For illustration purposes this project will use a 4" square single crystal solar cell that puts out .89 watts. Remember that although the current rating or amperage of each cell can vary, a single PV cell, no matter how large or small, will only put out .5 volts (half a volt). Watt output is equal to volts x amps, so for example, .5v x 1.78a = .89 watts.
Most panels, for a variety of design reasons, contain 32 to 36 individual solar cells. A 36 cell panel gives more voltage than a 32 cell panel. The higher voltage is useful if you are designing a panel for a location that tends to have a lot of cloud cover, as the panel can produce more watts with less sun.
You will need to figure how many cells add up to the voltage you want from the panel. In this project, we will use 32 single crystal solar cells, each .89 watt and 4" square. This will make a solar panel that, with full sun, will put out 16 volts at almost 2 amps. That's more than sufficient to charge a 12 volt battery supply system.
We now know the output of the panel (16v) and the size of the cells (4"), so next we need to plan the panel layout. Since we will use 32 cells, we can lay them out in a pattern of 4 across and 8 down (8 x 4 = 32).
Any layout will work, but this is a typical size and an efficient way to use the space. One of the advantages of building your own PV panels is that you can make them any size or shape you wish, even triangles or circles. This can come in handy if you are designing custom panels for places where the typical rectangular panels won't fit, and if you have particular aesthetic consider-ations. However, a basic rectangle or square is the usual configuration.
The position for the bus ribbon is marked at the bottom of the panel, and used to line up the template to slide the connected strings of cells into place. Once aligned, the template is gently pulled out from under the cells.