Phone batteries rarely last a full day anymore, so carrying compact chargers (小巧的充电器) is becoming normal. But many of these so-called portable devices are heavy, thick and inconvenient—until Solar Paper is developed.

    Chicago engineers have designed a super-thin, lightweight panel (面板) called Solar Paper capable of charging an iPhone in two hours and many panels can be combined to boost its power. It was created by Chicago-based Yolk. After raising more than $1million online for the production, it is now available to purchase throughout the country. It comes in four versions—2.5W, 5W, 7.5W and 10w—depending on the output needed for various devices. And these different models are created by combining individual 2. 5W panels together.

    A 2.5W panel will charge an iPhone 6 or Galaxy S3 in five hours. The 5W version charges the same devices but cuts changing time to two hours or three hours if it's cloudy. The 7.5W model Solar Paper changes the devices in the same time as the 5W version but produces more energy when it is cloudy. The 10W version is ideal(理想的) for the iPad Air 2, and will charge a device in 2.5 hours. Each individual panel measures 3.5 inches× 6.7 inches×0.6inches, weighs 60g and 1.5mm thick.

    Other features include a unique automatic reset (重置) function which stops and starts the Paper charging when cast with a shadow or placed in sunlight. Other solar chargers require you to re-plug the wire at these conditions. It also has a low-energy LCD screen that displays the amount of power the Solar Paper produces in real time.