AP Environmental
Science
Mr. Grant
Lesson 102
Ocean Energy
Sources
&
Hydrogen
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Mastery Check
Describe several environmental and economic
benefits of wind power. What are some drawbacks?
Wind power produces no emissions during operation,
it is more energy efficient than conventional sources,
and it also promotes local self-sufficiency. It does,
however, require significant up-front costs for
erection of turbines and transmission lines; it is an
intermittent resource, varying in both time and
space; some find turbines to be an eyesore; and the
rotor blades may pose a threat to birds and bats.
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Objectives:
• Define the term ocean thermal energy conversion (OTEC).
• Describe ocean energy sources and how we could harness them.
• Explain hydrogen fuel cells and weigh options for energy storage
and transportation.
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Define…
Ocean Thermal Energy Conversion
A potential energy source that involves
harnessing the solar radiation absorbed by
tropical oceans in the tropics.
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Describe ocean energy sources and the
ways they could be harnessed.
• Ocean energy sources include the motion of tides, waves, and
currents, and the thermal heat of ocean water.
• Ocean energy is perpetual renewable and holds much promise,
but so far technologies have seen only limited development.
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We can harness energy from tides, waves, and
currents
 Kinetic energy from the natural motion of ocean
water can generate electrical power
 Wave energy = the motion of waves is harnessed
and converted from mechanical energy into
electricity
 Many designs exist, but few have been adequately
tested
 Some designs are for offshore facilities and involve
floating devices that move up and down the waves
 Wave energy is greater at deep ocean sites
 But transmitting electricity to shore is very expensive
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We can harness energy from tides, waves, and currents
 Some designs work along coastlines
 One funnels waves into elevated reservoirs
 Another uses
waves to push air
into and out of
chambers, turning
turbines
 Kinetic energy from
the natural motion
of ocean water can
generate electrical
power
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Kinetic energy from waves generating electricity
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We can harness energy from tides, waves, and currents
 The rising and falling of
ocean tides twice each day
move large amounts of
water
 Differences in height
between low and high
tides are especially great
in long, narrow bays
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We can harness energy from tides, waves, and
currents
 Tidal energy = energy harnessed from dams that
cross the outlets of tidal basins
 Water is trapped behind gates
 Outgoing tides turn turbines to generate electricity
 Tidal stations release few or no pollutant emissions
 But they can affect the ecology of estuaries and tidal
basins
 Another design uses the motion of ocean currents,
such as the Gulf Stream
 Devices similar to underwater turbines have been
erected off of Europe to test this technology
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Energy can be extracted from tidal movement
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The ocean stores thermal energy
 Each day, tropical oceans absorb solar radiation
equal to the heat content of 250 billion barrels of oil
 Ocean thermal
energy conversion
(OTEC) = uses
temperature
differences between
the ocean’s warm
surface water and
cold deep water
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The ocean stores thermal energy
 Closed cycle approach =
warm surface water
evaporates chemicals,
which spin turbines to
generate electricity
 Cold water condenses
the gases to be reused
 Open cycle approach =
warm surface water is
evaporated in a vacuum
and its steam turns
turbines
 Costs are high, and no
facility operates
commercially yet
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Explain hydrogen fuel cells and assess future
options for energy storage and transportation.
• Hydrogen can serve as a fuel to store and transport energy, so that
electricity generated by renewable sources can be made portable and
used to power vehicles.
• Hydrogen can be produced cleanly through electrolysis, but also by
using fossil fuels – in which case its environmental benefits are
reduced.
• Fuel cells create electricity by controlling an interaction between
hydrogen and oxygen, and they produce only water as a waste
product.
• Hydrogen infrastructure requires much more development, but
hydrogen can be clean, safe, and efficient. Fuel cells are silent,
nonpolluting, and do not need recharging.
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Hydrogen
 Energy produced by the new renewables is not
easily stored in large quantities for use when needed
 This is why most vehicles rely on gasoline from oil
 Fuel cells and their fuel, hydrogen, promise a way to
store considerable quantities of energy cleanly and
efficiently
 Hydrogen is an energy carrier, not a primary source
 Like electricity and batteries, its energy can be
converted for use at a later time in a different location
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Some yearn for a “hydrogen economy”
 A hydrogen economy would provide a clean, safe,
and efficient energy system
 Electricity
produced
from
intermittent
sources
(sun, wind)
would be
used to
produce
hydrogen
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Some yearn for a “hydrogen economy”
 Fuel cells (essentially, hydrogen batteries) would
use hydrogen to produce electricity to power
vehicles, homes, computers, cell phones, etc.
 Governments are funding research into hydrogen
and fuel cell technology
 Iceland and
Germany have
converted their
public buses to run
on hydrogen
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A typical hydrogen fuel cell
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Hydrogen fuel may be produced from water or
from other matter
 Hydrogen gas does not exist freely on Earth
 Energy is used to force molecules to release
hydrogen
 Electrolysis = electricity splits hydrogen from water
2H2O  2H2 + O2
 It may cause pollution, but only if the source of energy
for the electricity produces pollution
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Hydrogen fuel may be produced from water or
from other matter
 The environmental impact of hydrogen production
depends on the source of hydrogen
 Using methane, biomass, or fossil fuels produces the
greenhouse gas CO2
CH4 + 2H2O  4H2 + CO2
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Production of hydrogen fuel
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Fuel cells produce electricity by joining
hydrogen and oxygen
 Once isolated, hydrogen gas can be used as a fuel
to produce electricity within fuel cells
 The chemical reaction
is the reverse of
electrolysis
2H2 + O2  2H2O
 The movement of the
hydrogen’s electrons
from one electrode to
the other creates
electricity
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Hydrogen and fuel cells have costs and
benefits
 Need massive and costly development of infrastructure
 Some research suggests that leakage of hydrogen can
deplete stratospheric ozone
 We will never run out of hydrogen
 It can be clean and nontoxic to use
 It may produce few greenhouse gases and pollutants
 If kept under pressure, it is no more dangerous than
gasoline in tanks
 Cells are typically 35–70% energy efficient (up to 90%)
 Fuel cells are silent and nonpolluting and won’t need to
be recharged
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