So I decided I had to use polycarbonate or acrylic sheet for the job. I heard stories about acrylic sheets melting in heat, solar cells getting destroyed by moisture etc. But I still decided to go ahead with it because it was the simplest, strongest and safest encapsulation I could think of.
The panel cost me around $35 to pack 22 3"x6" cells (.5V x 3A x 22 = 33W). The whole setup can be folded and connected in different ways to charge Li-Ion, SLA or NiMH Battery packs.
Step 1: Things needed
Optix Acrylic sheet: $28 (32x44inch sheet) cut into 4 - 16x8 sheet and one 1 16x12 sheet. Picked this one up from Lowes and they were kind enough to cut it for free. Thanks Lowes!
Silicone sealant - $6 (This one is from GE and is flexible, clear and cures in 24 hrs)
Rubber electrical tape (optional).
Small 3/8" tile spacers ($2 for a pack of 100).
Step 2: Solder the cells
Tab them and then connect them top o bottom, 4 cells in a line. Then solder both the ends with bus wire and attach 2 connecting wires. The picture has more cells since i soldered more cells to use the available space. But you can decide to make this for 4 cells or 6 cells or 8 cells. However, if you make the panels longer, you risk the fact that the acrylic sheet may become too flexible and that may break the cells.
Step 3: Encapsulate the cells
Then put some tile spacers. I used 3/8" spacers. I put them so that any direct pressure on the cover doesnt crack the cells.
Follow these steps:
1. Place silicone at the back of the cells and stick them to Acrylic sheet.
2. Place tile spacers.
3. Put generous dose of silicone at the edge of the acrylic sheet. Then take the upper sheet and stick over the cells.
Thats it! Let the silicone dry and the panel is ready .
Each cell produces about 2V and in the best case up to 3A of current. (6W of power).
Step 4: Testing the panels
the panels were producing close to 8.5 volts but they are connected to a battery which is at 6.3 V. So the battery drags the panel voltage down to about 6.3 volts. However, the panels continue to put about .3A of current into the battery thereby raising the battery voltage gradually. In about half hour battery voltage and gone up to 7V. Once the panels were taken off, battery went back to about 6.4 or 6.5V but it did get some charge.
You have to be careful not let the battery voltage go over 7.2-7.5V because it can damage the batteries permanently.
Another good idea would to cover all the edges of the solar panel with regular electrical insulation tape. Tape the sides with 2-3 layers to provide it a neat finish and added protection.
Next step for me is to design a charge controller for the panels. I have ordered some from eBay and will let you know which worked well.