I've been waiting for solar cell tech to be integrated with passive radiation to space. Our atmosphere is relatively transparent in a couple of relatively narrow frequency ranges. There's been some interesting materials developed that enable cooling via radiation to space - even in full sun. So far, the applications have centered around passive cooling (e.g. sun shelter for people waiting for a bus in places like Arizona).

As far as building on freshwater… I believe there’s been solar construction over canals in India which has the additional benefit of reducing evaporative water loss.