© 2011 Pearson Education, Inc. AP Environmental Science Mr. Grant Lesson 102 Ocean Energy Sources & Hydrogen

© 2011 Pearson Education, Inc. 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.

© 2011 Pearson Education, Inc. 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.

© 2011 Pearson Education, Inc. Define… Ocean Thermal Energy Conversion A potential energy source that involves harnessing the solar radiation absorbed by tropical oceans in the tropics.

© 2011 Pearson Education, Inc. 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.

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. 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

© 2011 Pearson Education, Inc. Kinetic energy from waves generating electricity

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. Energy can be extracted from tidal movement

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. 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

© 2011 Pearson Education, Inc. 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.

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. A typical hydrogen fuel cell

© 2014 Pearson Education, Inc. 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 2H 2 O  2H 2 + O 2  It may cause pollution, but only if the source of energy for the electricity produces pollution

© 2014 Pearson Education, Inc. 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 CO 2 CH 4 + 2H 2 O  4H 2 + CO 2

© 2011 Pearson Education, Inc. Production of hydrogen fuel

© 2014 Pearson Education, Inc. 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 2H 2 + O 2  2H 2 O  The movement of the hydrogen’s electrons from one electrode to the other creates electricity

© 2014 Pearson Education, Inc. 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