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 is less disrupt to the environment.
How to Make a Passive Solar Water Heater. Every morning, billions of photons are sent streaming from the sun toward Earth. When they strike a surface, the atoms get excited & begin to move faster, generating heat, or warming up. This is called thermal conduction & is the scientific principle behind the design of passive solar water heaters, which uses no moving parts or fuel. Following these directions you can build an inexpensive water heater that will heat water to 150 degrees.