I work in Oceanography.. The solar panels on individual buoys also get cleaned by rain, and can work ok vertically because of reflections. We have special diode bypass panels made so if 10% is covered in poop (SeaLion poop in our case) only 10% of the power is reduced.
Our biggest problem with small wind turbines on buoys is fishingpeople throwing line into them.
(i guess stuff like o&m, grid connection and yield are really project dependent)
edit: solar duck just announced 150mw combined pv wind project