Energy from Water

ENVIRONMENTAL SCIENCE

Lesson 18.2:

Hydropower & Ocean Energy

OBJECTIVES

1. Explain how river water can be used to

generate electricity.

2. Identify benefits and costs of hydropower.
3. Describe how energy from the ocean can

generate electricity.

GO to this link

https://phet.colorado.edu/sims/html/generator/

latest/generator_all.html

A) What does the magnet need to do near a coil to turn the lights on?

B) How can you get the lightbulb to burn brighter?

What is something else that could

be used to turn the magnet?

GENERATING ELECTRICITY WITH HYDROPOWER

➢ Hydropower (or hydroelectric power): use of the kinetic energy of moving

water to turn turbines and generate electricity; In the U.S., about 6% of
electricity use is from hydropower.

GENERATING ELECTRICITY WITH HYDROPOWER

➢ We draw more renewable energy from the motion of water than from any

other resource other than biomass.

GENERATING ELECTRICITY WITH HYDROPOWER

○ Two basic approaches to electricity generation from moving water:

■DAMS block rivers and the water is stored in a reservoir behind the
dam. As the river water passes through the dam, it turns turbine
blades, which cause generators to produce electricity.

■Natural movement of river water— flowing water turns turbines, but
some water may be diverted through a pipe and carried to the
turbines. This method doesn’t disturb natural habitats as much as
dams and reservoirs, but when the river is low, less energy is
generated.

BENEFITS AND COSTS OF HYDROPOWER

➢ The use of hydropower is unlikely to grow because most of the rivers

that offer the best opportunities for hydropower are already damed.

➢ Benefits of hydropower:

○ Renewable
○ Clean— doesn’t pollute
○ Inexpensive
○ Dams may also control floods

➢ Costs of hydropower:

○ Dams and reservoirs drastically change ecosystems

■Example: populations of many fishes, such as salmon

○ Construction damages the landscape, which can cause erosion

and landslides.

○ Can prevent sediments and nutrients from getting downstream.

Case Study

Three Gorges Dam

https://www.youtube.com/watch?

v=Jyrlmar501c

BENEFITS AND COSTS OF HYDROPOWER

➢ Example of benefits & costs:

○ Three Gorges Dam— on China’s Yangtze River (completed in 2008)

■ Benefits: It generates enough hydroelectric power to replace

dozens of large coal or nuclear plants. It also controls floods and
allows boats to travel further upstream.

■ Costs: The reservoir has flooded many cities and destroyed the

homes of 1.3 million people.
It has flooded 10,000-year-old
archaeological sites, farmlands,
and wildlife habitats. Also, water
pollutants may end up trapped in
the reservoir and make the water
undrinkable.

Tidal Energy

ENERGY FROM THE OCEAN

➢ Tidal energy: using the movement of tidal water to generate electricity.

○ How to do this: Build a dam across a bay or tidal river. When the tide

rises, water moves through the dam and enters the bay. When the
tide falls, water leaves the bay and passes through the dam and is
channeled through a system of turbines.

○ Best locations: along narrow bays, like Alaska’s Cook Inlet (below)
○ Costs & benefits:

■ Releases little to no pollutants.
■ Can harm the ecology of the bay or

river.

■ Few places where tidal energy can

be harnessed effectively.

ENERGY FROM THE OCEAN

➢ Thermal energy from the ocean

○ Every day, ocean water absorbs radiation from the sun— equivalent to

the heat content of 250 million barrels of oil.
■It could provide 20,000 times the electricity used in the U.S. every day.

○ Ocean thermal energy conversion (OTEC): process that converts the

thermal energy in ocean water to electrical energy that can be used
■ Temperature gradient: gradual change in ocean temperature as you

go deeper— OTEC methods use temperature gradient to generate
electricity. Warm surface water circulates around pipes that contain
substances that boil at temperatures below the boiling point of water.
These substances evaporate from the heat of the water and the
gases spin turbines. Cold water piped in from the ocean depths
condenses the gases for reuse.