NREL Solar Cell Sets World Efficiency Record at 40.8 Percent

Aug 13, 2008

(PhysOrg.com) -- Scientists at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) have set a world record in solar cell efficiency with a photovoltaic device that converts 40.8 percent of the light that hits it into electricity. This is the highest confirmed efficiency of any photovoltaic device to date.

The inverted metamorphic triple-junction solar cell was designed, fabricated and independently measured at NREL. The 40.8 percent efficiency was measured under concentrated light of 326 suns. One sun is about the amount of light that typically hits Earth on a sunny day. The new cell is a natural candidate for the space satellite market and for terrestrial concentrated photovoltaic arrays, which use lenses or mirrors to focus sunlight onto the solar cells.

The new solar cell differs significantly from the previous record holder – also based on a NREL design. Instead of using a germanium wafer as the bottom junction of the device, the new design uses compositions of gallium indium phosphide and gallium indium arsenide to split the solar spectrum into three equal parts that are absorbed by each of the cell's three junctions for higher potential efficiencies. This is accomplished by growing the solar cell on a gallium arsenide wafer, flipping it over, then removing the wafer. The resulting device is extremely thin and light and represents a new class of solar cells with advantages in performance, design, operation and cost.

NREL's Mark Wanlass invented the original inverted cell, which recently won a R&D 100 award. His design was modified by a team led by John Geisz that further optimized the junction energies by making the middle junction metamorphic as well as the bottom junction. Metamorphic junctions are lattice mismatched – their atoms don't line up. The material properties of the mismatched semiconductors allows for greater potential conversion of sunlight.

Provided by NREL

Explore further: New solar power material converts 90 percent of captured light into heat

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Soylent
3.2 / 5 (17) Aug 13, 2008
If one wished to adopt the same "peak-everything" scare tactics as many solar fanatics use against all other forms of energy one might note that the world-wide reserve base for indium is 6000 tonnes, which is 13 years of supply at current rates.
makotech222
1.3 / 5 (12) Aug 13, 2008
last i heard they can create synthetic indium. or maybe that was some other element that starts with an I, lol.
googleplex
4.3 / 5 (12) Aug 13, 2008
Extremely impressive. What I like about this is that it is for concentrator installation. It sounds like it might be both more efficient and cheaper than products currently on the market. Brilliant idea using a staggered lattice.
It should be noted that concentrators dramatically reduce the amount of photovoltaic (PV) material compared to ambient PVs.

To add to the previous comment...

Indium ranks 61st in abundance in the Earth's crust at approximately 0.25 ppm [2], which means it is more than three times as abundant as silver, which occurs at 0.075 ppm [3].

Recent Indium surge in LCD manufacturing have caused a shock in the price. Extraction will increase to meet/exceed demand.
bredmond
1.3 / 5 (9) Aug 13, 2008
Why the need for 326 suns? Why didnt tehy test it with one sun? will it perform differently with just one sun?
Decaf
2.5 / 5 (10) Aug 13, 2008
They needed 326 suns for lifetime testing. They can't wait decades before putting this thing into practice, so they have to simulate decades of use by bombarding it. I'm sure they're assuming that it couldn't possibly perform WORSE with only one sun, so no harm no foul.
sdfasgafasdfsdasd
4.3 / 5 (10) Aug 13, 2008
They use 326 suns to minimize the active PV area and higher intensities actually increase the efficiency, that is until the PV cell gets too hot. At extreme concentrations, say 500 suns, the PV cell needs to be actively cooled. Concentrators are very cheap compared to PV cell area. Its all about cost per Watt.
Zeddy
3.9 / 5 (9) Aug 13, 2008
The concentration factor is the key to this: this is designed to be used under concentrated light conditions (326x). That way you can use a small piece of silicon, a big plastic fresnel lens, and get more watts out than an equivalent flat panel (which would be 326x as large)
Soylent
2.7 / 5 (11) Aug 13, 2008
last i heard they can create synthetic indium. or maybe that was some other element that starts with an I, lol.


There should be a little bit of indium among the fission products of plutonium and heavier minor actinides; particularly if fast fission is used. As luck would have it there are only two isotopes of indium with long half-lives; In-133, which is stable, and In-115 with a half-life of 414 trillion years(96% of natural indium dug out of the ground is this very mildly radioactive kind). The short half-lives of unwanted isotopes mean you can wait for them to decay and then isolate the indium with purely chemical means if you do reprocessing of the fuel. It might be cost effective(along with extraction of several platinum group metals) if indium becomes scarce enough, but it's not going to solve your indium problem.

Dedicated synthesis of nuclei is only cost effective for isotopes needed in tiny amounts, like medical isotopes, americium for smoke detectors, lab sources for calibration of radiation detectors etc. The most common way to produce isotopes is with the neutron flow from a small reactor; because transmutation with radioactive sources or accelerators is even less cost effective.
out7x
1.6 / 5 (16) Aug 14, 2008
So what does 40% efficiency get you? 2 light bulbs instead of 1?
Soylent
3.6 / 5 (9) Aug 14, 2008
So what does 40% efficiency get you? 2 light bulbs instead of 1?


That's a good guess actually. Year round average insolation in southern Europe is about 250W per square metre; 40% of that is 100W. You get a good bit more than that using two axis tracking but if you're going to do storage it about evens out.
Roj
2.8 / 5 (4) Aug 14, 2008
You get a good bit more than that using two axis tracking but if you're going to do storage it about evens out.


Could tracking be eliminated for rooftops; in a process of lensing the 326x area onto individual cells. Perhaps bubble lensing for consumer panels.
Soylent
2.4 / 5 (5) Aug 14, 2008
Could tracking be eliminated for rooftops; in a process of lensing the 326x area onto individual cells.


How?

Perhaps bubble lensing for consumer panels


Replacing two axis tracking with giant hemispheres of solid leadglass(if even that will have high enough refractive index) is not an improvement and spheres do not even have an exact focus.
lengould100
1 / 5 (8) Aug 14, 2008
It's getting really hard to accept all the junk being put up by the professional negatives on every and all renewable energy systems. You'd improve your cred a lot by reducing the rate of false information you provide.
SLam_to
3.4 / 5 (7) Aug 14, 2008
I doubt these will be affordable for the average consumer any time soon. The cost/watt is very high for these types of PV's.
jburchel
2.2 / 5 (10) Aug 14, 2008
Hahaa! Oh, don't worry. As soon as somebody manages to make a profit on solar energy (even if it is totally dependent upon tax payer generated subsidies), the enviro-wackjobs will be all over it with how destructive the technology is and must be stopped immediately at all cost.

If one wished to adopt the same "peak-everything" scare tactics as many solar fanatics use against all other forms of energy one might note that the world-wide reserve base for indium is 6000 tonnes, which is 13 years of supply at current rates.
jburchel
2.8 / 5 (9) Aug 14, 2008
Hahaa! Oh, don't worry. As soon as somebody manages to make a profit on solar energy (even if it is totally dependent upon tax payer generated subsidies), the enviro-wackjobs will be all over it with how destructive the technology is and must be stopped immediately at all cost.

If one wished to adopt the same "peak-everything" scare tactics as many solar fanatics use against all other forms of energy one might note that the world-wide reserve base for indium is 6000 tonnes, which is 13 years of supply at current rates.
lengould100
3 / 5 (9) Aug 15, 2008
At least we're smart enough to avoid double-posting.
Lord_jag
4 / 5 (5) Aug 15, 2008
I just wish something would come out a little cheaper on the market. $600/120 Watt peak is just too much to pay. It just hurts to see all that sunlight wasted on my roof and then I have to pay to cool my house as well.

When will the day come that solar panels will be within reach? When will the day come that I don't waste all those precious square feet of roofspace for sunlight collection?
nano999
4 / 5 (5) Aug 15, 2008
Old news. Spectrolab came out with a 40% solar cell over a year ago. Anyone remember this - http://www.physor...887.html
Fritz
4 / 5 (5) Aug 16, 2008
And the University of Delaware recently came up with a 42.8% efficient solar cell: http://www.treehu...ency.php
sardion2000
1 / 5 (3) Aug 16, 2008
g
Roj
3 / 5 (2) Aug 16, 2008
And the University of Delaware recently came up with a 42.8% efficient solar cell: http://www.treehu...ency.php


Soylent, whats this stationary-optical concentrator that replaces 2-axis tracking.
Soylent
3.7 / 5 (3) Aug 17, 2008
And the University of Delaware recently came up with a 42.8% efficient solar cell: http://www.treehu...ency.php


Soylent, whats this stationary-optical concentrator that replaces 2-axis tracking.


They refuse to say. Googling gives me this:

http://www.udel.e...VSEC.pdf

If that's their design:

See fig 5. It gets >50% optical performance over a range of 15 degrees along one axis and over a range of 37 degrees on the other. The sun moves 15 degrees per hour so that gives you at most 2.5 hours of >50% optical transmission if your concentrator has it's major axis correctly aligned with the track of the sun. Without at least single-axis tracking that seems pretty useless to me.

If figure 3. is to scale it reduces silicon use by about a factor 16x over non-concentrating. The entire PV slice is not lit, rather a highly concentrated spot wanders along the cell as the angle of the sun changes.

A dichroic prism is used to split light of different frequency and aim it at a pair of PV slices, each with a different set of band gaps. Seems like a pretty good idea; two-axis tracking concentrators should steal this trick instead of using a single solar cell with a massive amount of junctions.

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