Those Europeans with long memories will recall that September and October was marked by fine weather with many long windless spells. I began following this story summarising wind data from the UK, Germany and Denmark. I then added France and Sweden in A Big Lull and in the comments to that post David MacKay said:
Great graphs! I think I spotted a typo “mimumum” in one of them. Perhaps fix this when adding Portugal and Spain to this magnum opus 🙂 Thanks
Well I fixed the typo and gave an overview of Spanish generation last week in Red Eléctrica de España. Now I add Spain to the Northern European stack to see if it helps smooth pan-European output.
Before proceeding I need to say that Roger is wondering why I am pursuing this since in his original post, Wind Blowing Nowhere, he showed that pan-European lulls were common throughout 2013. Hubert Flocard has also performed extensive analysis on this subject. Laying myths to rest is not easy.
Figure 1 Wind output from 22.9 GW of turbines in Spain, September and October 2015. The numbers 1 to 9 mark regional lulls in N Europe.
A good starting point is to look at the wind output for September and October (Figure 1). The numbers mark the lulls from my original post where I stacked Denmark, the UK and Germany. Its plain to see that the majority of these were also low-wind periods in Spain too. One exception is lull 4 and perhaps 8 and 9 where it was blowing a little in Spain but nowhere near enough to make up for windless conditions elsewhere. Lulls 1, 3, 5, 6 and 7 in northern Europe were all pretty calm in Iberia too.
Figure 2 Stacked wind production for Sweden, Denmark, UK, France, Germany and Spain.
Adding Spain to the stack confirms what we always suspected and now already know. Lulls 1, 2, 3, 5, 6 and 7 were all pretty calm in Spain too and having geographically spread turbines makes little to no difference in smoothing wind power. We can see in lulls 4, 8 and 9 that Spain helps to smooth out the stack a little, creating one of these mythical half truths that will no doubt continue to be repeated “geographic spread does help smooth wind output”. One just needs to build hundreds of GW of inter connectors to provide this partial assistance every now and then. The reality is this. On many occasions it is flat calm across most of Europe and 100% back-up from other dispatchable sources is required.
Figure 3 Normalised stack of wind output. Each country is normalised to a nominal 10 GW.
The size of the wind parks vary substantially between these countries and in my last post I normalised the production data to a common datum of 10 GW capacity in each country. I have now added Spain to that chart (Figure 3). Normalisation does make a material difference to the picture, reducing the dominance of Germany and elevating the prominence of Sweden and Denmark. We now have just 4 prominent lulls. It can be seen that adding Spain makes no difference during lulls 1, 2 and 3 but that it does make a small difference in lull 4. The conclusion is unchanged. On a regular basis the whole of Europe is becalmed. Not only under Arctic high pressure in mid-winter, but also when high pressure is in charge during September and October. Near 100% back-up is required and inter-connectors will not solve the wind intermittency problem.
To wrap this up, one observation to arise from my Red Eléctrica de España post is that the operation of solar thermal generation is exposed to cloud cover. With solar PV mounted on thousands of roofs across a country there is always some generation, even on cloudy days. But if it’s cloudy over the concentrating solar power plant (CSP), generation falls to zero. One may imagine (or wish) that when it is cloudy it may also be windy and that loss of solar thermal would be compensated by wind. Figure 4 explores this question.
Figure 4 Solar thermal production periodically disappears when the plant is occluded by cloud. On many but not all of the occasions that this happens, wind compensates.
The blue arrows mark low solar days that were fairly windy and wind would make up for any deficiency in solar. There is a tendency for wind and solar to be negatively correlated as one might expect. But the red arrows mark low solar days that were also relatively calm. There are days when the wind does not blow and the sun does not shine in Spain. Once again, near 100% back-up is required for 22.9 GW of wind and 2 GW of CSP.
Pan-European lulls in the wind stretching from Spain in the South to Sweden in the North, Britain to the West and Germany in the East are commonplace. The combined wind capacity of these six countries is 97.9 GW. On occasions the output from this gigantic resource falls below 3 GW, a load of 2.9%. At present and for the foreseeable future the only way to mitigate for wind variability is back-up from other dispatchable power sources. Building inter connectors may provide a marginal partial solution for some of the time but cannot provide a reliable solution at the pan-European scale.