Let's Make Robots!

How to make your own solar panels


 Well, I just thought I'd post what I've learned about solar panels in the past month. They are actually quite simple to make and will cost you alot less then buying one from a company.

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 Part 1 - Assembling the cells: 

  Parts List: 

·         Soldering Equipment 

·         Duct tape 

·         Wire cutters

·         Solar cells

·         Tabbing wire

·         Bus wire

·         A flux pen

·         Basic things From around the house and workbench

 


 I usually buy the tabbing wire, bus wire, flux pen and cells in a kit, they are hard to find alone. I also recommend buying these parts on eBay, as they are alot cheaper. Don't fear using cells with minor chips and breaks, this usually barley effects power output and costs alot less. A helpful hint: buy pretabbed cells; it saves you alot of work! (Tutorial based on pretabed cells) 

 

 Calculations:

 Most of the common solar cells (polycrystalline) are rated at about .5 Volts & 1.8 Watts. So let's say you have a robot that needs a 5V power supply; you would make a panel with 10 cells right? WRONG! To properly charge 5V batteries, you need to have 1.5 the voltage of what you're charging; you would need 15 cells in series. Now if you wanted to get more wattage out of the panel, you could wire two sets of 15 cells in parallel. For this tutorial, though, I'm actually going to make a full size 18V (for a 12V) 60W panel. But you can adapt it to your needs easily.

 

 Arrangement:

 You're going to want to arrange your panel in a nice looking way. For my panel, I'll do three rows of 12 panels. For the 5V panel, you could do 3 rows of five. Now remember, the rows of 12 must soldered together in series to get the correct 18 volts. To make it easy on myself, I'll make 6 rows of 6 and pair them up later.

 

 Tabbing cells:

 WARNING: The cells are extremely fragile and break easily, BE CARFUL! Ok, so the first thing you're going to want to do is lay out the panels (upside down) at the desired spacing. Here, you can fall into two categories, short tabbed cells (the tabbs on the of your cells hang off about 2mm) and long tabbed cells (the tabbs hang off enough to cover another panel). If you are in group one, don't do anything. Group two: make sure that your tabbs run from the front of the first cell over the back of the next.

 Side note: each cell has a + and a -. The thick lines running vertically down the front are + and the back pads are -. By tabbing from front to back, you are wiring in series.

 For this tutorial I will be using short tabbed cells, here are mine laid out:


 Group two can skip this: cut enough tabbing wire to tabb from each short tabb, over the three back pads.

 

 Carfully Place duct tape along the back of the cells trying to keep the tape in the center of each cell. When you are satisfied, press the tape down gently.

 WARNING: Do not take the tape off the cells! It will break them 99% of the time!

 

 

 Before tabbing your cells, you should add flux to make sure the bond is strong.

 

 This next part is tricky; You have to place the tabs so they hang off the cell enough for you to connect the bus wire. You should also find something to hold the tabb in place while soldering. Now, apply a little solder to the tabb and make sure it sticks to the pad.

 

 Position another tabb on the second cell. This time it should go under the first cells front tabb. Solder it to that. (group two can also skip this)

 

 Now use the past two steps to finish tabbing all of your cells. If you are in group one, you may want to add some tabbing wire to the end cell for bus wire. Group two should cut some of their tabbs off at the end. 

 

The tape definitely pays off when you need to move your cells

 

Front and back of completed set:

 

 

 Make sure to test your cells. The reading depends on how much light you're in. I was inside under direct light from a lamp and got about 2.48V.

 

The final step to complete a row of 12 is to solder the two halves together. Make sure to tape them in place first!

 

 Now just make two more rows of 12 and you have a 60 watt panel! almost... In part two I'll show you how to connect the rows and properly encapsulate your cells to make them weather proof.

 

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 Part 2 - Assembling the frame: 

 Parts list:

  • A 2x4 that is equal to 1/2 the desired frame size in height (but you should buy extra)
  • plexi-glass larger than your frame
  • paint
  • bus wire (same as above)
  • epoxy of your choice (I recomend 2 oz. per cell)
  • stuff to mix the epoxy in / with
  • an old extention cord or connector of your choice
  • clear silicone
  • packing tape

 To start, cut your 2x4 in half (try to be as exact as possible, because 1in. is not exactly half). Then, make two 3/4in. cuts all the way down. You'll end up with a lip like this:

 

 

 Cut that pice at 45 degree angles to form the basic frame for the panel. Make sure the lip is to the inside, it is for the plexi-glss. I've also painted mine white to keep the wood from warping. The next step is to cut the plexi-glass and fit it into the frame.

 

When you have that, use clear silicone around the edges to make it water / air tight

 

Carefully lay the strings of cells on the glass in even columns. Use the tape anywhere that epoxy may touch the glass, you want to avoid that. Try to keep it level as you do this. In the next picture, you can also see the bus wire I used to connect my cells. the rows should be connected by bus wire in a zig-zag pattern after most of the tame is placed.

 

 You will end up with one un-connected string at the top, and one at the botttom, run these connections with bus wire to the bottom of the panel. Cut the female end of the extention cord for use as the main connection and strip the wires inside. You can connect the pannels + and - leads to your cord and silicone it in place.

 

 Now the hard part, mixing the epoxy. Once you do it, it's not really that big of a deal. You should definatly find a video on this, but what you do is mix a perfect 2/1 ratio in ounces and mix thouroughly, pouring it into at least 1 other container with a high drop. Try not to mix in bubles. For this, I use MAX CLR - HP epoxy. MAKE SURE TO KEEP YOUR EXTENTION CORD OUT OF THE EPOXY SO YOU CAN USE IT!

 

Let that dry for about 24 hours and there you go! a fully functioning, water-proof solar panel! I may do a part three on how to use charge controllers and batteries soon.

:D  /\