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# Hydroelectric Power and the City of Ember

Power up! An underground hydroelectric generator powers the entire City of Ember. This week, Everyday Einstein explains the science behind the popular series.

By
Lee Falin, PhD
Episode #045

## Turbines

Now that we know how generators work, we just need to find a way to turn the rotor. As you might remember from the episode on potential and kinetic energy, energy can't be created from nothing; it can only be converted from one form to another. We're trying to create electrical energy using mechanical energy, the energy of movement. But where can we get the mechanical energy?

The most common method for getting the mechanical energy to turn the rotor is via a device called a turbine. A turbine takes energy from a flowing fluid and converts it to mechanical energy. Remember that when scientists talk about fluids, we mean not only liquids, but gases as well. Most turbines attached to generators work by harnessing the energy in flowing steam.

## Power Plants

Fossil fuel and nuclear power plants both use steam turbines in their generators. First they heat some water by either burning fossil fuels or using the heat energy from a nuclear reaction. That heated water turns into steam, which then flows past a turbine, causing it to spin. The spinning turbine is attached to a metal shaft, which is connected to a rotor, and this means the rotor spins when the turbine spins. As the rotor spins inside of the stator, electricity is generated through induction.

A hydroelectric power plant uses the same principles, but instead of using heat energy or nuclear energy to convert the water into steam, it uses the mechanical energy of falling water to turn the turbine.

Most hydroelectric plants involve building a dam across a river to create a large reservoir of water. There's a small tunnel through the dam called a penstock, which has a turbine at the other end. Gravity pulls the water through the penstock, converting its gravitational potential energy into the kinetic energy of movement. As it flows past the turbine, it causes the turbine to spin, generating electricity just like the generators in other power plants.

Wind generators work the same way except they use wind instead of falling water or steam to spin the turbine.