A new design for a hydroelectric generator could cheaply light up off-grid areas. The Hydro-Electric Barrel is a spinning water wheel that floats on the water surface and turns in the current. The spinning motion drives permanent magnet generators inside. It could generate enough power to light banks of LEDs and light up bridges, buoys, or even charge mobile devices in off-grid areas and developing countries. And, because it sits on the surface, it doesn’t disrupt the environment as much as other hydro-power technologies.