This collection of phone cases is designed to keep your phone powered up and running all day long. The cases are made with solar panels that absorb the sun's energy and convert it into usable power for your phone. They are lightweight and slim, so they won't add bulk to your device.
From Wikipedia
Solar powered flashlights or solar powered torches are flashlights powered by solar energy stored in rechargeable batteries. Most of these flashlights use light-emitting diodes lamps since they have lower energy consumption compared to incandescent light bulbs.