Shadow my apologies if I lumped you in with the denialist pillocks. Now they've shown their true abusive colours I'll not bother to have further correspondence with them.

Re my other comment that offended you - so you do in fact "acknowledge that x% of energy generated by renewables means x% less fossil fuels used and nearly that percentage less CO2 emitted"? If so then I apologize for assuming you don't.

Perhaps you'd like to comment on the following from an engineering perspective:
- About what percentage of baseload generation is 'spinning reserve' that is not actually use to generate electricity into the grid? The graph you'll find in the article (link below) shows Northern operating at 40-95% capacity. So coal power stations are obviously responsive to demand, albeit slowly (several hours to ramp up)?

- Northern coal power station in SA, will be closed down for half the year and used only in summer (that's what I meant by mothballed). Why would this not be feasible for more old coal fired plants?

- Playford coal fired plant in SA has been closed down permanently. Does this not belie claims that all or most of the coal generation will need to be retained even with 20% renewables? (I know new gas plants may do this job in the interim, as they are quick to respond to load and much lower emitting, but very expensive to build and use for a few weeks a year)
http://reneweconomy.com.au/2012/carbon-price-claims-sas-largest-coal-fired-generator-95197.

579 - quite right re solar PV/ hot water; those facts and figures were recently published in RenewEconomy.

The resident alarmist/cultist pillock cannot read her own link; it makes no sense; it shows that wind energy has no SMRC before and after the carbon tax compared with the coal power stations.

How wonderful; wind costs nothing. Delusional.

The cultist also says this:

"x% of energy generated by renewables means x% less fossil fuels used and nearly that percentage less CO2 emitted"

No, what it means is LESS energy produced period; and has been noted by everyone with 1/2 a brain, because renewables are so unreliable, fossils need to be kept running continuously to cover the unreliability of the renewables, which means that wind plus backup produces more CO2 than fossils by themselves:

http://wattsupwiththat.com/2012/08/18/mcintyres-talk-in-london-plus-the-uks-tilting-at-windmills-may-actually-increase-co2-emissions-over-natural-gas/#more-69484

Humph

Logged in, went to article and note once again that the OLO author and his OLO tag engages in ad hominem.

No surprise since the author/tag hypocritically cries foul when tables are reversed.

As to 'gold-plating' - yep. Since my last bill ...

'Energy supply' component has gone up 45%
'Energy usage' component has gone up 41%

The latter component specifies the carbon tax as 9.6%

ACCC and IPART have been made aware, I have since changed provider - without a termination fee.

Roses1,

Thanks for the recognition.

As for coal fired power stations, (or any steam based generation system), the turbines and boilers need at least 24hrs to slowly warm up and stabilize before they can be put in operation. Once they are in operation and spinning, the turbines can change load from 0% to 100% in 10 minutes (this can vary between turbines). The limit is really on the ability of the boilers supplying the steam, and this can take 30 mins to go from 40% load to 100% (Pulverized fuel boilers are faster). However, the boilers generally cannot operate much below 40% capacity.

As far as selling power into the grid, the 10 minute time slices that the generators bid for vary in price from $10/MWhr off peak to $4000 for peak generation (typically 6pm to 7pm). The generators make a loss off peak, and a profit at peak. The running at off peak is really to keep the boilers running so that they are ready. Whether they generate power or not below this minimum only gives a slight reduction in coal burnt.

So as far as 1MW of renewable energy replacing 1MW of carbon emissions, this is true at off peak or partially true in shoulder periods, but makes little difference off peak.

Gas powered stations can ramp up to peak from nothing in a short time, but the fuel and stress on the turbines makes this very expensive, and peak supply gas turbines cannot be run in a cogen configuration, making them not hugely less emission intensive than coal.

Thanks Shadow, you've shone a bit of light for me on the questions of steam turbine performance vs gas single cycle.

No comment on Playford and Northern though? (former to be closed and latter to work half the year). The graph in the link I posted earlier shows Northern working from 40% - about 100% of capacity before it was closed down. this would support your statement 'the boilers generally cannot operate much below 40% capacity'.

But I still have a lot of questions on my mind re this issue of base load power required for intermittent renewables. Reckon I might ask Giles Parkinson on Renew Economy if he can get an expert to write an article focusing on this issue, as it has been confusing informed debate.

Roses,

The economics of the plants closing down depend on many factors such as, the cost of extracting the coal, labour, the age and cost of maintenance of the equipment etc, so without detailed information, I can't comment.

The system needs to cope with peak demand, which typically occurs between 6pm and 7pm. Standard solar power here is useless, and wind is unpredictable. I saw a CSIRO paper about 7 years ago calculating that if present day renewables were capable of 100% of generation, base load cover would be 80% to 90%