I watched this interesting video earlier today, then went back to work. In the last few minutes, then, a few thoughts came to mind.
It would be interesting to create a pontoon-floated bridge between countries. Actually, I just ran a search for “pontoon bridge”, and was pointed to this article which already mentions what I was going to suggest next – pontoon-supported submerged tunnels spanning the Atlantic ocean. Doesn’t say it’s impossible – just expensive and unproven.
Another idea is to stick a load of photovoltaic arrays on styrofoam floats, and simply lay them out across a large area of water – after all, it’s not being used for anything else, is it? This would be bloody simple, in my opinion. You could gather the electricity from them either by using microwave transmitters, or by using small robot boats to shuttle uncharged batteries to the floats, and retrieve charged ones. This would allow the floats to be wireless, so sailing boats, etc could go through them without worrying about snagging on lines.