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Lesson: Chapter 18 — Work, Energy and Power

18.2. Energy changing form 3 of 4

Storing water for electricity

The largest potential energy store in the country is a reservoir, and the only thing that makes it a store is that the water is high up.

Figure to be added

Figure 18.10 — a cross-section of a hydroelectric dam: the reservoir held behind the wall, water running down through the dam to a turbine, and transmission towers carrying the electricity away.

The chain of conversions

Water stored in a reservoir at a height is allowed to flow down. The potential energy of that water is converted into kinetic energy, and the moving water turns a turbine, by which electricity is generated.

Potential energy of the stored water → Kinetic energy of the falling water → Turning the turbine → Electrical energy

Why the wall has to be tall

Because the store is m g h, a reservoir holds more energy the higher its water sits above the turbine. That is why a dam is built high rather than merely wide, and why the water is taken from the top of the reservoir rather than the bottom.

A reservoir is a battery made of height

Nothing is burned and nothing is used up. Rain lifts the water back up for free, which is what makes this store refill itself and makes the electricity renewable.