Cool, literally. Fresh water, probably fine, but salt is going to be big trouble - get some ions in there and electrolysis gets going even in things that are nominally "waterproof". I noticed in a panel closeup they were using Solarex panels - same as most of mine. They've quit making them here, sadly - it was nice to have solar panels made by an oil company (BP) in some weird philosophical sense. They were just too high a quality to compete with the flood of Chinese crap - and in this case, it mostly is truly crap that dies young.
At least the sq feet for the panels are cheap...probably help keep the water in the lake instead of evaporating, but I bet the maintenance is kind of tricky - algae and mold, things like that.
And yes, panels make more power when cooler, as the diodes that are the cells run into forward bias current draw at higher voltages. In fact, it's so prevalent that someone "invented" a switching supply that acts like a DC transformer to "impedance match" the cell optimum power voltage down to whatever the battery voltage happens to be at the moment, and it can give quite a lot of power gain in colder weather - 20-40%, depending on the state of both things. MPPT it's called now, and a feature of all the better solar charge controllers.
Did I mention *I* was that guy who invented this? I open sourced that too, a few decades ago, so no one has to pay extra royalty fees to use it - no excuse to rip customers off for that. They do cost more, as there's more electronics involved to get that job done, and they're not the cheezy kind, it takes quality components to avoid waste in the switching power supply.
My Volt is getting its first ever super high speed charge today - I'd bought more panels and a bigger inverter and the fast charger recently. Haven't had enough good weather to hook up the new panels, but with my MPPT controllers and the new inverter, it's keeping up even now, for a 4 hour charge, empty to full, in the good solar hours here - 10 to 2 in this season. So once again, my errand loop will have that really great fuel cost - zero. Good, I'm down to one beer and need to make that loop today.
Can't wait to get the other 2.4kw of panels up in the sky and connected up. That will get me two full car charges a day in summer (plus the house) or one in winter, on sunny days, or just do the house with no backup generator even on cloudy days...cookin' without gas, we'll be. You won't be able to see my roof anymore, but I don't care, and it will make the AC work less due to the house being in the shade of all the panels.
The new panels, since I can't get Solarex anymore, are Schott, made in America, your standard polycrystalline silicon wafers, same as the Solarex ones that have lasted decades already - that's the good tech to get, people. Early adopters are getting killed on the new cheap stuff that's thin film and tends to micro-crack when thermal-cycled.
The new ones were $1.47/rated watt - my first panels were over $7/watt - and in those dollars, not today's. The time has finally come for this! It's still not what most would call cheap, but ROI is getting really good, and you get to break another deal with a devil, the power company.