Make: Projects

Solar USB Charger

A simple-to-make charger that safely recharges many USB devices using solar power.

Solar USB Charger

Charge up your USB devices with the power of the sun. By adding a small solar panel and two diodes to a standard USB cable, you can plug that cable into USB devices needing a recharge. It’s so easy. Let’s get started making a solar USB charger.

Video shows the Solar USB Charger being tested on a sunny day.

Check out more Weekend Projects.



Step #1: Hack the cable

Solar USB ChargerSolar USB ChargerSolar USB Charger
  • Cut one end off of a USB extension cable.
  • Cut away the cable's outer insulation and isolate the power lines. These are the red wire (+5v), and black wire (Ground). Strip the ends.
  • The solar panel already has corresponding red (+) and black (-) wires.

Step #2: Add the diodes

Solar USB ChargerSolar USB ChargerSolar USB ChargerSolar USB Charger
  • Cut a 2-3" piece of 1/4" heatshrink tubing and slide it over the cut end of the USB cable.
  • Cut a similar piece of 1/8" tubing and slide it over either the red or the black wire coming from the solar cell. This tubing will insulate the wiring connections from each other.
  • Pick a rectifier diode from the pack; any one of them will do. Solder the diode between the red wires from the solar cell and the USB cable, with its cathode leg (that's the negative side, marked with the stripe) facing the USB side.
  • Solder the two black wires directly together.
  • Solder the smaller, red and black Zener diode across the two wire connections, with its black stripe facing the red wire side.
  • Slide the heat shrink tubing over the joints and shrink with a heat gun or lighter. (Hold the lighter flame over the tubing, rather than under, and move the tubing around to shrink all spots.) Always put the tubing on first, before you solder!

Step #3: Test it out!

Solar USB Charger
  • The rectifier diode eliminates incorrect polarity and prevents power from being drained from USB devices. The Zener diode protects them by preventing power surges over 5V (actually 5.1V).
  • To test your charger's output, place the solar panel in the sun and plug the cut-off end of the USB cable plug back into the other end. Use a multimeter to probe the voltage between the red and black wires.
  • Depending on how sunny a day it is, your multimeter should show something between 4V and 5V. The Zener should prevent anything from going too far above 5V.
  • I have used this device to charge a 5V USB battery pack. If you want to charge an iPhone, you will need to implement this modification that raises one of the other USB pins to 2.7V. The iPhone uses this as a signal to detect charging.
  • You can see video of the testing of the device in the intro section of this project.


If there's one thing we have in the US, it's sunlight. And where I live, the summers can get incredibly hot. It's a shame to let all of that free energy go to waste, and this project shows you how easy it is to put that solar power to use.

Steve Hobley

Steve Hobley

This week, I have been mostly working on...

I've been tinkering around with bits of technology since I was five years old. I used to take the telephone apart at home, just to see how it worked.

After a couple of years I could even put it back together again - and sometimes it would continue to work.

  • Nick Normal

    Sorry there isn’t one currently available – but it’s really only two diodes and two cables, so I hope the pictures alone are enough to follow along with.

  • Steve Hobley

    I would check to make sure the charger isn’t shorting out

    Are you charging an iPhone?

    • Djilali

      Can u use any phone to charger in this project

  • blanket

    i’m charging a samsung phone with android running on it.

    i’ve used a multimeter to check the voltage across the different components, and i’ve also tested it in the same way as in the last picture above. when the sun is steady, it produces a voltage right around 5V.

    i’m fairly new to electronics, so i’m not sure if there is another specific spot to check for a short, or if there’s something else i should utilize on my multimeter?

  • blanket

    oh yeah, i’ve also tried to ensure that all the wires and components are well insulated from one another when testing, so there shouldn’t be a short in that way.
    would the test in the last picture above work if there were a short, or would it produce a different result?

  • Nick Normal

    hi Blanket, sorry for the slow reply. Do you have a multimeter of any kind, to see where you are getting signal and where it is falling off?

  • Frank Carter

    @ blanket – “i bought all the parts linked to, with the exception of the 25 pack of rectifier diodes. this wasn’t available, so i bought some 1N4001 diodes”
    The 1N4001 is not a zener diode and blocks voltage. Zener diodes limit voltage. In this case, substitution is not allowed the part you have does a different job.

  • blanket

    @Frank Carter – I subbed in a diode from the 1N4001 pack for the rectifier diode in the relevant parts list, not the Zener diode. It turns out my phone needed a larger solar panel (2 panels actually), since this setup made it act as though it were charging but really didn’t provide enough power (i.e. wattage). Having it in this “charging” mode drained the battery more quickly than if it had simply been idle.

  • Hey, can I do this with an iPhone 5 charger? Does this have to be done with a dual end USB, or can I do this with anything that charges via USB? (This may be a dumb question, but I am totally new to the Make culture and this will be my first project – father’s day gift for my dear ol dad… :)
    Thanks in advance for any help and advice!

  • Brodie

    I have a solar panel that puts out 3.2 W and 18.8 v at max power the current is 170 mA at max power. What would I have to do to use this to charge an iPhone and or an iPad 2? Ay help is appreciated.

  • ashch

    my usb extension cable has red, black, white and green wires. Which one should I connect

  • Ash

    red & black are the wires you connect…
    White & green are the “sync” portion of the cable you cut…

    Next time – use a cheaper “charge only” cable

  • teknoah

    Any projects like this done solar panels on the exterior or the house with inductive chargers passing through windows?

  • odu

    You can try this: if you have a 12V solar panel lying about.

  • iPhone 4G is awesome works perfectly. I just bought new cover. Great website!

  • BLDH

    Could you use a higher voltages to the cellular devise and trust that the phone only uses the ~5 volts required? for example if my solar cells produces 6 or 9 volts.

    Could someone epxlain the meaning of the diods please!?

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  • Kenny1991

    What are the specs of the solar cell module you purchased? It seems Radio Shack no longer carries the one you have linked and they have various other panels. If I get something with a different wattage/voltage rating, do I need to use different diodes?

    • Karsten Spang

      At least, I can tell you what does not work. I bought a 277-052 (6V, 1.5W) solar module. In the shade, this kind of works (5.1V output, but not much charging current), but in direct sunlight, the voltage goes up to 5.4V, and my iPhone refuses to charge from it.

      I guess that you should get something less powerful, e.g. the 277-048 (4.5V, 1W). This matches what the article says about the expected output voltage being between 4 and 5 volts.

      Edit: I was able to make my iPhone charge by placing a ½” wide strip of duct tape over one end of the module, such that part of the module does not get sunlight, thus lowering the output voltage.

  • Courtney Clark

    Hi! I found this to be an incredible simple and thorough but I have one question with regards to Apple products. I was hoping to adapt this to be “iDevice” friendly but I’m not sure what resisters are required, and/or, if I need to change out my diodes. Does anyone have any suggestions. In the meantime I’ll keep researching, as I’m sure the answer is easy to find, I just enjoyed the simplicity of this particular article.

  • jenab6

    I bought a 50W solar panel and a voltage regulator to step down the voltage from about 20VDC to 14VDC. This charges a sealed lead-acid battery. When this battery is fully charged, I connect it to a COBRA 12VDC to 120VAC power inverter, which outputs in addition to house current, 5V USB from a special charging port. I use the 120V sockets to plug in wall-socket battery chargers, so I can not only charge my kindle and my USB battery packs, but also I can charge 9V NiMH and 18650 Li-ion batteries. It’s bulky, but I don’t need to carry it around.

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  • terre

    They have them at auto parts stores

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