6.9 Hydroelectric Power

How hydroelectric power works

Hydroelectric power generates electricity by using the kinetic energy of moving or falling water to spin turbines connected to generators. Most large-scale hydropower comes from dams that impound water in a reservoir, releasing it through turbines. This is a renewable energy source since it relies on the water cycle, driven by solar energy and gravity.

Types of hydroelectric systems

Impoundment (dam) systems store water in reservoirs for controlled release. Run-of-river systems divert a portion of river flow through turbines without large storage, causing less habitat disruption. Pumped storage pumps water uphill during low demand and releases it to generate power during peak demand, acting as an energy storage system.

Benefits and drawbacks

Hydropower produces no direct air pollution or CO2 emissions during operation and can provide reliable, flexible baseload power. However, dams disrupt river ecosystems, block fish migration (e.g., salmon), alter sediment transport, flood land (displacing communities and habitats), and reservoirs can emit methane from decomposing organic matter.

Key terms

Hydroelectric power

Electricity generated by using the kinetic energy of moving or falling water to spin turbines.

Impoundment (dam) system

Hydropower system that stores water in a reservoir and releases it through turbines for controlled electricity generation.

Run-of-river system

Hydropower system that uses natural river flow with little to no storage, causing less ecological disruption.

Pumped storage

System that pumps water uphill during low demand and releases it during peak demand to generate electricity, functioning as energy storage.

Ecological impact of dams

Dams can block fish migration, alter sediment transport, flood habitats, and reservoirs may emit methane from decomposing organic matter.

Try an AP-style question

How does a hydroelectric dam produce electricity?

1. Burning fuel boils water
2. Wind pushes the water
3. Sunlight heats the reservoir
4. Falling water spins turbines