DIY Solar Panel Build – Part 2 of 4

Part 2 – Cutting the Acrylic Front and Adding Tabbing Wire to the Solar Cells

Step 5 – Cutting the acrylic front

I purchased a 24 x 48 x 3/16 sheet of acrylic to cover the front of the frame. It was shipped with protective paper on both sides which I kept intact during the cutting and drilling process. Cutting is relatively easy if you use the right blade and don’t rush the process. I used an 80T blade in my table-saw and set the blade to a height of about ¾ inch. I cut the sheet to 21 ½ x 46 inches with relative ease.
Acrylic Solar Panel Cover
Plastic Drill Bit
Plastic Drill Bit Close Up

To get the mounting holes in the right position I drew lines 3/8 inch from, and parallel to, each edge and one line across the center where the panel divider sits. I then marked hole positions every 5 to 6 inches.

Drilling the holes is trickier than cutting with a saw. I used a special 3/16 inch drill bit for plastics. It’s the one on the right in the photos. It’s important that the acrylic is well clamped close to where the holes are to be drilled and that the drilling is performed at a very low drill speed. Also, it is necessary to slow the drill further just as the bit is about to break through the bottom of the material. This is where the drill can snatch and crack the material.

To countersink the holes I used a 45 degree reamer that fitted in my drill. I lifted the protective paper so I could monitor the reaming process better. Reaming was easier than drilling with little risk of damage to the acrylic. As I reamed I would periodically drop in a screw and check for depth. Once the top of the screw was flush with the top surface I was done and moved on to the next hole.

With all the holes drilled and reamed I then placed the cover on the frame and marked the positions of the holes on the frame. Using a 1/8 inch bit I drilled pilot holes in the frame so the #8 screws would be easier to screw in without danger of splitting the wood or, worse still, slipping with the screwdriver and damaging the acrylic.

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Step 6 – Preparing the solar cells for assembly into the panel

This is perhaps the trickiest part of the whole project. The solar cells are fragile and there are plenty of opportunities to screw up and damage cells. If you are working on a single cell it is no big deal but when you are working on strings and the cell in the center of the string is damaged then there is more work involved in fixing the problem, especially if the string is already glued into the panel. Care is essential and the axiom less haste more speed definitely applies to this part of the project.

Solar CellsThe top side of each cell is blue and is the basic crystalline structure of the cell. There are two bus strips across each cell to which are attached several much narrower lengthwise conducting strips forming a giant mesh that electrically connects all parts of the silicon cell structure while exposing as much of the silicon structure to sunlight as possible. This is the negative side of the cell. The back side is completely coated with conducting material and forms the positive side of the cell. No need here to create an elaborate mesh of conducting wires since this is the non working side of the cell. The Evergreen cells have 6 attachment points on the back to make the electrical connection.

Solar Cell With Tab WiresAdding tabbing wires to each cell – Since the cells are connected in series the negative bus strips on the top of each cell are connected to the positive attachment points on the bottom of the neighboring cell. Narrow tabbing wires with a length equal to two cell widths are used to make the connection. There are two tab wires per cell. So for 36 cells I cut 72 tab wires each approximately 6 3/8 inch long (2 x 3 3/16 inches). Don’t worry about the fact that there is a ¼ inch space between neighboring cells. The positive side attachment points do not extend to the edge of the cell.

Soldering iron wattage and tip size – I experimented a lot to find the right iron wattage and tip size for this project. I’d seen recommended wattages of 25 to 40 on the web. I tried my Radioshack dual 15 – 30 Watt iron but found I could not generate enough heat to make good joints. I then bought and tried a Weller 40 watt iron with a 1/8 inch screwdriver tip. It had plenty of power but tended to leave some burn marks on the front of the cells adjacent to the bus strips. In the end I got my hands on a Weller soldering station with adjustable temperature and finally settled on a temperature of 750F and a 1/8 inch screwdriver tip.

Soldering the tabbing wires to the negative bus strips – This takes a little practice to get right so if you have some broken cells hanging around practice on those first. The basic steps are:

1. Apply flux to the bus strips on the cell.

2. Lay a tab wire directly over a bus strip with one end flush with the edge of the cell. Use small weights if necessary to hold the ends of the strip down.

3. Apply a small amount of solder to the soldering iron tip.

4. Starting from the edge of the cell with the overhanging bus wire, apply the iron directly on top of the bus wire and, as soon as solder starts to flow, move the iron along the bus wire toward the far edge of the cell. Make sure solder continues to flow as the iron is moved. If the flow stops immediately lift the iron, apply more solder to the iron, and commence soldering where you left off. With practice you should be able to go from end to end with one smooth motion without lifting the iron. I will put together a video sometime soon to show exactly how this is done.

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Step 7 – Adding tab wires to the end cells

End Solar Cell With Tab WiresMy design required 6 rows of 6 cells. One end of each row would have the negative wires already attached (see previous step) but the other end needed the positive wires. So I took 6 cells with tab wires installed, flipped them over and added the positive tab wires making sure that the wire ends were pointing in the opposite direction to the negative wires.

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Step 8 – Making the solar cell strings

Solder Solar Cells In SeriesTo help create strings of cells with good alignment I drew an outline of the cells on paper complete with the ¼ inch gaps. I then laid 1 double tabbed cell (positive and negative wires attached) and 5 single tabbed cells (negative wires only) upside down on the outline with the negative tabs oriented above the positive attachment points. While keeping the cells in position I then soldered the tabs working from one end of the string to the other. When finished I slid the string on to another work surface and repeated the process with another set of cells. I continued in this fashion until all 6 strings were assembled.

Voltage Output Of Solar Cell StringI thought that this was perhaps a good time to see if the strings would work. I didn’t fancy gluing them into the panel only to find I had a bad cell or two to deal with. To do the tests I needed to flip the cells over and place them in direct sunlight. Since the strings were relatively short I simply grabbed the tab wires at each end and lifted and flipped the assembly over. The tab wires were plenty strong enough. All of the strings produced a healthy 3V plus so I felt pretty good that I’d done a good job to this point.

 

For the best guide on how to build a solar panel with really great videos, plus a complete list of where to buy solar cells and all the tools required Click Here. Super homemade wind turbine plans included too.

Part 3 – Installing the Solar Cells into the Panel Frame