237. How does hydroelectric power work?
Hydroelectric power begins with water descending from an elevated reservoir, such as a lake in the mountains. While it's in the elevated reservoir, this water has stored energy—in the form of gravitational potential energy. As this water flows downward through a pipe, its gravitational potential energy becomes either kinetic energy or pressure potential energy or both. By the time the water arrives at the hydroelectric power plant, it is either traveling very quickly or has an enormous pressure or both. In the power plant, the water flows past the blades of a huge turbine and does work on those blades. The blades are shaped somewhat like airplane wings and they "fly" through the moving water. Since the blades are attached to a central hub, they cause this hub to rotate and allow it to turn the rotor of a huge electric generator. The rotor of this generator typically contains a giant electromagnet. The electromagnet turns within a collection of stationary wire coils and it induces electric currents in those coils. These electric currents carry power out of the generator to the homes or business that need it.