Cheap methods of encapsulating?

[vermiman]

mdmiller1,

Any new news about using Through The Roof to encapsulate cells?

[mdmiller1]

The Thru the Roof test continues. I've poured half of a panel. Photo below.

My goal was to shoot for cheap but durable and tough. I priced double-strength glass and tempered and lexan. Too much money. I decided to use Optix acrylic sheet, the real thin stuff. A 20x32 piece was 10 bucks at Lowes. It's about .09" thick. This sheet is obviously too thin to function on its own. The plan is: the cells are encapsulated directly on the acrylic sheet, then I will overlay the back with a piece of thick pegboard, tape the edge, and pour Through the roof over the pegboard, effectively creating a bonded laminated panel. I don't plan on ever servicing the cells, hey the cells were $18 at ebay, this is an experiment. The pegboard is very rigid, and when coated with thru the roof, it should be water tight. It will be framed with an aluminum angle.

I tested pure Lexel on the acrylic sheet, I ran a 32" long bead right down the middle and let it dry for a day, then scraped it off with my fingernail and finished cleaning with pure mineral spirits. The scrapping was a pain it was incredibly tough to get off. The Optix took the abuse and was damage free after this. I figured if this material wasn't tough I shouldn't go any further with it anyway.

I created a dam to hold the encapsulation with some strips of matteboard and a thin edge of masking tape. This board is the stuff you make mattes for photos, it's about 1/32" thick and seems the perfect thickness. The mix ratio of 6:4 seems okay, it maybe could be a bit thicker. There were a few trapped bubbles but they worked out okay, I wish I could make a pour without any forming but I haven't found a technique that is 100 percent bubble free.

When the encapsulant is dry, I take a razor blade and run it along the edge of the masking tape (which trims the edge of the encapsulant) and then remove the matte-board dam.
I have 18 cells mounted, the cells are 8cm X 10cm, I've used 130 grams of thru the roof so far. There are 700 grams remaining which include the weight of the can which probably is not much.
Biggest concern right now is how long it will take for the mineral spirits in the thinned mix under the cells to evaporate. Hopefully it will evaporate before damage to the acrylic sheet occurs. Right there's "the rub" in this process.

[vermiman]

I don't plan on ever servicing the cells, hey the cells were $18 at ebay, this is an experiment.

I bought my cells on ebay also for $18.

40 3x4in. solar cells from lowcostsolar2010

Your cells look like the ones I bought

[mdmiller1]

more thru the roof

here's what I've learned about this Sashco Thru the Roof product:
1. my favorite ratio is 2:1 sealant:mineral spirits.
2. the material contains quite a bit of solvent so there will be some shrinkage in thickness. Thus, it's important to both get the bubbles out and have enough material around the cell perimeter when it dries.
3. I've encapsulated 9 cells at a time, trying different approaches. The one I did tonite is perfect - no bubbles, was easy and went fast. I raised one edge of the entire string of cells by slipping a yardstick under their edge, then tipped and shimmed the whole panel so one long edge was about an inch higher than the opposite edge, built a dam along the low edge with a piece of masking tape and poured the thinned sealant at the low edge until it was half way up the cell, then removed the yardstick from the high edge, lowering the string of cells into the mix and then removed the shim so the entire panel was flat.
4. I poured some straight unthinned sealant around the perimeter of each cell when completely done checking that the cells were settled down in the sealant. The unthinned sealant has the consistency of STP or a bit thicker.
I'm pleased, this looks good so far.
5. for each string of 9 cells, 300 micron, 8x10cm, the amount I feels works best is 80 grams of sealant and 40 grams of mineral spirits. Then I used about 6-8 grams of straight sealant poured around the cell perimeters.
The quart can contains about 800 grams.
6. the string of 9 cells that I only used 60 grams of sealant on does not look good. I did not do a good job sealing the edges, there are some large bubbles. The string with 70 grams is ok but not great, there is one large bubble. The two strings with 80 grams look nice.
7. the Optix acrylic sheet looks fine, once curing is complete I'll dig out the hand microscope and evaluate it more closely. So far it has weathered its encounter with the mineral spirits.

Cure time on this material can be 5+ days, cure being defined as the point at which it has no more tack when touching.

After a week of cure, the sealant is beautifully crystal clear.

[photovoltaik]

Nice post...Thank you very much!!......

[kenf729]

mdmiller1,

Now that some time has passed how do you cells look? did the thru the roof finally dry under the cells? how has it held up, thinking about giving it a try.

Ken

[mdmiller1]

thru the roof update

This project has taken a back seat for a bit, which probably is a good thing as it allowed time for the sealant to rest and cure. About half the cells have some larger bubbles in them, half do not. The bubbles typically extend to the edge to where the tabbing exits from the face to the back of the next cell. It appears that the cells without bubbles have more sealant material around them, or were ones that I added additional sealant to later. I think, but not certain, that what would have solved this: on day 2 after the original encapsulation, to have poured around the perimeter of each cell additional sealant so that as shrinkage occurred there would have been additional fresh material to suck in as the material under the cell shrank. I'll try to post some pictures in the next week. The Thru the roof product is beautifully clear, and incredibly tough. At this time I see no problems in the acrylic sheet due to prolonged contact with the mineral spirits used for thinning. After reading Dr. Komp's experiences, the bubble issue seems to be the tough one to conquer. However if the bubbles are totally sealed in, I'm not sure how they will affect performance as long as no moisture can get in.

[DeltaFox 25]

What if you pored a little sealent on the glass first then out your cells down then pore the rest of the sealent on to the back of the cells. that should take all the bubbles out i would think.

[mdmiller1]

After the pour there were NO bubbles. The bubbles occurred many days later, due to sealant material shrinkage as the solvents (toluene and white spirits) cure out. I probably didn't mix up enough sealant material originally. In comparison to a container of sylgard, which is .5Kg, and I used about half this much, that could be the issue.

[turbo2001rt]

Can you post some pics with examples of how you "tipped" the edges? I have been looking for some way to keep moisture away from the cells and this seems perfect. I want to get it right the first time thanks and great idea!!!

[mdmiller1]

The sketch below is a diagrammatic cross-section of how I tipped the panel, which allowed the air to escape out one side of the cells, instead of being trapped under the cell.
The important thing to remember with thru the roof, there is no rush during assembly. I came back 4 hours later after initially pouring the sealant, and positioned the string of cells a bit, and even squeezed a small bubble out, so you can take your time. Even the next morning things were fairly sticky. This stuff takes several days to dry. It may not be the right solution for you if you're short on time.

[turbo2001rt]

Great diagram! So when you pour in the sealant, do you put the cells completely in the mix or leave them partially out? Guess that is the part i am getting confused on. When on the yard stick some of the cells will be sticking out or do you go back later and push them in all the way?

[mdmiller1]

Position everything, including the cells, then pour. I poured about 3/4 of what I had mixed before it got up about half way on the cell, then I removed the yardstick. Let gravity work. Just wait, the cell will settle down into the sealant. Add more sealant at the low edge next to the tape dam which will force the sealant to flow out the opposite end eventually if you are patient. No rush, you've got time. Go slow, have a beer. As you are starting to see it flow toward the 3/4 point on the cell or so, remove the 2x4, now the panel is flat. Let the sealant continue to flow flat and gently push on the cell to seat it on down into the sealant, the last remaining air should come out the high edge and there should be no bubbles. But push Gently. I had the very thin 300 micron cells. Just don't get freaked out that everything is going to setup and is drying so fast you won't get done, because it won't. Take your time, go slow. What is the work time of the material when thinned? I'm not completely sure, but working in my basement from my experience I would guess about 4-5 hours, maybe more. What I didn't do consistently and I wish I had, was on day 2 or 3 or 4, if any of the cell edges seem to be "not under" the sealant, like they floated, pour just a bit of additional around the perimeter of the cell.

[turbo2001rt]

Great stuff. Gonna try this out very soon. I will get pics and details on methods I used. Thanks again!

[turbo2001rt]

Any updates on this? I would like to see how these turned out.