Breathless (a French auteur film about wind farms)
Emmanuel Macron finally inaugurated on Thursday, September 22, near Saint-Nazaire the first offshore wind farm in France, which is supposed to embody “France’s ambition for the large-scale development of renewable energies”: “80 wind turbines with a power of 480 MW capable of meeting 20% of the electricity needs of the Loire-Atlantique region,” writes “Les Echos”. A still humble ambition...
There is nevertheless a slight concern for wind energy, identified by Lucie Robequain, the editor in charge of investigations at “Les Echos”: the winds are weakening in Western Europe. They have rarely blown so slightly for forty years, as the latest report of the Copernicus program, European State of the Climate 2021 explained.
From Ireland to Germany, through the United Kingdom and Denmark, where the most offshore wind farms are located, the annual average wind speed has even dropped by up to 10% compared to the average recorded over the period 1991–2020. They are increasingly blowing elsewhere, in the south-east of the continent, in the Balkans, Greece, Turkey, where the wind equipment is minimal…
To go further than this alarmist headline (Breathless!) and the conclusions that follow (no need to build wind turbines), we had to go into the details of the data provided by Copernicus — and the European program is not stingy: for each quarter of a degree of latitude and longitude (4 × 360 × 4 × 360 = 1,036,800 points), at 10 and 100 meters (surface wind) for each half hour from 1959 to 2021 (62 years × 365.25 days × 24 hours × 2 = 1,086,984). Let’s round up to 1,127 billion data, time-stamped and geotagged.
With a little help from Pythagore and Python
How to process and visualize such a mass? A job for the team of Jules Grandin, the dataviz department of “Les Echos”. First of all, they have to define the space we are interested in (Europe, 68° longitude, 46° latitude, that is to say a little more than 50,000 points, 20 times less than for the whole world), the measure (the wind speed at 100 meters of altitude only). And to involve “the Javascript wizard” (Python, in this case, but you can’t change the artist’s name like that), Tom Février. Not to mention the contextual graphs that allow the interpretation of the map, devolved to Geneviève Thibaud.
Alas, laments Tom Février, there is a lack of data at a height of 100 meters: “Only the components of the wind are available, i.e. its horizontal speed u (eastward) and vertical v (northward). To recalculate the wind speed, i.e. the magnitude of the wind vector, one must use… the Pythagorean theorem.
For each of the more than 50,000 points in the area (271 longitudes / 185 latitudes), we must then recalculate the wind speed from u and v for each hour (8,760 per year), and take the average. Twice.”
Five hours of calculation later, they get a map of anomalies (where the wind blows stronger or weaker) in increments of 5% in isometric projection (each quarter-degree is the same size, so that the pole, which is only a point represents the entire width of the map). This is where the cartographer (Jules Grandin) intervenes to restore the roundness of the Earth and a representation in accordance with the real distances.
As a bonus, for the Web version, two animations, inspired by the wind map of Fernanda Viégas and Martin Watterberg (both professors at Harvard and members of Google’s People+AI Research initiative), allow to see, even better, the winds flowing differently in 1959 and in 1921 and the flows increasing or decreasing (especially off the Finistère, in the Ouessant, Iroise and Yeu areas ; at the mouth of the Rhone, the Ligurian zone; bordering Portugal, the Sao Vicente zone; the Peloponnese, the South Ionio zone; and all of Asia Minor, the Western Black Sea, Marmara and Aegean zones — reminiscent of old marine weather reports on the radio).
“In concrete terms, we generate several thousand particles that will move in the right direction and at the right speed depending on their position in the vector field (= the grid of 50,000 points), leaving a trail behind them,” Tom Février explains.
The feature of our three infographists, to be found in “Les Echos” of Thursday, September 22, 2022.
and its enriched web version :
How the drop in winds thwarts wind power
Further readings :
