Ken Zweibel

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    • Sat Nov 24th 12:40 PM | Rating: 0 0
      Commented on:
      First Solar Vulnerable to a Tellurium Shortage?
      I will probably be using other venues to publish about Te availability within six months, but until then, I am constrained.

      It's fine to discuss and dissect the Te issue; it's quite relevant. I think it's a real service to see the harder sides of companies and technologies. The web adds to our understanding. Too many existing, traditional sources present only one side of the picture. With the web, for example, I expect it will be harder for anyone to keep up the mirage of "clean coal" and hypothetical, low-cost CO2 sequestration. This is very important as we face the real energy and environmental challenges of the planet.

      Te availability will likely remain one of the most important issues in the future of CdTe, because the growth of CdTe, due to its cost structure, will be so strong.

      At 1 micron thickness, there are only 3 grams/m2, which even at $5000 kg is $15/m2 - at 12% (120 W) that's still about 13 c/W. This might be the worst case, and one the other PV technologies would have to be better than to survive (aggregated to the system level).

      Light trapping in a CdTe cell shouldn't be hard. Many TCO/glass makers like Asahi/AFG make textured TCO for a-Si modules right now; those glass/TCO substrates can replace the smooth ones CdTe uses. Similarly, transparent back contact CdTe cells have been made by IEC - just add a back reflector to that (like a-Si does with ZnO/metal), and you are there. That's what allows going below 1.5 microns towards 0.3 microns or so. Take that into account and adjust the cost and usage numbers above by 3 again and you have an even brighter story, just from existing sources.

      Did you know that astrophysicists believe that Te is the most ABUNDANT material with an atomic weight over 40?

      Ken
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    • Sat Nov 24th 05:28 AM | Rating: 0 0
      Commented on:
      First Solar Vulnerable to a Tellurium Shortage?
      Of course, CdTe is a direct band gap material, so it absorbs much more intensely than crystalline silicon. It's like CIGS in that sense - where 1 micron thickness is becoming the norm, because material costs for indium are so high (near $1000/kg). The only reason companies make thicker CdTe is it's more familiar and CdTe is not a cost driver. Good cells near 1 micron already exist - not hypothetical. Also: Have you noticed how easy it has been for x-Si to make thinner wafers? Thinness is the norm for cost reduction in PV.

      Interestingly, taken over 30 years, 30 GW/yr is close to a TW, so it sounds like FSLR is off the hook on that statement. BTW, since Te is not destroyed, like a fuel, it can be recycled, so once the Te is in the modules, it stays in use and can be added to the next generation of Te to get that much more CdTe. So 30 GW/yr recycled every 30 years, adds another almost 30 GW/yr to the annual supply. This can add up!

      Your comments about other Te uses: It's my understanding that these uses are tiny - under ten MT/yr each - and not growing like PV.

      My number is in g/m2 not g/7200 cm2-module.

      Ken Zweibel
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    • Sat Nov 24th 01:10 AM | Rating: 0 0
      Commented on:
      First Solar Vulnerable to a Tellurium Shortage?
      Of course, Cu is not the only source of byproduct Te. Pb, Au, other sources exist.

      One other important thing: the amount per W is not a constant. Today's 3 micron layer has about 9 g/m2 of Te, or 9 g/m2/100 W/m2 . That's .09 g/W. There are 10^9 W/GW, so that's 90 MT/GW. Let's use 100 MT and say at 1000 MT available, that'd be 10 GW/yr.

      But it only takes about 1 micron of CdTe to absorb the solar spectrum - experimentally, good cells have been made at 1-1.5 microns by BP and U. Toledo. This means 20-30 GW/yr at 10% efficiency. Of course, the efficiency can also rise, adding a bit more. And then there's potential light trapping - it's been demonstrated throughout PV, especially in a-Si and thin, indirect gap x-Si films and wafers.
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    • Mon Nov 19th 16:29 PM | Rating: 0 0
      Commented on:
      First Solar Vulnerable to a Tellurium Shortage?
      Stephen O'Rourke of Deutsche Bank wrote a good piece on this in a recent review, and he not only concluded that Te is not a short-term problem (say 20 GW/yr), but there are untapped, huge mid- and long-term sources. There are reasons people haven't been aware of them before.
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