How to make your own silicon solar cell

[satalaj]

discuss here about on following topic
How to make your own solar cell.
How to produce silicon from silica at home, economically.

[chux0r]

Ummm... I can't produce silicon at home economically.

[pyrocasto]

Well, good luck with this one buddy. I think the closest you will get will be a copper solar cell, where you will get micro volts...

[troy]

Yup, not possible in the home setting.  Although if you want to, there's lots of info on the web about how it's done.  Here's a summary from memory.

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

[Vernon]

There is one easy way to do it !

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.

[ghurd]

An LED will do it too, as is. Just not much power at all.

[veewee77]

Half a volt at 3 amps from a transistor, eh?

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. . .

[ghurd]

The .25 was probably surplus.

Wholesale by the 100 is about $1 each.

Don't forget about the 100 6" magnifing glasses!

G-

[stop4stuff]

Interesting...

A question or 2.

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

[ghurd]

Majic smoke.

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-

[Vernon]

True ... while it does work you do have to provide the magnifying glass and the mount, keep it in alignment with the sun ect. It might be better to get a real solar panel and use plywood panels covered with 12' x 12' decorative mirrors mounted on a sun tracking structure to focus 3 or 4 "suns" on that panel. Cooling the panel, especially under these "boosted" conditions would also help. It could be that the current high price of silicon would make the mechanical complexity worthwhile. Fixed mirror panels could also be mounted on the ground and overhead to increase output.

[Vernon]

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.

[wooferhound]

also don't forget the solar tracker system

You can make Solar Cells

it's cheap but not easy

and fairly temporary

http://www.scitoys.com/scitoys/scitoys/echem/echem2.html

[nothing to lose]

I checked out that linky.

They went about it the hardway!

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.

[commanda]

They ran an electric hotplate at 1100 watts for half an hour to heat the copper.

That's 550 watt hours.

The resultant "cell" makes 12.5 micro watts.

That cell would have to run for 44 million hours just to recover the energy used

to make the cuprous oxide layer. That's about 5000 years continuous, or 20,000 years at 6 hours sunlight per day.

Interesting, isn't it?

Amanda

[JW]

So anyway as one who has explore'd the possibilite of a copper oxide solar-cell I can tell you this much, perhaps the output of such a cell is infact dismall, BUT the lens-ing effect of the water in the cell, with relation to the "actual' surface/area of the copper-oxide surface, is infact relative, to the burn/0ut of a silicon solar cell under a frincell(magifiying glass) arrangement, equivelent or what have you.

 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

[ghurd]

Everyone knows you can just buy a solar panel, Right?

kidding.

G-

[nothing to lose]

Yes but they make it up in volume

Just make more cells

[Jeff7]

Heck with all that - I came up with an idea (which someone else already did anyway, and patented it) to use something like a satellite dish. Satellite dishes reflect radiation from a large area (in this case, the satellite signal) into a tiny area (the receiver). Just make the whole thing into a parabolic reflector, and use a high-temp solar cell, or else a small boiler in the center. Any sizable reflector will generate some damn high temps though. Loads of light, but a reflector only a few feet in diameter would be capable of melting or incinerating quite a number of materials.

[nothing to lose]

Yes that reflector may be a way to make many things without feul for heat.

Been lots of things around here posted about using "Dish" units to concentrate the sun.

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

[Texas Al]

Well, you could find out what silicon wholesalers the PV companies buy from, and buy from them as well. You won't get as much of a bulk discount as the PV companies, but it might still be cheaper than paying the PV companies to assemble your cells for you. And then again, it might not be.

The advantage, though, is that you can stockpile a lot more silicon wafers for when you need them than you can finished cells.

[gregwatson]

Hi Guys,

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:

0. 5v @ 3a = 1.5w =   9.4%
   
0. 5v @ 4a = 2.0w = 12.6%
   
0. 5v @ 5a = 2.5w = 15.7%
   
   

Power loss for silicon is about 0.5% per degree C temp rise so good heat sinking is important. Heat sink to about twice the lens area. Suggest you use at least 4mm thick aluminum and use a good heat sink paste between the transistor and the heat sink.

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

[TomW]

Greg;

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

[gregwatson]

Try:

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

[pyrocasto]

problem is, you cant turn silicone wafers into a cell at your house. At least not that I know of...

[gregwatson]

Guys,

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

[commanda]

I wonder if you wouldn't get more output if you shorted the Collector & Emitter, so you used BOTH P-N junctions in parallel.

And for a higher energy density, use TO-92 transistors (though cooling might be more difficult) and short focal length lenses.

Amanda

[Texas Al]

What's a TO-3 can?

[finnsawyer]

Use a Fresnel lens ala Sun Ball.

[powerbuoy]

If you go for the dish solution you might just as well use a stirling engine (heat engine) instead of the solar cells. The dish concentrator can easily produce 400 or more degC heat on the concentrator head. the solar cell will puff off in smoke by then.

Powerbuoy

[powerbuoy]

Producing couprous oxide (spelled right?) by blow torching copper can be toxic. (so I have read) ...be careful when using this stuff.

It does not produce too much power either.

Powerbuoy.

[solar transistor]

Guys,<p>
Here is a 2N3055 without it's top. Note the die size is very small, about 7.8mm^2.<p>

<img width="80%" src="http://www.otherpower.com/images/scimages/3907/2n3055.JPG">
<p>
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.<p>
Greg

[BrianSmith]

If someone were to put 15W on that little piece of silicon, the plastic would melt and the bond wires would disconnect in about 30 seconds.  If someone tries it though, please make a video....