In the long term, most countries on earth will not be able to function as they are now if they don't switch to alternative energy sources.

This will involve a mix of wind, solar, hydro, geothermal and nuclear on grids that span continents with massive battery stores to balance supply with demand. Between climate change and petroleum-fuelled kleptocrats, ditching fossil fuels is a necessity, not a choice. And the long term here is on the order of decades, not centuries, so within most of our our lifetimes.

I do not know, whether this is true, but: When I was in school, we learned in geography class, that one could power the whole EU, if we occupied some area of the Sahara desert with solar panels, at least when looking at raw energy output, disregarding day night differences and possibly hot and cold environment that a desert is.

I guess humanity is still not ready for such projects of enormous cooperation between countries, or, that there are too many things in the way, like said temperature rise at day and fall at night, the vast distance the energy would need to be transported (is that a problem?) and maintenance work somewhere in the desert. One can still hope, that some day we will be able to think globally and solve problems that way.

> we learned in geography class, that one could power the whole EU, if we occupied some area of the Sahara desert with solar panels

I sometimes hear that too. The YouTube channel "Real Engineering" did a video about the idea: [1] The TLDR is: the Sahara definitely gets enough sun, but transmitting the power into Europe would be hard.

[1]: https://www.youtube.com/watch?v=7OpM_zKGE4o