Introduction: Make Custom Sized Solar Panels

About: I love solar powered projects, electronics (µCs) and most recently 3D printing.

I only have 10x10cm sized 0.5Volts solar cells in my cellar. But I often need other Voltages and/or solar panels in other sizes, so I had to find a way how to cut them and put them into some nice waterproof housing.
I think I found a nice way how to do both, and wanted to share it.

What you'll need:
- "Raw" solar cells at any size
- Wires, soldering iron, solder
- Transparent (Polyester-)Resin
- Fibreglass mats
- Sanding paper
- Toothpaste
- Thinner
- Dremel or such
--- Diamond blade
--- Grinding-Head
- A piece of wood
- Hammer and chisel
- Optional: Paint (Lacquer)

Gathered the stuff? Good, let's start!

As usual: You are responsible to what you do. If you damage any property, human or animal or get harmed in any other way, I can't be held responsible, even if I told you to do so.
Working with the Dremel, the soldering iron, the belt sander, resin or any other tool or material may be dangerous and happens on your own risk.

Any measurements are in the metric system.

1 mm = 0.0393700787 inch
1 cm = 0.393700787 inch
Please use Google-calculator or any other calculator if you want to know the sizes in inches (or any other system).

The method to cut the cells is by far not perfect. If you have any other methods, please tell me :)

tudurache posted in the comment a very helpful link to his website . I have not tried the method he found, but I will soonish and tell you how it went.

Step 1: Custom Solar-panel: Cut 'em!

First: Get them to the right size!
To do this, you have to plan what sizes you want to have in the end. (Watch out: Try to let the cells as big as possible,
the smaller the cells the more work, the more loss etc you will have!)

Think of following points:
-What voltage do you need in the end?
-How many cells do you have?
-How big are they?
-What shape do they have?
-How many mA do you need in the end?

-Where are the main strives? (The thicker solder-lines, it's hard to impossible to solder the thin ones)
-You will lose some cells (they are so fu**in thin, they break so easily)

Every cell has normally 0.5V. How much mA per cm² they give you have to measure*² (usually around 1A@0.5V=0.5W per 10cmx10cm cell => 0.005A@0.5V/cm² ).
Now you always can either put them in:
- series
- parallel
Series raises the voltage (three cells in series provide 3x0.5V=1.5V etc), but only the amperage of the smallest cell (so try to use cell of similar sizes)*³.
Parallel raises the amperage (three similar cells with 0.5A provide 1.5A etc). Size doesn't matter here (you can put whatever you have).

Here is one Question from wasteinc - I think it clarifies it a little more:
Q: "[...]my first solar panel [...] is 12cells in series giving me 6.5 open circuit voltage, but when I try to charge something on usb power, the voltage drops to 4.7 even on the best light conditions. In overcast sky the voltage hovers around 3.8

so my conclusion is to put more 16-19cells on my new solare panel . did you experience similar behaviour?"

A: "Cells usually give around 0.6V open circuit and 0.5V with adequate load.

If the Voltage drops significantly below that, make sure that the cells are big enough (give enough current). Of course you will not be able to power a 1A 5V usb with a total cell surface of 10cmx10cm (One cell that size usually provides around 0.5V 1A - or 5V 100mA when perfectly cut into 10 pieces, so more likely 5V 80mA). So you would need a total of >1000cm² (e.g. 30cmx35cm) to have a full-powered usb-solar panel. [...]

I guess more cells would do no good (the open cicuit voltage would rise and getting dangerous for anything connected if small/no load is there). I would use the same amount of cells with a bigger area each and/or to use an (eg old mobile) battery, so you can charge that for like 12hrs and then charge via usb for 1hrs. That is better anyways, because you should quite precisely provide 5.0V for USB, otherwise your charged device can break.

You can e.g. use a cheap powerbank (~5$), replace the battery by several old phone batteries, load those with >=4.7V (the bat needs 4.7V to fully charge, they usually have a circuit included to control the charge, so 5 or 6V are okay too) via solar and then use the circuit from the powerbank for providing the stable 5.0V for usb.

If that still doesn't work, check every single cell for short-circuits!"

Only if you have this plan ready, continue.

I tried several techniques to bring solar cell to the right size, but in the end only one worked: Cut 'em!
I took the diamond-blade for my Dremel and build a little table* on which I could precisely cut them.

Here is the howto-vid:

Wear eye-protection and old clothes when working with the Dremel!

* Instructable may follow.
*² Think of the resistance of you device. Don't take the shortage-voltage, but don't take the open-circuit-voltage as well!
*³ You can combine both techniques. Think of following example
cell A and C are the same size, cell B1 and B2 are half that size. To get 1.5V and the full amperage put them together like this:
plus --cell A --|-- cell B1 --|-- cell C -- minus
.........................|-- cell B2 --|

| and - are cables . is not!

Step 2: Custom Solar-panel: Solder

Now you have to solder the cut pieces together. Now carefully follow your plan.
To put three cells in series , start with the first cell on top. Solder two wires to the main-strives. Continue with the next one but solder the same wires to the back. Cut the wires.
Solder two new ones to the top of the second cell. Solder them to the back of the third.
Now solder wires to the back of the first cell, bridge them with another wire and add a cable as plus. Do the same at the front of the third cell, that's your minus.
To conclude: Always solder back-to-top .

To put cells in parallel solder top-to-top and back-to-back .

Try to use as thin wires as possible*.

* But not too thin, the power should be able to pass thru' - Anyway that is VERY thin. One example: Two meter of wire, 500mA (Voltage doesn't matter) and a loss of 0.1V would need a cable with a cross-section of 0.145mm².
Formula: Q=I*L*0,018/ ΔU
Q =required cross-section
I = Amperes
L = length of wire (Watch out: The power has to go two times through the cable: One time from the cell and one time to the cell)
ΔU = acceptable Voltage-loss

Step 3: Custom Solar-panel: Prepare the Form

Next, we want these cells as a panel.
I used often used plexiglass and wood to make it, but its kinda thick and it's difficult to get it waterproof. So I decided to use another technique. I remembered that I had some resin in my cupboard. So I build a form for them. Follow the instruction in the pictures.

Step 4: Custom Solar-panel: Resin It!

Now the big showdown is there. Will it blend? Uhm, I mean will it work as I wanted? As usual follow instruction in the picture.

Additional annotations:
- Before sealing the cells forever, you should carefully clean them with a lobe and the thinner. The cleaner, the more energy.
- When the resin is hardening don't let anything fall into it . Looks unnicly and stops the light (less energy) - and don't leave finger prints :)
- Do it outside (not under a tree or such) or in a very well ventilated room. Or it'll smell like hell in your whole house!
- When you cut the fibreglass: It scratches like hell if you touch it. Don't touch yourself with the gloves you touched the fibreglass with.

Step 5: Custom Solar-panel: Final Touches.

Now you have to grind/sand the edges nicely and polish the surface.
A cheap method to do that is toothpaste. Gives quite good results, is always there and very cheap :)

When you sand the edges, be very careful with the cables . Once cut, you (almost) can throw away the panel...
--And wear (respiratory- and) eye-protection.

Have fun with your custom-sized and custom-dimensioned (electricity) solar panel. It should be 100% waterproof, resistant against most chemicals, very lightweight and very robust.

Please leave a comment if you have any question or correction. I would be happy if you post pictures, if you did it yourself.

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