So far as renewables and storage is concerned, a chart:
This is a daily chart for Victoria over the past 12 months to and including Sunday 13 February 2020 showing wind (green) and solar (yellow) generation only. The solar figures include the estimated total production from small (rooftop) systems as well as large solar farms.
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Looking at that chart, I draw attention to the periods of multiple consecutive days of low yield:
23 - 30 April inclusive (8 days)
11 - 14 June inclusive (4 days)
5 July - 10 July inclusive (6 days)
Those are what I and a few others are calling VRE droughts (Variable Renewable Energy - wind and solar) and looking back over the entire history of wind and solar in the National Electricity Market, we get a similar situation each and every year without exception, there's always at least one so they're not unexpected.
The particularly difficult problems being that they occur at times of high demand, the week 5 - 11 July was Victoria's second highest consumption week for the year exceeded only slightly by the week of 24 - 30 January 2020.
If we include the use of gas, on the assumption that there's a desire to shift that to electricity, then that relationship is even stronger with winter by far the highest consumption season and also the one where VRE droughts occur. Noting that gas dominates the space heating market in Victoria.
THAT is the elephant in the room with all this. How to cope with a week or so of terribly low yields which just happens to coincide with, if we assume a shift to electric heating from gas, the absolute peak of consumption.
Now before anyone says "but that's only Victoria Smurf, it won't happen in the other states at the same time" unfortunately it does. In the context of the NEM, the only state that didn't see low yields at the exact same time was Queensland although even it was below average just not drastically so.
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That the lights stay on is because:
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It's not a coincidence that the period of highest hydro output is the same period as lowest wind + solar output in multiple states. That's completely intentional.
And gas:
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And whilst on a smaller scale, diesel ramped up at the same time too:
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That there is the greatest challenge with all of this.
Storing energy on a short term basis, using the midday sun to run lights at night, is straightforward and very doable. It's the energy equivalent of investing during a bull market - it's not that hard to make it work.
It's coping with the week of poor yields which also sees a jump in consumption that's the hard bit.
It wouldn't be impossible to do it with hydro, from a purely physical perspective it's doable, but the big problem can be summed up quite briefly by saying that there are over 20,000 sites for pumped storage and the fall into two categories:
1. A very large number of individually small sites that store typically 3 GWh each although it does vary.
2. A very small number of individually large sites storing tens, hundreds or even thousands of GWh.
Now to get 8 hours of storage the sites in the first category are very doable. Take a 2 GWh site, install 250 MW of generating capacity and it runs for 8 hours.
Trouble is, if you want 200 hours out of it well now you can only install 10 MW of capacity and that kills the economics stone dead beyond belief. Go down that track and the problem is that, based on AEMO's calculations of 19GW of firm non-constrained capacity required, it's simply cost prohibitive to do it with lots of tiny schemes. They work if you're going to develop them for 8 or 10 hours storage, but not if you want a week's worth since the cost is just too high given the number required.
That leaves the large sites which, due to scale of economy, are far cheaper per GWh stored. One big dam versus a hundred or more "turkey nest" dams - the big one wins hands down. There are sites where 1000 MW or more can be installed at a single location quite easily.
Just one elephant ready to squash the table and all those sitting around it there and I think we all know what that one is - those big sites are mostly in National Parks or other similarly designated areas yes.
That's the primary reason nobody's going anywhere near that one. If we're going to build big dams in National Parks etc then that'll have to come from the Prime Minister, there's zero interest in the industry in starting a war on that scale. Even state Premiers generally won't go anywhere near the concept.
Hence the universal assumption that gas will remain part of the mix going forward with the only question being about the detail of what that gas actually is. Some of it will be natural gas, some will be diesel simply because it's so easy to store as a backup. But longer term there are certainly thoughts that hydrogen could be the gas used and that coal gasification might also play a role.
Personally I'd argue more toward renewables and that a scientific, not political, process ought to be the determinant of whether or not a dam can be built at any given location. There are certainly places that should be left untouched, wilderness has a very real value, but likewise the need to move away from fossil fuels is real and urgent and not everywhere that a big dam could be built is genuinely worthy of protecting.
Politically however nobody's going near that one at least not right now. Gas is the path of least resistance and the one that will be chosen. Hence AEMO and even the existing hydro operators are all working on that basis, gas is part of the mix going forward since politically it's hard to see any other option gaining traction in reality.
All charts posted sourced from OpenNEM