Generate Light from Darkness

Is it practical with current (no pun intended) technology?

Does it need further development?

How much area will it need to generate power. I read a figure,but.....................

Is it practical? Probably not, but I thought it was of interest that it could even be done, apparently with an off-the-shelf Peltier device and a voltage booster IC. They calculated 25 mW/m² from their prototype and extrapolated that under best conditions (dry air, high altitude, clear atmosphere) it could be increased to 0.5W/m². Compare this with about 150-200W/m² for solar panels.

I just thought it was interesting and passed it on...

Infrared processing materials is expensive per unit area. Like multi-layered solar cell about $200k per sq. cm.

I mean that's sure is doable but who would gamble say $200k/sq. cm with only 25mW/sq. m power generation?

All depends on whose money they are spending.

As the northern hemisphere phases into the mostly dark days of autumn, I wonder how useful this can be when the heat of the land approaches the heat of the cold sky.

"Everything at ambient temperatures radiates energy into space, providing the sky is clear."

What if it's cloudy?

https://farm6.static.flickr.com/5584/14494887971_6ca73f0fdf_b.jpg

Clouds image warmer than the open sky, although usually colder than the surface ambient. So, there would be some heat transfer, but not as much as to open sky.

If this energy could be channeled to frost protection for crops it'd be perfect. More energy for the frosty clear night.

If you think about it for a minute you should see that taking part of the heat energy leaving the earth to heat the earth just should not work.

Why not? That could amount to preventing it from cooling beyond the point of crop damage. "Could" applies only if the energy generated is sufficient though (so that may be doubtful). And other design considerations - area required, cost, etc might make it unfeasible.

What about the context of temperature inversion inside a greenhouse? Remember that the amount of heat required to prevent damage is not much. I'm not talking about winter heating or heat required for growth, just preventing a freeze on an unseasonably cold night.

It would probably be no good for spring, when the earth is too cold, but it might be applicable to frost in late summer and fall.

Why not?!?

Why for the exact same reason that perpetual motion does not exist. Now if one can store the energy taken out of the earth before it gets close to crop-damaging temperatures then that stored energy can get put back into the earth and plants. Once the plants are at risk of freezing crop-damage taking thermal energy out while trying to put thermal energy back in will just be counterproductive.

Ok I get what you're saying - the device is extracting heat from the earth, thus would cool it even faster than a cold night. Doh.

This process is highly inefficient as are all heat engines operating on a small temperature difference. The cold side radiator is only a couple of degrees colder than the hot side (ambient). Carnot efficiency = (T_h - T_c) / T_h.

To prevent frost damage it is much better to block the loss of heat in the first place by insulating the crops from the sky with a cover or with smoke, as is currently done now.

Thanks... It was only a couple months ago I read up on TEG's, Peltier device etc and how they work - which would have been informative if I had remembered any of it before I replied. (On the plus side, it all came back after "more coffee")

Instead of remembering the TEG, your description of clear nights reminded me of unsolved problem someone had with temperature inversion inside a greenhouse, which caused it to be colder inside than outdoors on those nights.

That's interesting and I wonder if it's practical...

Would it be possible to suck more power out of the ambient 60 hz noise?
A series capacitance and inductance tuned to 60 hz. Use it to keep your cell phone charged.

You imply the answer within your question. You cannot capture more power for other use than what is available. If your cell phone at idle uses less power than the 60 Hz power coupled to it by proximity to AC power lines then this is plausible but unlikely to be practical. Without knowing how much power your cell phone draws nor the coupled AC power density I cannot say if this is even plausible but I doubt it. Only ideal capacitors and inductors are lossless. I would expect the parasitic losses of the resonant circuit and the battery charge controller will exceed any coupled AC power one can nominally expect.