I suppose I shouldn’t be so despondent about this article; nonsense like this is why I started this blog. I am referring to an article in the Australian yesterday, which talks about a study which suggests that wind-farms don’t actually save any emissions, because the coal fired power which they are displacing is baseload.
It ran in the Australian, so to engage with this “debate” you’ll need to follow this link, then click on the first article “Hopes of slashing greenhouse emissions blowing in the wind.” Go and read the whole catastrophe and come back.
While you’re at it, if you haven’t read the first baseload post here that will provide some background.
The thrust of it is some research conducted by Victorian mechanical engineer Hamish Cumming, who has looked at “publicly available data” and determined that because there is no evidence in these data that the coal plants are burning less coal, then obviously the windmills aren’t abating any carbon.
I will leave aside the carbon permit and subsidies claims, that will take another post to tackle properly, and concentrate on this analysis. How right is he? What assumptions support these findings? Is the data actually available to make this determination?
From the article: “A forensic examination of publicly available power-supply data shows Victoria’s carbon-intensive brown-coal power stations do not reduce the amount of coal they burn when wind power is available to the grid.”
Is evidence of whether or not the coal fired power-stations are ramping down when wind comes on, evidence that the turbines are abating carbon? No.
The only reliable measure of how much carbon is abated by renewables and whether or not they are making a difference is in the long-run averages; by looking back over a year of data and comparing the MWh generated across the network with the tonnes released. If we start generating more electricity per tonne of CO2 then both renewables are contributing and the carbon price has had an impact. The data that is being described above does not include any hard data about tonnes emitted; this is a closely kept secret of the generating companies as it directly affects their competitiveness in the market. Note too that he has only considered Victorian power-stations; there is no requirement that the stations that power down are the ones near by, nor any requirement that the most polluting ones power down. Sure, it would be good if that did happen, but current thinking is that with a carbon price the most polluting plants will be proportionally less competitive, and so will be dispatched less frequently. If abating carbon was the only goal of the market then the bidding order would be based on carbon intensity and Hazelwood would only get dispatched a couple of times a year. But, the market is based on cost, with the addition of a carbon price a pollution proxy and so the most expensive generation is turned off first. Not the most polluting.
“Cumming says surplus energy is wasted to make room for intermittent supplies from wind.”
I have considered a whole post on this idea previously, but we can tackle it now. This statement show a disturbing lack of understanding for how electricity and the network actually operate, with a fair degree of entrenched baseload thinking to really skew the statement . What on earth is surplus energy? Our grid operates on alternating current (posts on this are at my old blog, here, here and here) and is managed to maintain frequency. Demand loads come and go during the day and generation is tuned to meet demand. If the frequency drops that means more demand has come on and so more generation will be dispatched. Obviously the reverse applies as well. The frequency is managed extremely tightly; if it gets too far from the 50Hz that equipment across the grid is designed to use, that equipment starts breaking. So frequency is managed to 50Hz, +/- 0.15Hz and if it goes beyond that emergency protection settings are enacted and loads get dumped. Note that nowhere in here is any mention of surplus energy (actually electricity, but that distinction doesn’t seem to matter to many). We always generate exactly the same amount of electricity as we use. Always. So while the signal of Victorian brown coal generators turning off at exactly the same time as wind turning on is not visible, it is wrong to use this information to make claims about whether or not any greenhouse emissions have been saved.
“Cumming’s findings have been confirmed by Victoria’s coal-fired electricity producers and by independent energy analysts who say it is more efficient to keep a brown-coal power-station running than turn it down and then back up.”
There is some ambiguous language here, but I am sure that the coal-fired power-stations would have confirmed that they prefer not to change load. That’s what baseload means. That doesn’t mean that they can’t or don’t change load and nor does it confirm the findings. A fairly typical 250MW turbine can change generation down to 30% of its rated load, at increments of about 5MW per minute, and a typical power-station will have 4 of these turbines. These generators have always had the capability to change loads; demand has always been changeable, and there is no network difference between an decrease in demand and an increase in generation. So wind turbines or other intermittent generators are just another element dragging the grid frequency away from 50Hz, but it is entirely manageable.
Here is the reference for the coal data used in this study:
In a letter to Victorian Attorney-General Robert Clark, Cumming said the owners of Yallourn, Hazelwood and Loy Yang power stations had confirmed in writing that the power stations combined consume about 7762 tonnes of coal an hour.
“They have confirmed that the power stations do not change the coal feed intake 24 hours a day, seven days a week, 365 days a year. The coal consumed by these three power stations alone makes base-load power available at a rate of 6650 megawatts,” Cumming wrote.
Given that Yallourn is partially under-water we know this is not true.
Beyond that though, this is an extremely technical field and I would expect this sort of analysis would have to include actual feed-rates of coal, compared to output, correlated across a wide number of sites, to have any hope of making the claim that wind-turbines do not displace coal fired generation. This seems to be an anecdote, aggregating across four (Loy Yang A and B) major power-stations and based on the assumption that output is constant.
There is one extremely technical point that is a possible mechanism for wind power not abating emissions, and I would be reluctant to say which way this fell. Baseload plants have a Best Efficiency Point, when their electricity produced per tonne of coal is maximised. Any deviation from that point means slightly less efficient generation. But there are two problems with this; the change in efficiency is minute and it assumes that the plant was already operating at its best efficiency point. The whole-cycle efficiency of a plant might be 30% plus or minus just a couple of points, until the extremes of their operating range. The question then is does efficiency move so far that it wasn’t worth turning the wind turbine on at all? Only long run data will confirm or deny this. Ditto with the operating point assumption. There is just no point commenting on the electricity network unless you have reams of data. It’s too complicated not to.
One hopes that those mentioned would like to discuss an alternative viewpoint. I am also a mechanical engineer and I’ve got a bit of an idea how electricity works. While Hamish Cummings analysis is a valuable contribution to the debate, I think it is a starting point only, and would strongly benefit from some more data. It is not possible to make those findings from the data presented.
I’ll post this on their blogs and we’ll see how it goes. Maybe if you see someone else running this line you could point them here. I think we could have a more nuanced discussion than this.
And big hat-tip to reader @andrew_hedge who pointed the Oz piece at me.
PS I’ve had some twitter discussions since this about what the actual abatement is: this report is a good starting point. But, these are modeled values which will upset a lot of people. Like I said, long run data is the only way to crack this one.