Wind keeping the system “nicely balanced”: does more wind power means better air and cleaner electricity?

Let’s continue with the open letter from the energy company Eneco (see previous post), in which its CEO complains that his company “felt obliged” to shut down some of their windmills despite it was windy. It is framed as the result of the “inflexibility” of nuclear power that pushes wind aside and, most importantly for this post, as a choice for better air and cleaner electricity (translated from Dutch, my emphasis):

Renewable energy could provide half of our consumption. In itself this is a good prospect: better air and cleaner electricity from wind & sun. We should all be pleased with that.

The framing in the open letter made me wonder how much wind power was curtailed exactly? Also, assuming that nuclear power would get turned down a notch during the lockdown, how much cleaner would electricity production then get?

In order to figure that out, I first downloaded the wind data between March 18 (start of the Belgian “lockdown”) and May 3 (just before the first phase of the unlocking that started on May 4) and looked for signs of curtailment. For example, this is how it looked like a few days before the open letter:

Although the forecast was a reasonably stable wind, production went in a nose dive when some of the windmills were shut down. This event inspired me to start mining for such steep changes, in the hope that I could fill in the rest, therefor being able to estimate what could have been produced.

Unfortunately, it wasn’t that simple. I found several examples of such steep changes between March 18 and May 3, but there were many other cases that were not so clear-cut.

Maybe I made it myself way too difficult by looking at it in such a fine-grained way. What if I would compare with the same period in a more “normal” year (without a crisis that drastically lowers electricity demand) in order to figure out what production would be like under those conditions? Looking at the 2019 data between March 18 until May 3, I found that there was a bit less produced than forecast: a tad less than 0.85% of the forecast values (compared to 7.77% less in 2020). Apparently, there was indeed more curtailment of wind energy between March 18 and May 3 in 2020 than in 2019. I could use this as a starting point for my estimation.

A total of 1,235,479 MWh was forecast between March 18 and May 3, 2020. If the prediction method was the same in 2020 as in 2019, then that would have resulted in a production of 1,225,039 MWh. That is a difference of 85,585 MWh. I am a bit underwhelmed, this is peanuts in the grand scheme of things. However, the question is: would we have better air and cleaner electricity when this 85,585 MWh wind power wasn’t curtailed?

That 85,585 MWh is only one side of the story and there are other things that need to be taken into account. The “flexibility” of wind is only going in one direction: production can be decreased in case there is wind, but production can’t increase when there is no(t much) wind. Lowering output of nuclear power will certainly help in case there is a lot of wind, allowing for wind farms to stay producing at better spot prices, but now it would be necessary to fill in the gaps left by nuclear when wind power production is low.

How big would these gaps be? With the numbers from my example (March 18 → May 3) it is possible to make an estimate by comparing two scenarios:

1. Actual production (wind is curtailed):
   • actual total load
   • actual production of solar
   • actual production of wind
   • actual nuclear energy power (a capacity of 4,110 MW during the lockdown).
2. Production of wind is not curtailed, combined with less nuclear:
   • actual total load
   • actual production of solar
   • potential production of wind based on the ratio forecast/actual produced (from reference year 2019)
   • one nuclear reactor less (4,110 – 1,000 = 3,110 MW).

This is the result:

March 18 → May 3	Scenario 1	Scenario 2	Difference
Total load (MWh)	9,407,935	9,407,935	0
Wind (MWh)	1,139,454	1,225,039	+85,585
Solar (MWh)	874,599	874,599	0
Nuclear (MWh)	4,636,080	3,508,080	-1,128,000
To be filled in (MWh)	2,757,802	3,800,216	+1,042,415

So, okay, now that 85,585 MWh wind energy is secured, but it also means an extra 1,042,415 MWh that has to be filled in by other power sources. In Belgium, this is primarily natural gas (there are also pumped hydro and oil, but these are only a tiny part of the energy mix).

There are however some consequences of replacing nuclear with gas. Wind doesn’t have direct emissions, but neither does nuclear. If replacing nuclear by an energy source that has emissions, then one should expect … more emissions.

How much more emissions would that be in our estimate? If found this table with emissions of several power sources. Wind and nuclear indeed don’t have any direct emissions in that table, but gas power plants have:

	Direct emissions CCGT (g/kWh)
	CO2	NOx	PM10
Before 2010	348.8	0.176	0.0008
Advanced technologies 2010	343.2	0.173	0.0008
Advanced technologies 2020	332.3	0.168	0.0008

The energy infrastructure of Belgium is rather old, so I will have to use the values of before 2010 (although it would not make that much difference when I would use one of the later years). Calculating with the pre 2010 values, this means extra emissions of 363,594 ton CO₂, 183 ton NO_x and 0.83 ton PM₁₀ during the 46 days lockdown…

So yes, we should be pleased with the prospect of better air and cleaner electricity, but lowering nuclear output in favor of wind power doesn’t seem to be the way to reach that goal.

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