hitzeflautes et dunkelflautesOn connaissait le terme dunkelflautes, qui signifie, surtout en hiver, jours gris et sans vent, où le solaire et l'éolien produisent très peu.
Dans un article d'aujourd'hui, le quotidien anglais The Guardian indique qu'un nouveau terme est sorti, le hitzelfalaute, de l'allemand hitzel qui signifie chaleur. Donc hitzelflaute indique les jours chauds et sans vent, où l'éolien produit peu. En journée, il y a le solaire, mais qui produit en telle quantité qu'il y a surproduction en journée, et prix très bas ou négatifs, et les centrales au gaz ou au charbon, qui doivent être arrêtées. Et au contraire, quand la nuit tombe, le solaire ne produit pas, et les centrales à gaz ou à charbon doivent être rallumées (les anglais n'ont pas beaucoup de nucléaire), et elles n'aiment pas, ce qui entraine des surcoûts.
Dans le Yorkshire, ils produisent même de l'électricité en brûlant du bois importé d'Amérique du Nord...
Et l'article indique que cela entraine un chaos sur les marchés de gros de l'énergie...
D'après l'article, avec les jours chauds mais peu venteux qu'à connu la Grande-Bretagne, la vitesse moyenne du vent, sur la période de Mars à Mai, serait tombée de 8.3 noeuds à 7.3 noeuds. Comme l'électricité produite varie comme le cube de la vitesse du vent, cela doit faire quelque chose comme 30% d'électricité produite en moins.
Au total, le prix de l'électricité augmente en Grande-Bretagne, et on voit quand même qu'ils ont une spécificité, en journée, ce sont eux qui ont les prix de gros les plus élevés, dans les 70 €/MWh, voir illustrations ci-dessous tirées des sites RTE et Electricitymap (Rq : c'est une très mauvaise idée de RTE d'avoir adopté le mode sombre, avec pour la France la couleur bleue foncée qui ne se distingue pas sur le noir)...
The weather phenomenon driving up Britain’s electricity bills
Clear skies, low winds and sunshine sound like perfect weather – but not for the energy industry
Jonathan Leake - 12 July 2025 11:00am BST
A surge of windless heatwaves hitting this summer is wreaking havoc on electricity markets and driving up bills for consumers, according to energy experts.
The industry is already familiar with “dunkelflautes” – the increasingly common spells of freezing windless winter weather when wind and solar farm output plummets. Now it is reporting a similar “hitzeflaute” phenomenon in summer, with longer spells of warm windless weather also becoming more prevalent with climate change.
Hitzeflaute comes from hitze – the German word for heat – and flaute, which means lull, reflecting the absence of strong winds in such spells.
It means Europe and the UK are becoming increasingly dependent on solar power during the day but, in the absence of wind, having to ramp up gas, coal and nuclear power stations in the evening.
The phenomenon also causes massive market swings with power prices often going negative in daytime when solar is peaking, but surging up to £200 or £300 per megawatt hour when the sun goes down, especially if wind output is low.
The UK faces just such a spell this weekend, with a high pressure weather system bringing clear skies, sunshine and low winds that will coincide with the Wimbledon tennis finals.
“These spells are becoming longer and more frequent and hitzeflaute is emerging as the new term for them,” said Jean-Paul Harreman, a senior analyst at Montel, which specialises in European energy data and convening the first conference on hitzeflautes this week.
“The weather is changing at a time when the energy transition is making us more dependent on the weather to generate our electricity from wind and solar. So it is all causing a degree of chaos in the energy markets.”
Met Office data confirms that British wind speeds have been falling, with recent spells of very low winds.
UK wind speeds from March to May this year were 14pc lower than the same spell last year – averaging 7.3 knots compared with 8.3 knots in 2024.
The Met Office said in a report: “March to May 2025 was the least windiest recorded for the period in the series commencing from 2001.”
Such weather phenomena have become increasingly important as the UK and Europe ramp up their dependence on intermittent sources of electricity such as wind and solar farms.
A spell of windless weather in winter or summer leaves the UK highly reliant on imports via the subsea interconnectors linking us with the Continent.
Recent windless spells have seen southern England sourcing up to 65pc of its electricity from abroad, mostly from France.
Yorkshire’s electricity is even more anachronistic. When wind speeds plummet and solar switches off, the county is often powered largely by wood imported from North America and burnt to generate electricity at the massive Drax power station.
Mr Harreman said the growing dominance of renewables and the growing prevalence of both hitzeflautes and dunkelflautes was changing British and European energy markets – often causing price spikes.
“On a sunny day we can see solar farms ramping up through the morning. They often produce so much energy that prices become negative and gas, nuclear and coal stations are turned down.
“But as the sun goes down demand surges as do prices – so we have to ramp them back up again. It’s not good for power stations to ramp up and down like this. And the costs all get added to bills.”
https://www.telegraph.co.uk/business/2025/07/12/the-weather-phenomenon-driving-up-electricity-bills-in-brit/
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