A Solar backpack is a backpack equipped with thin film solar cells and batteries. The solar panels convert sunlight into electricity, which is stored in the batteries and can be used to power portable electronic appliances like mobile phones and mp3 players.

Features
The solar backpack usually contains a flexible monocrystalline solar panel, battery, charge controller, plugs, cords and light bulbs. It provides users with power up to 120 watt-hours/day, capable of powering electronic equipment rated up to 300 W. It can also be utilized in international aid, disaster relief, emergency power and field research.

Applications
A solar backpack system known as Rucksack Enhanced Portable Power System (REPPS), developed by the United States Army Communications-Electronics Research, Development and Engineering Center, features a 62-watt solar panel blanket in a backpack for use by the US army based in Afghanistan. The US Air Force had previously employed solar panels on shipping containers, developed by Lockheed Martin, while the Marines developed suitcase units of foldable solar panels which can also be carried as a backpack. As military equipment like radios and GPS units require lots of energy, these portable solar power systems were designed to minimize dependence of troops on fossil fuels in combat zones. The REPPS is currently utilized by the 173rd Airborne Brigade Combat Team in Logar, Afghanistan. It is used to power electronic devices with a charging time of just 6 hours. As it weighs at around 10 pounds, it can be carried as a backpack easily. In addition to solar power, it can also convert ac power from wall outlets and utilize power from disposable batteries and vehicles.
Solar backpacks can also power laptops for up to 3 hours.
After an exposure of about six hours, it can power an emergency light for 14 hours.
Solar backpacks can also be used to power medical equipment and humanitarian relief efforts where power from the utility grid is not available.
These types of backpacks can also be used to power cameras for use in remote areas.

Advantages
Solar backpacks are light-weight, hence making it easier to carry.
Solar backpacks carry a green energy source for the environment.
Flexible solar panels also are light and portable, as well as waterproof.

Source from Wikipedia