1) Solar panels are expensive, and frankly not particularly green to produce.
2) Your devices would have a short lifespan because of corrosion from the sea
3) Getting the devices back to harvest the energy is a major running cost of your contraption
4) Given the cost of the building the solar part of the device, rigging it up to a solar power plant probably is cheaper, gives a longer lifespan and generates more collectible energy.
5) And sadly, finally and most importantly, Oil, Coal, Gas and Nuclear are waaaaay cheaper than any unproven technology that doesn't output tons of electricity for nearly free, because Oil, Coal, Gas and Nuclear are cheap, effective and we've already got the infrastructure for it. Hell, even Solar and Wind can't compete with those guys at the moment on cost - and they output lots of direct energy.
So as an scientist, I'm happy to say that your idea might just put out more power than it takes over it's entire lifespan. As an economist and investor, no chance.