Peltier / Thermo Electric.

Every now and then I like to think of ways to generate cheap green Energy and last night while falling asleep, I had this thought flow through my head.

What about Arrays and Arrays Peltier devices , imagine a sandwich, top half would be all black to absorb the suns rays and primarily making lots of heat, then on the underside of the sandwich waterproof coating, which is submerged into the sea to keep it nice and cool, water cool.

That in my head "works" but i then thought about Winter.... less electricity being produced, colder water, less heat from the sun, but now i'm left wondering if this could even work at all?

You can generate electricity from sunlight that way but I expect it will be less efficient than photovoltaics.

You can find peltier powered fans for use with woodburning stoves. That's up to 100F difference between the top part and stove side and all they drive is a little DC motor like you'd find in a CDROM player. There's power there but not much.

johnwasser: You can generate electricity from sunlight that way but I expect it will be less efficient than photovoltaics.

Something I've always wondered is why they don't combine (for a home) the photovoltaic panel with water heating.

The problem with photovoltaics is that as they heat up, they get less efficient. So - attach the cells to the "heatsink", and pipe water through it; circulate it to a tank in the house. Doing this would help cool down the photovoltaics (and increase their efficiency on very sunny/hot days) while giving you a bit of hot water (or at least it would lessen the load of the water heater - whatever it uses to heat the water). Basically - combine the systems to increase the overall system efficiency.

The only valid reason I can think of why they don't do it is potential failure modes (and the idea of water running near such a high-current DC system as some installations are). I'm probably missing something else, though...

You can extract energy from a system whenever there is a temperature difference (as the heat moves from the hot-side to the cool-side). So, you could extract energy from the difference between air and water temperature during the day when the air is hotter than the sea, and again at night when the air is cooler than the sea.

I'm sure if this was economically efficient, it would be done. Energy efficiency is not a factor, since there is plenty of sea & air and an inefficient system just has to be larger. It's the same issue with photovoltaics... There is plenty of sunshine and the energy is "free". But in the real world, the electricity from photovoltaics is more expensive than traditional sources.

But of course, the environmentalists won't like you if you start transferring heat between the sea and the air! :D