As the title says this instructable demonstrates how to solder individual solar cells together in preparation for building a solar panel.
First i need to give a few disclaimers:
1. Soldering irons are hot and will burn you if you are not careful. If you do not know how to solder you will need to learn how to first before attempting this project.
2. You need to have and understanding of basic electricity before attempting to work with solar panels. If you do not have this understanding have some one help you that does.
3. Tab wire and solar cells have sharp edges, they can cut you, be careful.
Now that the warnings are out of the way lets look at the items you will need. In the 2 pictures the items have a description of what each item is, but hear is also a list:
1.Soldering iron, there are many soldering irons out there but these are the ones I recommend:
A. Budget iron, it will get the job done but there are better and easier irons to use. Found Here
B. Mid range, its a little bulky but heavy duty and works well. Found Here
C. Top line, this is my most recommended. This one can be used all day and never quit. Found Here
2. Soldering iron stand
3. 2mm tabbing wire- pre solder coated. Found Here
4. 5mm tabbing wire- pre solder coated. Found Here
5. scissors. Found Here
6. ruler. Found Here
7. holding tool. Found Here
8. solder pen, Found Here
9. solder paste- only used to tin the solder iron. Found Here
10. solder wire- only used to tin the solder iron. Found Here
11. solar cells, this is an example of the kind of cells i work with. Found Here
12. electrical tape - not pictured. Found Here
Some of these components can be purchased in packages. Take some time and decide what size of panel or number of panels you are going to build and try to find a package with the amount of components you will need. Here are some examples: Package 1Package 2Package 3
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Step 1: Jigs
After you have all the items needed i recommend making 2 jigs, this will make things easier and faster.
The first jig is to hold the solar cells while soldering. I made this from a piece of scrap wood and some small nails. I laid out a few of the solar cells on the board and marked places to put the nails. Make sure you put the nails in places that when you are soldering that they do not get in the way of your solder iron. Make sure that the solar cells can easily slide in and out of your nails, solar cells are very brittle and break easily. The board i am using is large enough to put 4 solar cells in a row on it.
The second jig is used to make the tabbing wires for the solar cells. It is a piece of 3/8" x 6" black pipe. The outside diameter of a 3/8 pipe is a little more than 1/2". When using 1" solar cells i use tab wires that are 1 3/4" long. When you wrap the wire around the 3/8" pipe it comes out close enough to what I need(1/2"pipe o.d. x 3.14= 1.57"+ any slack deviations). I milled a slot down one side so one of the scissor blades could fit through it. At the end closest to the drill I welded a small piece of round stock in it that will fit into the drill chuck. I use the drill to wind the 2mm tab wire around it, then I use the scissors and cut the wire through the slot. You need to hold or tape the tab wire when cutting or it will unwind and make the wrong size tab wires. After cutting the tab wires you need to flatten them out. See the pictures for more information.
When setting up a work area I highly recommend good ventilation. When soldering you will make some smoke and fumes, you do not want to breath these in. I used some old computer fans, a circuit board soldering stand, dryer vent duct, cardboard, and duct tape. Look at the captions on the pictures.
Step 2: Soldering Tab Wires Onto the Front Side
After you have got your work area setup, and tab wires made you are ready to start soldering. The soldering iron i use is adjustable from 10-50 watts, I have it set for 40 watts. Be sure that your iron tip is clean and tinned properly, a dirty tip will not work well and might contaminate what you are working on.
You see in the picture there are white stripes from top to bottom. These are where you will attach your tabbing wires. You can see in the close up picture that the tab wire is not completely at the top of the solar cell. This is just to be sure it does not contact the cell that will be above it.
1. First you need to use the flux pen. put a light coating of flux on that white stripe. You see the darker blue areas, that is flux that flowed off the white stripe.
2. Lay your tab wire on this stripe.
3. Using a holding tool (or something similar) hold the tab wire in place. don't press to hard, you might crack the solar cell under the tab wire.
4. Moving from top to bottom, use your soldering iron and start soldering the tab wire down. Don't let your iron set in one place to long, you will burn the solar cell. You will need to move your holding tool around as you move the iron down, don't let the tab wire move. Hold the tab wire down until the solder cools.
5. Repeat for all tab wires across the cell.
Step 3: Connecting Cells
After you have the number of cells you need with the tab wires on them it is time to start connecting them.
1. Flip over all the cells that need to be connected, and put flux on the white areas.
2. Lay the tab wires from the top cell onto the back of the bottom cell. All cells need to connected front of one cell, to the back of the next. This puts them in series.
3. Solder the connections.
4. Repeat until you have as many as you need in a string.
These cells need to be connected in series because each cell produces 1/2 a volt DC. If you are making 12 volt panels you need 36 cells in series. 36 cells at 1/2 a volt = 18 volts, this is about what you should have when testing with a multimeter. This is a "no load" reading. When these cells are put under a load, such as charging a battery, the voltage should drop to 14-16 volts. This 14-16volts are needed to charge a battery in the same way a car produces 14-16 volts to charge the 12 volt battery.
Step 4: Connecting Strings
Depending on the size of the panel you are building you will probably need to use short strings of cells to get all 36 cell connected.
Now I will show how to connect 2 strings together.
As I stared before, cells need to be connected front side to back side. On the end of the string you need the 2mm tab wires protruding from the ends of the 2 strings you need to join. You can use shorter tab wires for this if you want to.
1. Add tab wires as needed to the end of the strings.
2. Lay the strings next to each other with a small space in between them. I would recommend doing this on the glass you will be using for the solar panel, or on something that these cells can be kept on until they are ready to be put into a panel.
3. Measure out the length you need for the buss wire. Then cut the 5mm buss wire to your measurement.
4. Use the flux pen on the places that the buss will be attached. You only need to put flux on the tab wires, not both tab and buss wires.
5. Line up your buss wire on one end of the tab wires. The buss wire does not need to stick out over the end, just make it even. Keep it close to the cells, but do not touch them.
6. Work your way from the first one you soldered, keep the buss wire flat as you move.
7. After you finish soldering, cut off any of the wire sticking out past the ends of the tab wires and the buss wire.
In the picture were the extra wire has been trimmed off you see an extra tab wire on the left string. I put that tab wire on there to test the cells to be sure they were connected. I stated earlier that cells produce 1/2 a volt, so 4 cells should be 2 volts. I was sitting under a florescent light when I tested these cells. I got a reading of 1.2 volts. That is very good since most cells will not work unless they are exposed to real sunlight.
Remember when testing and connecting the wires that will run out of the panel the top side of the cell is negative, and the bottom is positive.
Step 5: Connection on the End of a String
In addition to connecting strings you will also need to put a buss wire on each end of your cells (cell 1, and 36). This is done in the same way as connecting 2 strings, but you are only connecting the 3 tab wires on that one end cell (1 and 36). But on one end of the buss wire I leave a little extra hanging over. I do this so that when I add a copper wire that will run out of the panel I can fold the buss wire over the copper wire and solder it together, making a stronger joint.
This buss wire can be done before or after connecting strings, that is up to you.
Step 6: Broken Solar Cells
At some point you will have broken cells. Maybe from shipping, maybe from working with them, but at some point you will have some. As long as the places you need to solder to are intact these cells can still be used. Just be sure that tab wires do not touch through a broken cell. this string is made up of all broken cells held together with packaging tape. The little pieces that broke off the edges can not be used, and you can not solder cells back together. I save all good pieces of broken cells and put them together, someday I will have enough to make a whole panel. Broken cells will produce less since there are pieces missing, but they do produce something.