A “skewed” distribution: the overlooked consequence of decommissioning nuclear power

In previous post, I detailed the contradiction of Belgium wanting to profit from German cheap import while employing the exact same balancing strategy as Germany. I illustrated this by comparing German electricity export and prices on days of the lowest, highest and median output of solar and wind. This showed that when Germany exports its excess electricity, prices are generally low, but at that time Belgium is also busy exporting its excess electricity. And vice versa.

Now you could object that this is not a good representation of the argument of our Green Minister of Energy. Her argument is that nuclear power stands in the way because it can’t modulate its output (enough) to follow the intermittency of solar and wind, sometimes leading to wind power being curtailed and/or exported at times when Germany is exporting abundant and cheap electricity. The goal of the Minister is to get rid of nuclear power generation so Belgium doesn’t need to curtail its own production when it is sunny and windy, while also being ready to profit from cheap electricity from Germany. Ka-ching!

That is true, decommissioning nuclear will allow for more cheap import from Germany, but this will only be temporary and lead to an even bigger problem…

Let me first say that I can understand this reasoning. Nuclear power meets on average about half of our electricity demand. If nuclear isn’t there anymore, this will lead to a big gap that can be filled in with more flexible power sources (natural gas) and import. When there is a lot of solar and wind, natural gas power plants can go out of the way and solar & wind can produce uninterrupted, so no electricity needs to be curtailed or exported. Because nuclear power will only be partly replaced with natural gas, there will still be a deficit that could allow for the import from Germany at pretty low to negative prices. That all is true.

The downside of this is that Belgium will be structurally dependent on import, not only when there is a lot of sun and wind (summer), but worse, also when there isn’t and we need a lot of electricity (winter). Unfortunately, these two will not compensate each other. Remember, the output of solar and wind forms a “skewed” distribution, from plenty of output in summer to a minute output in winter. This is the graph that I recreated based on a similar graph from the Netherlands (annotated with the dates of the lowest and highest production):

Fig. 1: Daily sorted contribution of solar and wind in Belgium from January 1 till November 30, 2021 (annotated)

 

In this post, I will focus on both ends of this graph and see what was happening during those two days and I will also see how this will play out when I increase solar and wind capacity to the values expected in 2030.

On the one end, there is November 16 that was the day with the lowest electricity production from solar and wind in the period January 1 until November 30, 2021 in Belgium (and also in the Netherlands). Now I also have access to the December 2021 data: November 16 is still the day with the lowest production in 2021. None of the days in December had a lower production than November 16.

On the other end is May 21, that was the day with the highest electricity production from solar and wind in Belgium in 2021.

I can also make a projection of what the electricity production by solar and wind would be in 2030 in the same situation. It is expected that capacity of solar in 2030 would be 11 GWp, offshore wind 4 GWp and onshore wind 3.5 GWp. That is 2.3x, 1.8x and 1.3x the current capacity. If I multiply the current values with these multipliers and put both days side-by-side, then I get this different view of the “skewness” of solar and wind production:

Fig. 2: highest vs lowest production of solar and wind in 2021 (Belgium)

 

[For those who want to know the relation between the first and the second graph: the first graph shows the daily production and the second the quarter hourly measurement over the day. If you make the sum of all values of the thick orange line of the second graph, divide that by 4 (quarter hour → hour) and divide again by 1,000 (MW → GW), then you get the values of the first graph (110 GWh for May 21 and 4.7 GWh for November 16).]

This graph shows the huge difference in production between the two days. The production on November 16 came barely loose from the x-axis while production on May 21 met a large chunk of demand. The discrepancy between production and demand is also somewhat visible (the difference would even be greater when the day of highest demand would be a summer day).

Finally and most interestingly for this post, there is a huge difference in projected production when adding the expected output of the capacity expected in 2030. The November 16 scenario shows only barely more production while production on May 21 promptly exceeded demand roughly between 9 AM and 5 PM. This is not hard to understand. Multiply a small number by for example 2 and the result will still be a small number. Multiply a large number by 2 and it will be an even larger number.

On the one hand, when increasing the capacity of solar and wind, production of electricity by solar and wind will evolve into a situation where that production will exceed demand when it is sunny and windy. Therefor loosing the ability to import cheap electricity from abroad rather quickly and ending up where we are now. On the other hand, the gaps will stay large for quite a while and they generally occur at times of higher demand (winter) and therefor Belgium will have to rely more on import of (expensive) electricity from abroad. This at times when the neighbor countries that employ the same strategy will run into the same issues and want to import electricity themselves.

We are screwed…

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