Purify the silicon until it has less than one part per billion contamination. This involves heating the silicon until it is molten (in a clean room environment with a controlled gas atmosphere).
Once it's ultrapure, then heat it up to molten again and insert a seed of ultrapure crystaline silicon. Pull the seed out at the same rate as the molten silicon crystalizes onto the seed, I think a few cm per hour. Temp, atmosphere, growth rates, all have to be controlled extremely precisely. You have to add dopants to the growing matrix, in very carefully controlled amounts so you can end up with two different types of crystaline material (n-type and p-type, one electron rich and one electron poor.)
Once you have a monolithic crystal 4" in diameter and a few feet long, saw it into wafers that are way less than one mm in thickness. Somehow magically join the n-type and p-type, solder on leads, solder individual cells together, encase in low iron glass with an inert potting compound to seal out all the moisture, yet is UV resistant for 50 years or more.
This is not a basement job we have here. It's awe inspiring to think of the folks who did it the first time, because there are almost insurmountable difficulties. Surprising solar panels don't cost more.
Sorry,
troy
I once purchased a hand full of 2N3055 power transistors at an electronics surplus store. Price was perhaps 25 cents each. I carefully cut the top off one of them (TO-3 can), exposing the die. I obtained a cheap magnifying glass about 6 inches in diameter, connected an ammeter to the collector and base leads and used the magnifying glass to focus the sun on the chip. It produced in excess of 4 amps ! In a circuit you would get best power at perhaps .5V and 3 amps so you would have to put a few of them in series to do anything useful.
Some solar data:
Irridation of 1,000w/m^2 (Max surface level). Probably better to use 900w/m^2.
6" dia lens or 150mm = 0.01767m^2 area * 900w/m^2 = 15.9 watts input to transistor (not including lens transmission losses of about 10%)
Irridation efficiency:
So heat load = 15.9w (solar input) * 0.9 (lens efficiency) * (1 - .126 (efficiency @ 4a)) = 12.5 watts to heat sink at no more than 10C above ambient for good cell efficiency.
For the lens I suggest you use a rigid acrylic Fresnel lense as they have lower losses (about 92 - 93% efficiency).
To get the best efficiency adjust the distance between the transistor and the lens until the bright image of the sun just coveres the silicon of the transistor. There is no need for the image to be focused but just to fully illuminate the silicon surface.
Then you need to track.
Commercial solar concentrator cells are available with efficiencies in the 25 - 37% efficiency range. Checkout: http://www.sunpowercorp.com/html/Products/SPG/conc.html
All the best, Greg[ Parent ]
For the lens I suggest you use a rigid acrylic Fresnel lense as they have lower losses....
Do you happen to have a good retail source for fresnel lenses in the States?
Thanks
TomW
"Education consists mainly of what we have unlearned."--Mark Twain[ Parent ]
http://www.3dlens.com/ (my choice)
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=2040&CFID=4720972&CFT OKEN=f4d403ff0ce4bc18-CB4A8AAF-3048-41AD-8413698030D68AB7
http://www.alltronics.com/lenses.htm
http://www.anchoroptics.com/catalog/product.cfm?id=24
http://www.fresneloptic.com/html_en/fresnellens.htm
http://display-optics.com/products_solar.htm
BTW my company is designing a innovative and visually attractive concentrating tracker designed for domestic roof top installation which will deliver more than twice the annual kWh that fixed panels can and at about the same cost per peak W.
All the best, Greg Watson Green and Gold Energy Adelaide, South Australia Australia[ Parent ]
Here is a 2N3055 without it's top. Note the die size is very small, about 7.8mm^2.
Even with concentration I'm amazed it can produce 1.5 to 2 watts as there does not seem to be a lot of bare silicon. Most of the surface seems to be covered with conductive fingers.
Greg[ Parent ]
And for a higher energy density, use TO-92 transistors (though cooling might be more difficult) and short focal length lenses.
Amanda[ Parent ]
So to get enough to charge a 12V battery you'd have to have 28 of the transistors.
28 x .25 = $7.
Charging a 12V battery at 3A is 36 watts.
That's $.19 (nineteen cents) per watt. . .
Why is the world still messing with expensive solar panels! Just buy scads of those transistors and space them out and make a grid of magnifying lenses each with a transistor under it and let 'r fly!
And I bet if you bought the transistors by the thousands, you could get them far cheaper than $.25 each!
Doug
P.S. not poking at you at all. . . It is just intriguing that if something like this works, why is no one using the technology. . .
Don't forget about the 100 6" magnifing glasses! G-[ Parent ]
How small a patch of sunlight would give the 3A?
Would a large parabolic mirror focusing sunlight onto the whole group of 100 transistors work instead if individual magnifying glass/transistor?
cheers, paul[ Parent ]
At 100% efficiency, 1000w per square meter of sunlight under 100% perfect conditions. The 3A is related to volts, efficiency (horrid I'm sure), temperature...
Transistor compounds are doped for other reasons. Solar silicone is doped to make power.
Transistors reacting to light is just a side effect.
Also, just a regular 3 cent diode will make power when exposed to light, thats why they are black. Thats how LEDs were invented (or is that discovered?). Years ago someone forgot to turn the power off to an experiment. Went back to the dark room for something. Noticed the 'regular diode' was emiting light. LED!
The technology is being used. A simple example is the redrok.com LED based solar trackers.
G-[ Parent ]
Something like this .. the panels are mounted with the long axis horizontal and similar mirror panels are mounted along the ground and overhead ....extending beyond the panels so the moving sun still gets boosted. [ Parent ]
I was thinking make a rack to feed one sheet at a time into the collected area and let the sun bake the copper sheets to a black oxide. Drop it out the bottom and feed another through the top and bake it. It would be nice if you could just feed a roll through, but after baking the oxides on you can't roll it back up or you will crack the oxides I think.
Now you could feed a roll of sheet copper into the sun area to bake, then as it exits cut to size instead of rolling it up. A problem to be solved though is copper conducts heat very well, so how would we stop a roll from sucking up the heat from the area being baked. Then again, that could be a slightly good thing if the roll is in an insulated chamber, sort of preheating it all and baking the area exposed to sun a little faster maybe?
I have gave some thought to copper roof shingles. Or maybe like metal roofing pannels like you buy now, but copper pannels instead of steel.
20' X 60' house is over 1200sqft of roof! Expose that to the sun covered in copper cells and how much power would it produce? Course you still have to cover it and cool it, lots of heat there, but I bet the copper would be cheaper than solar pannels. And if one stops working take it off and re-bake it. Possibly an easy repair?
I just don't have time to work on any of this myself right now, but I think it's an idea worth experimenting with! Might be great for Desert Homes with no wind? Also a side of the house could use the same copper pannels on the sun side, and I was thinking for cooling the pannels heat water at the same time.
Though it looks I may be more interested in SNOW power than Desert sun power before long :). nothing to lose
Spelin and tpying are my strong points, not electronics.[ Parent ]
Powerbuoy[ Parent ]
You can make Solar Cells it's cheap but not easy and fairly temporary http://www.scitoys.com/scitoys/scitoys/echem/echem2.html W o o f -={([ Parent ]
Take a copper sheet, heat the back with a propane torch till the front has the black oxide. I did not heat as much as they say and mine did not flake off easy. I had to use some steel wool or wet dry sand paper to get the black oxides off (been a year or 2, forgot a few details), don't remove the red oxide, that's what you need!
Once you have the black off and only copper back and red oxide front your done. Connect a lead to the back copper and touch the other lead to the front red oxide and in the sun or under a 100watt bulb you have power. No need for the salt water or other sheet of copper.
I don't remember how much power it was, not much, probably as much as they got I would geuss. Now if you add some kind of grid to the front of the cell you just made you will get more power also. Something like maybe aluminum window screen, it spreads out the area your picking up the power from on the front side, not just where the lead touches. Problem is the grid then covers that area so that it is also shaded. Not sure how well screen worked, I think I lightly sanded it and can't remember how I mounted it now either. I might have laid the copper cell on flat glass, screen on cell, glass over screen, kinda a gentle press fit to hold it together?
I may try this again after reading that link. I decided it was to hard to get the black oxides off and other reasons I didn't mess with it much. I did a couple and they worked Looking at the pics they had on that link, I did not heat the copper enough to form a thick enough black oxide probably. Mine certainly did not "JUMP OFF" as it cooled, it took a little work to get it off.
I have some copper sheet bands here from an industrial welder I found at a scarp yard once. I should have got the whole welder, but then I only wanted the copper bands. If only I knew then what I would be doing now and things I would want for various projects! Oh well, at least I have the copper bands :)
If I can find them I might give this another try, been thinking about it anyway, and now seeing the link saying the black oxide should jump off makes me want to try that again.. nothing to lose
It does not produce too much power either.
Powerbuoy.[ Parent ]
Interesting, isn't it?
Nevertheless, One could at least in theory, fuse' a globul of doped borosilicate, or silicon carbide, or N and p-type silicon, some way with a primative heat source, and so what is there are some impurites.
The key to success would be electroplating surface anodes and back conductors, AFTER one had some basic P/N Junction to work with. after one figured out how to cast tiles of appropiate semiconductor sandwich cobinations of various compounds, then the electroplating/and possibly REDOX-plating of the opposing surfaces of such tiles or plates could yeild something useful :)
JW[ Parent ]
The advantage, though, is that you can stockpile a lot more silicon wafers for when you need them than you can finished cells. Help us write a manual on how to reboot a crashed civilization!
