It's a good thing then that there is a long history of all state agents in northern Africa maintaining friendly and stable relations with European governments.
(Yes, said Europeans also carry a great deal of responsibility for this situation, but that doesn't make the situation any more tractable).
The solution for taking out high voltage powerlines? A pair of Skilsaws hanging under a quadcopter. Drop down onto it and... something bad's going to happen!
edit: I also missed the link: https://www.youtube.com/watch?v=m1lhGqNCZlA
edit 2: I scrolled around a bit and it's near the 30 minute mark.
Since we're talking about hypotheticals, I could say these things are also true:
1. There are counter-drones deployed and patrolling air space above the towers.
2. There are hundreds of independent power lines with 2N redundancy, so cutting 5-10 high voltage lines would do nothing.
3. The undersea cable points are protected by state agents and have good security for amateurs to compromise.
4. Europe will have 24-48 hours worth of storage even if ALL the lines are cut from the Solar Generation plants.
5. Europe will have backup power generation capacity in the form of locally stored and operated fossil fuel plants.
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In other words, there's absolutely no evidence that the future hypothetical solar installation is going to be more vulnerable than the infrastructure that already exists today, and surprisingly Europe doesn't plunge into darkness every week.
As to points 4 and 5, although storage and some backup capacity is reasonably feasible, this would mean that Europe could very well be forced to go to war in short order to get their full power supply back if a rogue organization gained power in North Africa.
Well, how many towers do you have to knock down using explosives before the lines fail?
The feet of the towers are simply accessible, so there's nothing stopping people from even just using a metal file. It wouldn't be safe, but you'd get the job done.
Or just plow a truck into their feet. You only really need to bend one of the feet and the wind will do the rest.
The thinking is in fact correct. The parent should have used a better, more serious, and guaranteed inevitable scenario: war. Bomb the concentrated infrastructure and take down all of Europe's power supply. It wouldn't take very high precision and it wouldn't take a vast number of hits: it would require a few, clumsy hits, which would be nearly impossible to stop.
The present system, which tends to be far more distributed than not (to take down all the power in Europe today, you need to hit a lot of spread out targets), is vastly superior to extreme concentration.
I agree with most of what you've said, but cutting a few inch thick conductors doesn't seem all that hard. I think a single stick of dynamite would do it pretty easily. Two for good measure. This would still be an act of war of course.
"Just cut the cables" isn't trivial. Have you ever seen a high voltage tower? Not only are they not accessible without professional gear, it's also going to require even more expensive gear to cut multiple inch thick conductors.
In all likelihood he power to Europe will be transmitted via multiple undersea cables, the effort of disrupting which would be unavailable to all but state agents, in which case the security issue is irrelevant, as you are likely already in a state of war.