A central tenet of wind power advocates is that the wind is always blowing somewhere and thus on a regional scale intermittency becomes smoothed out. This is one of these half truths. If one is to have turbines at all, it is of course sensible to have them geographically dispersed as this most certainly helps to smooth out highs and lows in the wind. But it is not the day to day vagaries of the wind that matters but the extremes of wind blowing everywhere at once and worse still, wind blowing nowhere. It is when the wind is blowing nowhere that back up is needed and the physical low points reached defines the amount of backup that is required.
This is a theme we have covered often on Energy Matters. In January this year Roger Andrews had a post called Wind Blowing Nowhere that summarised a year of wind data for seven European countries and showed categorically that geographic dispersion does not smooth wind significantly on a pan-European scale. Hubert Flocard has shown similar. And yet the myth of wind being smoothed by geographic range just refuses to die.
Last week I had a post called Flat Calm Across the UK focussing on the spell of what seems to be uncommonly calm weather across the UK and Northern Europe. In this post I add wind data for Denmark and Germany for the months of September and October. On 19th October, for several hours, the combined output of 55 GW of wind turbines was less than 1.5 GW, that is below 3% average load. It was effectively flat calm across the whole of Northern Europe, not just on this occasion but on several other occasions in this two month period.
Figure 1 Atlantic pressure chart from the BBC / Met office for 4th November 2015. This has been a fairly typical configuration for several weeks with high pressure over Europe, the North Sea and the UK resulting in regional calm conditions. Weather fronts move through which are clearly visible from the wind generation data, but then the high re-establishes and calm conditions return. Atlantic depressions have been tracking to the north of the UK on a deeply meandering jet stream.
I need to thank Paul-Frederik Bach for helping me access recent wind data from Denmark and Germany.
Danish wind data was accessed at the Energinet.Dk site. German data was accessed from various sources as detailed on Paul-Frederik’s wind data base. UK data was accessed from BM reports via Gridwatch. All data have been recalculated to hourly averages and are presented on European time, with 1 hour added to UK time series. It would have been nice to include Ireland, but the data is no longer readily available from the Eirgrid web site.
It is not straightforward to find out the amount of wind turbines connected to the grid and metered by the various countries. The following are estimates garnered from various sources. Uncertainty over metered capacity means that inferences made about load factors are uncertain to the point where they may be totally wrong.
- UK 9136 MW metered from a total of 13339 MW installed.
- Germany 41360 MW installed according to the Fraunhofer Institute.
- Denmark 4890 MW installed at end 2014 according to The Danish Wind Industry Association.
Total = 55386 MW
The raw wind data, at hourly resolution for September and October are plotted in Figure 2. The chart is dominated by the gigantic German wind fleet. The German data show clearly how the wind has come and gone between extremes of 331 MW @ 18:00 hrs on 29th October to 24127 MW @ 13:00 hrs on 6th September. That is a dynamic range factor of 73.
It is clear that there is a high degree of correlation between the countries with a tendency for the lows to be alined. See for example 17, 18, 19 and 20th October. When high pressure was in charge, the wind blows nowhere.
For geographic dispersion to act as a smoothing agent a negative correlation between regions is required. In fact Germany and Denmark are positively correlated (Figure 3) and the data for this period shows that Denmark and Germany cannot help balance each other’s wind output. The correlation coefficients with the UK are zero and nowhere near the negative correlation required to provide load balancing service. The zero correlation masks the periods when wind is blowing nowhere in Northern Europe.
Figure 2 Raw wind output, hourly data, for Denmark, UK and Germany, September-October 2015. Click on chart to get a very large version.
Figure 3 Denmark is adjacent to Germany and it is therefore not surprising that their wind data is strongly correlated. These two countries can do little to assist each other load balancing high against low wind production. But as we shall see, Germany finds Denmark to be a handy import / export conduit to Scandinavia.
What we want to see is the combined wind output from all three countries and that is shown in Figure 4. Figure 4 is a stacked area chart where the data are added to the stack to provide a picture of the combined outputs. Nine spells where the combined outputs fell below 5000 MW are numbered. Let me focus on the period 17th to 20th October (number 8). For most of this four day period, the combined output fell below 2500 MW, that is below 5% load. Lulls such as this CANNOT be and NEVER will be met from storage. Nor can they be met by importing wind power from somewhere else. Let us imagine that somewhere else was Spain. Spain would have to reliably produce a 10 GW wind surplus for 4 days that would have to be transmitted to northern Europe requiring 10 GW of HVDC power lines. And since the wind in Spain can never be relied upon to fulfil this role, as shown by Roger Andrews, it is plainly madness to contemplate such scenarios.
Figure 4 This stacked area chart adds the wind production from the UK on top of Denmark and Germany on top of the UK. The profile of the green shaded area gives the aggregate production of all three countries. In this two month spell, the wind was blowing nowhere in northern Europe on 9 separate occasions. Click on charts to get very large versions.
How has Denmark Coped?
Denmark has the advantage of being small and attached to Norway, Sweden and Germany via inter connectors. Figure 5 shows that Denmark simply overcame the problem by importing electricity from its neighbours when the wind stopped blowing. Denmark imports hydro power from Norway and nuclear + hydro power from Sweden. Denmark has in fact become an electricity parasite feasting off its Scandinavian neighbours. Note how in this two month period net exports were almost non-existent. And Denmark is buying high and selling low, and we all know that is the dumbest way possible to play any market. The parasite is not getting a free lunch.
Figure 5 When the wind drops in Denmark it simply imports more electricity from Norway and Sweden. Peak load in Denmark is of the order 5 GW. Hence, at times of low wind about 50% of Danish electricity supply is from imports.
Figure 6 This chart is not stacked, all data originate from the zero datum. The lines show wind production and net imports. The negative correlation is plain to see. The main features are near constant imports from Scandinavia throughout the period and near constant exports to Germany. This may seem odd, but what in fact is happening is that Germany is importing from Norway and Sweden via the Danish inter connectors.
The import / export picture is in fact rather complex. The details are shown in Figure 6. Note that this is not a stacked area chart since XL does not manage negative numbers in a stacked chart in a rational way. What we see is Denmark exporting electricity to Germany throughout most of this period. Whilst at the same time importing electricity from Norway and Sweden. What in fact is happening is that Germany is importing electricity from Norway and Sweden through Denmark. The sixth of September is the only day when significant electricity was exported to Norway and Sweden and we see that most of that came from Germany via Denmark. I calculate that Norway and Sweden exported 1.23 TWh of electricity to Denmark during September. I don’t know what impact that has on their magazines, but it has also been quite dry with high pressure in charge.
Has September / October 2015 been unusually calm over northern Europe? That is a complex question to answer. The wind data is there is to answer it, but it is a huge amount of work to go back over years of production data and match it to installed capacity.
I have compared UK wind data for 2015 with 2014. Results below:
Installed capacity 13169 MW
Sep + Oct wind generation 3.08 TWh
Installed capacity 13445 MW
Sep + Oct wind generation 2.68 TWh
Grossing up the 2014 generation for the marginal increase in capacity yields 3.15 TWh for 2014. 2015 is 15% below 2014 wind generation for September and October. So my perceptions of flat calm are not misjudged but nor are they highly significant. Scotland has had a dismal summer and this spell of very fine weather has heightened my sense of quiescence.
The bigger questions here revolve around the wisdom of this whole energy strategy. For example, there seems to be a commitment to build the North Sea Grid. Its one of these ideas that has taken root and simply will not die. Had the North Sea grid existed today it would not have made any difference to the performance of N European wind apart from extending the financial losses that are picked up by the consumer. It might have helped in shunting a few GW of French nuclear power around Europe to countries left short.
The central question lies in the wisdom of distributed power generation. Generating your own wind power down on the farm or solar power on your two bedroom semi’s roof may sound like a great back to nature green solution to electricity production. That is until the wind doesn’t blow and the sun doesn’t shine and your dependency is shifted to the owner of the 3000 mile long, 200 GW HVDC power line to Saudi Arabia. Is it not better to be dependent upon the 100 mile long, 1 GW power line to your local nuclear or gas fired power station?