materials and assembly procedures … Spring 2014

Materials

Solar PV Cells

4 (to cover breakage) - Si poly-crystalline, 150 x 80 mm (3” x 6”), cut into ¼ size cells (40 x 75 mm), 12 pieces (12 x .5V = 6 V), ¼ cell = .9 A.

Si Caulk (100%)

One tube, (GE Silicone1) clear Si caulk.

One 9” x 12” picture frame

(Try a $1.00 store) includes frame, glass & backing board.

Solder, ribbon, wire and tools

Kester brand, elec. solder – rosin core; Weller brand 40W soldering iron; tabbing ribbon (.05mm x 1.5 mm thick) tinned copper; wire stripper; scissors; razor knife; caulk gun; elec. tape; red & blue insulated 16 AWG wire; diamond cutting wheel (Dremel type); stiff cardboard, cut for scoring the PV cells (40, 75mm); 2 - 1/8” thick plexiglass pcs (3” x 6”) for breaking the scored PV cells; an electrical multi-meter for testing the voltage and amperage of each string.

Procedure

Cut the full size (3” x 6”) Si cells into ¼ pieces (40 x 75mm), using the cardboard guide and the diamond cutting wheel, to score the cells. You may need to remove the ribbon already soldered to the cell, and cut one direction at a time. The important aspect is to keep the soldering spot in the same position for each cell. (middle on front [neg] side, with one pad on the back [pos] side). This is to align the cells into equal size ‘strings’ (4 cells x 3 strings = 12 cells), some may break unevenly during scoring or breaking along the score line. (You may also use cells already broken, making sure the soldering spots are aligned correctly). After scoring the cell in one direction with the guide and diamond cutting wheel (5 or 6 times across should be enough, your pressure will determine this), then align the score mark on the edge of and on top of a piece of plexi. Then place the other plexi piece on top of the scored cell and using the edge of the table, allow the top plexi to break the cell along the scored mark. This may take a few times to get correctly, and why we have extra PV cells. Next, score and break the other measure, using the cardboard guide, the diamond cutting wheel and plexi pieces. We do need 12 pieces of cut Si PV cells, each cell is .5V, the size determines the amperage (1/4 cell = .9 A). The finished cell charger is 6V x .9A =5W, rated.

Next we will solder the cells in a series connection, Neg (front side) to the Pos (back side), which adds the voltage together (a parallel connection, pos to pos, and neg to neg, adds the amperage), using the tabbing ribbon, leaving only 1/16 “ between each cell. Each string will have 4 - ¼ cells, 3 strings x 4 cells = 12 cut cells in all. The ribbon is soldered to the front solder strip with enough extra ribbon to meet the solder pad on the back of the next cut cell in the string. Heat the solder pad or strip with the iron and apply a small bit of solder, spreading it flat. Then hold the ribbon in place and slowly pull the iron along the ribbon and watch the heat transfer to the solder on the strip, melting, and as you remove the iron the ribbon is attached. (You will notice that the ribbon does heat up as you apply the iron, try not to over-heat the strip or pad). Repeat for each cell in each string. We will have 3 strings, each with a ribbon from both ends (one neg [front] and one pos [back]), for our final soldering with all 12 cells in a series connection. We will test the output in full sun (if available) with the multi-meter. Each string should be 2V and .9A, (rated), so we are checking that each string has the same output.

The picture frame is opened from the rear and the backing cardboard removed, marking the space for the 3 strings so the frame will not hit or interfere, and there will be room for a 16AWG wire to fit inside the frame edge. The 3 strings of 4 – ¼ cells are placed onto the inside of the backing board, and a bead of 100% Si caulk is applied across the back of each cut cell, and the full string is then ‘gently’ placed in position and pressed down ‘gently’ onto the backing board. (If there is breakage at this point, we can remove and replace a cell if required). After the 3 strings are placed (each string has pos and neg ends alternating with the next string end, for series connection with solder and ribbon between each string), and caulk applied, the ribbon is cut to connect each string to the next on both ends (so, neg to pos, and pos to neg) and a series connection is accomplished with the solder and iron. A strip of cardboard ¼ “ wide is inserted between each string as well as on all 4 sides of the cells, and caulk added to secure the strips to the backing board. This will allow the glass to touch the strips, so the cells will not be in contact with the glass. Make sure the strips are high enough to accomplish this. Before the final wiring and closure, we will test the entire PV module with the multi-meter, there should be approx. 6V and the .9A for the rated module output.

The framing is checked for a tight fit, with no interference from the glass, cells and frame. The two ribbon ends (one pos and one neg), will have a coordinated 16 AWG wire (red for pos, and blue for neg), soldered to the ribbon and one wire will be placed along the edge of the frame, inside, and come to the other end of the module (so both wires will be on the same end). The two wires will then be put through a hole in the backing board and caulk applied in the hole as well as along the wire inside the frame edge, to hold that in place. The inside perimeter of the frame should be caulked before the backing board is sealed with the pieces designed for closure of the backing board. The PV is thicker than a picture or certificate would be, so there will be a tight fit. The elec. tape (or masking / duct tape) can be applied for extra secure fitting and the multi-meter used again for a final test. As the red and blue wires are both coming out through the backing board, they should have an equal length, approx. 12”. The wires will be matched to a plug from the required phone charger (each phone may have a different plug) and the ph can be charged from a window in the sun or outside facing the sun. We have found that most phones may be charged with this PV module, except an apple I-phone that may require a DC charger plug from Apple …