A portable solar charger? Yes, harnessing the power of the sun has come a long way since 1839, when French physicist Alexandre-Edmond Becquerel discovered the photovoltaic effect that creates electricity from photons in sunlight. Becquerel put silver chloride in an acidic solution, connected it to platinum electrodes, and when the chemical concoction was exposed to light it generated current and voltage.
Nearly 175 years later inexpensive solar panels to charge a cell phone or GPS can be found in any sporting goods store across the land—and they don’t require a chemistry set. But there’s no better way to understand how a photovoltaic system works than by building one yourself. All it takes is a soldering iron, a $20 bill, and a visit to Radio Shack.
Portable Solar Chargers Basics
Most off-the-shelf solar panels or photovoltaic cells are made of crystals that generate electricity when exposed to certain wavelengths in the sun’s light. Instead of just heating up like a snake crossing hot Texas pavement, electrons in the crystals break free and move, producing a current.
The most efficient cells (think NASA) can turn around 50 percent of the available light into energy, but the small consumer models we’re dealing with range closer to 15 percent. All that magic is remarkably cheap these days. A 0.5-watt 6-volt cell, about the size of a deck of cards, can be had for $10 or less. By themselves, they’re efficient enough to charge a small electric device, or can be connected in a multiple-cell array for more power.
After the panel, the next most important component of a portable solar system is the diode; this regulates the flow of the electricity to and from the cell. Without a diode, the panel would draw power back out of your battery when it isn’t exposed to sunlight or could send too much power and overload the battery or device. For these projects a 1N914 blocking diode acts as a solid regulator; this can be found for pennies online or in $2 12-packs at Radio Shack. From this point on you have options.
Direct or Battery-Based?
A direct or pure solar system can be made by wiring the panel and diode directly to your device’s charging cable. It’s as easy as wire-stripping a USB cable and attaching it to the panel. The sunlight is converted and ported direct to the device. It’s light and eco-friendly, but lacks power storage and doesn’t work well for gadgets requiring lots of amps.
The power flow can be inconsistent, depending on the strength of the sun. Battery-based systems are heavier but ultimately more user friendly. As you do with commercial portable solar panels, you can hang a panel up during the day at camp, the batteries charge up, then you can plug in your device for a charge at night.
For the amount of change buried in your sofa, you can get a battery holder with wire leads to connect into your portable system. Slot in some rechargeable batteries and let the sun do its work. If you’re running a handheld GPS that takes AA batteries, then you’re good—just charge and go.
But if you want to power a device with an internal battery without cutting the power cable, you’ll need a USB charging circuit. These can be found for about $10 on eBay or on electronic project sites like browndoggadgets.com, which has an excellent “Instructions & Guides” section worth exploring. But if you’re cheap like me and have a box of outdated gadgets lying around, you can take apart a USB device and harvest the circuit and plug.
Portable Solar Panels
There are tons of small solar panels on the market now—from matchbox-sized to truck-bed long. For these portable projects I relied on Radio Shack 0.5-watt 6-volt cells, which I picked up for $10 close to home. Radio Shack sells larger versions, and the online options are endless. If you go bigger, or for a faster charge with more power, just make sure to check your math (see “Know Your Power Flow” on page 70) to stay safe.
Pure Solar USB Charger
This will power most cell phones and GPS units. Materials include:
- Portable solar panel
- 1N914 blocking diode
- USB charging cable
- 1/4-inch heat-shrink tubing
- Soldering iron
- Wire stripper
Instructions:
- Cut the end off the USB cable that plugs into the computer or wall outlet adapter. Strip the wire insulation to expose the red positive (+) and black or white negative (-) wires.
- Radio Shack solar panels come wired. Solder the diode to the red wire with the negative side (-) of the diode, marked black, facing away from the panel. This prevents the panel from draining power back off the device. Solder a few inches of wire to the opposite end of the diode.
- (optional) Next you can solder in line a 5-volt regulator, which will prevent the power from spiking over 5.1 volts. But as cell phones and most other devices can handle 6 volts, it isn’t necessary.
With the heat-shrink wrap, cover and seal the diode into your wire. Put more heat shrink on the red and black wires of your USB cord. Then solder the wires to your panel and shrink the wrap with some heat.
Note: If you have an iPhone, you can run into frustration with this build. Apple products require a steady 5 volts to activate the battery charge. Your best option is a solar battery USB charger (see below).
Solar Battery USB Charger
Good for cells, Apple devices, tablets, GPS units, lithium ion battery packs. Materials include:
- One portable solar panel
- 1N914 blocking diode
- AA or AAA battery holder
- USB charging circuit
- Case to hold your charger
- 1/4-inch heat-shrink tubing
- 1/8-inch wire
- Soldering iron
- Wire stripper
- Double-sided tape or super glue
Instructions:
- Solder the diode to the red wire on the solar panel with the negative side (-) of the diode, marked black, facing away from the panel. Add heat-shrink tubing, then twist and solder a few inches of fresh wire to the positive (+) side of the diode.
- Twist the black wire (-) on the battery holder to the black wire (-) on the solar panel so the wires run parallel and you have a new exposed connection made up of both the panel and battery holder wires. Do the same on the red positive (+) side.
- The USB charging circuit converts DC power to USB and provides the plug to connect your USB cable. You can get these circuits for cheap online, or take them out of a USB device. I tore mine out an old USB battery pack. Inspect the circuit board carefully and find the solder points marked (+) and (-). Solder your wire bundles from the solar panel/battery pack to these points very carefully.
- Tape or glue your system into its case. Small Otter Box or Pelican-type cases work great.
- To test your system, put a charged set of batteries into the battery holder. Then plug in your phone or device. If it doesn’t work, check your solder points. Once the device pulls a charge, try a dead set of batteries, leaving the system to charge in the sun, and enjoy all that free electricity—courtesy of outer space.
Note: For a larger system, add a second panel in array, with a diode between the panels for faster charging. You can also easily add in an LED charging indicator light or an on/off switch just by connecting your reds and blacks between the panel and the battery holder.
Solar Battery Charger
Use with any rechargeable lithium ion batteries. Materials include:
- Portable solar panel
- 1N914 blocking diode
- AA or AAA battery holder
- Case to hold your charger
- 1/4-inch heat-shrink tubing
- Soldering iron
- Wire stripper
- Double-sided tape or super glue
Instructions:
- Solder the diode to the red wire on the solar panel with the negative side (-) of the diode, marked black, facing away from the panel.
- Put heat shrink on the wires of the battery holder. Then solder the black wire (-) on the battery holder to the black wire on the solar panel and the red wire to the diode.
- Take your case—I’ve used Otter Boxes, but with a smaller panel and AAA battery holder an Altoids tin works, too—and tape or glue the system in place and you’re good to go.
