I'm sure smurf would be able to say whether the companies were warned that an over supply situation might occur
I'm somewhat typecast as 'that guy' who's been on about it for a very long time.
I claim no special brilliance there, it just comes down to math.
Solar output from fixed position arrays (eg rooftop) will as a whole peak at midday and that peak will, depending on what assumptions you make about the orientation of panels in the real world, be circa 5 times their average output.
Meanwhile electricity demand at midday is moderate. It's not the minimum but it's nowhere near the peak either. During hot weather the peak of consumption is mid-afternoon. During cold weather it's a bit after 6pm with a secondary peak in the morning circa 8am (exception of Tasmania where the morning peak is the larger of the two). Demand at midday is thus either on the ramp up (hot weather) or is the lull between two peaks (cold weather).
From there it's just straightforward math. Put one solar power system on one roof and it's irrelevant but put more of them up every day and a point comes where it fails to work. Just because getting 10% of annual generation from solar is easy, doesn't mean you can just install ten times as many panels and get 100%. A point comes where that approach stops working.
Now for the painful and brutally honest bit, rooftop solar has a lot in common with using trucks to move freight.
If you want to move small amounts of whatever well then just buying some trucks and driving them on existing public roads is a perfectly reasonable way to do it.
If however you want to move millions of tonnes of freight each year well then no, buying a lot of trucks, widening all the roads and turning the town's main street into a highway starts to become a dud idea. Better off building a railway line that goes around the town not through it in that case or using some other method to move the freight (for one of the more unusual, iron ore from a mine in Tasmania is transported by pipeline, not a single truck or train involved from the mine to the pelletizing plant 85km away).
Now for a couple of charts:
Rooftop solar generation in Queensland over the past 3 days:
Yellow is solar output, red line at the bottom is market spot price.
Now for large scale solar farms in Queensland over the same period:
Large solar farms intentionally located in places highly suited to them, and with single axis trackers on the panels, achieve a far more consistent output day to day, and throughout the day, than do fixed position panels on house roofs with sub-optimal orientation and no tracking.
A small large scale facilities is also much more easily adjusted to match consumption versus trying to fine tune the output of a few million tiny systems each subject to their own issues with shading, weather and so on.
Note last Friday and Saturday, and for shorter periods Tuesday and Wednesday this week, for large scale solar in SA:
It can be and routinely is cut back when the full output simply isn't required. In that regard it's just as controllable as any other power station.
Where all that goes is that putting solar panels on house roofs makes perfectly good sense so long as it can make use of existing infrastructure, akin to using trucks to move modest amounts of freight on existing roads.
Once it comes to having to upgrade electricity networks though, well it's much like freight. A separate large scale option is a cheaper way of doing it. In this case, that's a few large solar farms and transmission lines.
In that context it needs to be remembered that in Australia it's the "electricity" bit which is valuable not the "rooftop". If there's one thing we're really not short on, it's land that's not useful for much. The only reason to put panels on a roof, instead of putting them somewhere else, is to make use of the electrical infrastructure that's already present, that the house is connected to the network. All good but once it comes to the point of having to spend a fortune upgrading the network, well it's cheaper to put them somewhere else where that problem doesn't exist, near a transmission line, rather than having to spend all that $ on upgrading a network to cope with power flowing in the opposite direction.
For that reason I've long maintained that we'll get to roughly 50% of homes with solar then that's it, the economics preclude sensibly going any further. On a state by state basis at present (data is from late 2020, exact date varies between states):
Queensland = 39.8%
SA = 39.3%
WA = 32.2%
NSW = 24.6%
NT = 22.8%
Victoria = 20.9%
Tasmania = 16.3%
That said there are state-specific issues which will influence the limits:
Queensland and Tasmania both have a relatively consistent electrical load overall which facilitates a higher use of solar in those states.
SA, Vic, WA all have the basic problem of a network that wasn't built with high capacity and a highly variable load which tends to be low when solar output is high. That's not a good situation and limits the deployment of solar in those states. Tasmania's the opposite - high network capacity per customer and relatively more stable demand.
NSW and Queensland both have an advantage of a high portion of homes having electric hot water on a remoted controlled off-peak tariff, enabling a substantial load to be intentionally switched on during the middle of the day as a workaround. They also have a pretty decent network.
Tas has extreme dominance of electricity for water heating, market share is about 94% if heat pumps are included, but it's not under any form of remote control. Much the same in the NT although hot water energy use up there isn't the big load that it is down south, it's not a factor to worry about really.
SA, WA and especially Victoria gas water heating dominates and what electric water heating does exist mostly isn't under remote control (or any time control at all for most of them in WA's case).
So broadly Qld, NSW and Tas are in a good position to accommodate a lot of solar whilst Vic, SA and WA have more limitations. NT it really depends on what town you're in.
Me personally?
Yes I have solar. Just over 5kW, that being limited by unshaded and otherwise suitable roof space. Suffice to say every panel that could be fitted up there is up there and without cutting down three large trees, there's no real benefit in adding any more.
Yes I have a battery.
Me being me, the hot water's heated by a heat pump and that's very intentionally powered between 10am and 3:00pm ACST only. This is on the Off Peak Controlled Load meter and is separate to the solar. That detail isn't about when I use hot water, it's just about intentionally shifting load to when supply is abundant - quite often I'm heating water using wind or solar energy that would otherwise go to waste.
Now if it were up to me then I'd be doing two things right across SA (and Victoria).
1. Change the operating times of electric storage hot water from night to middle of the day. Only reason it hasn't already been done is in SA bureaucracy and regulators (of the legal and economic variety) are in the way and in Victoria's case they installed smart meters without enabling any smart functionality.
My view is get it done, do it now, worry about bureaucracy later.
For the Type 4 meters just tell the retailers to do it ASAP. It can be done remotely since the meters communicate. Could have the whole lot done within two days.
For the Type 5 meters it needs someone to go around each house physically and change the programming. No problem - just get a list, some workers and some cars and go do it.
Every house with solar installed prior to December 2017 will have a Type 5 meter, everything more recent (including new homes or meter upgrades without solar) will be Type 4 meter.
For Type 6 meters, the old rotating disc and analogue timer, well changing that is clockwork, literally so. Cut the seals, pull the cover off, undo two screws one on each timing pin, move the pins to the required times by sight, tighten the screws, lap the dial to make sure it works and set it to the present time, put the cover back on, apply new seals. Only takes a few minutes each and it's all mechanical, zero electronics in those.
Could do all the Type 4 straight away, Type 5 over 12 months, Type 6 over 3 years would be about right and fast enough to be a solution.
2. Given we've all this renewable energy available during the middle of the day, and storing hot water is about as easy and low tech as it gets whilst still being reasonably efficient (circa 85% in practice), it really doesn't make sense to continue pushing the public to use gas for that purpose.
WA and SA both do it to some extent at the state level but Victoria's extremely forceful and so are some individual councils in NSW. Might have made sense sometime but those days are over - heating water, especially with a heat pump, using solar that's otherwise being wasted beats gas for sure.
Note that I'm not advocating that gas be banned or anything like that, only that the practice of pushing consumers toward it as a means of water heating be ended and that heat pumps running on controlled load supply be encouraged instead. But if someone still wants gas well OK, no problem.