6 kWh / m^2 / day is the solar insolation for southern California. It’s not what you’d get from a solar panel. Solar panels only convert a fraction of the solar radiation to electricity. That fraction today is around 1/5, or a little less. So you’re really only going to produce 1.2 kWh / m^2 / day, assuming a solar environment similar to southern California.
I feel like this is SOLAR FRICKIN ROADWAYS! all over again. Even down to the hexagons.
Hmm… I like your thinking! However, could we use the plastic to encapsulate all the world’s nuclear waste, too? Kill two birds with one stone! It shouldn’t matter if the plastic is radioactive if it’s already in an oceanic dead zone, right?
That’s such a stereotype. Like great ideas come to non-engineers, and engineers are there only to handle the “mundane trivial details”. 
A significant fraction of the worlds richest people are engineers, just FYI. A significant portion of innovations in the fight against climate change is by engineers, too.
I will have to ponder this proposal more deeply, but my immediate response is that this is supremely kooky and only a crackpot would even suggest it as a serious proposal that we should take seriously.
I’m also worried that it could hinder my plan to cool the core of Terra (aka Earth, or the “Rocky Primary” as they insist on calling it now) before the Crust, where all human activity takes place, shatters and sends us all to a molten Hell. Think about that before you go around rearranging icebergs on the Titanic!
Yes, it may help to prevent barnacles or some such.
Except that economics doesn’t work this way. This only works if there is infinite demand for power and water with infinite money to pay for it. In reality even if your first lily pad worked, and started to make money, at some point you will saturate the market. You would need to be cheaper than existing competition, (which includes land based solar and land based solar desalination) in order to capture market. And pretty soon you would start to depress prices. You next lily pad would go into a market with already suppressed prices. Whilst you might posit a rain follows the plough argument that cheaper power would open new markets, you are still selling cheaper, and no matter what, the market will saturate at the minimum price you can make power and water for. At this point using the money to make another pad will be competing with yourself.
There is almost no upside to building something in the water. All it does is add ruinously expensive engineering challenges that simply don’t exist on land. Have a look at the costs of oil rigs in the ocean. Just build you solar farms in deserts. They provide a great environment. You know a-priori the weather is good for solar, and you won’t have to contend with messy engineering to cope with water damage. Delivery of goods and workers to the site is done with a truck, and maintenance access is similarly easy. Distribution of power is done with cheap overhead lines, rather than insanely expensive armoured undersea cables. Maintenance is transmission lines does not require saturation divers fumbling about in the depths and crippling cost.
No desert nearby? Any land at all is going to be an order of magnitude cheaper than trying to make it work on th sea.
No doubt that’s true, but there’s still some floating ocean solar power out there:
OK, those pages aren’t set up properly, but they are for companies that are working toward ocean-based solar power. They are targetting places with little or expensive land but high demand for power. Here’s a recent article about it:
https://www.greentechmedia.com/articles/read/race-on-for-commercial-deployment-of-solar-in-open-seas
This thread somewhat fulfils my need for more XKCD What Ifs.