How Solar-powered Backpacks Work

A young man listening to headphones with his solar backpack.
Humanity is so wired nowadays that when our technology fails us, it can feel like the end of the world. Solar-powered backpacks are here to help with that.

The world moves pretty quickly these days, and as a result, the modern human is constantly on the go from one place to another. The advent of the cell phone, laptop and the personal digital assistant (PDA) has made us even more mobile. Technology has advanced so much that people can now take their work with them, unchained from their cubicles. More and more public areas are hooked to the World Wide Web via wireless Internet, allowing people to connect in parks, coffee shops and plazas. You can't walk 10 feet (3 meters) in a major city these days without seeing someone closing a deal on a cell phone, searching the internet with a PDA or checking e-mail on a laptop. There's no doubt that it's a digital and portable world we live in.

The problem with this kind of technology is that it all requires juice to make it happen. As advanced as these handheld devices are, every PDA, cell phone and MP3 player on Earth is limited by its battery life. The most advanced pocket computer you could imagine becomes nothing more than a paperweight once the battery runs out.


But take heart, techno-man -- there's a solution. Some smart people have married solar cell technology with the old-fashioned backpack to create a charging station you can take along with you. All you need is a little sunshine and time, and you'll never be short on battery life again. Solar-powered backpacks are the latest travel gadgets in the tech world to make sure you stay connected.

Mechanics of Solar-powered Backpacks

Solar cell
The key to this travel gadget -- a hand-sized solar cell
ason |

To figure out how a solar-powered backpack works, we need to understand a little bit about the mechanics of the solar-powered backpack, or solar technology. It may seem complicated, but it's really pretty simple -- photovoltaic (PV) cells are what make it all happen. The cells, grouped together as modules or panels, collect light from the sun and convert it to usable electricity. They're able to do so with the help of something called a semiconductor. These are substances that can conduct electricity. In the case of solar cells, silicon is the semiconductor of choice.

­When sunlight hits a solar panel, the silicon semiconductor absorbs a portion of the light and its energy. When this happens, electrons in the silicon are knocked loose and they begin to flow freely. Electric fields in the photovoltaic cells wrangle those electrons and force them to flow in one direction like a cattle rancher guiding his heard. This creates an electric current that can be harnessed by attaching metal contact points at the top and bottom of the PV cell. Once the energy is collected, it can be used immediately as electricity or stored in a battery or series of batteries for later use.


The silicon semiconductor is naturally shiny and reflective, which isn't great for drawing in sunlight. To solve this issue, an antireflective coating is applied to the cell to keep energy loss at an acceptable five percent or less. Add a protective covering to the panel and you have an energy-harnessing machine. This is enough to get you a basic understanding of how this solar technology works. Now, let's learn more about how solar-powered backpacks puts this technology to work.

Solar-powered Backpack Applications

Laptop bag
The Voltaic Generator has enough power to charge a laptop.
Image courtesy of Voltaic Systems

If we have solar technology and we know that the modern human is wired and always on the go, it seems like a no-brainer to bring the power of the sun with you. Some clever backpack manufacturers have done just that. Solar-powered backpacks have small solar panels attached to the outside of the pack so you can harness the sun's rays to charge your cell phone, PDA or MP3 player. The panels are lightweight, waterproof and can produce up to four watts of power. This means that just one hour of direct sunlight can produce enough energy to power a cell phone for about an hour and a half.

The key to the solar backpack is the fact that it has a lithium-ion battery pack inside to store this energy. One hour of sunlight might charge your phone for a short time, but a full 10-hour charge provides up to 55 hours of stored energy. For those cloudy days, the packs also have an AC adapter that allows you to charge the battery using your car's power. The packs come with a variety of cell phone adapters and a USB plug for your MP3 player.


There are several companies manufacturing solar backpacks and they range in price from $75 to $250. The less expensive models generally only have a single panel and, as a result, less overall capacity. One company has even introduced a more robust version in the form of an over-the-shoulder bag that can generate a whopping 15 watts of energy -- enough juice to charge your laptop. That kind of versatility comes with a heftier price tag. You can plan on spending $500 for anytime, anywhere laptop power.

For more information on solar-powered backpacks, solar-powered backpack applications and other travel gadgets visit the links on the next page.


Lots More Information

Related HowStuffWorks Articles


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