Fluttering wind power

The original article can be read as “Schlumpfs graphic 118” in the online Nebelspalter of 8 July 2024.

Construction Director Martin Neukom recently announced that the Zurich cantonal government has selected 20 regions of the canton as highly suitable for wind turbines. A total of around 70 turbines could be built on these sites. In most cases, these would be over 200 meters high, which is tantamount to a massive industrialization of previously untouched natural landscapes.

The justification for this radical step: better security of supply in winter thanks to electricity from wind turbines. On closer inspection, however, this turns out to be extremely questionable.

What is important:

• German onshore wind plants generate almost two thirds of their electricity in winter, apparently compensating for the winter weakness of solar plants.
• However, this is not worth much because electricity generation from wind is very unpredictable and fluctuates massively.
• Production data show this: Even in winter, there are always periods when the wind is almost completely absent for several days.

My following analysis of wind power generation relates to the German electricity system, as wind power only plays a marginal role here: The 44 operating Swiss wind turbines generated 170 gigawatt hours (GWh) of electricity in 2023. This means they only contributed just 0.2 percent to our national generation.

There have always been weak wind years

The size ratios between Germany and Switzerland are best illustrated by the current installed capacity of wind turbines: Swiss turbines have a power capacity of 88 megawatts (MW), while German wind turbines have a power capacity of 61,000 MW – that’s almost 700 times more. This only includes German onshore wind turbines, i.e. turbines on land – as would only be possible in Switzerland. Turbines installed in the sea (offshore) have an additional output of 8760 MW in Germany.

Let’s first look at the annual yield of German onshore wind power. In 2023, Germany generated 116 terawatt hours (TWh) of electricity from wind – a new record. However, two years earlier, in 2021, it was only 88 TWh – the lowest yield in the last five years. If the large expansion in capacity between these two years is taken into account, there is still a difference of 20 TWh, which also represents a challenge for the German electricity system: Obviously, the wind strength fluctuates considerably in the annual total.

Almost two thirds of wind power is generated in winter

Next, we take a closer look at the seasonal distribution of wind power. In the winter half-year from October 2022 to March 2023, Germany generated 63 TWh of onshore wind power. In the following summer half-year from April to September 2023, it was only 38 TWh. This means that 62 percent of the total annual yield was produced in winter. In the two previous years, the winter shares were 65 and 61 percent respectively. It would therefore appear that a good 60 percent of the annual volume of wind power in our latitudes can be generated in the winter half-year.

Half-yearly balances distort the actual situation

However, this half-yearly balance sheet inadmissibly smoothes out and thus obscures the real conditions of wind power production: Only an examination of generation in real time clarifies when the wind is blowing and how strongly, and when it is not.

The source of my real-time view used here is the Fraunhofer ISE (Fraunhofer Institute for Solar Energy Systems, see here) with its interactive energy charts. All the important key data of the German electricity system is graphically presented there. In the case of wind power generation, this is done using quarter-hourly values obtained from data provided by the transmission system operators.

In the following, we look at such a real-time graph for a typical summer and a typical winter month. The first graph shows electricity generation from German wind turbines and consumption (load) in Germany in August 2023:

Such a power-time diagram from the Energy Charts shows how much power was generated by the various energy sources in each quarter of an hour of this month – measured in megawatts (MW). For this chart, I have only selected the figures for “Wind Onshore” (light green area) and for “Load” (equal to consumption, black curve). It is important to know the consumption requirements because the total electricity generation must be identical to the consumption at all times.

In August, only one eighth of the wind potential is utilized

How well does wind power, now the largest single generator in the German electricity system, fulfill this role in this summer month? As you can see in the graph, extremely poorly. On the one hand, it can only make very limited use of the potential of its installed capacity, which amounted to 60,000 MW this month (purple line above, drawn by me): Namely, an average of only 7640 MW per quarter of an hour (light green line below, drawn by me) – this corresponds to a meagre 13 percent or one eighth of the installed capacity.

On the other hand, the electricity input from wind is extremely fluctuating, or rather flighty: between a maximum of 32,400 MW and a minimum of 520 MW, it goes up and down rather unpredictably. However, this is “poison” for any power supply, because all these fluctuations must always be corrected: Sufficient controllable backup power must be available at all times to fill all these gaps.

In contrast, what do the conditions look like in a winter month? The next graph shows the results for January 2023:

First of all, it is noticeable that the consumption curve in January 2023 is around 10,000 MW higher than in August 2023. Nevertheless, the green wind area moves closer to the consumption curve overall because the wind power yield in January was two and a half times higher than in August. This is also reflected in the better capacity utilization in January: With an installed capacity of 58,000 MW (purple line), wind power generated an average of 19,200 MW of power per quarter hour (light green line) – this corresponds to 33 percent or a third of the installed capacity.

In the second half of January, the yield collapses almost completely

However, as the amount of electricity increases, so does the extent of the fluctuations: the peak values from August of just over 30,000 MW rose to over 44,000 MW in January, while the minima (always close to zero) remained within the same range. And yet the volume distribution is different: In January 2023, there is a two-week phase until the middle of the month where around 10,000 MW of wind power is relatively secure. This would never have been possible in August. However, in the period after that – from January 18 to 29 – the electricity yield from the wind turbines almost completely collapsed again due to a lull in the wind.

The conclusion is clear: even if more electricity can be expected from wind turbines in winter than in summer, you can never count on it for sure – as I said, this is “poison” for any electricity system. And to achieve this, natural landscapes are to be disfigured by giant plants made of concrete, steel and plastic?

Much higher than the Prime Tower in Zurich

By the way, can you imagine what it looks like to stand in front of a wind turbine over 200 meters high? I failed at first because I didn’t know how high the Prime Tower in Zurich was, which I imagined as a comparison. Well, this Zurich “skyscraper” is 126 meters high, so the planned Zurich wind turbines would be almost 100 meters taller than it.