Rare enough to make the news should be a freaking hint that something unusual is going on even if you know nothing about he topic. But, in case you where actually confused underwater HVDC cables are far from the norm, which is why people are commenting on it.
As to the topic, if you want to bring up unrelated and experimental storage technology then don’t pretend to be “shocked” that the topic expands.
Let’s look at a HVDC list: https://en.wikipedia.org/wiki/List_of_HVDC_projects
VS say: https://cecgis-caenergy.opendata.arcgis.com/datasets/260b451...
Looks like as I said HVDC are rare. It’s ok not to be an expert on something but don’t try to fake it you just look like a fool.