LED with 230% Efficiency Developed @ MIT

Even at 230% efficiency for the LED, you'd end up losing energy because of the low efficiency of solar cells. I wonder if this "drawing of energy from lattice vibrations" could be used to produce electricity directly, or is it a phenomena specific to the emission of photons?

 

Log in or Sign up to hide all adverts.

Unfortunately the very best PV cells out there are around 42% efficient, which means you would still lose energy (and gradually increase temperature) even if you captured every single photon (which is next to impossible.)

OTEC (and other Stirling engine based systems) are heat engines that work on a heat differential. In other words they work by transferring heat from one place to another and extracting work in the process. This is fundamentally very different, if repeatable.

 

Log in or Sign up to hide all adverts.

Different, yes, because there is not an actual heat differential, which is what allows for extraction of the energy from the higher-temperature body (by, for example, using colder water to cool a low-vapor-pressure gas used in a gas-turbine at the OTEC facility; comparable to a conventional boiler turbine that then uses cold water plus radiator to chill the steam back into a liquid).

However, this is theoretically on a similar basis. But instead of a colder temperature heat differential, there is the equivalent of a colder temperature in the form of a radiator - when it radiates, it cools. That is, it dumps the energy into a 'heat-sink' that is actually an ability to remove a photon, i.e. the 'heat-sink' is at a lower energy potential, even if at the same temperature, and utilizes a quantum phenomenon to radiate away a photon.

Or so it appears from the article and the comments.

 

Log in or Sign up to hide all adverts.

To me it's completely different. Heat engines obey the laws of thermodynamics, and their energy comes from temperature differentials. This device violates the second law of thermodynamics. That, to me, makes it a different beast completely. Definitely interesting but many of the rules don't apply any more.

It's like claiming you have created a new magnet and claiming "the flux density created by this magnet doesn't fall off with distance." That wouldn't be similar to a magnet in terms of theory; that would require a whole new way of looking at Maxwell's Equations.

 

It's not violating anything if you measure the total input and total output. The 230% is not factoring in the other source of energy. What's important is how outside sources are being tapped to produce more photons, using the initial energy as a catalyst.

 

It's using the room power. I do that when I breath.

Please Register or Log in to view the hidden image!

 

Well then it's definitely violating the second law.

Which outside sources?

There have been any number of devices that attempt to tap Brownian motion to do useful work. They have all failed due to the second law of thermodynamics. If this gets around that, that's a very big deal - and is way different than a heat engine.

 

Yes, that was my initial take on it. I discussed this (via an email exchange) with a retired NG engineer, and he said as such also, that it violates the second law, concluding that the article will be disproven because of that.

But I looked at it from a slightly different perspective. It is essentially extraction of energy based on a heat differential. But in an unusual sense. The ambient room temperature is the one heat level. The other heat level is outer-space (quite cold). The hot-room is linked to the outer-space heat-sink by the photons, which convey the heat-energy to the heat-sink. This is allowable apparently because of the quantum effects 'forcing' emission of photons.

If you read the comments section for that article, you will read a few similar comments (though I did not read them until after I had theorized as such above.)

 

For this I asked:
"I am curious to know to what value the temperature drops, into fully insulated enclosure, inside which there is such a LED ?"
This would imply the existence of an absolute temperature of reference (not theoretical but practical).
Otherwise it violate, as others have said, the second law of thermodynamics.

 

They are explicitly heating the LED, so the electrical input is not the total input energy.
http://prl.aps.org/abstract/PRL/v108/i9/e097403

http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.108.097403

http://www.physorg.com/news/2012-03-efficiency.html (Check out the graph)

 

That was given in the opening post, that the electrical input is not the total input energy, and that it is not violating the First Law in that it is drawing energy from the ambient temperature:

"However, while MIT's diode puts out more than twice as much energy in photons as it's fed in electrons, it doesn't violate the conservation of energy because it appears to draw in heat energy from its surroundings instead. When it gets more than 100 percent electrically-efficient, it begins to cool down, stealing energy from its environment to convert into more photons." http://www.wired.co.uk/news/archive/2012-03/09/230-percent-efficient-leds

Elsewhere they discuss that a higher ambient temperature, by heating, makes for an easier demonstration:

"These initial results provide too little light for most applications. However, heating the light emitters increases their output power and efficiency, meaning they are like thermodynamic heat engines, except they come with the fast electrical control of modern semiconductor devices." http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.108.097403

What the posters here have been concerned about is not the violation of the First Law (energy conservation), but the Second Law. At first glance, it appears to do as such.

However, as I noted, it actually doesn't because the higher ambient temperature of the device is higher than the temperature of "outer-space" into which the energy is deposited (or very close to outer-space; i.e. the photons escape to a heat-sink equivalent). Unless someone else has a better take on how it doesn't violate the Second Law.



http://physics.aps.org/synopsis-image/10.1103/PhysRevLett.108.097403

 

Yes, but not in this thread.

 

See post #24: "This device violates the second law of thermodynamics."

See post #27: "Well then it's definitely violating the second law."

This has been a common theme by persons versed in physics.

 

If that is the case, and you're effectively generating energy via thermophotovoltaics, then I agree - it does not violate the second law. However, it's also not 230% efficient, since you are exploiting the difference between a heated emitter and a cooler photovoltaic cell. In a real world application, for example, you could not run this thing at 70F and have it cool things down while the energy was absorbed by another 70F receiver. You'd have to keep the emitter warm and the receiver cool, and that would require work to be added to the system to maintain the temperature differential.

This is similar to blackbody radiation in a thermophotovoltaic system. An object (say the filament of a bulb) is heated and begins to emit thermal photons. This cools it down. Unfortunately it cannot be used to "pump" heat from one place to another, since it relies on being hotter than its surroundings. (and it is certainly not more than 100% efficient.)

 

Versed in scientific models is more accurate. Which is why I'm not allowed to answer.

 

Fallacy in logic. No such thing is physically possible in the universe we have come to know and love. Reading the study reveals it is simple journalistic incompetence.

 

Nothing beats the second law-the law of entropy in the long term.

 

doesn't this violate first law of thermodynamics?

 

No. It is not 230% efficient overall, it merely puts out more light that the electricity put into it can account for. The extra energy it needs is taken from the environmental heat. If you count the total energy input (not just the electricity) and the total energy output, I'm sure it's less than 100% efficient.

As we typically consider ambient heat to be "wasted" energy anyway, though, it is an exciting find.