Regarding land use, just yesterday I was pondering about what technology it would take to create survivable off shore solar. Some loose grid of floating collectors happily bouncing on the waves like a flock of resting seabirds, perhaps cleverly reeling in and out link and anchor lines to match the geometry of the waves? Or just the right amount of springyness, dynamically tuned to the wave situation?

Then it occurred to me that even nature hasn't really solved ocean surface plants, what could be a more clear indicator that it's a really hard problem...