A month ago I looked at how much wind farm output in Europe varies during the day. On average that is.
Today let us look at monthly variations in output. I will do this for six countries: Britain, Germany, France, Spain, Ireland and Denmark. In each case I will look at mean output in megawatts (MW) over the last 4 years. (Though in the case of Spain I don’t have data for 2014, so I’ll only do three years.)
Below is a plot of mean monthly output from Britain’s wind farms between 2011 and 2014. Note in each case the axes are not identical. I have done this to make the seasonal cycles as easy to see as possible. The seasonal cycle is also obscured (slightly) by the addition of capacity during the year, but this does not make a major difference to the numbers.
Monthly variations in Britain’s wind farm output are clearly significant. In 2011, 2013 and 2014 the best month had mean output that was 4 times greater than that in the worst month. Output is typically at its lowest point in summer, with wind farm output typically being at least two times greater in winter.
Things are reasonably similar in Germany. Output is always lowest in summer and highest in winter. The best month can also be four times greater than the worst month, as happened in 2013.
In Ireland, a similar pattern holds. Peaks in winter, troughs in summer. As with Britain and Germany there is a seasonal pattern, but it is a rather spiky one.
Denmark’s wind farm output appears to be much more consistent year round than the countries looked at so far. The best months are more similar to the worst months. But they are still reasonably different. The best month is typically between 2 and 3 times better than the worst month.
Spanish wind farm output is even more consistent. The best month was at most 2 times better than the worst month between 2011 and 2013. This is a good thing, because lower levels of seasonal variations means Spain is likely to have to curtail less wind energy than countries with a more pronounced seasonal cycle. A subject I might return to in a future post.
Finally, France. The yearly low normally occurs in summer. And as with every other country the best wind farm output happens in winter, with the best month being 2-3 times better than the worst.
What does all of this mean? There are two problems with wind farms: too much electricity and too little. As wind farms are expanded, eventually they start producing more electricity than actual electricity demand. This will require either storage or curtailment. Given the lack of cheap energy storage it is more likely to equal curtailment.
But what the graphs above show is that wind farm output varies much more each month than does electricity demand. The result will be that wind electricity is more likely to be curtailed in winter when it is windy. These levels will vary by country depending on the daily and seasonal cycles of wind farm output and of electricity demand. I will leave that subject for a future post.
Note on data
Wind farm output data was downloaded from the website of PF Bach. Data was analyzed and plotted in R using ggplot2 and a custom theme. If anyone wants the code used for this just let me know.