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Solar Cell Voltage and Current
The amount of voltage produced by a solar cell is related to many material and operational properties, but one thing it's not related to is the area of the solar cell. A silicon solar cell the same area as your two hands puts out a voltage identical to that of a silicon solar cell the size of your pinky's fingernail. Specifically, each silicon solar cell provides a voltage of about half a volt. The power, though, is equal to the voltage times the current, and the current generated by a solar cell does depend on how large it is. All else being equal, the larger the solar cell, the higher the current.
Solar Panels
Solar panels are made by wiring a bunch of solar cells together. There's no standard way to do this -- every manufacturer makes different choices for the solar cell size, the number of solar cells and the way to wire them together. For example, if you wire 24 solar cells in series -- that is, the back electrode of one wired to the front electrode of the next -- then the voltages will be added to one another. That means your solar panel will have a nominal voltage of 12 volts. Most miniature solar panels in solar calculators already consist of a few cells wired together to produce a couple of volts of output. The current of a chain of solar cells wired in series is limited to the current produced by a single cell. To get more current, solar panel manufacturers connect separate chains of solar cells in parallel. That is, the first cell in one string is connected to the first cell in the other strings as well.
Connecting Your Cells
You'll want to connect wires to each of your solar cells in order to connect them. It's simplest if you use a special wire called "tabbing wire." If you solder a 1- or 2-inch wire to the back of each cell to begin with, then you'll save some work later. Then lay out your solar cells on some kind of mechanical support, such as a sheet of plywood or sheet metal. If you use sheet metal, you'll need to place some kind of insulating material between the metal and the solar cells. Take the wires from each solar cell in a chain -- whatever number of solar cells you've decided to connect in series -- and solder them to the front of the next cell in the chain. Then solder the first wires of all the chains together and the last wires of each chain together. You now have a solar panel.
An Environmental Enclosure
Solar cells are brittle, and their performance degrades when they're dirty. That's why you'll want to put them in an environmental enclosure. Essentially, you'll take a piece of plexiglass or a sheet of glass and place it on top of your plywood, making a sandwich with the wired-together solar cells in the middle. Then seal the edges of your solar panel -- with wood, metal or silicone caulk -- leaving the wires from each end protruding from the enclosure.