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Making Sense of the Numbers

Some useful information in making solar power:
How to make sense of the numbers:

The basic and very important formula you need to know to make sense of solar cells is this:
Power (P) = Current (I) Multiply by Voltage (V), or P=I*V
Power's unit of measure is watt,
Current's unit of measure is amp,
Voltage's unit of measure is volt.

So in our solar cell's specific example, if each solar cell is rated at 1.75 watts on average, and the voltage is 0.5, you do a little algebraic math, then to get the amps (I), since P=I*V, so I = P / V , therefore I (amps) = 1.75 watts divided by 0.5 volts = 3.5 amps.

It's important to understand the concepts of series connection and parallel connection when stringing these solar cells together to make a solar panel. Series connection of the cells increases voltage but not amperage; parallel connection of the cells increases amperage but not voltage. Series connection is when you connect the positive terminal of a cell with the negative terminal of the next cell. Parallel connection is when you connect the positive terminals of all cells in the set of cells with a tabbing wire and all the negative terminals of all cell in the same set. You can use a combination of series and parallel connections to get the right voltage and amperage for your solar panel.

The cell specifications above were given to us by the manufacturer as averages. Variations are possible. To make a 18 volts panel, for example, you connect 36 cells in series (36 cells times 0.5 volt each = 18 volts). And 36 * 1.75 (each cell in theory averages 1.75 watt) watt = 63 watts. The amps you will be getting is 63 watts divided by 18 volts = 3.5 amps.
Solar cells basics:

The front of the cells (blue side, aka Sunny side) has two thick white lines, called bus bars. They are the negative terminals of the cell. The back side, where the 6 square dots are, are positive terminals. Connect the tabbing wires from the bus bar of the first cell on one side to the three dots of on the back side of the next cell. That way you have a series connection. Repeat the process on the other side of the cells. In panel making you should connect all the tabbing wires on the front for all the cells first, then flip the cells over to solder the back side in a second step. Some solar cells such as SunPower cells have both positive and negative terminals at the back of the cells, but we don't have to worry about them. Most cells are negative on the front and positive on the back.

The white color bus bars (two thick lines) on front and the contact points on the back are made out of silver, and you should keep them intact. Apply flux on your them and the wires should bond. Do not scrape them off like you saw on some Youtube videos. They did that perhaps becaues the contacts are very very old and have heavy oxidation. The most you should do is to use a pencil eraser and rub on the contacts. But without cells, even this is not necessary. Just make sure that the contacts are clean, and always remember to apply some flux first before using your iron to solder the wires on the cells. Our cells are already coated with tin solder, so you don't need extra solder.
Make sure that you test the cells under strong sun light with the front of the cell facing the sun, at the same time connect your meters to the right terminals. If you are inside the building, make sure you shine your sun simulating lamps onto the front of the cell while testing. Place the solar cells on a metal plate, ideally made from copper. With a warm light (ie halogen lights) shining on the cell, put your positive lead from your multimeter on the plate, and the negative lead of your multimeter on the bus bar. Your multimeter will be set to typically check amps or voltage at one time.
Panel configuration:

For those who are new to solar panel making or if you don't have an engineering background, here is our recommendation:

1) Make small panels first so you gain experience.

2) In most situations, make either 36 or 72 cell panels, and connect them in series. 36 cells give you 17.5 or around 18 volts or so. And 72 cells doubles that. These panels are very useful, and you will find a lot of matching products that will want to buy! For example, you almost always want to use a charge controller if you make your panels to charge batteries. Charge controllers usually come in 12 or 24 volt settings, which match your panels' 18 and 36 volts very nicely. Yes, your panel voltage should be 1.5 times the voltage of the battery you intend to charge. Connect more panels together if you want to tie to the grid, in which case, always use an inverter. However, we always recommend that the panels that you make for yourself be used in off-grid applications, such as charging your batteries to be used in RV, remote cabin, or marine settings. If you intend to connect to the grid, it is wise to buy the professionally made, UL certified panels.

3) For a lot higher voltage panels and configurations and connecting multiple panels to get high voltage, consult a professional. Just don't fry yourself.

If you want to become a serious panel maker, buy a good soldering iron whose temperature can be adjusted. Don't get a cheap iron. It's one of the most important tools you need to have. If you can't buy an adjustable solder iron, get one that's rated at 90 watts. Also when you solder, all you need to do is to apply flux on the bus bars and the backside contacts before soldering. Do NOT scrape off the whitish substance on the bus bar or the backside square contacts. Those are made of silver and must be kept intact. Just apply flux and solder the tabbing wires. The wires are already coated with tin solder so you don't need to use extra solder AT ALL. Use a smooth and continuous motion to solder the wires onto the bus bars of the cells.

Disclaimer: We are not experts in power systems and the above are what we learn through experience but we share what we know, and you should take it with a grain of salt. Buy books written by experts or take classes from the pros. These are about as much as we can help you with to get started, and we hope that this free consulting will reduce the flood of eBay messages that come into our inbox on a daily basis. Some people just keep asking question and taking time from us without buying, and we love to give, but please be considerate. Our resources are not limitless.

2. Packaging

The solar cells are very fragile so be very very careful when handling them. But out of all of the solar cell packages that we sent so far, broken cells via transit are relatively rare occurrences, though theoretically it's quite possible. We invested a lot of resources to make sure that the cells are well protected by a combination of foam pads, paper pad, bubble wraps, manufactured foam forms, inner box, and outer box. We have won rave reviews from our customer feedback on our outstanding packaging, just check our feedback so you can rest assured that your cells arrive intact. Our warehouse personnel take great pride in their packaging. And we are developing even better and efficient packaging solutions to bring the cells to our customers whole.

Each package is clearly marked and labeled with how many inner packs and how many cells there are in each pack. We also weigh each package and everything is recorded and signed off before shipping. All shipping paper work is double printed - one for our customer and one for our record, so that we have documented proof that we have shipped everything that our customers bought. This is done to prevent suspicious claims of not receiving the goods. In extremely rare occurrences where cells were shipped short, we would gladly make up the cells that you paid for but didn't receive.

You might break some cells during panel making process, so we always give our customer extra bonus cells for free just to show consideration for our customers. The number and percentage of extra cells we give vary, and it's purely at the discretion of the management, but all of our customers have been pleased with the deal they get.