hermit, you're wrong about the basis of my assumption. It's based on the law of conservation of energy: if you're taking more energy out of the system (via the turbines) then to maintain a constant temperature you have to put more in (by adding more coal). Conversely if the turbines are running on a lower power setting, they're not removing energy as quickly, therefore to keep the temperature constant doesn't require coal to be added at the same rate.

I don't know where you got the crazy idea that you can't vary the fuelling rate. Did you read that some nuclear plants have this problem, and then assume the same was true of coal? Or were you basing it on the report in The Australian that Victoria's wind turbines hadn't resulted in any decrease at all in the amount of coal that state burns for power? If the latter, there's something important you should know: the reason is that the extra power was exported to NSW!

Switching it off completely is a different matter. Yes it takes a long time to power up again, but we do have pretty good weather forecasting ability; we know when the wind's coming, and conversely when the lack of wind's coming.

And if you do shut it down, is there actually any need to let it cool before powering it up again?

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Raycom, a more effective way of regaining Australia’s natural energy cost advantage would be to exploit the lower running cost of renewable energy generation by funding it with concessional loans.

Peter,
Your comments on effectiveness are hard to interpret.
Consider a single turbine - it generates electricity when sufficient wind is blowing. Its effectiveness in generating power is totally dependent on the wind regime.
Now place a second identical turbine nearby. Its effectiveness will be identical, provided they both have unhindered wind flow.
Each M Watt generated abates the same amount of CO2 - provided wind generated electricity is dispatched ahead of coal generated electricity.
Put a hundred in very similar wind regimes, and effectiveness per turbine does not alter (roughly).
Now, add battery storage to each turbine, using Tesla batteries or similar, and effectiveness increases as electricity is only drawn when required, and electicity is stored when not needed.
What have I missed?

Aidan, I have never suggested that you can't vary the fuelling rate. I suggested that that is not what is happening in reality. I understand that for less required output you need less heat. But that doesn't mean that's how it works at the practical end. You are right about the physics. But I question practicality of changing fuelling rate every 15 mins. Even every 30 mins. Even every hour. We are talking about large amounts of water. And to rise the temperature of large amount of water, even marginally, takes time and lots of energy. It takes less energy to keep water at the same temperature and just release any unneeded steam. I got this idea from some coal power generation engineer. And it makes sense to me. The consumption of coal is meaningful only nationally. As you point out, exporting power to other states can give distorted picture.
Hermit