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Step 1Buy some solar cells
I bought a couple of bricks of 3 X 6 mono-crystalline solar cells. It takes a total of 36 of these type solar cells wired in series to make a panel. Each cell produces about 1/2 Volt. 36 in series would give about 18 volts which would be good for charging 12 volt batteries. (Yes, you really need that high a Voltage to effectively charge 12 Volt batteries) This type of solar cell is as thin as paper and as brittle and fragile as glass. They are very easily damaged. The Ebay seller of these solar cells dips stacks of 18 in wax to stabilize them and make it easier to ship them without damaging them. The wax is quite a pain to remove though. If you can, find cells for sale that aren't dipped in wax. Keep in mind though that they may suffer some more damage in shipping. Notice that these cells have metal tabs on them. You want cells with tabs on them. You are already going to have to do a lot of soldering to build a panel from tabbed solar cells. If you buy cells without tabs, it will at least double the amount of soldering you have to do. So pay extra for tabbed cells.
I also bought a couple of lots of cells that weren't dipped in wax from another Ebay seller. These cells came packed in a plastic box. They rattled around in the box and got a little chipped up on the edges and corners. Minor chips don't really matter too much. They won't reduce the cell's output enough to worry about. These are all blemished and factory seconds anyway. The main reason solar cells get rejected is for chips. So what's another chip or two? All together I bought enough cells to make 2 panels. I knew I'd probably break or otherwise ruin at least a few during construction, so I bought extras.
I also bought a couple of lots of cells that weren't dipped in wax from another Ebay seller. These cells came packed in a plastic box. They rattled around in the box and got a little chipped up on the edges and corners. Minor chips don't really matter too much. They won't reduce the cell's output enough to worry about. These are all blemished and factory seconds anyway. The main reason solar cells get rejected is for chips. So what's another chip or two? All together I bought enough cells to make 2 panels. I knew I'd probably break or otherwise ruin at least a few during construction, so I bought extras.
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http://cgi.ebay.com/36-3x6-Solar-Cells-Short-Tabbed-BOTH-SIDES-4-DIY-Panels_W0QQitemZ120504865161QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item1c0ea65189
but it is Multi-Crystalline.
it is not mandatory to have mono-crystalline or multi-crystalline, and modules made up of both works fine. The only difference is that mono-crystalline cells provide higher power, compared to multi-crystalline cells. Conversion efficiency of multi-crystalline is around 16% while that of mono-crystalline is around 17-18%, and hence for mono-crystalline cells you have to pay more, but on the other hand to produce same power, you have to install less cell modules for mono, therefore you save space. Its a compromise between cost and space.