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Are the octagonal soiar cells only because the silicon ingots are cast round
Back on the original question, I think it boils down to:What are the dimensions of the square that encloses the maximum area of a circle?I was hoping some of our mathematically inclined correspondents might take up the challenge, but apparently, they all ran away.
Yes, in retrospect, I was talking complete nonsense. (A first for me!) The most efficient use of silicon would be to use complete circles.
I would expect all the subsequent wafer processing to be done prior to trimming the wafer edges off. I think this is likely because all the equipment for wafer processing is designed to handle circular wafers, even though I expect the photcell manufacturers are nothing like state-of-the-art in this respect. So the cost of chopping off bits of the wafer are effectively related to the final processed wafer cost rather than the raw wafer cost. Having said this, the cost of masking, processing and handling for photocell designs is nothing like that of making ICs and I suspect they are probably getting good value by using 150mm diameter wafers that the IC industry hardly uses any more, being on 200mm to 300mm (even some 375). As a result the cost of NOT using all the wafer is not as high as may be thought especially as it only amounts to (in the above pictured example) about 10% of the total available area. In fact 150mm wafers with some preprocessing sell for only about $4 to $5. The cost of connecting up the wafers and putting them in a housing may be much more significant and the benefit of minimising the total area of panelling more attractive.
Wow, you have got some spare time, Imatfaal. I drew it out on squared paper and estimated it.
It is easy enough to calculate the area of a circular cell, and the area wasted around it by mounting on a square grid, or the area wasted by trimming to a perfect square. I.E. Maximum wasted space, minimum wasted silicon, or visa versa.
Nice work Matt! If we can get you up to speed on a CAD program now, you'll really be cooking with gas
I tried Dave's diagram editor - it took me twice as long as the entire calculation to get a square, a circle and labels - and then I managed to lose it. So I gave up - two minutes later my pencil sketches were uploaded; never managed to properly attach them tho. Is there still a bug about displaying attachments in the text?
I understand that 450mm wafers are the latest thing
Quote from: syhprum on 16/02/2012 20:24:22I understand that 450mm wafers are the latest thingThat's almost 18 inches! (woops - maybe I should not have said that.)Pretty soon they'll be able to measure them in meters.
Quote from: Geezer on 16/02/2012 20:31:48Quote from: syhprum on 16/02/2012 20:24:22I understand that 450mm wafers are the latest thingThat's almost 18 inches! (woops - maybe I should not have said that.)Pretty soon they'll be able to measure them in meters.Can I get that built up into a single IC?Just think of the possibilities with and 18" single chip computer.
I look forward to your conclusions as the optimal size of a square to cut out of the circle. My guess is that you will have the two cases I demonstrated above with either 100% circle & no square, or 100% square and no circle. If one chooses square corners, one might also choose to oversize the cells slightly, say 1/4" to allow rounded/blunted corners.