Failed Solar Panel -
Well maybe a better description is a panel that was not as elegant as I wanted.
In building the solar system for the house, I wanted to keep costs down so for my second endeavor I purchased cells on e-bay that did not have tabs attached. This was a savings and I felt sure that the assembly would only involve some additional steps and that I could build one as successfully as I did the first one.
My design was to lay out the cells three across in parallel and then continue down a piece of plastic peg board in series. I had purchased enough cells to make three 35 watt panels that could be interconnected on the mounting board. (well it sounded good at the time)
I set up the back panel with a positive and negative buss using copper foil. The idea was to run additional foil for each row and then use short lengths of foil to solder to each cell.
The first problem came when I found that soldering to the cells was not working. Cleaning with an eraser and scraping with a hobby knife did not do the trick. I tried different soldering iron temperatures, smaller solder, a different tip and nothing worked with any degree of reliability. Some would solder and some would not.
At the end of several frustrating hours I had only managed to put a few cells on the board and did not want to look at doing the whole board this way. In addition I had broken a number of cells while I was soldering them. They are very delicate and too much heat for too long will fracture them.
Therefore, before I go much further, it is time for a mid-course correction and rethink the project…… The plastic peg board was chosen because it was light and should reduce the weight of the panels. Good idea but I did not consider that I would be soldering on the board and it would melt. The copper foil to connect the solar cells was a bad idea. Therefore, I ordered some foil on e-bay that was intended to connect solar cells.
When the new foil arrived I found it does make it easier to solder the cells together. However, it is far from fool proof. I would say that the skill level in soldering to the cells is that of an expert. I was able to solder the foil to the front of the cells in about 90% of the cases but often it required several attempts. Finally, I had to use paste flux and this causes another problem in cleaning the excess from the face of the cell. The use of cells without tabs is much more difficult than I expected and I will not attempt to make any future panels using un-tabbed cells. It takes too long and the complexity factor is too high.
As noted in the picture above, I found that my original construction methods for the second panel is not going to work out. The original calculation called for very close spacing of the cells and this is just not possible. I have therefore gone to placing them in series strings and then connecting them in parallel. The result uses two different orientations and is not at all aesthetically pleasing. Functional perhaps, but it sure lacks the professional look I wanted.
When I completed the panel it was truly a Rube Goldberg and I was far from pleased with the end result. The solder joints were not solid and it took multiple hours of troubleshooting to finally get the panel to where it would work at all.
I have built a box, similar to the boxes I used with the other solar panels, that will house what I now call the “failed panel”. The peg board was screwed in place because any movement would doubtless break another solder joint or a solar cell. The edges are made from 1X2’s, just as the others were made and the back is made of half inch plywood. I had run out of paint so a second can of white exterior was purchased at Home Depot to finish the job.
Once the pegboard was set in place I again spent a few hours tracing down broken solder tabs and then re-soldering. This was without a doubt the biggest headache I have had to encounter during the project.
I wired all three sections in parallel and have been able to get a bit over 2 amps at 17 volts DC….. good enough to call it a 35 watt panel. It is however, half of what I had expected because of the number of broken cells I either could not use or had to jump around.
While it does not look very professional and clearly is prone to reliability problems, I was able to salvage an otherwise throw-away panel. This will keep the overall system costs down but I will always have doubts about this panel when I take measurements.
Final assembly after it was repaired and working
Update July 1, 2008
The failed solar panel lived up to my expectations and failed. Several cells cracked and 6 of the solder tabs broke away from the solar cells. This required removing the panel from the roof, troubleshooting to find the bad connections, re-soldering them and making jumpers for the broken cells. In the end I was able to get about 17 volts at 1.9 amps out of it but I did discover an interesting point regarding the actual cells.
I had expected the aperture for maximum output to be relatively narrow and was surprised to see that it is over 35 degrees. While this is an approximation, because I was not taking a precise measurement, it nonetheless was interesting as it shows that by angling solar arrays to cover the suns progression across the sky it should be possible to extend the solar day. For me this is very good news because I loose a good deal of my solar day due to shade from a neighbors tree. This may be a way of improving my system output.
By that I mean that while you will compromise the peak current that is available when the sun is at your zenith, you are able to catch more sun in the morning and more in the afternoon. This should enhance your total daily output.
Once I have the micro-controller up and working I can validate this theory and will post the results.
Herb & Barbara our interests and family