Do wind and solar “complement” each other during winter?

The second fact check of the “factchecker energy” of SER is titled: Is there a future for solar energy in the Netherlands?. Although the author of this fact check admits that solar energy only has a very tiny share (0.1% of the energy consumption) and that it needs to be balanced by other flexible energy sources, he is very optimistic about the future. His “fact” check seems to rely on future developments related to solar energy.

As a whole, it seems a quite bland and overly optimistic fact check, but there was one statement that caught my attention (translated from Dutch, my emphasis):

There is a factor of ten difference between summer and winter output of solar panels. What the share of solar power in the electricity mix will be, will depend to a large extent on the developments in electricity storage (for short and longer periods) and of the expansion of the electricity connections with other countries. Wind power and solar energy complement each other in that respect: the supply of wind power is higher in the winter when the supply of solar energy is lower.

That is an interesting statement. Apparently wind energy produces more power in winter and this compensates for the loss of output of solar cells during the same time. I decided to have a look at the data to find out to what extent “wind complements solar”, but also the significance of this phenomenon in a continuous working grid.

I almost immediately ran in the first problem: there was no detailed information about the production of wind and solar energy production in the Netherlands. On the other hand, the Belgians have detailed information of their wind and solar energy production. Belgium, being a neighbor country of the Netherlands, I thought that I could use the data from Belgium and recalculate that to the installed capacity of the Netherlands (they have roughly double the installed capacity of wind and half that of solar compared to us). It is not entirely correct, but it will probably rather close.

When comparing last summer (July 2016 → August 2016) with last winter (December 2015 → February 2017) it was perfectly clear that this statement was true. Wind energy got a boost in winter and more than compensated for the loss of production of the solar cells.

However, last winter is not necessary a good comparison. That period was an exceptional time for wind production and several records were broken. When I compare the current winter with the summer of 2016, then wind production in winter was only marginally better than in summer and combined production wind/solar was similar to that of summer.

The data of the last fifteen months seems to suggest that indeed wind turbines performs better in winter and their production compensates on average for the loss of production from solar cells.

With the emphasis on “on average”. People don’t take power from the grid “on average” over three months. It is consumed in cycles over the day (lowest at night, higher at daytime and two peaks on working days), the week (more consumption on working days then in the weekend) and the year (lowest in summer, highest in winter). This is what elia expects as a weekly cycle:

This is what wind and solar delivered in the same period:

Look carefully: the total load graph is not starting at 0, but at 8,000, the solar + wind graph from roughly 35 to 1,600 (two very short peaks, but everything else is (well) below that).

The point is that wind and solar don’t follow the consumption cycles. The highest power consumption is on working days in winter during the morning, but especially the evening peak. These are the most important times: the consumption during these peaks that will determine the necessary production capacity of our country.

It is at those peaks that the tandem wind and solar will fail at our latitude. In January, the sun doesn’t shine yet during the morning peak and the sun has already set in the evening peak. So solar energy will not contribute to the production of the working day peaks and wind energy will be on its own to do the lifting.

The worst day in January 2017 seemed to be January 8, in which there was not much wind and no sun at the time of the peaks (I highlighted the time of the peaks as a grey area):

Compare the scale of both graphs (also here: the total load graph is starting at 8,000, while the solar + wind graph already maxed out at 250).

Production by wind was roughly between 30 and 35 MWh during the evening peak while there was a need for about 11,600 MW. That comes down to a contributing of about 0.3% of the need. If this would be the worst case scenario, it would mean that the rest of the production capacity needed to be at least 11,600 MW minus 35 MW (plus of course a safety margin). This is capacity of conventional sources that has to be available to cover the need in winter, even with a combined installed capacity of 4,913.69 MW for wind and solar.

By the way, even if we would double installed wind and solar capacity (which would be incredibly expensive and would disrupt the grid when it is sunny, windy and only little consumption), the combined output would still only have been that of a 70 MW turbine (or roughly 0.6% of the needed capacity).

Concluding, I am not really impressed by the statement that wind and solar “complement” each other during the winter months. Sure, the average power production of windis higher in winter than in summer and this will compensate on average the diminished power production by solar panels. But all in all, it is a pretty meaningless phenomenon at the specific times we need the most energy at our latitude.

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