If you have a bunch of old solar garden lights that don't work so well anymore, and you're thinking about pulling the solar panels off and making something cool with them (since, even if the lights themselves are dying, the panels probably still work), this instructable is for you! This array combines versatility with efficiency; it can produce several different voltages, but without using a power-wasting voltage regulator or boost circuit. It can be made with a few simple parts, tools, and minimal electrical knowledge. The wiring is kind of complicated, so I'll endeavor to explain it as best I can. Post a comment if you have any questions.
Step 1: Materials and Tools
Solar cells; I used nine panels from the tops of solar garden lights; note that I mean only the panels themselves, not the batteries, charging circuits and lamps. Save these for some other awesome project.
Wire; lots of it. I used wire salvaged from two broken strands of incandescent christmas lights.
DIP switches; if you don't know what these are, they're little banks of two-terminal switches, usually used for programming microchips. You'll need about 28 switches for 9 panels, or three banks. Two should be ten-switch banks, one can be an 8-switch bank. You can buy them from many electronics stores for a few bucks, and I guess you could just use a whole bunch of individual two-terminal switches if you can't find any. These are just more convenient.
Wire clamps; the most versatile power output system. You'll need two; red and black makes things easy.
A surface to mount the panels on; I used cardboard. You could use almost anything.
Soldering gun; you'll probably need this to make wiring connections. If you don't have one, good ones can be had for not very much money, and soldering will make your life easier. Trust me.
Step 2: Voltages and Currents
Step 3: Switches and Wiring
Step 4: Optional, Auxilliary Stuff
You might want some kind of a handle; I used one from an old briefcase. You'll also probably want some kind of a stand, since the panels work most efficiently when facing the sun as directly as possible. I used part of an old ventilation grating, but many things might work. A useful accessory is a DC extension cord; you can make one by putting color-coded clamps on both ends of a piece of two-conductor wire.
Step 5: Setting Voltages and Powering Stuff
First, determine how much power the device you want to power uses. If it has a DC power port, it should say right on it how much voltage to use. You can also power things that take batteries; just remember that the cylindrical batteries are l.5 volts each (Multiply!), those little box-shaped ones are 9 volts, etc.
The first setting you need to know is this; engage all the switches on the two main output banks, and none of the ones in the bank of eight. (Note that you don't have to use the tenth switch on the two larger banks; just ignore it). Your output is now 4.5 volts at 500 milliamps.
This can power devices rated to that voltage, or close enough, some USB devices, and devices that run on two, three, and sometimes four 1.5 volt batteries.
The next setting is 9 volts. Engage the first switch on the negative output side, skip the next one, engage the one after that, etc, engaging every other switch. Do the same to the bank of eight switches, and on the last bank, skip the first switch, and engage the second, skip the third, and so on. Your output should now be about 9 volts, at 200 milliamps. This is suitable for powering devices that run off 9 volt batteries, 4 to 6 1.5 volt cells, and things with DC ports rated to 9 volts, or close to it.
The final setting is 12 volts. Engage the fist switch on the negative output side, skip the next two, and engage the fourth, then repeat the pattern. On the bank of eight, engage the first two switches, skip the next one, engage the next two, etc. On the positive side, skip the first two, engage the third, skip the next two and so on. When finished, your output power should be 12 volts, at 170 milliamps. You can use this to power some 12 volt devices, and sometimes devices that run on 8 1.5 volt batteries. You could also use it to charge a car battery, or other 12 volt battery cell.
Don't be surprised if a device won't work; it probably just takes more current than the solar panel can supply. It's best at powering radios and other low draw devices. Gameboys, boomboxes, remote controls, and battery chargers are just some of the things I've powered with this! Good luck!