Germany needs a connection from the coast into the south and most of it as of now will be build under ground.
> Laying a 380-kV high-voltage line underground poses a number of risks. The electrical behaviour of underground cables differs from that of overhead high-voltage lines. This results in a loss of transmission capacity. To compensate for this loss, additional devices (e.g. coils) have to be installed at various points along the route.
> The combination of cables and coils creates resonance similar to a radio where multiple jammers continuously change frequency. Cables and coils can cause disruption locally, jeopardising the stability of the entire grid. In addition, it is easier for Elia to identify faults and carry out maintenance on overhead lines.
[0] https://www.elia.be/en/infrastructure-and-projects/infrastru...
You can't really build a "grid" out of HVDC, because you can't easily convert between what the solar plants produce (a few hundred volts), what the local distribution grid needs (a few thousand volts), and what is needed to get that power across the country (tens of thousands of volts). On the other side you need to convert back down to a city-level distribution grid, down to a street-level distribution grid, and in your home down to whatever your equipment needs.
DC-DC conversion is significantly more expensive, more failure-prone and less efficient than AC-AC conversion. Why bother with a bunch of expensive active electronics when a simple transformer can do the job even better? Besides, who's going to pay to retool the entire country? Just because a solar panel produces DC and your computer needs DC doesn't mean it's viable to use DC for the entire chain.
HVDC is excellent for long-distance transmission lines, especially when power almost always flows in a single direction. Want to hook up a solar plant in the desert to an urban area 1000km away? Use HVDC! Replacing the entire grid grid with it? Probably not the best idea.
Remember, early generators from Edison’s company were DC. They caught fire _constantly_. Obviously technology has caught up since then but AC power generation and distribution is simpler engineering overall. Use HVDC where you need it and it is cost effective to do so.
It’s doable; but for longer distance runs when buried or under seawater, it’s usually more economic using DC which doesn’t have that issue.
Yes, it can (apparently), since these are mostly indirect effects of atmospheric vibrations (aka 'wind'). The vibration itself isn't usually the root cause of a blackout — but it sets off a chain reaction that leads to one (line contact/short circuit; conductor breakage; overcurrent & load shedding; protection system malfunction or overreaction, etc.)
Sure, there may be exceptions that might make it worth while. However, if long distance high voltage underground wires was practical and cheap, you would see deployed much more often.
That is always the case for the various failure modes of any high voltage line (and all the related equipment).
That said, you have it exactly backwards. Above ground lines are much easier to inadvertently come into contact with. Once faulted the breaker trips within a matter of milliseconds. It's the initial contact that's deadly.