Shockley-Queisser Limit is 34% ...

[WindyOne]

"Generation One" type Solar Cells are limited by the Shockley-Queisser limit of 34% efficiency.
Pages 20 - 23 of the article below explains how that limit can be exceeded.

http://issuu.com/alexeeweb/docs/pulse_volume_87_-_richard_barry__issuu_/21

[XeonPony]

Interesting little article.

Not a spam post people safe to check the link!

[dnix71]

People are slow to learn. The generation 3 cells descibed in the article are nothing more than what plants have been doing all along in photosynthesis. Bump electrons up in steps to use whatever energy is available from different wavelengths. Sunlight is a broad mix of energies. There is a lot of energy in the infrared if someone can tailor a cell to take advantage of it.

[DamonHD]

Well, "slow to learn" is a little harsh.  "Slow to emulate cheaply" might be more on the mark.

Expensive satellite PV is often multi-junction to convert more of the incident light into electricity, but is hideously expensive.

I have some (UniSolar) multi-junction stuff in my garden, but it's not very efficient.

Rgds

Damon

[bart]

Graphene: A Material That Multiplies the Power of Light

http://www.sciencedaily.com/releases/2013/02/130224142831.htm

[WindyOne]

People are slow to learn. The generation 3 cells descibed in the article are nothing more than what plants have been doing all along in photosynthesis.

And it took nature about 5 billion years to accomplish that !

... Sunlight is a broad mix of energies. There is a lot of energy in the infrared if someone can tailor a cell to take advantage of it ...

Here is some research to capture the "broad mix of energy" from the sun ...
http://www.rsc.org/chemistryworld/2013/01/laser-guided-maglev-graphite-air-hockey
"... The disk could also be spun using sunlight focused at its edge, reaching a speed of around 200rpm. Abe suggests that this might lead to a new way of harvesting solar energy, if the movement could somehow be harnessed to do useful work ..."

[oztules]

One wonders at the new science writers of today.... eg.

"Graphene: A Material That Multiplies the Power of Light".... is clearly overunity   ..... nothing is for nothing.  Graphene is interesting but it  does not change the rules of the universe..... which is really what they are claiming in the headline.... why do they do that?

"Generation 3 cells to beat the "Shockley-Queisser limit "  concept is similar.... hype without substance. They are not beating anything, just adding different band gaps into the mix....  a big wow.


poor science writing for mine.



......................oztules

[DamonHD]

Possibly a bit harsh: it would be a major achievement if instead of soaking up ~18% of incident sunlight on a roof we could make that 60% or 90%!  My small roof collects enough for us to be net-zero energy over a year, but 5x as much per unit area of available roof space in crowded urban areas could be a game-changer.

Not all of it is fiddling with multiple band-gaps.  In particular getting one photon to generate multiple electrons and a little heat rather than one electron and a lot of heat is a very different thing, and may eliminate some of the waste that the quanta / band gaps for current materials otherwise imply.

Rgds

Damon

[oztules]

Thanks Damon,
Do you have specific arguments to point to (relevant site etc) regarding the multi electron low heat v/s single electron lots of heat argument



.................oztules

[DamonHD]

Hmm, I haven't been keeping those links to hand.

Basically the SQ limit exists because for a conventional single-junction device the photo energy has to be at or above the band-gap voltage/energy to cause an electron to flow and the rest becomes heat.

Multi-junction devices stack higher-bandgap devices in front of lower ones to try to pick out the high-energy photons first then lower ones that the initial layers cannot absorb.  Still getting one electron per time, but some of those much more energetic.

Quantum dot and this graphene work manage to finesse that entirely as I understand it, using a different mechanism, and can generate several electrons for electricity from each photon, with little residual heat.  Those are the developments that I'm hoping will bear fruit, but they are at such an early stage that I'm not holding my breath.

The best way to avoid the SQ limit is to play a different game...

Rgds

Damon

[oztules]

Ok,
Single and multi junction are as we suspected..... just stacking with different band gaps..... no new thing here.

Quantum dot is simply the same thing via a different mechanism, where the size of the crystal dictates the bandgap, (smaller crystal, larger the  bandgap)  and so when we have different sized (graduation) crystals bunched together, we can take different wavelengths at the same time.... same as multi junction, but using the crystal lattice physical size as the multi junctions. This is over  30 years old too. (colloidal suspension anyone?)

You cannot..... may not .....can't have......... a photon dislodging two or more electrons unless it has  at least  (just over) twice the electron volts of the band gap.
You can have a luminescent converter to down size the EV to closer to the bandgap, but this does not release any more electrons either.

The output power is a function of the bandgap X the current. If we chose a low bandgap ( to make more use of the energy of the incoming photons), then our current may increase ( just what you wanted....more electrons), but the power won,t/may not increase, as the voltage is less.... so getting the band gap high enough to make efficient power  (ExI) versus lowering the band gap in nett to get more electrons at a lower voltage out??

Just releasing electrons from the lattice is not the whole story.... we need pressure as well (V).


I think thats how it works



.................oztules

[WindyOne]

One wonders at the new science writers of today.... eg.

"Graphene: A Material That Multiplies the Power of Light".... is clearly overunity   ..... nothing is for nothing.  Graphene is interesting but it  does not change the rules of the universe..... which is really what they are claiming in the headline.... why do they do that?

"Generation 3 cells to beat the "Shockley-Queisser limit "  concept is similar.... hype without substance. They are not beating anything, just adding different band gaps into the mix....  a big wow.


poor science writing for mine.



......................oztules

Oztules,
  But what if the newer 3rd Generation PV Panels can capture, up to, 42% of the energy per square instead of just 15% of the energy per square foot and eventually they get the production costs down. Do I really care if the newer 3rd Gen PV Panels are just "adding multiple bad gaps to the mix", as long as they are cost effective and last a long time? Would 2.8 TIMES the wattage generated per square foot be a significant improvement for those of us with PV power? Maybe that's not a "big wow for you" but that is a "big wow for me".

 Is there anybody on this board that would not want almost three times the wattage from the same sized PV Panels and at the same cost then please raise your hand. OK, I am looking .... Oztules! come on, put your hand down. 

[WindyOne]

Sunlight is a broad mix of energies. There is a lot of energy in the infrared if someone can tailor a cell to take advantage of it.

Solar Heat Tubes can absorb the Infrared energy.
So with current technology we need both PV Panels and Solar Heat Tubes to capture a wide range of solar radiation.

[DamonHD]

Or "PV/T" PV/Thermal (combined PV with water cooling) which I have considered a number of times, and would do if my roof was not already full...

Rgds

Damon

[Bruce S]

WindyOne;
Please go read some of Oz's previous posts, he kinda knows what he's talking about.
He's always up for a good civilized discussion, but if you don't know what you're talking about down the the science level then re-read even more.
WHAT he's trying to say and as I read it>> the info doesn't add up you can't get something for nothing, you can get more efficient by going after the wavelengths and then stacking,BUT...
This was the approach MIT, CALTECH was pursuing was doping for specific wavelengths then stack the panels as the other wavelengths would be invisible to the previous panel.
 
See, what the current PV do is a broadband approach to solar, to get more PV out of a given space, then the manufacturers will need to get into the specific wavelength regions and harvest from those.
THIS really isn't new, Electronics Weekly wrote about it way back in the early 80s, so what (I THINK) OZ was saying about shotty reporting was the writer didn't seem to do his/her homework on the history or rather went into hyper-Media mode to pump up a story.

AND Solar heat tubes ARE supposed to absorb solar rads if they didn't they wouldn't be doing their jobs  .
Cheers;
Bruce S