Dunkelflaute 2037

"Dunkelflaute is a German word, derived from "dunkel = dark" and "Flaute = no wind". This German word is slowly making its way into the English-speaking world, much like "Kindergarten". "Dunkelflaute" is the worst case scenario for a system based on renewable energy sources, because at night we have no solar PV and when the wind dies down there is no wind power. But in a country as big as Germany, there is always sun or (offshore) wind. Or maybe not? As in my last article, let us look at a day in the year 2021. For this analysis I choose the 13.11.2021, the data are from Smard.de:

There is not a lot of renewable generation. It is an autumn day; the load is moderate. At night it can be seen that onshore and offshore wind go to sleep – and of course there is no sun: Dunkelflaute!

With a simple methodology (which is explained in detail here) we can predict what the renewable generation and load may look like in 2037. We know for example that the installed Solar PV capacity in Germany was about 53 GW in 2021. Now a German policy scenario says that solar PV will be 345 GW in 2037. This is 6.5 times the installed capacity compared to 2021. If I multiply the solar PV generation curve from 2021 by 6.5, then we get a good estimate of the solar PV infeed in 2037, and I do it similarly with wind power. I double the load as we expect a significant increase of the load. For the time being I do not take any “smart” power use into account – that we will do in later steps. I will use the following numbers:

If we multiply offshore wind, onshore wind, solar PV and load for 13 November 2021 by the figures as shown above the new diagramme looks like this:

This does not look good. Throughout the day, renewable energy sources cannot cover the load. In the evening we see a gap of around 100 GW – more than today’s peak load!

Of course we need to supply the load at all times, so the system needs to be adapted to the new challenge. And before you get overly excited about this this picture, please remember, everything here is simplified and in this case the simplifications make the picture look worse than it will be in reality for the following two reasons:

• Other types of generation as hydropower, power generation from biomass etc. are not shown. They would cover the load at least partly.
• The load will be more flexible as I did not take any “smart” power use into account.

At the same time, we have to face the facts. We need solutions for this situation and the magical term (please read how magic defeats the trolls) is “flexibility”. There are several kinds of flexibility:

• Shifting the power in time: short term (day-night-shift) and long term (seasonal storage) storage.
• Shifting the power across space: use the grid to connect areas with different generation and consumption patterns.
• A powerful flexibility option is to combine different primary energy sources. Already in this case you can see that wind and solar are a good combination, if you add further renewable energy sources (e.g. biomass) the picture will look even better.

Many solutions are known today, and I will show some in the articles to come. In addition, we will see innovation.

In this article we learned that energy will be cheaper in 2050 than it is today. But the challenge is not to produce the ENERGY with renewable energy sources but to have sufficient affordable FLEXIBILITY to always supply the load.

Personal Note: It is interesting to see that everyone is worried about energy production, when the real challenge will be to provide flexibility so that we have security of supply in a renewables-based system. It will not be easy, there is no silver bullet. It will require innovation and a redesign of the energy system.