Solar cell making -update

[iFred]

Since I have so many cells to deal with I starting building a simple production line, The cells are so fragile that this was the only way to insure that the cells integrity would not be compromised. So I'm starting small, in the photos you can see a piece of very flat and straight piece of wood, to which I have cut two slots into and into these slots I then mounted two thin  pieces of wood to act as guides. The guides are somewhat sloppy to the size of the cell within 2 mm or so, however when soldering together the cells, I have found I can put the cells up to the guides and have no alignment problems. So this solves making the cells nice and straight.

Since the cells are so fragile and I didn't want them moving around this is the perfect solution. Also it helps keep the cells flat and less chance of breaking I have found. The temperature is also stabilized. Do not put the cells on spongy type materials!! They will crack easily. Use a hard surface for all work on cells.

Soldering problem was finally solved. A very fast swipe with a "soldering gun" will produce a very nice thin layer pre-solder layer to adhere the main bus line to. The cell does not even have time to react to the temperature if done quickly and correctly. But it does do a nice job.

Glass: I mentioned that I was working with cells to friends of mine and one of them mentioned that they had a create full of tempered glass. SCORE!! So I went and checked it out, he had a create and they where tempered glass, 28x26 perfectly cut. A little wheelin dealin and I got the entire create. With these I can place 7x4= 28 cells on the glass I figure. Talk about luck! I am blessed.

So far 7 cells produce 3.88 in full sun and 3.94 in cloudy sun. The reason for this is temperature. The cells get hot fast. As the heat increases on and around the cells in full sunlight the voltage decreases. As air flow or cool air blows on them the voltage increases. They are very sensitive to heat, but also very stable in voltage. They fluctuate very little on a nice day.

So now it's onto production line once again. Also got my other genny to do and finish. So little time.

[E man]

Hey, iFred.

I recently purchased about 250 solar cells from The Electronic Goldmine (www.goldmine-elec.com)...just because they were cheap! Item G14648: 0.5V, 0.5A.

I'm glad to see you're slogging ahead, trying to solder the darn things.  These thin cells are a pain to handle and to solder.  I can't decide if I broke more of them out of clumsiness, anger, or just for shear fun of it!  I like your idea of a fast "swipe"of the solder gun.  I'll try that.

iFred, just wondering, what kind of backing material you are considering using to mount the cells on? Also, do you intend to allow air flow between the cells and the glass (to cool them) or will you be closing them off for humidity/moisture reasons?

Thanks

E-man  

[iFred]

Yes, try the hi heat fast swipe before it knows what hit it method. The back of the panels are another issue however, these should be done very quickly and with less heat.

I am going to simply apply a single dap of clear silcon (rubber stuff) to the back of each cell and simply lay the entire row on top the glass and let it dry. Then later I intend to experiment with sealing it and adding a clear mineral oil, baby oil or something like this to fill in between the glass plates and the cells.

[Kemper73]

Well,,

I did some research last week on the sealing method,, I looked at different potting compounds to use, One that I found was Dow Corning Sylgard 184.. It's a low viscosity silicone, that has good heat transfer capabilities..

They also sent me about 1L of the stuff as a sample,, Now I just have to

actually buy some solar cells to try things out,,,

To many projects not enough time

Jeff

[juiced]

I have enough time to experiment DEEPLY every day. I simply dont have $ for materials and my shop sits idle as i look for a solution. Anybody in quebec who would like to take advantage of this may contact me at my site. Im willing to travel for actual work.

[ghurd]

Hi Fred,

I would check the V at load.  The V will drop a lot under load.

The 7X4=28 cells is 15.5v open. Factory panels go about 20-22v open, 17v max power under load. Even the self regulating panels go 16.5v open, and they do nothing if conditions are not about perfect.

Don't forget to take out a volt or 2 for the controller, and a volt or 2 or 3 for non-perfect conditions, half a volt for wire losses, and several volts for the drop with a load.

Is the plan 3 panels in series for a 24v system? The numbers look better for that.

2 in series for 12v gets 30v open, past most controllers Vin max.

G-

[iFred]

Ghurd, I'm still working on that issue, I was wondering how they where calculating it... You think 32 in series might do it, or should I put 2 panels in series?

THANKS!

[wiredwrong]

Just a thought, since you said these cells are so sensitive to heat, What about water cooling the cells, producing electric and hot water from the same panel, or at least pre-heating the water. I think that I have read about someone doing this before, Ill see if I can find an article about it again and post it.

[iFred]

Hi Ghurd. I have read everything you have said about the cells in both posts, so I figure I can get away with this setup, tell me what you think.

If I make each panel with 28 cells (4x7) this would give me .5 x 28=14 vdc @3a. This is about as much as I can pack into a window that is 26x28 safely and still have lots of room for wiring and rubber strip around the perimeter. This would be one complete panel.

Two of these panels hooked in series would produce (14x2) =28vdc @3a, which I think is perfect and would leave lots of room for even the worst cloudy day. Charging voltage is the priority apparently. So this is achieved.

I have approximately 600+ of these cells, which would give me about 20+ of these complete panels. If my estimation is correct I should get 10+ panels at about 28vdc @30+amps total flow. 840+ watts.

As for the controller, I am building and designing one for myself.

[iFred]

I have tried to think of a way to circulate either oil or water, but it really bugs me, yes there is a lot of heat being generated and if you could do it it would be really sweet, but what about Canada winters? We got some nice drops in temp here, and fluids are a problem. I like the idea however, But i can't do it, but others may be able to.

[ghurd]

Most (all?) companies use 36 cells in series for a normal 12v panel.

I don't see 32 doing much good in cloudy/humid/morning/evening. I think thats what some brands use for self regulating panels (most reputable retailers won't sell them without many warnings about low performance and only being good for special purposes).  Self regulating means it can't overcharge the battery under any circumstances... It'll barely charge a dead battery. They about stop before the battery is full. They don't do anything in poor conditions.

2. of your proposed panels in series will have Vopen at 31.5v, that's too much for most 12v controllers (and a waste of all the cells past cell #36, wasting 20 cells or 36%).
   
3. of your proposed panels in series would be OK for 24V. (4 cells per panel extra, or 12 cells per string)
   
   

With the glass you have, you could put 18 cells in series for a 6v panel, then put 2 panels in series for 12v. You could cut the glass, or leave a lot of room for sealing   I'd get new glass the right size.

With the money, time, and effort you are going to have in these, I think new glass would be a small price for something that works like it should.

This is a pair of quotes from NAWS, about 2 brands of self regulating panels.

""This is a low voltage panel and is not recommended for hot climates. This panel is often sold in RV stores as a "self regulating" panel. Actually it is not - it has no regulator, it is just lower voltage than most panels. You still need a regulator or you risk roasting your batteries in cool weather. We don't recommend this panel for anything but replacement use.""

""Since it is a lower voltage panel (so called "self regulating") we do not recommend it for hot climates.""

G-

[ghurd]

Forgot this part.

Its low V already, take out a v or 2 for the controller, and that doesn't leave much to do any charging. Especially if it was designed to be used without one.

Sounds like they are covering their A**.

G-

[foster]

Hi ghurd,

What would be the best "build" for a solar panel from a hot climate, I come form one and am very interested in find out.

A

[ghurd]

Everybody uses 36 cells for about everything, for everywhere.

Only exception I can think of is up by 'hiker', I might say 38 or 40 to try to get something on those twilight only type days, but he's wayyy up there, with a lot of those days.

Output drops, and life is shortened, when they get very hot. They do get hot.

Keeping them cool is important.

Mount them at least 8" (or more in very hot climates) above the closest things around to allow for circulation.

Leave some space between them for circulation.

Tilt them toward the equator (North if Foster's is brewed locally) at the same angle as your latitude.  Minimum tilt should be about 12 degrees to allow flow of heat up and out, and dirt or dust to wash off in the rain.

Don't just nail them too the roof, no matter what the guy who sold them to you says, or how many photos you have seen where they did it.

Kind of a warning... Amorphous panels don't do so well in extreme hot climates, by what I've seen. Those are different than the crystaline type iFred is using. You almost have to buy those panels. They look like glass with brown paint on one side, and you can't count the squares.

I don't know why they had the warnings about hot weather for the self-regulators.

I have a complicated guess related to battery chemistry, but still pretty irrelavent.

G-

[nothing to lose]

If heat is a problem any way to make a heat exchanger to mount them too for heating water, use a closed loop system with an antifreeze and run that to a heat exchanger elsewhere where freezing would not be a worry to heat the normal water.

Where are the cells comming from, sounds like you guys got em cheap. I'd like to play too

I saw a site mentioned and will check out that one, but where's the best deals, was that it?

[ghurd]

With 2 in series it will work just fine.

Is this a 12v system?  Then the watts will be 13v x 30a = 390w.

If you want to get really carried away with the controller...

How about some provision which will switch them between series and par?

Like if its sunny and the batteries are at 11.0, then the individual PVs should have enough power to put 60a in.

When the batteries are high enough, or not enough sun, where each PV can't reach charging voltage, they would go to series.

Sort of like the wind controllers that switch between delta and wye, but series and parallel.

I know I wouldn't bother with it, but I don't make my own controllers any more either. Old, lazy, and busy.

Possibily a Max. Power Point (MPP) type controller would be the best of both worlds?

They kind of take max watts (840w at 28v) at some V, and convert it to max watts (840w at 12v) at the desired V.

Most of them are designed for the oposite I think. Getting some amps into 13v, from a panel at 10v. Not sure though.

I never used one because of the price and the small size of the typical systems I do. I could about double the PV for the cost of the MPP tracker, that claims a 30% gain.

I have seen homebrew MPP plans on the internet. Somewhere. Bill Boden (Bowden?) maybe.

If you could figure it out, it would greatly increase your useable watts.

You have a potential of 840w, but with normal controllers, you can only get 390w.

A closer way to figure your true output would be about 0.45v per cell, and 2.7 amps.

They are looking really good.

G-