How hard is it to build a solar panel? How long would it take to build one? More importantly, can we build a solar panel that is useful in real life?
To find out, I ordered almost 1 KW of solar cells. It came in 12 packages of 43 cells each (12×43 = 516 cells). Each cell is rated at 1.8 Watts (0.5 Volts at 3.6 Amps). So the total power is 928.8 Watts (1.8 x 516). Since this was our first project, I figured most of these cells would probably break and I didn’t want to spend a lot of money for experimentation. I bought a kit that included the tabbing wire, the bus wire, the flux pen, and a diode. All this was $225 with free shipping from ebay (MLSolar), mostly because these were cosmetic rejects with less than 10% breakage. Each cell measures 3 inches by 6 inches.
I received the package in a short period of time. The cells were very carefully packaged. When I opened one of them to see one of the cells, I could see why. These cells were very thin and felt very brittle. You really could not put any force on them. I thought at least some of them would break while soldering the tabs on them.
Because we are building our own solar panel, we can organize the cells any which way we want. Because this was our first solar panel, we wanted to build a small panel. We decided on building three strings of 12 cells each and connect them in series. Each string produces 6 Volts (DC) for a total of 18 Volts. The power rating would be 36 x 1.8 = 64.8 Watts.
Tabbing the Cells
The tabbing wire and the bus wire are both flat ribbon style wires, the only difference being the width. The bus wire is wider.
We needed two tabbing wires for each cell. The length of the wires will need to be twice the height (2 x 3 inch) plus the distance between each cell (maybe quarter of an inch). Total of 24 tabbing wires for the first string.
The front of each cell is the negative and the back side is the positive. So in building the string, cells will be wired such that the front of each cell will be connected to the back of the next cell. And we will use the tabbing wire to accomplish this task.
The question is: do we start by soldering the front sides of the cells or the back sides? Because it is harder to solder to the front side, we started soldering the tabbing wires to the front of the cells. Two tabbing wires are soldered on the front of each cell of the string.
It helps to put a little bit of soldier on the tabbing wire before soldering it onto the cell. When I tried it, I was surprised how easy it was to do this. But shortly after that, I realized the first big mistake. Cells are very thin and any heat applied on this side is almost 100 percent transferred to the back side. The cell was on a painted surface and the cell got stock to the board underneath it. From then on, I put two boards side by side and made sure that there was nothing directly under the line that I was soldering on.
In the picture above you can see the two boards closely spaced together and the cell positioned above it. If the cell gets stuck to the board underneath it, it is very hard to get it loose without breaking it. Notice that one of the tabbing wires is already soldered on, and I am working on the second one.
Building the String
After 12 cells are tabbed as explained above, line them up on a board as shown in the picture below face down. You can see that there are three spots to solder the tabbing wire of the previous cell (on the left in the picture).
Duct tape comes handy at this point. Cut a long enough duct tape to span the length of the string and carefully tape the duct tape at the center of each cell. The duct tape fixes the cell positions so that they don’t move and makes the soldering of the tabbing wire much easier. Again make sure that there is nothing underneath the cells when soldering the wires.
The picture above shows two more cells are tabbed and ready to go. Five cells are already tabbed and lined up in the center of the board.
Once all the tabbing wires are soldered on, cut a long enough bus wire and connect two wires in parallel. After the other two strings are built, solder the strings together with the bus wires such that voltages will add up. Here is how it looked like after this step.
After I built the first string, I taped it onto a window and measured the voltage of the string. Although it was not in direct sun light, it still produced more than 6 Volts.
The most difficult part of building a solar panel is weatherizing it. The panel I built can be used indoors, or if mounted outdoors it would have to be sheltered from rain, etc. Or you could put it outside only during the summer and move it indoors during the winter.
I hang the solar panel as if it was a picture on the garage wall next to the electric meter. Pair of wires carry the power into the garage. A close up picture below shows that at least one of the cells already broke in the middle, and some of the tabbing wires are coming loose. In spite of these problems, the panel is still producing power (closer to about 40 Watts I think at full sun light).
Using the Solar Power
I bought a 400 Watt Power Inverter from Harbor Freight. It takes 12 DC Volts in and produces 120 AC line voltage. The only problem with this inverter was the fan noise. The tiny fan was spinning so fast that it was making a high pitched whining noise. I opened it up and disconnected the tiny fan. I hooked up two big-mama 12 Volts PC fans in series such that each one was getting 6 Volts DC. This allowed adequate ventilation and virtually no audible noise.
UPDATE 08/29/2013: This inverter from Harbor Freight is not efficient at all and most of the power produced from the solar panel goes to operate the inverter. I disconnected the inverter. Currently using the 12 Volts DC from the battery directly.
I forgot to mention that MLSolar also included a diode in the package. I connected the solar panel to the car battery with the diode such that the current can only go into the battery. The orange extension cord carries the power to a power strip for general use in the garage.
At first I connected a number of gadgets to the power strip but soon I realized that only a few hours of afternoon sun was not enough to power all that stuff. Also remember the cloudy days. (: I have a battery charger that I plug in to the wall if needed to charge the car battery. What would be nice is if I had some kind of circuit that would automatically use the power from the utility company when there is not enough sun shine.
Also something else that would be nice is to know how much power is generated from the panel.
Ultimately I would like to build a large enough panel that will power the refrigerator in the garage.