Solar cell

A solar cell converts sunlight into electricity. There is much information on the web on solar cells to find, but I do not know much about us. There are even sites that describe how you can make a solar cell. But that is something nice for once, but certainly not an option when making large solar panels.

The solar cells that I have found all have a voltage of about 0.5 volts but the amperage is different every time. The mostly sold solar cell on ebay is that of Evergreen. A number of suppliers on ebay claim that these cells are not suitable for DIY, but I fortunately only read them after I had already ordered :-) Of course, these providers have the right cells for DIY, duh.

Purchase

As I said my first set of cells were purchased on ebay. The first 100 cells I bought for the price of 180 dollars. These were A-cells, according to the supplier cells with small defects. I have chosen these because I do not know what the result of this project will be so maybe it turns in a complete flop and then it is good I bought the cheaper cells.

Pakje met 100 cellen van EbayHere is a photo of the first packet cells. It is smaller than I had expected. The cells are packaged in two "blocks" of 50 cells and 10 cells (bonus). It is well protected package and I do not believe that the cells have suffered from the transportation. Furthermore, there was a flux pen, some (silver) tin and not unimportant bus wires.

The cells are 0.2 mm (yes 200 umeter) thick. This is very thin and they are very fragile. A cell is 81 x 150 mm wide and weighs almost nothing. It feels and looks very much like tin-plate. It is a (very small) bit flexible and very fragile. It will break or crack very easily.

Below a photo of a solar cell on top of 50 eurocents coin. It shows how thin the cell is:

Solar cell on top of 50 eurocents

Soldering

My first solar cells arrived yesterday (May 14, 2009). First I tried to solder a tab wire to the cell, but I came immediately into trouble because my soldering iron is only 15 watts. Fine device for a little simple electronics soldering, but not suitable for soldering of solar cells. Today I borrowed a Weller at work and will try this .... By the way; the first cell is broken in little pieces during the testing of soldering. So more details on the soldering.

In my work I spoke with a colleague who does the soldering for all projects. In the beginning it didn't became all much clearer, but that was partly because I do not know exactly what I wanted. Eventually it became more clear to me and now I think I understand pretty well what to do. First this: I come from the S-39 era. Most know it, but some may not. S-39 is a flux, but it is very acid. It is not only unhealthy to use, but everything what you soldered with it gets reduced in life expectancy. It eats everything away everything in time. Of course I am familiar with solder with flux in it. I believe that we formerly called resin, but the details I do not know. In addition, since some time lead-free solder is used. Not for test projects, but within our company for what is sold to customers. This is because lead is bad for nature and has become forbidden to use. For my project I can still use lead solder (even if it is bad for nature and a bit for me). Let me make one thing clear, I am building solar panels because I like and hope that a "reasonable" investment, but I'm certainly not a green guy. The solder what came with my package from ebay also got silver, but only 0.7%. It is in this case (as I understood from my colleagues) a lead replacement for an alloy to make. The silver in this tin does not cause less electical resistance or a more pure connection. This is possible with silver tin, but then you are talking about a much higher content of silver and solder that will be much more expensive. By the way, this tin (with high silver percentage) is virtually not available for the normal man. The disadvantage of the supplied solder is that a slightly higher temperature was needed, so I will stick to lead solder. 

It took a while before I realized how to get the flux out of the pen ;-) You should press the point a few times and then it will start to run. The flux is working fine. As I have said I have little experience with soldering so I just started. The aim is to solder a tabwire of 15 cm (8 cm in front + rear at about 7 cm) to the front of the cell. Then this wire is soldered on the back of the next cell to create a series connection.

Zonnecel, wires en resultaat.

Above a photo of a cell with some tabwires. At the right is the result. Let me say that this result was only achieved after many trials, but I am well satisfied with it.

The tabwire is a flat wire (of what I do not know, copper or something) which already contains (silver) solder. The idea is that the flux is put on the cell flux (on the track where the tabwire is to be soldered) and the solder the tabwire onto the cell. This will work fine in production environments (factories), but I am not so successful. I needed a lot more solder to create a good connection. The first thing I've tried is extra solder on the tabwire to and then the cell soldering. That was not good, but mainly because I did not know how to use the flux pen. In addition I tried that method with my own simple bolt, so this method might work fine with better equipment. After this trial I tried to put solder to the track of the cell and then solder the tabwire to it. First, flux it and then put solder it. Then solder the tabwire on it. That worked well, but a number of findings. I used a glass substrate, which absorbed the heat. So for the tabwire soldering I had a 400 degrees setting on the bolt. While the tinning of the cell only needs 360. Indeed, if I used 400 then the track (which is like a white silver appearance) located on the cell is burnt away, and then you have a problem. But this worked well and I have the first cell made so looks like a reasonable method of working.

As I went on with my project, it became increasingly easier and ultimately I did the following: I have made a toolbar. See the pilot for details thereof. At this bar I place a number of cells. The bolt is at a temperature of 350 degrees and never higher. In my left hand solder (I use solder with flux in it) and in the right soldering iron. Then I go from right to left and I place solder on the cells. I leave a lot of solder behind and it doesn't look really nice, but it is fast and ultimately it is very good. In the beginning I put flux on the cell before I started but I stopped that because it is not necessary and it takes time to do, and I don't know  if this flux needs cleaning afterwards. If both tracks are with solder I will place the tabwires. I start at about 1 cm from the end of the tabwire and solder it on the cell. Sometimes I do a little solder to the bolt so it starts to flow easier. If the wire is stuck I pull it and hold it just above the cell. Then I pull the bolt slowly over the wire from right to left starting at about 1 cm from the side. If there is enough solder on the cell is then you can process without additional solder. In the beginning I tried to put the solder on the cell as beautiful and clean as possible but that is not necessary and it only costs additional time and effort. After soldering the tabwire to the cell eerything smooths out is beautiful to see.