A few comments and hard facts about SA and my intent is to be politically neutral here.
I've decided to post in the form of questions with the answers since this may help aid understanding I think.
Q. What is the maximum demand (peak demand) for electricity in SA?
A. At the absolute extreme about 3400 MW. A more certain answer that could be expected to be reached in most years is 3150 MW. This occurs late in the afternoon during Summer when it's hot.
Note that these consumption figures do not include power produced by distributed "behind the meter" sources, most notably rooftop solar. The figures relate only to what's supplied from centralised generation sources (power stations, wind farms) into the grid.
Q. How much generating capacity does SA have at present?
A. The output capacity of power stations is subject to various influences, it's not a "static" number, so I've used the capabilities under hot weather conditions here since that's when demand peaks and power is most needed in SA.
Gas-fired capacity including all of Pelican Point = 2522MW. Of this 229 MW is from the second unit at Pelican Point which is not being run unless the owner (Engie) is directed to do so by AEMO.
Oil (diesel mostly) = 239 MW with Snowy Hydro planning to set up another approximately 30 MW of diesel generators in SA as soon as they can. This plant is being physically relocated from NSW so just needs to be dismantled, transported then reinstalled in SA. They have the site etc ready to go. So should be about 269 MW of diesel generation for next summer.
Wind = That's a hard one since the wind speed is always variable. There should be 1194 MW of installed wind generation in SA for next summer, 100 MW of which is still being built.
Reality however is that the wind tends to not blow too strongly at times of high electricity consumption in SA and for this reason AEMO considers that the "firm" (reasonably certain) output of these wind farms will be 112 MW for next Summer. Anything over that is a bonus which can't be counted upon to be available on any given day (especially when it's hot and most needed).
So in total, the capacity of all gas, diesel and "firm" wind generation in SA is expected to be 2903 MW next Summer.
Q. What about breakdowns?
A. Wind farms comprise a very large number of individually small generators such that one failing makes minimal difference overall. Wind speed is the critical factor there.
For large generating plant any engineer would want the system to be able to cope if the two largest generating units were to both be out of service (for whatever reason) at the time of peak demand and this is also the basis AEMO works on.
Based on that up to 458 MW could be lost from the system due to two faults, that being the capacity of the two largest generating units.
Q. What is the capacity of the transmission lines (also known as interconnectors) between Victoria and SA?
A. There are 3 circuits connecting the two states, one DC system (also known as "Murraylink") and two AC lines following the same route (on the same towers mostly).
The AC lines have a theoretical capacity of 650 MW having recently been upgraded. Actual capacity is presently being limited to 600 MW however.
For the DC line there are network constraints elsewhere in the system, particularly in north-east Victoria, which limit its capacity when demand is high in that local region. This arises due to the original construction having been "opportunistic" and simply joining together the two networks which already existed via the shortest route but did not include upgrades elsewhere in the system to handle higher power transfers. So capacity of the DC line will be high when demand in both states is low but can be reduced, sometimes close to zero, if demand is high enough in north-east Victoria. The absolute limit is 220 MW however.
So the total limit for transfer is 820 MW, potentially increasing to 870 MW, however 220 MW of this depends on network loads and conditions in Victoria.
Q. Does Victoria have sufficient power to supply to SA during the peak?
A. In short, no.
Victoria's peak demand is about 10,400 MW at the extreme and generally occurs at about the same time as SA's peak with only minimal difference between them. That's because both states tend to experience major heatwaves at the same time and there's only a half hour time difference (which affects when people get home and turn the A/C on etc).
Victoria's total generating capacity is as follows (this excludes Hazelwood power station, 1600 MW, which closes at the end of this month):
Coal - 4470 MW
Hydro - 2191 MW
Gas - 2175 MW
Wind - 819 MW installed of which 61 MW is considered to be "firm" based on practical operating experience.
So all up there's 8897 MW of coal, gas, hydro and firm wind generation in Victoria.
In addition Victoria can access 594 MW from Tasmania, limited by the capacity of the Vic - Tas cable (Basslink) and can access 340 MW from NSW.
Note - Supply from NSW comes via the same lines used by several hydro stations. When those hydro stations are not operating, additional power could be transferred from NSW however this doesn't help meet peak demand since it's one or the other, you can't have the hydro stations running and a high rate of transfer from NSW at the same time since both use the same transmission lines (which were built for the hydro stations, that they connected NSW and Vic together being just a side benefit albeit a very useful one).
So the limit of supply available to Victoria is 9831 MW, assuming everything works perfectly and nothing breaks down, versus peak demand of 10,400 MW. So Vic does not have surplus power available to supply SA during peak demand times (though it generally does at other times when demand is lower).
Q. Can NSW and Tasmania be counted on to actually supply that power into Victoria?
A. NSW - Depends on the weather. Yes if demand is low to moderate in NSW. No if there's also a heatwave affecting that state since NSW is also running short of generating capacity.
Tas - Yes so long as no major failures occur, the primary risk being failure of Basslink. Assuming Basslink works it would require multiple transmission or generation failures within the state to cause a problem. For transmission that's plausible if lighting or bushfires occur. For generation that's extremely unlikely (the chance isn't absolutely zero but it hasn't happened yet).
Q. So what's a summary of all this? Add all the numbers up please Smurf!
A. Vic and SA can for practical purposes be considered as the same place at times of peak power demand since neither state has spare capacity to send to the other one. As such there's very little chance, at a time of very high demand, of one state having plenty of power but being unable to get it to the other one due to limits on Vic - SA transmission capacity. So for that reason they're effectively the same place - both are in the same situation at the same time.
On that basis, combined peak demand is about 13,800 MW.
Combined generating capacity from coal, oil, gas, hydro and firm wind generation is 11,800 MW with a further 934 MW available from Tas and NSW (with some risk that NSW may not be able to supply its part).
So overall, peak demand if 13,800 MW at the extreme versus supply of 12,734 MW if everything works perfectly.
Since everything won't work perfectly in practice, a more sensible approach would be to exclude the two largest sources of supply on the assumption that something, somewhere, will break (and that sure does happen in practice!). On that basis supply capacity to the two states is about 11,620 MW.
So overall there's gap of about 2200 MW between what we have and what's needed.
Q. How did we end up in this situation? Why haven't I heard about this in the past? What went wrong?
A. Simple answer, in a technical sense, is that a number of power stations in Vic and SA (and also in NSW) have closed in recent times. List as follows:
Morwell (Vic, 190 MW) - closed 2014
Anglesea (Vic, 160 MW) - closed 2015
Playford B (SA, 240 MW) - closed 2016
Northern (SA, 540 MW) - closed 2016
Hazelwood (Vic, 1600 MW) - closing 31 March 2017
Total of all closures = 2730 MW (versus the shortfall between what we have now and what we need of 2200 MW).
So the problem is a recent one, this summer being the first where we didn't have enough overall capacity, hence why it has suddenly become a mainstream issue.
With the imminent closure of Hazelwood the supply deficit is about to increase dramatically.
Q. So why were they closed? Whose fault is that? Why did government let it happen?
A. All are private businesses following the break up and sale of the SECV and ETSA many years ago and, from a legal perspective, as with any business nobody can ultimately insist that the owners carry on operating if they choose not to. (Note that Anglesea is an exception, having always been privately owned since construction).
From a more pragmatic perspective and trying to be non-political:
Morwell and Playford B = worn out and would need very serious $ spent to keep operating. Just not worthwhile with outdated, inefficient plant that dates from the 1950's and 60's.
Hazelwood = needed a lot of $ spent so the owners decided to close instead of fixing it or trying to sell it. 4 (of 8) units at Hazelwood are known to be in bad enough shape that workplace safety regulators got involved and issued formal demands last year. Of the rest, the general understanding is that 3 are "OK for a while" and 1 is "pretty good". The owners have decided to close the whole lot however.
Anglesea - Owned by a company not primarily involved in electricity generation and with no ongoing interest in running a coal mine and power station. They made a fairly serious effort to sell but ultimately could not find a buyer and so closed instead.
Northern - Simply unprofitable since energy retailers and large users in SA were unwilling to sign contracts at a sufficiently high price to make it viable to continue operating. Those prices were, but the way, somewhat lower than the prices now being experienced on a daily basis although that wasn't the case at the time.
Q. Would it be possible to return any of the closed power stations to operation either permanently or as a temporary measure until something else can be done?
A. Some of the info required to properly answer that is known only to the owners but to my understanding:
Playford B - no chance as it's being demolished already (I'm 100% cetain on that point).
Morwell - too many bits, 8 boilers and 5 generators, for too little output so not really worth bothering with unless someone wanted to resume manufacturing briquettes at the associated briquette factory. In the absence of that aspect, as a power station it would be more sensible to just build something new from scratch.
Hazelwood - doable if someone's got enough money to throw at them. Could run the 4 units that are in reasonable shape and for about $140 million they could get a few more years out of the others too although that would take some time to implement.
Anglesea - unsure whether or not they've started demolishing anything or not. If not then it wouldn't be overly hard to put it back into operation, a few months at most, although the local community had a strong dislike of the plant prior to closure and would thus likely protest etc.
Northern - fairly straightforward. Just need to get miners back at Leigh Creel, start mining again, check that everything's OK to run and and so on. A few months.
Of them all, Northern is in the best condition, is the most modern plant and needs the least effort to do a re-start.
Q. Does the SA government's plan fix the problem?
A. They're going to add 250 MW from gas plus 100 MW from batteries. That does't fix the problem for Vic + SA by any means but it would greatly reduce the frequency of problems in SA if (1) they can ensure that the owners of other power stations don't close them and (2) can make sure that nobody decides to "share the pain" and black out SA in order to send power into Vic.
It's not a total fix for SA, get a properly hot day with no wind and they're still in big trouble, but it will reduce the frequency of blackouts compared to what would occur without it (assuming it's actually built etc). It's nowhere near enough to be a complete solution however.