An inexpensive thermoelectric device harnesses the cold of space without active heat input, generating electricity that powers an LED at night, researchers report September 12 in the journal Joule.
Above – In this photograph, the thermoelectric generator harnesses temperature differences to produce renewable electricity without active heat input. Here it is generating light. CREDIT Aaswath Raman
The device developed by Raman and Stanford University scientists Wei Li and Shanhui Fan sidesteps the limitations of solar power by taking advantage of radiative cooling, in which a sky-facing surface passes its heat to the atmosphere as thermal radiation, losing some heat to space and reaching a cooler temperature than the surrounding air. This phenomenon explains how frost forms on grass during above-freezing nights, and the same principle can be used to generate electricity, harnessing temperature differences to produce renewable electricity at night, when lighting demand peaks.
Raman and colleagues tested their low-cost thermoelectric generator on a rooftop in Stanford, California, under a clear December sky. The device, which consists of a polystyrene enclosure covered in aluminized mylar to minimize thermal radiation and protected by an infrared-transparent wind cover, sat on a table one meter above roof level, drawing heat from the surrounding air and releasing it into the night sky through a simple black emitter. When the thermoelectric module was connected to a voltage boost convertor and a white LED, the researchers observed that it passively powered the light. They further measured its power output over six hours, finding that it generated as much as 25 milliwatts of energy per square meter.
Since the radiative cooler consists of a simple aluminum disk coated in paint, and all other components can be purchased off the shelf, Raman and the team believe the device can be easily scaled for practical use. The amount of electricity it generates per unit area remains relatively small, limiting its widespread applications for now, but the researchers predict it can be made twenty times more powerful with improved engineering–such as by suppressing heat gain in the radiative cooling component to increase heat-exchange efficiency–and operation in a hotter, drier climate.
SOURCES- Stanford, Journal Joule, Eurekalert
Written by Brian Wang
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Yes, I remember those reports.
I want the roof of my car painted with that stuff.
Yes. Both scenarios are described using the worth “path” but they are not the same.
There’s already research into surface treatment/paint that’s a narrow band IR emitter for the atmospheric window as a roof treatment, so painting your roof with it makes it cooler. If you had your finned radiator facing up with slanted fins (similar to fixed solar PV panel groups but pointing away from the sun to show minimum area to the sun) so every fin has good visibility to the sky while having good convection cooling, it might work to paint the topsides of the fins with such a paint. Keeping the surface clean becomes important though.
Ah, you were thinking full streetlight basically then. Gotcha.
Probably better and cheaper to create a temp diff by collecting solar at day and heating up some salt or something and then use it during night. Not only is the efficiency pretty bad but the conditions it must operate exist for limited time at most locations.
its interesting that this is possible. If you throw in reality and economics, its worthless.
1 meter per 25 milliamperes? That’s kind of big… you basically need one slab per led light…. you would get better results planting potatoes and inserting potatoe clock electrodes…
States like Arizona are the bane of the automotive industry; We’re required to build everything so that it can survive being parked in the sun with the windows closed on a hot, sunny day there. (Actually, Death Valley, which is slightly worse!) It is not easy to make car interiors survive that sort of thing.
I doubt garden lighting companies have remotely that stringent of requirements.
Might be cooking the batteries too.
I wonder if you’d get a lot more value trying to just use this for cooling.
As an air conditioner just have heat pipes or pumped water running from your room to the sky-radiator where it dumps heat to outer space.
Sure, it might just have a 20 or 30 degree temperature drop relative to the environment, but that’s perfect for an air conditioner rather than terrible for a heat engine.
OK, I was thinking of something that would illuminate say a bike path through a park.
Say like this
But the ratio between solar/heat radiator are the same.
30 lumens, that works out to a half watt. At 25mW per square meter, that’s 20 square meters of radiator. Those would be some pretty bulky garden lights.
The basic problem here is that this approach does not enjoy a very good temperature difference, which means that not only isn’t there much heat flow, such heat flow as there is, is converted to power at extremely low efficiency.
I guess I could see it used in a VERY niche application, where you wanted something to run off environmental energy for centuries, at extremely low power levels. But nothing more conventional than that.
Don’t forget that those heat radiators need clear skies to achieve reasonable efficiency.
Yeah, maybe it doesn’t work out well (barring the IR emitter maybe being always available at night), but what kind of outdoor path lighting are you using that needs 250W of LED’s though?
I was thinking small ones like this
http://www.moonrays.com/products/path%20lights/metal/91754
Not surprised, those little panels probably get hot enough that the cells deteriorate. And I doubt they’re built with Arizona in mind.
They are claiming 25 mW per sq. m. Compared to say 250 W for the same area of solar cells during the day.
Given solar generates power for about 1/6 of the day, and you’d want your lights on for say 1/2 of the 24 hour period, to run a 250 W light you’ll need 1500 W.h = 3 sq. m of solar panel plus a battery.
That 3 sq.m solar panel gives the same energy as 1 hectare of this new tech. I can’t actually think of any situation in which 1 hectare of heat radiator would ever cost less than 3 sq. m of solar panel plus 1.5 kW.h of battery storage.
I suspect the size of the IR emitter would be a limiting factor for path lighting 🙂
But at least here in AZ-USA, solar path lights seem to last less than a year before they die.
This might be nice for outdoor path lighting, as an alternative to those little solar PV LED path lights. Which ends up cheaper though, a TEG module and this narrow band emitter, or a PV+capacitors?