AP Environmental Science Mr. Grant Lesson 103

1. AP Environmental Science • Mr. Grant • Lesson 103 Ocean Energy Sources & Hydrogen

2. 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.

3. Define the terms ocean thermal energy conversion (OTEC). Ocean Thermal Energy Conversion A potential energy source that involves harnessing the solar radiation absorbed by tropical oceans in the tropics.

4. Describe ocean energy sources and the ways they could be harnessed. • Major 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.

5. We can harness energy from the oceans • Kinetic energy from the natural motion of ocean water can generate electrical power • 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 • Tidal energy = dams cross the outlets of tidal basins • Water is trapped behind gates • Outgoing tides turn turbines to generate electricity • Tidal stations don’t release emissions • But they change the area’s ecology

6. Energy can be extracted from tidal movement

7. Wave energy • 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 • Another design uses the motion of ocean currents, such as the Gulf Stream • Underwater turbines have been erected off of Europe

8. Coastal onshore facilities • One coastal design uses rising and falling waves, which push air in and out of chambers, turning turbines to generate electricity • No commercial wave energy facilities operate yet • But demonstration projects exist in Europe, Japan, and Oregon

9. 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 surface and deep water • Closed cycle approach = warm surface water evaporates chemicals, which spin turbines to generate electricity • 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

10. 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 re3newablke sources can be made portable and used to power vehicles. • Hydrogen can be produced through electrolysis, but also by using fossil fuels – in which case its environmental benefits are reduced. • There is a concern that releasing hydrogen could have negative impacts on the atmosphere. • Fuel cells create electricity by controlling an interaction between hydrogen and oxygen, and they produce only water as a waste product. • Hydrogen can be clean, safe, and efficient. Fuel cells are silent, nonpolluting, and do not need recharging.

11. A hydrogen economy • A hydrogen economy would provide a clean, safe, and efficient energy system by using the world’s simplest and most abundant element (hydrogen) as fuel • Electricity produced from intermittent sources (sun, wind) would be used to produce hydrogen • Fuel cells (hydrogen batteries) would use hydrogen to produce electricity to power cars, homes, computers, etc. • Governments are funding research into hydrogen and fuel cell technology

12. A typical hydrogen fuel cell

13. A hydrogen-fueled bus Germany is one of several nations with hydrogen-fueled city buses

14. Production of hydrogen fuel • Hydrogen gas does not exist freely on Earth • Energy is used to force molecules to release the hydrogen • Electrolysis = electricity splits hydrogen from water 2H2O  2H2 + O2 • It may cause pollution, depending on the source of electricity • The environmental impact of hydrogen production depends on the source of hydrogen • Using methane produces the greenhouse gas CO2 CH4 + 2H2O  4H2 + CO2

15. Fuel cells can produce electricity • 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

16. Hydrogen and fuel cells have costs and benefits • Need massive and costly development of infrastructure • 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 up to 90% energy efficient • Fuel cells are silent and nonpolluting and won’t need to be recharged