NREL Solar Cell Sets World Efficiency Record at 40.8 Percent
August 13th, 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
Feb 25, 2008 |
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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.
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.
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.
Could tracking be eliminated for rooftops; in a process of lensing the 326x area onto individual cells. Perhaps bubble lensing for consumer panels.
How?
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.
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?
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.