Wouldn't change things much
The world's oceans in total receive over 1000 times the energy than all of mankind uses... so even if enough energy could be captured to supply even 10 times as much energy as the world consumes now, it would only reduce the solar energy input to the oceans by 1%.
Sea Solar looks like a great idea, but not a factor in reducing ocean heating.
Besides which, 3 million square kilometers of solar panels would cost several hundred trillion dollars, plus supporting structures and distribution systems, etc.