Chapter 4.11.2: Wind Replacing Coal?

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It was announced with great fan fare by the Liberals 7 years ago.  All coal-fired plants would be closed.  Though not on target, the claim is still all coal-fired plants to be closed.  Those promoting wind claim they can make up that loss of capacity, if you just build enough turbines.  But is any of this possible?  The only way to know is to directly compare wind to coal hour by hour and see if coal is reduced when the wind is blowing.

You will recall in the previous chapter that wind occurs in spikes.  Collectively output is a series of nested spikes. 

This is coal and wind for the Summer months July 14 to Aug 29 (period of the start of coal data obtained so far).

Click to enlarge.  The black lines are coal’s Hourly Capacity Factor for all plants.  Blue is wind Hourly Capacity Factor for all locations. Coal is undulating during the day to supply increased demand.   This is a typical two days for coal (July 14 and 15, 2010):

They start to ramp coal up around 5am, to the top requirement by 10 am.  Then by 10pm, they allow coal to fall for the late night drop in demand.  The questions is, how does wind fit into this?  There are four ways that wind can fit into coal’s profile:

This is for illustration purposes only, not real data.  The black line is coal’s profile over a 32 hour period.  The other coloured lines is a spike in wind in each of the four places where a spike can occur inside coal’s profile.  The orange line is when the spike in wind occurs during coal’s off-peak period.  In this case there is nothing for wind to do anyway.  The red line is when the wind spikes while coal is being ramped up for the day’s demand.  Because of the way coal works, it takes time to feed the fires and coal to start to get to temperature, there is nothing wind can do to stop that ramp up of coal power.  Those at the coal plants can’t be certain when wind will peak, and at what level it will peak at.  So they have no choice but to keep ramping up coal for the mid day demand regardless what wind does.  For if they did pull back goal for the few fleeting hours of wind, they could very well find themselves behind when wind suddenly drops.  So wind cannot have any effect of cutting coal use during the morning ramp up.  

The third possible time is during the 12 or so hours that coal is filling the peak demand of the day.  That’s the blue line.  Two problems for coal producers.  The first problem is they do not know when the wind will peak and start to fall, and at what megaWatts it will peak at (hence reduce coal the same amount).  The second problem with coal is they can’t let the fires go out because it would take too long to fire back up when wind suddenly decides it doesn’t want to play any more.  So the fires have to be kept up the entire time wind is running.  If they do cut back on coal’s output, all they are doing is substituting expensive wind for cheap coal, but no change in emissions from that coal.  So wind can’t help there.

The last phase is in green where wind spikes during coals power down at the end of the day.  Since demand is dropping, a spike up in wind can be a real problem producing in a short time frame more power than is needed as demand drops off.  This too must be a real headache to try to balance.

How many of each of these phases happen?

At the moment of this writing we only have mid summer 2010 coal data.  Once a more complete history is obtained we will see a better picture.  But this will have to suffice for the moment.  The only possible contribution wind could have is in the winter. But that will have to wait.

Just in the first graph you can get a rough idea how many hits occur in each phase, but a closer look will help.

Click for a closer look.  This is just from July 14 to 31, 2010.  Coal in black, wind in blue.   There looks to be 4 spikes in the first phase, 15th, 16th, 22nd, 28th.  The 28th for the second phase.  5 spike in phase 3 at the peak of coal’s output.  Of those 5 there only appears to be 2 where coal was cut back to compensate.  We will look at both in detail in a moment.  2 in phase 4, 16th and 17th as coal is being powered down.

There are 13 days of coal’s peak where there is no appreciable wind at all.

The two days that appear to have a drop in coal in response to wind look like this close up.

The first thing you notice is the time lag between the peak of wind and the trough of coal.  On the 16th the drop in coal preceded the peak in wind.  Did they anticipate that the upcoming wind would allow then to scale coal back?  Almost looks that way, but within two hours coal was back to peak when wind peaked.  Did they change their minds?

Understand that coal can’t be turned off an on like a switch.  It takes time for the fires to die down and time for them to be light back up to required temperature.  There is no way in that short 4 hours that they reduced the amount of coal being burned.  They may have reduced the electrical output in response to wind (we can check for that too).  But they did not reduce the amount of coal being burned.

Same on the 17th, after only a one hour drop in coal output it was right back up to the max again.  There is no way these two drops could have been from wind’s contribution.  But we can check for that by seeing the megaWatt difference in the two.

Coal dropped 680 megaWatts while wind increased 4,920.  So coal was not reduced to compensate for wind on the 16th.

On the 17th an argument could be made that coal was replaced by wind, magnitudes very close, except the timing is off.  Did they expect wind to keep rising and pulled back coal’s output only to find wind started to drop on them?  Good question.  If this is what happened, it would show the real problems they have with wind.

This is just two points, but the only two that could have been candidates for wind replacing some coal, but on closer look this does not appear to be possible.  If anything, coal is just throttling back some output but not altering the fire temperatures that they need to run the steam turbines, the time frame is just too short to do that. 

So the premise that coal is being replaced by wind seems to be incorrect.  Beyond that, fundamentally wind cannot replace coal because coal is being used to ramp up in response to the daily cycle of demand.  Wind cannot do this, no matter how many turbines are built.

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