At first glance, building your own solar panel does not seem like a do it yourself project, but actually it is a lot simpler that many other DIY projects. The solar cells are the complicated part of a solar panel, and you can buy them fairly cheaply. Once you have the solar cells, you basically have to sold them together, place them in a frame, and wire them to terminals. The good news is you can build a solar panel for about $ 1 per watt while purchase prices for a completed panel run $ 2 1/2 to $ 3 so your savings on a 3600 watt system amounts to range from $ 5,000 to $ 7,000.
Buying your Solar Cells.
Polycrystalline solar cells are available to the consumer is small quantities from a number of suppliers on the internet. Probably the best source is eBay Since there are many suppliers so pricing is very competitive, and eBay has a seller rating system so you know by their rating that you are dealing with a reputable supplier. The size that is most common is 80mm by 150mm or 3 1/4 "x6" that output 0.5 volts, 3.5 amps or 1.75 watts. They are available tabbed or untabbed. The tabbed version has the tabs used to connect the cells together already soldered to the cell so they are much easier to work with. I would suggest you use the tabbed version for at least your first panel.
You also will find blemished cells with minor aesthetic issues and broken cells available for less money. The blemished cells perform well, you just will have a spotty looking panel, so they will work, but the broken cells will be very difficult to sold together and will not produce a consistent power so I would leave them to the hobbyist. Additionally, you should make sure your shipments are insured since the cells are very fragile and you do not want to pay for broken cells.
Constructing your Solar Panel Framework.
The first consideration is the size of your panel which will be determined by the number of solar cells used for each panel. Remember in your planning that you want to make all the panels the same size with the same electrical output. For example, if you use 36ea 3 "x6" solar cells arranged in a 4 x 9 matrix, you can build a panel that would output 65 watts and measure 55cm x 70cm (25 "x 32"). The least expensive panel can be made with a plywood backing and a wood frame. This would need to be painted with an exterior primer and several coats of UV resistant paint so it will last. If you want a longer repeating panel, you could use an anodized aluminum frame.
Soldering your Solar Cells Together.
Assuming you are working with tabbed cells, and using the 4 x 9 matrix mentioned above, you will need to make 4 strings of 9 cells each. Each cell will have two tabs soldered to the back or negative side of the cell. These tabs will be long enough to reach across the back of the next cell and should be soldered to each of the contacts of the next cell. Be sure to leave about 1 cm or 1/2 inch between cells, and it is a good idea to crimp the tab in this gap before soldering so you have a little wiggle room for expansion and contracting due to weather and imperfect measurement. Continue soldering cells in this manner until you have completed your string of 9 cells. Finally, you need to sold tabs to the negative contacts on the first cell so you have leads on both ends of your string. Test each string in full sun with your multimeter to make sure your connections are working and you are getting at least 4.5 volts and 3.5 amps ..
Final assembly of your Solar Panel.
Lay the four strings on the panel you made making sure they fit evenly and cells are not touching. Make sure you rotate your strings so the positive leads coming off the end of one string will be next to the positive leads of the next string. If everything looks good, attach each cell to the panel with a dab of silicon caulk. Next we have to sold the strings together with copper wire or tab ribbon. Connect the positive leads to the negative leads of the next panel so all strings are connected in series. Finally sold a 25cm or 12 inch wire to the negative lead at one end of the panel and a wire to the positive lead at the other end of the panel to create the wires that will be used to connect panels together. Test once more to make sure you are getting the output of 18 volts and 3.5 amps. After waiting several days for the silicon to dry, you should cover the cells with a Plexiglass or tempered glass cover, seal edges with silicon and you are done.