Good question! Solar cells come in all different sizes and shapes so there is a formula to help answer that question. Lets use the size cells that I worked with, they are 3 x 5. Three inches tall and five inches long.

We are going to figure the width of the frame. Here’s the formula step by step… You have 4 cells going across at 5 inches each that’s 20 inches. We want a 1/4 inch between the cells including the front of the first cell and again after the last cell. That equal 1.25 inches. Then we want 1 inch for the frame on the left and on the right, that’s 2 inches. That equals 23.25 inches.

Now let’s do the length. That’s going to be a bit different.

Here’s the formula step by step… You have 9 cells going down the row at 3 inches each that’s 27 inches. We want a 1/4 inch between the cells skipping the first one and the last one, so that’s 8 x .25 which equals 2 inches. Now we want to add 1inch for the bus wire and add 2 inches for the bus wire and junction box ( j-box). Now add the 1inch for the frame at the top and bottom that equals 2 inches. That equals 34 inches.

A little side note here the bus wire is thicker and wider tabbing wire for a simple explanation. You use the buss wire to connect your rows together. So your panel would be 23.25 inches wide and 34 inches long. Once you have your measurements you can make adjustments to the length as you desire.

As you can see I made adjustments to my math. A few things to keep in mind here, you may notice in this picture some of the gray backing is missing on a few cells… No problem. At this point and time you really want to keep the tabbing wire off the frame. If light gets on the blue side of the cells they will conduct electricity and possibly short out cells.

When you are arranging your rows, you will want to set them up so they either run in series or in parallel. I will explain that when I get into some of the math. After you have the rows arranged the way you want then the bus wire is soldered to the tabbing wire ends. What I have found to be helpful is to use some silicon in various places to hold the cells in place. Once the silicon has dried and the cells are in place, now would be a good time to test the solar panel. The worst thing to find out after you’ve sealed the panel would be to discover you have a bad solder joint but you can’t do anything about it, because it’s to late.

Sealing the back of your solar panel. Ok, you checked your panel and you soldered the wires that will become the positive and negative lead onto the bus wire. As I mentioned earlier, aim to keep the solar panel as cool as you can when it is in use. You can put a back panel on or you can use a product called Sylgard 184 . I used Sylgard and it will dry as a clear silicone. Good stuff, a little pricey. The only thing I didn’t like about Sylgard was the drying time. I can take several weeks for it to dry and even more time depending on humidity and temperature. Another note on Sylgar, make sure you run about a 1/2 inch bead of silicon about 1/4 of inch out from the edge of the solar cells. You are creating a well to keep the Sylgar from running into the corners of the frame. A mistake I made and a mess I had to deal with. Remember once you pour it on your panel there’s no turning back now. There are two good videos on working with Sylgar on YouTube, Youtube video 1 and Youtube video 2. Notice in Video 2, how he has a silicon bead going around the outer part of the solar cells. The last two things to install is the j-box and an appropriate sized diode. The j-box can be siliconed on top of the dry Sylgar. The diode gets soldered to the positive lead with the silver line side attaching to your positive lead coming from the solar panel. The diode keeps electricity from flowing back into your solar panel, which would burn-out the cells in time. Remember, most importantly run your solar panel into a charge controller never directly to a battery or device. I picked-up a simple charge controller for about $15.00.

Let’s take a look at some terms and formulas that you will need to understand to do this correctly. When you look at solar cell ratings you may see W, V and A. W is watts, V is for Volts and A is for Amps. Sometimes you will see Imax, no this isn’t a movie theater. The “I” is also used to express current or amps when you see Imax, you are being shown the maximum amps. Here is a good video on YouTube, check it out, http://www.youtube.com/watch?v=-mHLvtGjum4. In electronics there is what is called Ohm’s Law. It is a way of figuring out Volts, Amp, Resistance, Watts and more then what is needed here.

In the far corners you see V, for volts, R is for resistance measured in Ohms and so on. So if you want to work with Wattage issues, “P” you would go to the green quadrant for your formulas. This site has very good explanations about electronics.

Let’s try this: Your solar panel is 12 volts, V and your Amps is 3.5A. What is the Watts or Power?

To find Watts we take 12V x 3.5A = 42W To find Amps we take 42W ÷ 12V = 3.5A To find Volts we take 42W ÷ 3.5A = 12V

So in the above picture, “I” being Amps… I x V = P, P ÷ I = V, P ÷ V = I. For now there is no reason to deal with resistance. Now the next thing that is very important to understand is circuits. There are three different types of circuits, though when you’re building a solar panel you will only use two. They are series and parallel. In series you are just connecting negative to positive. In parallel you join the positive together and then all the negatives are joined and you end up with one positive and one negative. In electronics the effects of a series circuit is very different then a parallel circuit.

Here’s what happens: When you connect your rows of solar cells in series, the voltage goes up though the current, Amps stay the same.

So let’s say for example you connect in series two solar cells. Each solar cell rating is 1V, 2A. Your end result will be 2V, 2A. See how the amps stayed the same.

Now working with the same solar cells though connected in parallel. Each solar cell rating is 1V, 2A. Your end result will be 1V, 4A. Now the volts stayed the same.

So what’s better? They both work great and can be used in combination to achieve your desired result.

Keeping things simple let’s create a 12V, 2A solar panel. We have 12 solar cells, each solar cell is 2V, 1A. The first thing is to create 2 rows of 6 cells, they are wired with tabbing wire in series. We now have 2 rows of 12V, 1A. Now we connect the rows in parallel. All the positive tabbing strips are connected with bus wire and all the negative tabbing strips are connected together with bus wire. What you end up with is a 12V, 2A solar panel. What’s the Watts? You should get an answer in the twenties.

I realized that I simplified some of the information and examples. This information should only be one of many resources that you have looked into. Good luck with your solar system. I’m currently running my Hydroponic system pump off my solar panel.

Checking out the system – Solar Panel is hooked-up to the regulator and regulator determines the charge going to the battery.