Better Homemade Panels

[springgrove]

There is a good supply of solar cells out there.  The problem seems to be putting it togeather in a panel that will last.  Moisture, expansion, and cells or glass cracking seem to be the major issues.  Most people will say go buy one.  I think we can do better and have some ideas.  I don't want to spend a fortune on specialized materials, but use materials that can be purchased locally.

The best I have seen (just my opinion), are cells between two pieces of glass with silicone around the edges of the glass creating a seal all the way around.  The cells are secured usually by silicone on the back of the cell.  I am experimenting with filling the complete area between the glass with silicone.  

Silicone purchased at the local hardware store in tubes is easily thinned with Mineral Spirits.  Just about any consistency you wish.  I had problems with it drying all the way through when it was thicker than 1 inch but adding glycerine prevents that from happening.  When you thin however the drying time can be a week at room temperature.

The picture is a coin between two pieces of glass sealed in a 1/4 inch of thinned silicone.  The close up of the coin shows what happens when you use silicone that contains Acetic Acid (Ethyl Triacetoxysilane).  You can see the chemical reaction with the coin (green around the edges).  I have found that GE Silicone II does not contain Acetic Acid.

Sealing in silicone I hope will keep out moisture, secure the cell (similar to laminating), strengthen the two thin front and rear panes of glass, secure connections, and provide good expansion and contraction of the assembly.

What do you think?  I have 36 cells waiting.

[zap]

Interesting experiment.

It has me wondering how much expansion you'll get.  Have you measured that yet?

[juddley]

I have noticed locally all the DIY panels that actually worked and lasted more than a year were about 2 feet square. A lot of people do a small panel first and have good success..... then try to "multiply" that into a larger unit and have a failure.... then go buy panels. I often wondered if this wasn't because of the expansion problems you mentioned.

I call GE Silicone II "poor mans RTV". It works great. I had problems with a tube of "Brand..X" Silicone which must have had some kind of acid in it. After a few months it rotted the copper wires I had potted. I like your idea of thinning it with mineral spirits, I will try that. I know all the products that are marked "latex" or "clean up with water" are useless.

The other thing that comes to mind with two sheets of glass is the side facing the sun would expand a lot more than the back side. Would it be possible to bond to front sheet of glass and maybe use a very thin Mylar sheet behind the cells?? I know the double glazed windows have to be "spaced" to accommodate this in their frames.

My final note, I have recently noticed some imported panels that have a "folded" interconnect in the long dimension of the panel. Only seen a couple like this from "offshore" I figured they did that to help eliminate the expansion problem as well.

Judd

[Opera House]

Are those white plastic X tile spacers?  Always thought those would be useful for something.  Why is there a need to pot?  Seems like any home made panel would be subject to more failure than a commercial one.  Why make it impossible to fix.  I would use two pieces of glass with spacers and seal around the edges like they do with organic thermopane windows.  Blow through something dry like nitrogen before the final seal.

[GeeMac]

What is a good source for solar panel cells and parts?

[ghurd]

Potting is almost a requirement, for solidity if nothing else.

Notice the upper right, and the bottom...

http://www.otherpower.com/images/scimages/12186/_Strider1_my_pictures_digital_cam_Damaged_package_IM
G_6268sml.jpg

The nitrogen thing has been done (professionally) a few times.  It didn't work.

G-

[Ungrounded Lightning Rod]

I thought it had already been determined that using silicone would damage or destroy the cells - in much the same way as letting water (with impurities) get to them would do it.

Silicone is thinned by acetic acid - essentially very strong vinegar.  This is corrosive due to both the acidity and conductivity, especially when it is bathing electrodes with a voltage between them and encouraging electroplating / galvanic corrosion.  Not what you want to soak your cells in.

(Don't recall if the polarity on cells is typically oriented so it would try to remove the transparent metallic electrode and plate it onto the substrate and wires to the next cell or rot the wire to the next cell and deposit the metal on top of the cell surface.  But neither is what you want.  Nor is migrating metal ions into the silicon until they change the doping enough to make it stop being a solar cell.)

[springgrove]

Nope.

[springgrove]

I am worried about even the Silicone II contacting the cells, I have not tested (neeed 5 days) it like the regular silicone above and think it will be an issue.  I have 36 cells ready to go (sacrifice) and Sunday I am going to Vegas for a week.  I am going to try the silicone filled panel one way or another as it will have 7 days to dry while I am gone (hate the waiting to dry part).

At this point thinking (from the bottom up), glass - cells - food wrap (plastic wrap covering only cells and bus) - thinned silicone - glass.  I would leave glass exposed between the cell rows (4 X 9) and around the edges for the silicone to adhere to.  Between the panes of glass would be 1/4 inch tile spacers for correct thickness.  I already purchased tubes of clear silicone but now I think white would have been better to keep the heat down.

To thin the silicone I start with 50% silicone and 50% mineral spirits.  This produces a honey consistency.  If you want thinner just add more mineral spirits.  Make sure you use liquid glycerin.  You can purchase at just about any drugstore, just purchase some a...... I mean...... a....... suppositories.  I usuallly ask the wife to grab some.  I use 4 drops per ounce of mix.  If the mix starts to thicken while your working with it just add more mineral spirits. Mix well. Have good ventilation and avoid flame and sparks.  Remember this is slow drying, at least 5 to 7 days.

If anyone has thoughts please post.

[springgrove]

Great picture, hope it wasn't your panel.

[springgrove]

You can go to Ebay.com and do a search on solar cells.  Some of the sellers also have on-line stores.

[Volvo farmer]

You have an interesting idea there. Back in '05-'06 I was also infatuated with the homebrew solar panel idea. I took the best of what I saw on here, modified it for how I could do it cheap and ran with it.

I built six (72) cell panels from Evergreen surplus cells and wired them for 12/24V. I did like you first mentioned and glued the cells to one pane of glass, then sealed them up like a double pane window. I used heated butyl to seal, and primerless auto glass adhesive to mount, not silicone though.

Anyway, 4 of them survived my rough handling with no glass breakage.  They have been mounted and making power for three years now. I have seen moisture in a panel or two after almost every heavy storm we have had here. I have seen no deterioration in any of the connections between cells. My panels are more-or-less vented to the atmosphere, through small holes, and I live in a very dry climate, away from the ocean, with 300+ sunny days/year.

Because I used chipped/broken cells, I get about 10a@24 volts out of my array at noon. I am grateful for all those watts, but I am one of the people that say they would have been watts ahead buying commercial panels. For one thing, I have 2 panels sitting in the garage that need new front glass, because I shattered it, Then there's the experimental 12V 50W panel I made that I cannot implement into my system, because it is 12V.

Don't get me wrong, I really enjoyed soldering over 2400 cell connections  by hand, it was like a meditation. I can point to the panels when people visit and say.. I did that myself! and feel satisfaction in their open jaw reaction... But honestly, dollars to watts, I might have done better buying panels.

Here's my story when I first mounted these panels.

http://www.fieldlines.com/story/2006/9/16/05931/0581

I say, mount the things in silicone. It's better to be an innovator or a failure than a copycat ;-)

[shmuu102]

I would find something better than food wrap.

There are a few sellers selling EVA on ebay. and one or two selling Tedlar. Both of these materials are used in commercial panels.

on the one i'm building now (36   6x6 cells), i used corona dope to insulate the backs. I think it also gives the a bit of strength to any cracks

I have also considered tyvek, or thin rolls of polycarbonate (www.usplastics.com)

I am using recycled freezer doors, which happen to be low iron tempered glass. I am siliconing the cells to the glass and using the tile "X"'s as spacers, so my sheet of aluminum doesn't touch the cells.  I would like to thermally couple the cells to the aluminum, so I can use   45 deg "wings" as concentrators (increasing the heat load) , but I have yet to come up with a way to make it serviceble And coupled to the aluminum back plate.

My experience so far  says buy the pre-tabbed cells; or expect to break 15% of your cells. Some say to add more solder to the tabbing wire. To me, this seems to make the wire too thick, and cracks the cells when cooling.

[springgrove]

shmuu102

Why tyvek?  What do you like about it?  Shure would be easy to get.

Pre-tabbed is defintlly the way to go.

[springgrove]

Volvo Farmer

Some great information!  If a person can experiment with that many cells, I have no excuse to experiment with just 36.

Silicone it is!

Will keep you updated.

Jerry

[shmuu102]

I haven't used tyvek, i am just floating the idea.

I did order some Tedlar off ebay, and minus the smooth shinny surface, it reminds me of tyvek a bit.

Then I looked at the actual thermal properties of tedlar are not really that good. This makes me think heat is not really the issue its made up to be, and commercial panels don't do a very good job of dissipating the heat.

[Simen]

I got one 85W GPV panel for free, because the glass was shattered. It was the kind of glass that shatters into thousands of small pieces. The backside of the panel are a plastic-board of some kind, and the cells sits between there, bathed in a silicone(-like) substance. (Not sure if it is silicone, but it behaves like it...)

I've tried to pluck out the glass pieces out from the silicone, without success...

As the panel is now, it produces around 15W, because of the shattered glass...

Something to have in mind if one are going to bath the cells in silicone.

Cornelius.

[shmuu102]

Usually, I hear they "bake" the cells between two layers of this clear plastic called EVA (Ethel Vinyl Acetate. )

If you can heat it up uniformly, to around 100deg C, you should be able to extract the cells.

[Tritium]

Best of luck on your experiments in panel building. I wanted to do just that very badly for many years. I just can't justify the extra expense and work when commercial panels with a 20 year warranty are available for under $2 per watt.

Thurmond

[springgrove]

Thurmond

Thanks! Should be fun.  Might be heading in your direction later!

Was wondering if you or anyone had information on what roughly the panel warranties cover?  Breakage? Poor output?

I think a lot of people would buy panels but their waiting and hoping for prices to drop.  I have heard people say they don't want to pay the price because who's to say the manufacturing company will be around for 20 to 25 years.  I actually work for one of the large well known manufacturers (can't say who), and I can't even get a company discount on our panels, not fair.

Jerry

[shmuu102]

most of the warranties i have read cover 1 year manufacturing defects, and 20 years rated output.

[Volvo farmer]

BP is five years material and workmanship. I had a hot spot appear in a 170W panel and it was replaced, free of charge, even though it still made full rated output. I didn't even have to return the faulty panel, they only wanted the sticker off the back.

[ghurd]

I bought some used surplus panels billed as "military".

Imagine a SS cookie sheet.  A thin layer (far thicker than heavy paint) of silicone.  Cells on the base layer. 3/8" more silicone over them.

The output is still good, and the silicone-looking-goop is badly yellowed.

The cells are multi crystalline.  The goop is not exactly well adhered to the cookie sheet.  The goop lifted at the corners of one or 2, a LOT, and flexed a lot, and they still work fine.  The cells are not tabbed, but connected with insulated wire (#22?).

There is a ~6" hole in the middle of the panel (no idea why), and it you can see it here, the smallest PV leaning on the window.

http://www.fieldlines.com/images/scimages/2050/PVsnow.jpg

I can not say if it is silicone, but it LOOKS like silicone.

Maybe the acid free stuff will be good.

I recall something in a caulking tube called PV850 marketed for PVs.

No idea what it is, but might be worth a look.

G-

[ghurd]

Must be another glitch?

Correct stuff is PV804.

G-

[springgrove]

I picked up 2 pieces of glass 26 X 34, 1/8th inch thick.  They told me I could get glass tempered with an additional 25% charge and it would take about 1 week.  If this works I may do so next time.

Here are some pictures of the solar sandwich.  This is the cells on the glass waiting for the silicone.

Here are the materials I used.

Mineral Spirits, GE Silicone II, Glycerine, eyedropper, strong mixing stick, and empty 2 liter bottle.  I ended up using 8 tubes of 10 oz silicone.  To 1 tube of silicone I added 8 oz of Mineral Spirits and 80 drops Glycerine.  Next time I will probably add 10 oz of Mineral Spirits to make the mix a little thinner.  I left it thick so the mix did not get under the cells (I hope).  Also had gloves on as it's messy.  Working time with the mix was acceptable although next time I will use a bigger container and mix it all at once.

Here is a finished picture of the sandwich assembly.

I placed wooden strips on the glass over the tile spacers and applied slight pressure a little at a time with the clamps.  I stopped when I saw no more silicone coming out along the edges.

Well that was about it.  My biggest fear at this point is that cells may have cracked from the pressure or that silicone leaked under the cells.  Like I said before, it needs 7 days to dry.  Will post then, I'm off to Vegas for vacation!

[Volvo farmer]

Sweet!

I built mine with tempered glass, I think tempered stands up to heat better than regular glass, at least that's what is stuck in my head at the moment.

Post back when you test it, with more pictures, plz!

[dnix71]

Why isn't fiber glass resin used for potting? It isn't very expensive or corrosive.

[dnix71]

You might want to read up here:

http://www.sungroper.asn.au/project/solar-panel.html

They built their own for a solar car because commercial panels had too much weight.

Double-sided tape secured the cells to fiber glass base panels and a commercial grade conformal coating was sprayed on. They tabbed their own cells with ribbon tape.

[springgrove]

That was my first thought, easy to mix up.  I went with the silicone because I am not sure how much the cells expand and contract and silicone is pretty flexible.

Would be a good experiment.

Jerry

[stickalose]

Just wanted to add something I found out while trying to make double paned windows. Silicone cures by reacting with water vapor in the air. Also it is not impervious to water vapor.

[springgrove]

It has been a week drying time.  I removed the clamps and flipped the solar sandwich over for inspection.  None of the cells where cracked which was good.  The Silicone II did not get under any of the cells which was also good.  I also did not see any signs of chemical reaction with the cells or solder joints.  I did however see what to me looks like a few small thin pools of "Mineral Spirits", not vapor, but more like a thin layer of clear oil on a few of the cells.  I am thinking this may be a result of not stirring the mix enough.  Don't know if it will be an issue at this point.

Today I picked up some 1/2" aluminum U channel and attached it to the edges with Silicone II.  It's just the right size.  This is a rear view.

So another day or two of drying and I will take it outside.

One other note.  The unit seems very solid.  There is basically two sheets of glass with a solid core of silicone between them and I wonder if tempered glass is really required??

Jerry

[springgrove]

The panel is finished.  Here is a picture.

With the u channel frame it feels even more solid.  Next step is get it mounted and see how it handles the elements.  The days are getting shorter here (North of Chicago) and winter is on the way, so it will not see much heat for a while.

I feel confident it will hold up, we shall see.  I think I am going to build another one.

Will update how it works as time goes by.

Jerry

[springgrove]

Yes that has been mentioned a few times and a worry.

I use to raise tropical fish and built many custom tanks with silicone. It was very rare to find a leak or damp area at the base of a tank, even a 50 gallon one.

I can see however that it may be different with air between two pieces of glass. On this panel I have filled areas that normally would be occupied by air with silicone.  That is why glycerine was added, no water available for drying and the silicone would have stayed soft in the center of the panel.  My hope is with the silicone there, water has no reason to occupy the space.  

However the silicone does have air bubbles, I would have had to place the silicone in a vacuum to remove the air bubbles.

It will be interesting to see what happens.  Time will tell.

Jerry