DIY Solar Panel FAQ

 

3. HOW TO CONNECT solar cells (series, parallel, combination, etc., use of tabbing wires, bus wires, flux)

Q3.1: How to solder cells together?

Q3.2: How to build a 100 watt solar panel?

Q3.3: I'm interested in making an array for my RV. I'm thinking that two sets of 24 cells should generate 12 volts at 2x42x1.75=84 watts, is this correct? When does Ďno tabsí mean? Is this where I would solder the wires? What type of wire? Do I affix these to plywood and over with glass?

Q3.4: How can I solder them to make a small panel? Which is the positive and which is the negative?

Q3.5: How much rosin and solder would I need?

Q3.6: I am trying to tab these cells and am having a hard time getting lead free silver solder to stick to the contacts on back. Here is my process: I tin the ribbon with silver solder. I lightly scratch off the coating on the 6 contact points on the back of the pv cell. I then lightly rub each contact with a flux rosin pen. Then I put the tinned side down to the contacts, and at each of the six contact points add more silver solder. I am using a 30 watt soldering pen. Any suggestions?

Q3.7: Do you have to scratch the film off the tabs before soldering or do you solder as is?

Q3.8: What kind of soldering iron should I use?

Q3.9: How long will these cells work? In other words, when I make a panel, for how long will it be serviceable?

Q3.10: I can't get any voltage reading. What am I doing wrong?

Q3.11: How do I connect the cells? What is positive and what is negative? I donít know where to start, and what material do I lay the cells out on?

Q3.12: Should I apply solder to the wire before I place it on the cell? On the videos I saw some do and some do not. I tried first without the solder and it did not come out good. I'm using a 40 watt iron. Do you have any suggestions?

Q3.13: When soldering the cells together (tabbing), do you have to clean the anti-corrosive coating and what do you recommend to do that?

Q3.14: Case: "I have put together a solar array using your solar cells and I was wondering if you could help me solve this problem I am having. I have 16 volt configuration using 30 .5 volt cells in series and two rows of six .5 volt cells in parallel configuration. Can you tell me why I am getting eradic charging. I am thinking that maybe the solar cells are overheating because for the first 30 minutes when the sun makes contact the charging is excellent and fast and then after 30 mins later the charging of the battery becomes terrible very slow like a 1/4 of a volt in 7 hours. Do you have any ideas what can cause this? Please help I have run out of ideas."

Q3.15I cannot get the solder to stick to the back of the cell. Do I need a special soldering rod and what do u recommend.

Q3.16Your literature indicates that 108 cells provide 3.5 amps and 150 cells also provides 3.5 amps? Are the amperage ratings correct?

 

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Q3.1. How to solder cells together??

A: Do you see the two thick white lines (call bus bars) on the surface the solar cell? You apply rosin flux along those bus bars, and lay the tabbing wires on them, and run your soldering iron (90 watt soldering iron recommended) on the surface of the tabbing wires. That will bond the tabbing wires to the solar cell. Please remember that since the size of the solar cells is 3 inches by 6 inches (80 mm x 150 mm to be exact), your tabbing wires should be 6 inches in length. So after the first step of soldering, half of the length of your tabbing wires sticks out of the first solar cells that you already soldered. And the wires that stick out are connected to the BACK side of the next cell. There are six soldering points on the back of the solar cell, 3 on each side. The solder points correspond to the tabbing wires to the solar cell before it. On the back side of these six soldering points, you will need to use solder. Please take a look at free videos on YouTube by typing in 'how to make a solar panel' to learn how that is done.

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Q3.2. How to build a 100 watt solar panel?

A: Typically panels are rated by wattage and sold by dollar per watt. To make a 100 watt solar panel using these cells, you will need 100 / 1.75 (each cell is approximately 1.75 watts) = 57 cells. Based on the voltage and layout requirements, itís better that you make a 72 cell panel. 

Also, cell production quality varies and some cells can have lower power than the standard rated cells. According to Evergreen Solar, 2% of the unsorted cells can have low power, and if you connect all the cells in series, the panel wattage power will be a multiplier of the lowest power cells. Just like the water flow is determined by the narrowest pipe in your whole plumbing system. Before connecting all the cells together on your panel, you need to test each cell and take out the very low power cells. We give our customers 10% more cells than what they paid for, and we think that more than compensates the potential loss of wattage power.

To calculate how many amps you will be getting, divide the wattage figure by voltage. Let's say you use 72 cells to make a panel that's rated 120 watts (finished panels will always be a little less efficient than the single cell's efficiency), and you connect your panels in series and parallel to set your panel's voltage to 17 volts, then the amperage you will be getting is  120 / 17 ~= 7 amps.

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Q3.3: I'm interested in making an array for my RV. I'm thinking that two sets of 24 cells should generate 12 volts at 2x42x1.75=84 watts, is this correct? When does Ďno tabsí mean? Is this where I would solder the wires? What type of wire? Do I affix these to plywood and over with glass?

A: When we say 'no tabs', it means there are no tabbing wires that have been soldered on to the cells. You have to solder the wires yourself. The tabbing wires are simply flat wires. There are two thick white lines on the cell's surface. These two lines are called bus bars, and you solder the tabbing wires on the whole length of the bus bars. The tabs should be about 6 inches long for these solar cells. And you have many of these 6 inch long tabbing wires (we provide them in a roll, you have to cut them). Solder these tabbing wires on the bus bars of ALL of the cells first, then you can solder the other end of the tabbing wires to the bottom of the next solar cell. For details, you can go to Google or YouTube and search for 'how to make a solar panel', and watch free videos on how to do that.

These connected solar cells might be OK to be affixed to plywood, but you need to be absolutely certain that your glass cover etc. They will be able to prevent the solar cells from getting wet. You know water and electricity does not mix well. So you need to seal the panel really well.

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Q3.4: How can I solder them to make a small panel? Which side is the positive and the negative?

A: The front of the solar cells, the blue side that's facing the sun, is negative; the back side, the gray side with 6 soldering points, is positive. What you do is to use the flat tabbing wires, usually copper wires coated with tin, after apply rosin flux on the white main bus bars on the solar cell, and use the solder iron the run through the surface of the bus bar. And the tabbing wires should bond with the solar cells along with the bus bar. Then you use a combination or series and parallel connection to get the desired voltage and wattage. Test each cell and take out the low power cells, prior to string them together.

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Q3.5: How much rosin and solder would I need?

A: You don't need very much rosin and solder. The tabbing wires that we will be offering for free if you purchase our cell kits. You just need to solder these tabbing wires after you apply rosin on the white bus bar lines on the cells first. You could use a little more solder on the back side of cells at the six soldering points.

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Q3.6: I am trying to tab these cells and having a hard time getting lead free silver solder to stick to the contacts on back. Here is my process: I tin the ribbon with silver solder. I lightly scratch off the coating on the 6 contact points on the back of the pv cell. I then lightly rub each contact with a flux rosin pen. Then I put the tinned side down to the contacts, and at each of the six contact points add more silver solder. I am using a 30 watt soldering pen. Any suggestions?

A: You didn't buy the tabbing wires and solder from us, so it's hard to figure out what they are and why they don't work. Our tabbing wires come from Evergreen Solar directly, and they are the same ones that they use to make big panels costing a lot of money. If you buy the tabbing wires from us next week, we will guarantee that they will work. With all that said, we just to continue our tradition of being helpful, you can try solder paste, and get a 95 watt soldering iron set at 734-743 degrees Fahrenheit (for unleaded).

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Q3.7: Do you have to scratch the film off the tabs before soldering or do you solder as is?

A: The two solid lines on the front (blue side, sunny side) of the cells, called bus bars, are both negative. The six dots on the back are positive. You solder tabbing wires onto the bus bars first, and then solder the tabbing wires get solder the back side of the NEXT cell. You daisy chain (series) these cells together. A good order is when you solder the front side of ALL of the cells you want to connect first, then the back side. Cut the wires to about 1/2 foot first (160mm) each.

You do NOT scratch the film off the tabs. If you did, you would have damaged the cells. The whitish material is silver that should not be scratch off. The most you should do is to use a rubber to rub it in case there is any oxidation on the surface of the contacts. Yes, gently rub it if you feel there is a need. Always remember to apply flux before soldering. It's best to soak our tabbing wires in flux liquid for about 6 minutes or so, and then solder. Do not use too much flux so that it makes a mess on the surface of the cells.

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Q3.8: What kind of soldering iron should I use?

A: Soldering iron is perhaps the most important piece of equipment that serious DIY panel enthusiast should invest in. Ideally you should get an iron whose temp can be adjusted. Get a 90 watt or 150 watt adjustable soldering iron if you want to get serious in making good panels. Set your iron to 370 degrees Celsius if your solder (tabbing wire) is leaded, and 390 to 395 degrees Celsius if unleaded.

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Q3.9: How long will these cells work? In other words, when I make a panel, for how long will it be serviceable?

A: The cells will work for a long time! Silicon based solar cells have been proven to work for years and years.

However, the longevity of your panels is based on your workmanship. If water gets into your panel, then your panels will be damaged. It's easy to put together a panel yourself, but it's not that easy to make one that lasts a LONG time. However, thousands of customers have bought from us and they are making panels themselves from the cells we sell to them. We have shipped literally hundreds of thousands of cells to them!

Several important things to consider when making a panel:

1) Make sure that your solar cells are laminated or otherwise protected from water, moisture, and air. Yes, your cells should see air. Long time exposure (years) to air will eventually created an oxidation issue.

2) Make sure you invest in a good soldering iron whose temperature can be adjusted.

3) Give your solar cells strong protection from impact, such as hail, small rocks from high wind, etc. Solar glass would be a good choice.

4) Make sure that you clear the surface of the panel of any dirty spots such as bird drops etc. after your panels are put into used. They will damage the cells and possibly the whole panels.

5) If you are building a bigger panels such as 72 cell panels or above, make sure that you use diodes in our junction boxes to divide your strings (series) into 3 or more segments, so that in case on segment is damaged the other two will still generate power.

There are lots more, but if you are a novice, this is probably enough precautions for you to worry about.

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Q3.10: I can't get any voltage reading. What am I doing wrong?

A: Check the voltage and amperage on individual cells first to make sure that the cells work, and then solder. Chances are your soldering iron temperature may not be set to the right temperature if nothing sticks, or you did not apply flux on the bus bars and the tabbing wires. The thinner tabbing wires are coated with tin, and put your iron (get an adjustable soldering iron and set the temp to 695 degrees F) on the tabbing wire, when you see that the surface of the wire gets melted, and then start to move and solder the whole bus bars. Solder the front bus bars for most of your cells first, then the back side.

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Q3.11: How do I connect the cells? What side is positive and negative? I donít know where to start, and what material do I lay the cells out on?

A: The two thick lines on the front side of the cell are negative. The 6 dots on the back side of the cell are positive. Most of the time you want series connection. Cut your tabbing wires into 6 inch sections first. Then solder the tabbing wires onto the bus bars for ALL of the cells you want to connect. With tabs, set them on a table, back side up, and bring the tabs of the first cells and solder them to the back contact points of the NEXT cell, making series connections. After you are done connecting the cells, put additional tabs on the back side of the first cell, and use BUS wires to connect the two tabbing wires of the fist cell of the string and the last cell of the same string, and now you have the positive contact and negative contact of the entire string, with the voltage that is the multiple of the number of cells (~.5v x number of cells in this string)

Then to make things simple, you can just lay the strings on acrylic panelís front and back to protect the cells. The more professional way to encapsulate the cells is to put the strings in between two layers of EVA, and at the back side, put TPT. On the front, add solar glass. You then use the a heat gun to heat up the glass, all the while use a roller to apply pressure on the glass, with the shop vacuum taking the air out of the laminate as you work.

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Q3.12: Should I apply solder to the wire before I place it on the cell? On the videos I saw some do and some do not. I tried first without the solder and it did not come out good. I'm using a 40 watt iron. Do you have any suggestions?

A: If you bought the tabbing wires from us, you almost never need to solder. They are already coated with tin. The reason they don't stick is because your iron temp might not be high enough. That's why we recommend that people get irons whose temp can be adjusted. Set your iron to 695 degrees but not much higher, as it could damage the cells. Also make sure that your bus bars have flux applied on to them. Or dip your tabbing wires into a flux jar and let it soak for 6 minutes and then take them out to drip dry and then solder.

When soldering, always put your iron on the surface of the tabbing wires. And when you see the surface of the tabbing wires' tin melt, that's when you move the iron to cover and solder the entire tab on the full length of the bus bar.

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Q3.13: When soldering the cells together (tabbing), do you have to clean the anti-corrosive coating and what do you recommend to do that?

A: The ďanti-corrosive coatingĒ you are referring to may be the solder contact you are talking about. No, you do not remove those. If you did, you would have ruined the cell. Simply rub the contacts with pencil eraser if you feel that there's oxidation on the surface of the cells, and then apply solder on the bus bars, and then solder the tabs onto them.

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Q3.14: Case: "I have put together a solar array using your solar cells and I was wondering if you could help me solve this problem I am having. I have 16 volt configuration using 30 .5 volt cells in series and two rows of six .5 volt cells in parallel configuration. Can you tell me why I am getting eradic charging. I am thinking that maybe the solar cells are overheating because for the first 30 minutes when the sun makes contact the charging is excellent and fast and then after 30 mins later the charging of the battery becomes terrible very slow like a 1/4 of a volt in 7 hours. Do you have any ideas what can cause this? Please help I have run out of ideas."

A: We have always recommended 36 cell configuration to get 18 volts or so, because you need 1.5 times the voltage from the panels to charge 12 volt batteries to compensate for the voltage loss from the wires leading from the panels to your battery, voltage loss from the diodes, etc. The thing with the battery charging is that even if you are below 12 volt just a little bit, it won't charge at all. Higher voltage is fine, 17, 18, 19 volts, etc. are all fine. You just can't go lower or too high. Connect all of your 36 cells in series for a simple configuration will do you a lot of good.

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Q3.15I cannot get the solder to stick to the back of the cell. Do I need a special soldering rod and what do u recommend.

A: Make sure that you apply flux on the square dots on the back of the cells before soldering. And make sure that the tabbing wires are clean. Also make sure that your soldering iron can heat up to 690 degrees F. Use an adjustable soldering iron if possible. 

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Q3.16: Your literature indicates that 108 cells provide 3.5 amps and 150 cells also provides 3.5 amps? Are the amperage ratings correct?

A: That is correct when you are using series connection. If you connect the cells in series, the amperage for the whole 108-cell panel stays at 3.5 am, but the voltage increase from 0.5 * 108 = 54 volts. If you parallel connect the solar cells together, then amperage multiplies by 108 but voltage stays at 0.5v. Such low voltage is too low to be useful for hardly anything. Therefore most solar panel configurations always start by series connect solar cells to a certain voltage, then parallel connect several sets of that to get to the desired voltage / amperage combination.

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