Making decent solar panels part 3

[oztules]

Dave, your making some fine looking little panels there now..... and doing enough experimentation to help other folks too.

Pebbles.

I just bring the bus wires out. I can do whatever I dream up after that.
For me, I just use transformer paper/ motor winding paper etc. if I need insulation,  and every layer of anything I put in there (paper etc) always has a scrap of EVA on both sides of it. You can't put too much in there really, as it all turns into a liquid when it is baking, and redistributes throughout the panel..... but this does mean it WILL have eva on all surfaces. This helps mechanically as well as electrically..... as does the paper. It sets very very solidly.

I can't see how it could be done poorly, (unless you short buss to cells etc (Dave has been good enough to do testing in this area for us.....)). As long as there is plenty of eva,  and paper to insulate and strengthen it, then it will be plenty tough.

Ibdilbert,

I don't know your oven setup, but if you look at the pictures shown so far from a few folks now,  bubbles are not that prevalent. Are you sure your getting sound vacuum. You have a bigger pump than me, so it will hide some leakage better than mine. The tiniest leak will drop my vacuum significantly, yours not so much.... this tiny leak will set up pressure differentials across the panel if your wicking material cant redistribute the leakage fast enough..... then bubbles will likely occur in the EVA . It should make little difference to how shiny/coarse the EVA is, as it all goes liquid.... once in that state, we need to just give the bubbles a reason to move.... pressure from outside, and vacuum from within. I too had the shiny on one side stuff, and could not get any fix on which side was best, it seemed to make no difference in my testing..... but all mine are in a slow change oven. Is your hotplate (I think you use that instead of an oven?) too hot, or uninsulated on the away side..... I cant figure why your having the problem.... but there must be a simple reason..... and I'm still of the opinion that leakage is the key .


This thread is becoming very useful I think, and will become more so as more folks add their testing and results.
Maybe this technique or something similar, will be the thing that legitimizes the DIY solar panel as a viable alternative to commercial ones.... who knows..



............oztules

[Harold in CR]

 Morning all.
 Have gotten the EVA ordered and shipped to the USA to my Son. He will be sending a crate down, very soon, with electric Bicycle parts, large DC Generator for my 3 wheel Moto build, lots of small but essential items, and, I need to dig out my Vacuum Pump today, and see if it still works. Need to buy a gauge.

 I have a sawmill, so, I am gathering large plastic feed sacks, and stuffing Planer chips into those bags. I have built a solar dry kiln for lumber drying, and insulated the walls with plastic bags of dry sawdust. Works a treat. I have a dismantled electric stove, and both heat loops from the oven-broiler area. I'm going to try to use the smaller one, and see if I can regulate the heat with the proper control switch. I have a meat and an oven thermometer for watching the temps. Of course, lumber for the frame is no problem.

 I need to get into town and secure the frames and glass.

 I'm thinking about laying a length of small diameter PVC pipe at the base of the strips of cells, and running all the insulated wires through that, to a plastic switch wall box. I already have all these things, so, no cost. I will also mount the Diodes in that box area, although on the outside on a metal bracket, to keep it in the open in case anything gets out of hand.

 I have a roll of heavy plastic Contractors Trash bags, big enough to put a whole panel inside, so, I can re-use it, maybe, and just have one layer also glued to the back of the cells. They are damn tough to tear, so, should protect the underside very well.

 Any other suggestions, I am all ears, before the crate ships.

 Dave has added some great stuff to this thread, so, I see NO reason why someone could not put together great working panels, and get their friends/neighbors to cut their power consumption from the grid.

 I just wish batteries were less expensive down here. A typical 220Ah Golf car 6V battery is ------------------------------------$210.00 each + 13% sales tax.  I'm going to get a couple heavy equipment 12V batteries, and flush them, and experiment with converting them to Alkaline. Stuff that Acid crap.  Then, I can make a nice cabinet and place them inside the house and vent the air outside, so I don't blow up the place.

[mikeburg]

I have been looking for this for a while and now I have the source code to procede. I was on the path to use Sylgard, and I had reservations, with the possibilities of bubbles. It left me waiting to go, and start tabbing cells.
   Thanks!

[ibdilbert]

Using the rougher EVA from Mars Rock, I've made two larger panels with no bubbles.  The only issue I'm having now is cracking some of the cells.  Today I was using polycrystalline de-tabbed cells that I obtained cheap from ebay.   I'm also cutting them in half and I think the fact that they have been Tabbed, De-tabbed, cut in half, then re-tabbed is causing the cells to be stressed.   I'm going to order some Monocrystalline new cells and try them out later this month.   


For the box on the back, I've just been using a project box, "Hammond 1551kbk", they can be purchased cheap for just a few bucks from Newark Electronics.    I'd like to find a waterproof box for the panels I will be making for my RV.   

[oztules]

Well there are some good looking panels being made now.

You have been busy for sure.

I tried to look carefully at your last photo, and it looks to me that your tab soldering have  some lumps of solder .... these are prime to crack the cell...

.... however, I have found on the big 6x6 cells, that simply bringing them up to 50-55C BEFORE the initial (replace the room temp with 50C) vacuum, will  allow these anomolous humps to sink into the soft (not melted yet) EVA rather than crack the cells because the solder lumps can't sink, and the pressure takes no prisoners....

I found I can be pretty lax with the solder finish if I do this simple thing....otherwise I can look forward  to cracking particularly the larger cells. I'm getting 8A out of these arrays now, and I put that down to no microcracking that I must have had in the original panel. (Originals were 3x6 two in parallel... now the later ones using the 50C initial suction  can get 7.5- 8amps too for the 3x6 cells   later 6x6 are 8amps plus)

Good to see you have cracked (pun intended) the cell cutting business too...... I have not given it a real go yet,  but will look into it later for sure.

Keep us in the loop, were still all learning at this stage .




.............oztules

[ghurd]

Looks good Dilbert.

Might want to rethink waterproof boxes.
If they are sealed up too tight they can't breath, trapping moisture, rotting the stuff in the box.

I have been sealing the top, sides, and just a bit in from the corners on the bottom with silicone.  The idea is the water can not get in, but moisture can get out during the thermal cycles.  Seems to be working fine and 0 failures from water or moisture in the box.
G-

[DanG]

My new-old-stock panels came with a tube of silicone gel and instructions to make all wire terminations then coat the cover seal O-Ring and paint everything metal in the box with a thin film of gel. The through-the-EVA buss traces should get a coating front & back to reduce chances corrosion might tunnel along the conductor. There are large tubes of automotive ignition 25,000V dielectric gel available for $5-7 that are nearly the same thing - unaffected by temperature & moisture and non-conductive metal protectorant.

My Schott double-glass panels junction boxes are 'potted' with a poured-in lightweight silicone jello that has worked very well; One panel shows lightning traces that blasted 2-3mm wide holes through the gel as the bolt went to ground but the gel kept collateral damage down to near-zero inside the black-plastic junction box.

[jaskiainen]

hi jaskiainen,

looks like some kind of shell game going on with the power ratings in those listings. have to believe the power requirements will be about the same for the 12v and 24v fans listed.... (40ish watts) the 28 watts may be the air moving power? not sure how they will behave..specs say locked rotor protected,  don't really know what that is but like the sound of it. were you hoping to run this direct? no battery? any controls at all?

we need to be aware of the temp rating with the plan ..only 50 or 75*c  depending on what cut sheet you read.

6 x 1.5" cells? that's an odd size. seems we can reasonably expect to get about 0.07watt per square inch (of silicon) for a battery system and 0.09w with matched loading or with electronic magic. so about 22 (real world) watts with a 36 cell module.

curious to hear how the motor testing goes, kindly keep us updated.

it's all good fun!
cheers, dave

Hi Dave,
Got my blower for testing now and the results are close enough to the given specs.
My measurements gave me just about 2 amps with full voltage 14V.
I have no other equipment to measure air flow or noise.

I'm still waiting my EVA to arrive. It's been a month since i made my purchase from Canada?
Everything else i have purchased from US or even far east came sooner.
If i don't get my order here in next week i'm gonna give a very bad feedback for the seller.

It seems that i'm gonna use all 39 cells for my panel so the real output would be nearer 25 Watts.
Still haven't chose what to use for backing or junction box but will deal with that later.

I've been thinking of using regular plastic vacuum suit bag for vacuuming the panel if they will manage the proper heat.
Just need to buy one for oven testing.
Also i have been thinking places where to get right size tempered glass and already have a few thoughts for that.

The cells are 150mm x 40mm (6" x 1.6") rated 1 W each. Funny size i agree maybe they are cut from broken
bigger cells?

Best regards jaskiainen

[dave ames]

Hey jaskiainen,

about that EVA delivery time..seems like it may arrive faster the more remote the location?

to the usa east coast it took 18 days. had the roll here a week before i noticed that the tube that the EVA was rolled up on was several meters of tedlar backing material 

wondering what that suit bag is? (you can't mean a dry cleaner bag) can it be sealed up real good? no zippers to let any air leak.. nothing i can see to make any of these bags reuseable..one time only.

about the number of cells. it's worth the effort to cull out any dogs even if it means having to use fewer cells with your project (IMHO) and it's hard to tell the output until they are tabbed and in bright sunlight..but worth the effort.

we will be following along.

it's all good fun,
dave

[jaskiainen]

Hi Dave.

By suit bag i mean those plastic bags where you storage your suits in closet.
There are several types of then available in stores. Some come with zippers and some with other closing types.
And there is a hole for vacuum cleaner to suck them empty and saving space in your closet.
Thats what i wanna try out.

I contacted the seller and he promised to check where my delivery is?
Mainly everything i have ordered so far have come to me within 3 weeks of postage.
From US or far east. This one have been on the way for 5 weeks now.

Best regards jaskiainen

[MrDoctor]

Hi everybody!

Please forgive me for my question, but I'm a beginner is solar panels. It is a bit expensive to get TEDLAR in Hungary, so I'd like to know, glass fibre good for the back of the panel? Will it work with EVA, or should I use epoxy instead?

Thanks forward

[oztules]

I've fixed some older solar panels that had glass fiber in the eva. I see no reason not to use it, but i would not bother myself, as you will still need to use a plastic or similar material backing to contain the errant EVA. It will run like water when it is "cooking", so will soak into the glass matt, and beyond if there is nothing to stop it gluing itself to your vacuum bag.

I now only use :    glass, eva, cell, eva, plastic sheet for the back,      and thats it. It leaves the backing transparent, which I think looks good, and helps hide any inadequacies in your gapping of the cells (it is not as stark as a white background)

I have over 2kw now and another one kw or so to go..... figure that will be enough for the moment.

Now using the 6x6 cells, much faster as less to do in a single panel.... can do 2 per day (approx 250 watt panels 8A@34v  2 square meters of glass) when I get into it (500w total/day). I only have 66 cells per panel (4 watts each cell).



................oztules

[MrDoctor]

Thanks for your help and fast reply!

[Ovais]

Oztules,

Which plastic do you use for the backing? Would PVC sheet survive 110 degC?

Many thanks.


Regards,
Ovais

[willib]

Fantastic work OZ
i didnt comment earlier But i've read all three..

Now using the 6x6 cells, much faster as less to do in a single panel.... can do 2 per day (approx 250 watt panels 8A@34v  2 square meters of glass) when I get into it (500w total/day). I only have 66 cells per panel (4 watts each cell).

Amazing !!
i've gotta try this!

[oztules]

Ovais, there are plenty of different types of plastic that we call pvc.... so I don't know the real answer.... but I know how to get it.

Just try a test cell, and you will know for sure. Your going to do a few test runs........ aren't you?...... but I expect it will be fine. The stuff  I'm using is from a farmer who used it for green house tunnels.

Willib....

Thanks.... but it is not as impressive as it seems. I bought the last few KW from fred380v. They are pretabbed front and back...(cut off at the edge), and this speeds things up incredibly.
 It takes about 1 min/cell to short tab it with two 1" tabs, and about an hour or so to join them up into a 2x1m panel 66 cells ...... so I'm not very amazing at all when you know all the facts... sigh....


............oztules

[ibdilbert]

Had a chance to make another panel over the weekend, no issues this time.  No Cracks, no bubbles, all appears to be perfect!



These cells are Mono-crystalline, 5x5", ~2.35 watts per cell.   I cut them in half, final result should be a panel around ~42 watts.  My soldering skills have improved to the point were there isn't too much lumping, I assume that skill improves with practice.

[Harold in CR]

 You are becoming a pro at building panels.    That looks really good.  IF I EVER get my stuff shipped down, I would be ecstatic to do that well.  2 thumbs up. 

[artv]

Hi Ibdilbert,....very nice ,I was wondering why you cut the cells in half?? Don't you just have to connect them back together again??
I want to give this a try ,but need to get my solar water heater going first. Too much to do not enough time.Also is there an ideal size cell to buy to save cutting them??...Sorry for all the questions but I never even considered solar till I read this thread.........thanks Oz.....artv

[ibdilbert]

Thanks Harold! 

artv,

The voltage output of the panel is determined by the number of cells.  Each cell puts out ~.5 volts, and you need about 36 of them to achieve 18 volts. 18 volts is well above whats needed to charge a 12v battery, so there is room for voltage drops over wire, diodes, ect...

By cutting the cells in half, each piece will still put out ~.5 volts, but its total watt power is divided amongst the pieces.

The glass that I have isn't big enough for 36 full size cells, but it is big enough for 36 half size cells, that is why I cut them in half.   

[klsmurf]

Very nicely done! I'ld be curious what extra heat the dark background will cause.

[ibdilbert]

Personally I think a white backsheet makes more sense as it shouldn't collect the heat that a black backsheet would.

[artv]

Hi Ibdilbert,.Thanks for the reply ,but now I"m totally lost......how can you still have the same voltage after cutting them in half??

But the power be only half of the original cell???...Is it because the resistance of the cell is also halved??......Or is the resistance doubled???..........because it has less area to transfer the flow of electrons.....................can't seem to get my head around this stuff...........artv

[ibdilbert]

artv,

If you cut a cell in half, each piece will still measure the same voltage, however the watts will be divided in half. 

A quick pic of the the last panel framed.

[oztules]

It's nice to see the theory turned into practice.

Was there any hiccups that others should be aware of, or things you feel we can do better?


Black /white.... if you use white, you don't get to radiate as much heat out the back, and if you use black, you radiate heat much better from the back, but get a bit more from the front...... but the cells take up much more room (get hot regardless of front colour) than the interspacing....... Think I'll toss a coin..... black may even be better.??


.............oztules

[Madscientist267]

White on front, black on back, laminate? Best of both worlds... ?

IBDilbert - Very nice indeed. I'm gonna have to give this thing a try one of these days... if I ever get to the end of my currently astronomical 'wish list'... 

One thing is for certain, DIY panels will never again be a mystery thanks to Oz, and everyone who has posted their trials, tribulations, successes and failures about the process.

Steve

[Ovais]

The following paper will be of interest to the members:

LAMINATING PV MODULES WITH EVA USING SOLAR OVENS by Dr. Richard Komp, etc.

This paper can be downloaded from: www.mainesolar.org/EVA.pdf


Regards,
Ovais

[oztules]

Nicely done from those folks. I think I will stick with the vacuum system to avoid those bubbles.

It is nice to see someone else doing low temp cross linking..... just wish they had done it or published it before I took an interest..... would have saved a lot of testing things that didn't work as well as I had hoped.

Nice to see were not alone in this venture.

I think they are streets ahead of their U tube counterparts.

Thanks for the link  Ovais...... also, I notice you have been to the EVA shop in China...... any pictures yet??


.................oztules

[Ovais]

Oztules,

Yes, I have received the EVA from the China shop that you recommended. Their service is quite good.

My oven is ready, the solar cells have arrived. I will soon be testing a single cell and then proceed to a 60 to 70 W panel.

Many thanks for sharing your precious experience.


Regards,
Ovais

[richhagen]

The results posted here seem most impressive, especially for someone who has attempted various methods with less stellar results.

I have access to a small laboratory type vacuum oven, and have made some small sample panels with it on tempered green glass which was available to me at the time.  If I can figure out a method with consistent good results i will order low iron tempered glass.  I have invariably obtained some bubbles thus far with what I have tried, at first from applying too much temperature which resulted in the EVA outgassing,  but even with better control I still have gotten some bubbles.  I obtained the EVA through a vendor on Ebay.  I may try a different eva vendor to see if that makes any difference, but I am not sure if that has been any part of the problem. 

I am thinking that this bagging method outlined by OZtules seems to yield more predictable results even if it is a bit less convenient.  It occurrs to me that the force on the plastic bag from atmosphere outside may be important to collapsing any voids left behind in the plastic layers.  Although I have seen videos which seem to uses similar in essential function, vacuum ovens to what I have tried which are used to make commercial panels, I have not achieved reproducible good results to date.

I do have a specific question for IBDILBERT though.  I have tried glass cutters, a dremel, and even got some wafer dicing blades, and although I have managed to cut some cells, I have yet to develop a reliable method of cutting the cells within a reasonable time frame without too high of a percentage of them breaking or chipping up on me.  For this to be efficient enough to be worthwhile I need to figure out a reliable method of dicing these cells.  What is your method for this?  Do you get reliable results for only specific types of cells? 

My ultimate goal at present with this non priority project is to have the option of being able to make a large batch of small panels for our remote lighting expeditions.  Rich

[artv]

Hi all,...I've been following this info, and it seems the "bubbles" are major concern............can you not just stretch fit the plastic before you heat it??.........That way eliminate the chance of a wrinkle or bubble....maybe that sounds easier than done.....I haven't tried yet so I don't know......but I will try it....artv

[ibdilbert]

richhagen

I wish I had an easy solution for cutting these things, but don't.   I looked at wafer blades online, but it looked like it might be some work getting something machined to hold the blades, as they don't seem to have a standard size hole.   

Diamond flaked dremel blades kinda work too.  I've tried various scribers too.   And I've been told a CO laser wont do it either, but I don't own one to try for myself.   So for now I struggle with the diamond flaked blades.

[dave ames]

looking good ibdilbert! seems you have your system down to a science now 

richhagen, we have found that a thin kerf rock cutting blade can give us repeatable results..at least on these string ribbon evergreen cells. some info a few pages back in this thread about the set-up.

http://www.lopacki.com/sawblades/

kind regards, dave