The question isn't about power lines. The question you started with is "Hydroelectric is generally counted as a renewable, and it's also a storage system."
The problem is that yo uneed to build a lot of them, and you can't just build them abywhere you want.
> What's the ampacity of a typical high voltage line?
Zero. The storage capacity of a high voltage line is zero.
Needless pedantry as everyone uses transmission lines so that power creation and storage aren't in the same physical location as the end use.
If you've got a 5 GW line going from Berlin to, say, the Czech border (where there's currently already a 1 GW hydro plant, I make no claims about environmental capacity for more even though it seems plausible at first glance), then you've got hydro storage keeping the lights on in the city even though it's 215 km away because there's nowhere here to put any hydro storage.
That's why it matters what the amp-acity of a HV line is.
I might be overestimating power lines or people's willingness to have transmission lines near them.
What's the ampacity of a typical high voltage line?