1. Joined
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    04 Jun '12 10:525 edits
    I want to know if the known laws of physics, esp second law of thermodynamics, rules out any hope of making either a solar cell or an electric lamp that is 100% energy efficient.

    The second law of thermodynamics rules out turning a less 'useful' type of energy into a more 'useful' type of energy without generating even more 'less useful' energy usually in the form of waste heat so that there cannot be any net increase in the overall 'usefulness' if the total energy from an energy conversion.

    BUT, purely within this narrow thermodynamic context, is electric energy any more or less 'useful' than visible light energy?
    Because if the answer is “no”, then surely it IS possible ( at least in theory ) to make BOTH a solar cell and an electric lamp that are both 100% energy efficient! -right?
    But, even if the answer is “yes”, then which type of energy is the more 'useful' type? Electric or visible light?

    If visible light is more 'useful' type of energy than electric then does that mean it IS possible ( at least in theory ) to make a solar cell that is 100% efficient but not an electric lamp that is 100% efficient?
    And if electric energy is more 'useful' than visible light energy then does that mean it IS possible ( at least in theory ) to make an electric lamp that is 100% efficient but not a solar cell that is 100% efficient?


    I also want to know if how 'useful' ( in this narrow context ) visible light is is partly dependent on how broad the range of frequencies that light consists of.
    Is, for example, light that just consists of one wavelength, say 550nm only ( which is monochromatic green light which I assume can only be produced by a laser ) , more 'useful' ( in this narrow context ) than white visible light consisting of many wavelengths but with an average wavelength of 550nm?

    It is my understanding that visible light energy of lower frequencies i.e. longer wavelengths is less 'useful' ( in this narrow context ) than the same amount of light energy consisting of higher frequencies -is that correct?
  2. Wat?
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    04 Jun '12 11:10
    Change 'useful' to 'controllable' and you may find you are half-way there to your own answer. 😉

    -m.
  3. Joined
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    04 Jun '12 11:57
    Originally posted by humy
    I want to know if the known laws of physics, esp second law of thermodynamics, rules out any hope of making either a solar cell or an electric lamp that is 100% energy efficient.

    The second law of thermodynamics rules out turning a less 'useful' type of energy into a more 'useful' type of energy without generating even more 'less useful' energy usually in th ...[text shortened]... amount of light energy consisting of higher frequencies -is that correct?
    I forgot to also ask:

    Does the answers of most of these questions depend on the voltage of the electricity we are talking about and, if so, what is the mathematical relationship between the two ? Does it depend on the frequency or wavelength of visible light?
  4. Standard memberScheel
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    04 Jun '12 23:27
    Originally posted by humy
    I want to know if the known laws of physics, esp second law of thermodynamics, rules out any hope of making either a solar cell or an electric lamp that is 100% energy efficient.

    100% is not obtainable, the entrophy is increasing.
    There were a thread in this forum a month or two ago on current, practical and theorethical limits to solar cell eficiency. Enjoy the reading.
  5. Joined
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    05 Jun '12 08:311 edit
    Originally posted by Scheel
    100% is not obtainable, the entrophy is increasing.
    There were a thread in this forum a month or two ago on current, practical and theorethical limits to solar cell eficiency. Enjoy the reading.
    100% is not obtainable, the entrophy is increasing.


    it is my understanding that this only necessarily applies to heat engines and, while entropy can never be DEcreased, there are circumstances where it would be theoretically possible, albeit with all sorts of 'constraints', for an energy conversion to occur with 100% energy efficiency. What I really wanted to know is the fine detail of exactly what are those 'constraints' that would specifically apply to solar cells and electric lamps.

    There were a thread in this forum a month or two ago on current, practical and theoretical limits to solar cell eficiency. Enjoy the reading.

    Oh yes, I had completely forgotten about that thread!
    That was my “28.6% energy efficient solar cell” thread.
    I should have revised that before making this thread.
    Unfortunately, the conclusion of that thread was that nobody currently knows the answer to my question there which was:

    “what is the absolute limit to how efficient a solar panel can convert indirect sunlight to electricity given the known laws of physics and the constraint that the solar panel must be made of ordinary matter? “

    -DAMN!
  6. Joined
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    05 Jun '12 11:12
    Originally posted by humy
    I want to know if the known laws of physics, esp second law of thermodynamics, rules out any hope of making either a solar cell or an electric lamp that is 100% energy efficient.
    I would think yes. It doesn't rule out the theoretical possibility, but it does rule out any hope of actually making it.

    You see, for such a device to work at 100% efficiency, it would have to be perfect. Not nearly perfect, but perfect. That's not going to happen. Even if it happens, I would think busybody interfering quantum effects would put an end to perfection quite soon.
    And then, for a device like that to remain perfect, it would have to be isolated from outside damaging effects. Specifically, it would have to be very well shielded from busybody interfering human beings with their tendency to try and fix what isn't broken, or to make, shock horror, practical use of these devices. But if we're not allowed to make practical use of them because that would mean reducing the efficiency, well... they're useless.

    Richard

    Richard
  7. Subscribersonhouse
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    05 Jun '12 12:441 edit
    Originally posted by humy
    100% is not obtainable, the entrophy is increasing.


    it is my understanding that this only necessarily applies to heat engines and, while entropy can never be DEcreased, there are circumstances where it would be theoretically possible, albeit with all sorts of 'constraints', for an energy conversion to occur with 100% energy efficiency. What sics and the constraint that the solar panel must be made of ordinary matter? “

    -DAMN!
    The limit to solar cells has to do with what is called electron re-combination. That is to say, electrons generated by converting photons to electrons have to find their way out of the cell before being attracted to a positively charged site. The reason the 33% figure is used as the max for solar cells is the rather narrow bandgap sensitivity of silicon. Here is one system that beats that % #:

    YouTube

    They claim to use 72% of the energy of the sun, by converting to electricity and capturing the solar heat.

    That is one way for sure. That record will probably get broken when multi-bandgap materials are included.

    Not 100% but getting close.
  8. Subscribersonhouse
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    05 Jun '12 16:321 edit
    Originally posted by sonhouse
    The limit to solar cells has to do with what is called electron re-combination. That is to say, electrons generated by converting photons to electrons have to find their way out of the cell before being attracted to a positively charged site. The reason the 33% figure is used as the max for solar cells is the rather narrow bandgap sensitivity of silicon. He ...[text shortened]... ll probably get broken when multi-bandgap materials are included.

    Not 100% but getting close.
    Here is some of the latest work at Stanford, polymer nanocones as photon concentration putting more photons to work in an inexpensive way, but so far the efficiency is under 12%.

    If the modules can be made for 50 cents a watt, it could be THE PV cell that makes it economically viable. Still a long way from 100% but that is not the ultimate goal, that goal is to be able to make them reasonably efficient at as low a cost as possible.

    If it is cheap enough, it doesn't matter much if it takes 2 panels to make as much power as one high efficiency high cost panel would.

    That said, there is still a place for high cost high efficiency panels, of course, that would be in space, where they have already proven to be long lasting, around 25% efficient and light enough to ship to space.

    There, the cost of the panels is secondary.

    http://phys.org/news/2012-06-nanocones-key-inexpensive-solar-cells.html
  9. Germany
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    05 Jun '12 19:17
    The maximum possible efficiency in a heat engine is produced when the cold reservoir is at 0K and the process is reversible.
  10. Joined
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    05 Jun '12 20:35
    Originally posted by sonhouse
    Here is some of the latest work at Stanford, polymer nanocones as photon concentration putting more photons to work in an inexpensive way, but so far the efficiency is under 12%.

    If the modules can be made for 50 cents a watt, it could be THE PV cell that makes it economically viable. Still a long way from 100% but that is not the ultimate goal, that go ...[text shortened]... panels is secondary.

    http://phys.org/news/2012-06-nanocones-key-inexpensive-solar-cells.html
    Note a bad link. it says:

    http://phys.org/news/2012-06-nanocones-key-inexpensive-solar-cells.html

    "...One of the biggest challenges facing the silicon photovoltaic industry is making solar cells that are economically viable. To meet this goal, the module cost, which is currently about $1/watt, needs to be decreased to just half that. Much of this cost comes from the silicon material and the expensive fabrication processes often used. In a new study, a team of scientists and engineers has demonstrated that a hybrid solar cell covered in silicon nanocones and a conductive organic polymer can address both cost-cutting areas while providing excellent performance. ...
    ..."

    but it sounds like it will be some time before it would be mass-produced.
  11. Subscribersonhouse
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    06 Jun '12 00:55
    Originally posted by humy
    Note a bad link. it says:

    http://phys.org/news/2012-06-nanocones-key-inexpensive-solar-cells.html

    "...One of the biggest challenges facing the silicon photovoltaic industry is making solar cells that are economically viable. To meet this goal, the module cost, which is currently about $1/watt, needs to be decreased to just half that. Much of this cost com ...[text shortened]... rmance. ...
    ..."

    but it sounds like it will be some time before it would be mass-produced.
    That article just came out today so they are in preliminary work.
  12. Subscribersonhouse
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    07 Jun '12 17:14
    Here is another PV cell, no thermal capture, pure phonics to electricity coming out at 43%:
    http://phys.org/news/2012-05-sharp-solar-cell-worlds-highest.html

    Triple junction, 3 separate band gaps to tune each cell to a specific part of the visible spectrum.
  13. Joined
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    08 Jun '12 08:22
    I may have become disappointed in not quite finding the answers I was seeking for the theoretical maximum energy efficiencies for electric lamps and solar cells, by I have just found this video about spintronics ( sending signals down wires not via electric current but by changing the spin of the electrons ) research that give extremely good clues of what, in very bold-figures, the theoretical maximum energy efficiencies for the ultimate computer would be.

    YouTube

    about half way through, it says:

    “they will be the ultimate in energy efficiency.....in principle, it should be possible to run a computer for a hundred years on a single battery.”

    Well, that sounds very impressive!

    But, and I would be the first to admit this is a miner consideration given this context, if we were to assume that, one day, we would make room temperature superconductors, how would the energy efficiency of the most energy efficient possible spintronic computer compare with the energy efficiency of the most energy efficient superconducting computer per instruction executed? ( I assume the two types of computer could not be meaningfully combined? ) I know that the prediction for the power consumption for superconducting computers is roughly in the order of about 1000 times less than that of a conventional computer and that it would run between 20 and 50 times faster so that's, say, very roughly, 40*1000 = ~40,000 times less energy consumed per instruction executed than the energy consumed per instruction executed in a conventional computer. What I want to know is, how, in theory, how that would compare with the energy consumed per instruction executed in the most energy efficient possible spintronic computer and are we talking about at least one order of magnitude of difference? Would anyone in the scientific community have a clue on this?
  14. Subscribersonhouse
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    08 Jun '12 14:14
    Originally posted by humy
    I may have become disappointed in not quite finding the answers I was seeking for the theoretical maximum energy efficiencies for electric lamps and solar cells, by I have just found this video about spintronics ( sending signals down wires not via electric current but by changing the spin of the electrons ) research that give extremely good clues of what, in v ...[text shortened]... order of magnitude of difference? Would anyone in the scientific community have a clue on this?
    Not sure about that but I know when quantum computers are ready for prime time, they will blow everything out the water power consumption wise vs conventional or spin computer.
  15. Joined
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    08 Jun '12 15:308 edits
    Originally posted by sonhouse
    Not sure about that but I know when quantum computers are ready for prime time, they will blow everything out the water power consumption wise vs conventional or spin computer.
    Quantum computers will be able to do some tasks a zillion times faster and with much less energy than even the most energy efficient spintronic computer could do in theory for doing those tasks.
    In particular, I once heard that they could be made to computer simulate any quantum system better than any conventional computer or any other kind of computer and that would prove to be very important.
    This is the only really useful task I have heard that quantum computers can do And do better than other computers -I am not at all too impressed by the other said tasks such as breaking encryption codes and finding very large prime numbers that quantum computers can do. Still, computer simulating any quantum system a zillion times faster is surely extremely useful.

    BUT, unless some kind of ingenious way around the laws of quantum physics or other constraints can be found, quantum computers can only do a very limited range of tasks better than conventional computers and that would mean that most computers and computing would always be done using other types of computing and for the vast majority of the different tasks.
    You certainly could not have, say, a quantum computer that is also an AI with general intelligence and learning ability. Nor could you have a quantum computer do all the tasks your PC normally does AND do so with greater energy efficiency. Pity.
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