Powering the Big Units

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Powering the Big Units

Short Version: Energy is the ability to do something, and is measured in joules or calories or kilowatt-hours or in other ways. Power is how fast you do it, and is measured in watts or horsepower or in other ways. Your 2000-calories-per-day diet is the same as a single 100-watt light bulb burning all day. Let's take a closer look!

Friendlier but Longer Version: Suppose that you are an employee at a Pennsylvania power company. Your customers buy a lot of kilowatt-hours of electricity to run their microwave ovens and music players, but your power plant needs to be turned off for maintenance. Your boss tells you to buy some power from a hydroelectric company in Quebec but they don't have any kilowatt-hours for sale -- all the offer are megajoules. What do you do?

Water above Glen Canyon Dam on Colorado River in Arizona at higher elevation than water below the dam.
This isn’t Quebec, but it is hydropower. Water above the Glen Canyon Dam on the Colorado River in Arizona is at a higher elevation than the water below the dam, and so has higher potential energy.
Photo Credit: Richard B. Alley
Giant yellow turbines that spin to make electricity as water falls through the dam.
As the water falls through the dam, it spins giant turbines that make electricity.
Photo Credit: Richard B. Alley
Power lines that carry electricity away, stretched across the water.
The water comes out at lower elevation with less potential energy, and the electricity is carried away in power lines to be used in various ways.
Photo Credit: Richard B. Alley