Here's some early calculations and commentary.
Taking a neutral perspective, the big question is what is the ultimate goal?
Most analysis of energy options over the past 50 years, that being as long as there has been any real contention about the issue in Australia, from an "environmental" perspective have always implicitly assumed that fossil fuels, primarily coal, would remain the predominant source of generation indefinitely.
That assumption was embedded in the debate about Newport D power station in the 1970's. Coal was going to be the future, anything else including Newport D was a sideline.
It was also the underlying assumption of all anti-nuclear argument here and overseas. Indeed one anti-nuclear catchphrase at the time widely used in the USA was simply "why not coal?".
From the 1990's to today there has been a lot of argument favouring the direct use of gas in homes and businesses for space heating and in particular water heating. That ended up going as far as one state government (Victoria) making it all but compulsory to do so and two others (WA, SA) gave a push in that direction. Again, the underlying assumption was "coal forever" so far as electricity generation is concerned.
Now with Snowy 2.0, or indeed any pumped hydro, the same argument once again applies. Assuming coal remains the predominant source of generation indefinitely then two things are true. One is that it would increase emissions compared to a new coal-fired power station and the other is that there's no actual need.
On that I will make two observations, one of which is fact and one of which is opinion. Note that I am referring to the combined NSW, ACT, Vic and SA region in this context. That is, the National Electricity Market excluding Queensland and Tasmania due to the different circumstances in those two states and the constrained interconnector capacity Qld - NSW and Tas - Vic.
The first, factual, one is that if coal is to remain the mainstay of generation then we need to build more capacity to replace that which is wearing out. Liddell is 48 years old and not in good shape, Yallourn W 1 & 2 are 46 years old and so on. All except two coal-fired generating units in NSW, which have a combined capacity of just under 10% of the state's peak demand, are likely to be shut by the mid-2030's with significant closures during the 2020's.
Meanwhile Victoria already lacks sufficient generating capacity to reliably maintain supply - this summer's load shedding certainly won't be the last such incident if nothing changes and it was pure good luck with the weather that such a high level of supply just happened to be available from SA at the time, otherwise it would have been far worse. No guarantees that there's a cold change in Adelaide next time it gets hot in Melbourne of course.
Whilst wind and solar are adding
energy as many have pointed out, they are not adding much in terms of useful firm
capacity. In the context of a predominantly fossil fuel based system they reduce the quantity of coal (or other fuel) consumed and associated emissions and they reduce the electricity generated by coal-fired power stations but they do not meaningfully reduce the installed generating capacity needed.
The simple reason there is that demand peaks late in the afternoon / early evening when solar output falls steeply and wind generation is commonly low under the same conditions. At least it is at all present wind farms sites in SA, Vic and NSW.
As such, and in view of the impending closure of existing plant, there's a need to build
something which operates as and when required. From a technical perspective it matters not whether that's coal, gas, oil, nuclear, hydro or whatever so long as it generates regardless of the short term weather.
The second point, which is my opinion only, is that the CO2 and climate change issue is probably real and that, whether or not it is real, the international community seems to be moving firmly in the direction of reducing emissions.
I have zero qualifications concerning climate but having read plenty on the subject over the past 30 years that's my conclusion. No doubt there will be some political posturing and so on involved but the issue as such does seem to be real. Regardless, it seems that action is going to be taken.
That being so, it seems very plausible to me that the underlying assumption that coal remains the predominant, and marginal, source of generation is incorrect. An alternative future where coal-fired generation progressively declines to literally zero by the late 2040's seems at least plausible. Critically, it is the assumed future and business plan to which all major owners of current coal-fired generation are actually working - all existing coal plant in the NEM is planned to be closed within the next 30 years and most of it considerably sooner.
If that's so, if coal is going to zero, well there's not much point committing to new coal-fired plant now and then having to build batteries or pumped hydro to replace the relatively new plant a few years later. May as well just do it once, build the pumped hydro now, and live with any short term costs either economic or emissions.
The life cycle of all this stuff is relatively long. The decision to develop Yallourn W was made in 1966 and it's still fully operational today (announced closure is in 2032). Bayswater and Eraring commitment was late 1970's and both will be generating through to the mid-2030's. Etc, it's all fairly long term stuff.
I haven't mentioned gas for the simple reason that, on the context of south-east Australia, there's quite a scarcity of the stuff and we are of course already effectively committed to ongoing use in homes and business through to at least 2050 indeed the infrastructure is still being expanded. That in itself isn't a great idea if we do end up with 100% renewable electricity or close to it, but that's another story.
In SA the Cooper Basin production is slowly trending down and has been for years. It used to supply all of SA, NSW and the ACT but SA itself now uses more than it produces and that's due to production decline not rising consumption. NSW, ACT and Tas are all totally reliant on supply from interstate.
And of course the big one, Victoria which presently supplies it's own consumption, 100% of Tasmania's and a fair bit of that for NSW/ACT and SA. All good until the expected production nosedive about 5 years from now turns Victoria itself into a net importer of gas. Importing from ??? Importing from overseas realistically hence the now 4 LNG import terminal proposals - one each in NSW and SA and two in Vic.
All that being so, the choice for new dispatchable generation capacity really comes down to:
Open cycle plant fueled by imported LNG or diesel. This carries the risk of fuel prices, physical supply from overseas and the value of the AUD given that pricing is in foreign currency.
Coal. Could be done but in practice would be a government project and carries the risk that the international community forces cuts in emissions within the next ~50 years.
Nuclear. As with coal would be a government project in practice almost certainly. Big hassle would be getting it done quickly enough - construction alone would use up most of the available time so would need a "wartime" approach where planning proceses are suspended and construction just gets going ASAP using an "off the shelf" design purchased from France, UK, USA, China or wherever. Chance of it actually happening = virtually zero.
Pumped hydro built upon an assumption that new wind and solar is later built to do the pumping. It carries the risk that the future does turn out to be coal or that battery prices plunge. That said, in the event that the "problem" is cheaper batteries, the pumped hydro remains useful as such just unnecessarily expensive.
So there's no no-risk option but personally I'd take pumped hydro (or batteries) and a gamble that wind and solar will be built over a gamble on international oil/gas prices or that the CO2 issue turns out to be false. Nuclear I just can't see happening in the required time so I don't take it seriously for that reason.
For reference, announced closures of existing plant over the next 15 years:
Torrens Island A (SA, gas, AGL), 480 MW closing progressively 2019 - 21
Liddell (NSW, coal, AGL) - 1680 MW in 2022
Vales Point (NSW, coal, Sunset Power International) - 1320 MW in 2029
Yallourn W (Vic, coal, Energy Australia) - 1480 MW in 2032 (but a lot of speculation that could go earlier given the age of units 1 & 2).
Closely followed by Bayswater (NSW, coal, AGL) - 2640 MW and Eraring (NSW, coal, Origin Energy) - 2800 MW in the mid-2030's with both companies having announced plans to that effect.
Whilst everything I've written here is "off the top of my head", if you were to read a stack of AEMO reports and those of generating companies and gas companies then ultimately the information is all publicly available. None of it's secret in any way, including the closure dates I've mentioned - they're the dates given by the relevant companies and being used by AEMO and others (including rival generating companies) for planning.
At a recent workshop run by AEMO there was agreement among multiple generating companies and others (networks etc) that one thing needing to be considered is that these dates could well be earlier but are unlikely to be later. That is, if something has a technical life through to 2032 then that's a "hard" limit but it doesn't preclude earlier closure due to financial concerns or if a major incident were to occur (eg fire etc). AEMO are going to try and model some more realistic scenarios taking this into account.
Another complexity is fuel prices and any emissions price. For one random example, if AGL are going to become a major gas supplier (importer) in Victoria as seems reasonably likely then what price will Energy Australia be paying for AGL's gas which EA will then use to compete directly against AGL in the electricity market? That's not suggesting any wrongdoing by either company, for the record Alinta already buys 100% of their coal from AGL's mine literally just across the road, but it does get a but murky in trying to work out the costs and what decisions that will prompt.