Oct
15
Is a Ball of Silicon the Super Solar Collector?
October 15, 2007 | Leave a Comment
We’ve all seen the common photovoltaic solar collector, a flat plate of gray silicon with small gray or reddish lines dividing and carrying the current. Their main cost is that silicon sheet which in most configurations requires the sheet to collect the sunlight directly and as straight on to perpendicular to the sunlight as possible. This means that you can collect the sunlight equal to the area of the sheet. Much effort is being spent to use lenses and other devises to concentrate a larger sunlit area to the silicon’s area and articulate the silicon to more directly face the sunlight.
Now imagine you could put a parabolic reflector under your silicon to increase the area and skip the lens production with all of the cutting grinding and polishing. If you’ve wear and buy glasses you can imagine what that will do the cost. You could make a low cost plastic reflector much like that used in an auto headlight for your parabolic reflector. The cost calculation is very different now for collecting the light of a given area. The parabolic reflector also reduces the amount of articulation to keep a large percentage of the sunlight straight on to the silicon.
Interested now? In the 1980s Texas Instruments looked into the idea of a ball of silicon to replace the flat sheet. Likely the plunge in petroleum prices put the brakes on pushing forward. But in 1994 in the midst of the low petroleum prices the Japanese company Kyosemi pressed on.
By using a drop tower that operates in a near vacuum Kyosemi can meter a small drop of molten silicon into free fall that mimics a near gravity free descent that allows the silicon drop to from a solid sphere. With coatings and setting positive and negative connections they have a sphere of solar cell. Set into the parabolic collector, that little sphere is accomplishing the work of the silicon sheet equal to the size of the reflector.
See:
http://www.kyosemi.co.jp/product/pro_ene_sun_e.html
The development looks to be at its earliest stages. As you look over the page from the link you will see that Kyosemi has stayed the course and studiously run development up to the point where they have small working units at or near sale. In the “fact sheet” link on page three there is a little graph that shows 17.8% efficiency from a test by Riso National Laboratories, Denmark. Nearing 18% is very encouraging.
Moreover there is the attribute that the spherical collector is getting use from the indirect light. This observation and the properties we’ve looked at above make this one of the most interesting photovoltaic designs.
Its just a matter of time until some sharp optics people realize that they can optimize the parabolic beneath the photovoltaic and top it with a transparent cover that could enlarge the sunlit area even more with cast in lenses. The parabolic reflector could allow a much less exacting lens above the collector. This is an exciting technology to be watched closely.
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