That's what this is for, in general: https://energy.ec.europa.eu/topics/infrastructure/trans-euro...

Also, Germany currently has the problem of much more and more reliable wind generation in the north, but not enough network capacity to send it all south when needed. It is being addressed, but as expected, it is very complicated because infrastructure across the whole country touches the interests of a lot of groups with very different interests.

We might need much better tunnel building equipment and a deep sub-terranean network... (useful sci-fi idea, needs to be able to cope with mild earth quakes in some regions).