive electricity.
Initially coal was imported from NSW to Pt Adelaide.
Then mined in Leigh Creek & hauled by rail (with a change of gauge!) 550km to Adelaide.
Then said same coal was burnt at Pt Augusta, less than half the train ride but 300km of transmission (that original line was the only one which didn’t get wiped out in 2016)
50 years ago they built a gas steam plant at Pt Adelaide, now thoroughly out of date, inefficient, inflexible & thankfully half retired.
Should we mention AGL, Origin & Engie all have gas burners in Pt Adelaide and how mysteriously the price goes through the roof at 10:55pm on a windless night. (Off peak traditionally hits at 11pm)
All the while SA has a network footprint the same size as Victoria but with only 25% of the population to pay for it.
And the load is incredibly peaky. The network is built for full utilisation on a handful of hours on a handful of stinking hot afternoons.
So it’s very expensive heavy duty wiring that on average runs at 40%.
At least that means EVs aren’t too hard to cope with provided they’re timed correctly.
The fundamental reason behind SA electricity expense is treason… brought to you by the Liberal Party privatisation of ETSA.
What? A 200 year(!) lease for 2 billion dollars is used in legal schools as an example of a horrendously bad contract.
However it was made worse by cancelling the NSW interconnector 25 years ago. That’s the kind of utterly short sighted sh!t the LNP never seem to be called out for.
Yes that was treason absolutely. Deliberate removal of competition, then selling an asset they knew was less competitive, so the monopoly operator could double the price of power thereafter.
https://www.adelaidenow.com.au/news/south-australia/sa-power-networks-owned-by-billionaire-li-kashing-makes-four-times-more-profit-out-of-us-than-its-uk-group/news-story/d00954c420ee1173a7549360eac879b7
That was a good run down the status quo in SA. No wonder the states are hooked on the postage stamp transmission cost allocation model. How about a run down on Qld? where almost 50% of residential bills is energy movement, transmission and distribution charges. Maybe that cash cow is untouchable? Maybe that is why the pollies can only talk about generation costs be it nuclear solar wind or whatever. Generation is now a minor cost component of residential electricity bills
It’s ironic, that SA with so much renewable energy is paying such a high price per kWh. I feel we are being taken advantage of and nobody is pressuring the retailers to treat us fairly.
Hi Stewart,
As I mentioned elsewhere, SA has always had expensive electricity.
Initially coal was imported from NSW to Pt Adelaide.
Then coal mined in Leigh Creek was hauled by rail (with a change of gauge!) 550km to Adelaide.
Then said same coal was burnt at Pt Augusta, less than half the train ride but 300km of transmission (that original line was the only one which didn’t get wiped out in 2016)
50 years ago they built a gas steam plant at Pt Adelaide, now thoroughly out of date, inefficient, inflexible & thankfully half retired.
Should we mention AGL, Origin & Engie all have gas burners in Pt Adelaide and how mysteriously the price goes through the roof at 10:55pm on a windless night. (Off peak traditionally hits at 11pm)
All the while SA has a network footprint the same size as Victoria but with only 25% of the population to pay for it.
And the load is incredibly peaky. The network is built for full utilisation on a handful of hours on a handful of stinking hot afternoons.
So it’s very expensive heavy duty wiring that on average runs at 40%.
At least that means EVs aren’t too hard to cope with provided they’re timed correctly.
The fundamental reason behind SA electricity expense is treason… brought to you by the Liberal Party privatisation of ETSA.
What? A 200 year(!) lease for 2 billion dollars is used in legal schools as an example of a horrendously bad contract.
However it was made worse by cancelling the NSW interconnector 25 years ago. That’s the kind of utterly short sighted sh!t the LNP never seem to be called out for.
Yes that was treason absolutely. Deliberate removal of competition, then selling an asset they knew was less competitive, so the monopoly operator could double the price of power thereafter.
https://www.adelaidenow.com.au/news/south-australia/sa-power-networks-owned-by-billionaire-li-kashing-makes-four-times-more-profit-out-of-us-than-its-uk-group/news-story/d00954c420ee1173a7549360eac879b7
How do those graphs relate to graphs on apps such as NEM Data and PocketNem, which show that across Australia, coal and gas still dominate the supply by fuel type?
As the post says, it’s “a simple weekly simulation of Australia’s main electricity grid using scaled-up amounts of solar and wind generation and real demand data”. Follow the link in the post for more details of the simulation’s assumptions etc.
I suppose what I was asking is – if I interpret the modelling correctly, in that it assumes the existence of more solar than what we have, more wind generation than what we have, and more battery than what we have, then we don’t need much in the way of “emergency” supplies such as gas fired. If I have interpreted it correctly, then isn’t it just playing with numbers and statistics to show that if we build lots more solar and lots more wind generation, then we don’t need coal generation? Isn’t that a bit like me saying that if I had lots more money, I could afford a Porsche Taycan?
Hi David,
I’d suggest that if you had lots more money you could afford a dozen GWM Ora rather than one Taycan.
Renewables continue to get bigger/faster/cheaper every year so having “excess” energy is a feature, not a bug.
Agreed – I’m not really a Porsche person anyway…..
A bit off topic, but I thought it might be a reasonable topic for someone at SolarQuotes to tackle at this early stage. I’ve had first-hand experience of what can happen when a big bucketload of money (including rebates and incentives) is tipped into new technologies and the take-up is rapid and considerable in size. When the technology asset is nearing its use-by date, there is no “renewal” money available to replace it – Pollies can cut a ribbon on a new piece of infrastructure, but not so with maintenance or renewal, s there is usually no – or very little – money allocated to replacement – especially when it all starts failing at the same time because it was all constructed in a very short time originally. How is Australia placed financially to replace its Solar and wind generation assets and battery storage when they reach EoL? Is it;
– realistically planned and budgeted for,
– given lip service, or
– will the user (us) be expected to pay for the replacements of obsolete and failing energy assets?
Hi David,
I think the answer lies in the design of the national electricity market and the bodies running it. We’ve had 9 years of dithering and active vandalism during which time the LNP only managed to build 1 badly sited gas turbine at KuriKuri as part of the failed “gas fired recovery”
Though Snowy 2 will be a good asset if ever they finish it, the position we’re in now is needing to replace capacity like Eraring as quick as we can.
Renewables are fast to deploy so we should be fine, provided the NIMBYs don’t arc up too much.
I’m still in some disbelief that they decided to rebuild Calide after it self imolated… the most catastrophic and longest ever unscheduled outage on the NEM should have been a wake up call to the Queerslanders.
HI Anthony. Its all very well to say wind and solar provided 100% of power for 10 days. Are there any figures over 365 days.? And also how much did the Wind and Solar farms cost.? Regards Hans
Hi Hans,
They cost much less now than they did when we started 15 years ago and cost continues down.
100% is hard but 98% is pretty doable.
Actually we already have excess renewable capacity going to waste which could be yield that is stored in car batteries and hot water services.
https://m.facebook.com/groups/NEMWatch/permalink/1405330229865617/?_rdr
The network hasn’t melted and the sky isn’t falling in either…
https://reneweconomy.com.au/the-stunning-wind-and-solar-leaps-in-australias-most-advanced-renewable-grids/
Moreover the data is readily verified as we continue the transition. 98% renewables is quite doable with current technology.
https://reneweconomy.com.au/a-near-100-per-cent-renewables-grid-is-well-within-reach-and-with-little-storage/?fbclid=IwAR2iUzugisOp3G1bmwfLUxYQxDPiy_zYX_RzcY4HRwko9muHlqqJu0oI-S8
With many reports of clean cheap energy achieving records in SA, how is this not reflected in the retail price in SA which is the highest in the country?
“South Australia set an impressive new renewable energy record in the final days of 2021, with the state’s solar and wind farms and rooftop solar systems supplying an average of just over 100% of local demand every day for a period of almost one week.”
Curtailment means we’re well on our way from energy scarcity to energy abundance
But it has also been indicated that it could have been Put to better use like the off peak controlled load circuits often used for hot water or floor heating.
The government has given energy relief payments that almost covers the fee charged to be connected to the grid. But how much of this has ended up in at business and government connections.
The modelling of renewables is only considering current usage. If the transition away from home gas and to EV on roads, this would be a major increase in demand that isn’t planned or modelled.
Domestic fridges are a demand that can’t easily be shifted to better suit electricity generation.
All the while there is a large number of people who are not interested for various reasons.
“With many reports of clean cheap energy achieving records in SA, how is this not reflected in the retail price in SA which is the highest in the country?”
If you look at the AEMO dashboard, SA has the 2nd cheapest wholesale prices in Oz so far for 2025. It would be even cheaper if not for some volatile prices like on August 5th 2024, but this volatility should reduce with more batteries and Project Energy Connect. Unfortunately because SA has the more wires & poles per capita than other states its network charges are the highest in the country and this feeds into its high retail prices.
“The modelling of renewables is only considering current usage. If the transition away from home gas and to EV on roads, this would be a major increase in demand that isn’t planned or modelled.”
The AEMO ISP covers future demand in their complex modelling and comes up with pretty similar figures to David’s simple simulation. Both show that you only need a small amount of gas (<5%) and a modest amount of storage to power a high Solar/Wind grid.
Regarding footnote 3, as well as giving premium FiTs for late afternoon supply there should be a premium for any feed in during late autumn & winter months, especially here in Vic. Price signals are very effective at driving behaviour…