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« New EPA Rule Would Mandate More Ethanol in Gasoline | Main | New Book: "solar energy will inevitably become the most economic solution for most energy applications" »

September 08, 2006

Comments

Greg Woulf

Where do they get the Silicon from?

I was of the understanding that processed Silicon was the bottleneck for Solar panel production right now.

That's why The CIGS announcement from California was so exciting.

olconnom

Uni-Solar has no need of silicon. They use (di)silane gas and there is no shortage of it!

Greg Woulf

That's great, I was just reading the article and it says, "thin-film amorphous-silicon alloy solar cells," so I was thinking that it had silicon in it's main product line, but I wasn't thinking of what other type cell they might make along with the silicon.

mjtimber

Well, it does have silicon in it, but it uses so much less that the silicon price is not really significant, but the processing cost is. My guess is that the price can drop rapidly in mass production, because it isn't too different from LCD panel production, which is dropping about 30% per year. This amorphous process uses about 1/400 the silicon (about 1/600 the thickness minus efficiency losses).

Jim from The Energy Blog

A previous post About Amorphous Silicon Solar Cells discusses the way amorphous cells are made and the various structue of the cells. A paragraph from the post:

United Solar Ovonics manufactures modules using a-Si/a-SiGe/a-SiGe triple junction cell. Amorphous cells with different light absorption properties deposited continuously, one on top of another, to capture the broad solar spectrum more effectively. This increases the energy conversion efficiency of the multi-cell device and improves performance stability. In other words their structure enhances the ability of the cell to absorb different wavelengths of light and helps stabilize the cell in regard to the SWE effect.

Paul Dietz

There's no great shortage of silicon, just of high purity poly-silicon. a-Si is grown from various kinds of silanes, and because it's disordered the purity requirements should be much less strict. Also, a-Si absorbs light much more strongly than x-Si, making the active layer about 100 times thinner.

The downsides of a-Si have been lower efficiency and degradation with time due to the formation of 'dangling bonds' that trap carriers (the Staebler-Wronski effect, IIRC).

Chaz

Here is the deal on Silicon.
We will never run out - silicon comes from sand, which is SiO2.
The bad news is that Si really likes to hang out with the oxygen - and is very difficult to purify. Currently, most solar cells are crystal silicon and are made from solar grade silicon which is highly purified, though not as clean as what they use to make computer chips. Currently, there is a shortage of this solar grade silicon - and this is driving up costs because of simple supply and demand. This will eventually be remedied as they build more factories.

In contrast to crystal silicon based PV, amorphous silicon PV is made directly from silane gas. Silane is actually a middle step in taking sand and making solar grade silicon. And there is no shortage of silane. Equally important, amorphous silicon solar cells are only ~1 micron thick, while crystal silicon solar cells use >200 microns of material.

So ... the current silicon shortage is good for the PV makers using amorphous thin film materials because they are made directly from silane and are much, much thinner.

-Chaz

Paul Dietz

It's my understanding that PV cells used to be made from recycled scrap silicon from the IC industry, but that as PV volumes increased this supply was exhausted, and now they have to pay full price for the silicon.

BTW, I thought trichlorosilane was the precursor for bulk manufacture of high purity crystalline silicon, not silane.

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