1. Chapter 18: Renewable Energy Alternatives

2. Lesson 1: Biomass and Geothermal Energy

3. The Reasons for Alternative Energy
Alternative energy resources are needed to replace fossil fuels, reduce air pollution, and reduce the emission of greenhouse gases.
Benefits of renewable energy
Most of them are unlikely to run out
If renewable energy resources replace fossil fuels, they will help decrease air pollution and greenhouse gas emissions
Become less dependent on other nations to supply us with fuel
Will create jobs for people to design, build, and maintain the needed technology

4. Renewable energy today
Fossil fuels supply 80% of our energy
Use of renewable energy sources is generally growing much faster than use of nonrenewable energy
Currently renewable energy sources cannot yet produce enough power to replace fossil fuels and nuclear energy

5. Biomass Energy
Energy derived from biomass is used for cooking, heating, powering motor vehicles, and generating electricity.
Biomass is material that makes up living organisms or comes from organisms.
Biomass energy is energy that is produced from this material
More than 1 billion people still burn wood from trees as their main energy source
Wood, charcoal, and manure account for 35% of energy use in developing nations
Biomass energy can now power motor vehicles and generate electricity

6. Biofuels Liquid fuels from biomass sources are known as biofuels
Ethanol
Produced by the fermentation of starches or sugars
Used in gasoline engines
In the US it is mainly produced from corn
A blend of gasoline and alcohol called gasohol is widely used in the US because it releases smaller amounts of many pollutants

7. Biodiesel
Produced from vegetable oil
Can be used in its pure form, but is usually mixed with conventional petroleum-based diesel fuel
Cuts down on emissions

8. Biopower
Electricity that is generated by the combustion of biomass is called biopower.
Many of the sources used for biopower are the waste products of existing industries or processes such as sawdust and cornstalks.
The decomposition of biomass by microorganisms produces gas that can be used to generate electricity.
The methane produced in landfills, called “landfill gas,” is captured and sold as fuel.

9. Benefits of biomass energy
The carbon produced by the combustion of biomass is the same amount of carbon that was removed from the atmosphere by photosynthesis to make the biomass in the first place.
Biomass is distributed worldwide
Help reduce dependence on imported fuels

10. Costs of biomass energy
Biofuel crops take up land that might be used for growing food or left in its natural condition
Deforestation, soil erosion, and desertification can result if wood is cut down too rapidly for fuel
Can cause indoor air pollution and increases the risk of respiratory system problems.
Corn ethanol provides only a small amount more energy than the energy needed to produce it.

11. Geothermal Energy
Steam and hot water produced by geothermal energy can be used for generating electricity and for heating
Deep beneath the surface of Earth, high pressure combined with the breakdown of radioactive elements produces heat – geothermal energy.
Hot springs and geysers are the result of geothermal energy

12. Harnessing geothermal energy
Steam from geysers at the surface is used to supply energy
Usually wells must be drilled down hundreds or thousands of meters toward heated rocks and water

13. Generating electricity
Magma heats ground water
Wells tap underground heated water or steam
Steam turns turbines and generates power
Steam is cooled and condensed
Water is returned back into the aquifer
Some geothermal plants will pump cold water deep underground where it reaches heated rocks and turns into steam

14. Hot groundwater can be used directly for heating homes, offices, and greenhouses
A ground source heat pump takes advantage of the fact that the temperature of soil a few feet underground stays the same all year.
In the winter, the water in the pipes picks up heat from the ground and transfers it to a building
In the summer, the water in the pipes transfers heat from the house to the ground.

15. Benefits and costs of geothermal energy
Can help replace the use of fossil fuels
Causes less air pollution
Releases smaller quantities of greenhouse gases
Sources may not always be truly sustainable
The water of many hot springs contains chemicals that damage equipment and add to pollution
Some geothermal energy projects may trigger earthquakes
Limited to areas where heated groundwater is easily accessible

16. Lesson 2: Hydropower and Ocean Energy

17. Generating Electricity with Hydropower
The movement of river water can be used to generate electricity
In hydropower, or hydroelectric power, we use the kinetic energy of moving water to turn turbines and generate electricity.
In the US 6% of the electricity is generated by hydropower

18. Using water stored behind dams
A dam blocks a river and water is stored in a reservoir behind the dam
As the river water passes through the dam, the water turns the blades of a turbine which cause generators to produce electricity
Most hydropower is generated by dams

19. Using the natural flow of a river
Called the run-of-the-river approach
Some of the river water is diverted through a pipe, which carries the water to the turbines.
This method does not disturb natural habitats as much
When the river is low, little electricity is produced

20. Benefits and Costs of Hydropower
Hydropower is nonpolluting and relatively inexpensive, but dams can harm ecosystems and disrupt people’s lives.
Most of the rivers that offer the best opportunity for hydropower are already dammed.

21. Benefits Renewable resource
Considered “clean” because nothing is burned
Does not pollute the atmosphere or release greenhouse gases
Relatively inexpensive
Dams can also control floods

22. Costs Drastically change ecosystems
Interrupts the natural flow of water
Negative impact on fish populations
Dam construction can cause damages to the landscape, erosion, and landslides
Dams can prevent important sediments and nutrients from getting downstream

23. Three Gorges Dam On China’s Yangtze River Completed in 2008
Generates enough hydropower to replace dozens of large coal and nuclear plants
Controls floods and enables boats to travel farther upstream
Cost $26 billion to build
Flooded many cities, destroyed the homes of 1.3 million people, and flooded 10,000 year-old archeological sites.
Rising water has destroyed farmlands and wildlife habitats.

24. Energy From the Ocean
The movement of tides and ocean thermal energy can be used to generate electricity
Tidal Energy
The term tidal energy refers to using the movement of tidal water to generate electricity
Twice a day, as ocean tides rise and fall, large amounts of water move upward and then draw back

25. In one method, a dam is built across a bay or tidal river
As the tide rises, water moves through the dam and enters the bay and as the water from the receding tide passes through the dam it is channeled through a system of turbines.
Harnessing tidal energy works best in long, narrow bays such as Alaska’s Cook Inlet or the Bay of Fundy in Canada because the differences in height between high and low tides are especially great.

26. Tidal electricity stations have the benefit of releasing few or no pollutants
Can harm the ecology of the bay or river
There are few places where tidal energy can be harnessed effectively

27. Thermal energy from the ocean
Each day, ocean water near the equator absorbs radiation from the sun
Ocean thermal energy conversion (OTEC) is a process that converts the thermal energy in ocean water to electrical energy that people can use.

28. The natural temperature gradient in ocean water is used to generate electricity
Warm surface water circulates around pipes that contain substances that boil at temperatures that are lower than the boiling point of water.
The heat from the water makes the substance evaporate and the gas spins turbines to generate electricity.
Cold water piped in from the ocean depths then condenses the gas so it can be used again.
Costs remain high

29. Lesson 3: Solar and Wind Energy

30. Harnessing Solar Energy
The sun’s energy can be used to heat buildings and generate electricity
The sun provides energy for almost all life processes on Earth
Using sunlight directly, without involving mechanical or electrical devices is called passive solar heating
Involves designing a building to collect, store, and distribute the sun’s energy naturally
Greenhouses and homes that are designed with windows that face south and east to capture sunlight in winter are using passive solar heating

31. An active solar heating system uses technology to collect, move, and store heat derived from the sun.
A flat-plate solar collector generally consists of a black, heat-absorbing metal plate in a flat box with a glass cover and has a long tube running through it
Sunlight passes through the glass and heats the metal plate and the fluid in the tube absorbs heat from the metal plate

32. In a photovoltaic (PV) cell, solar energy is converted directly into electricity.
Contain two plates typically made of silicon
One plate is rich in electrons and when sunlight strikes this plate it knocks some electrons loose which are then attracted to the other plate
The flow of electrons creates an electric current
PV cells can be arranged in panels or contained in special roofing tiles

33. Concentrating solar power (CSP) is a technology that uses mirrors to focus sunlight in order to generate electricity.
A “power tower” has hundreds of mirrors positioned in a large area surrounding a tall tower that houses a receiver.
Heated fluid in the receiver is used to produce steam which turns the blades of a turbine and powers a generator.

34. Benefits and Costs of Solar Power
Solar power has many benefits, such as its limitless supply, but it depends on weather and is currently expensive

35. Benefits Endless source Technology uses no fuel
Quiet and safe technology
No greenhouse gases released
Requires little maintenance
Reduces dependence on power plants
Possible to sell excess solar electricity to power companies
Creating many new jobs

36. Costs Manufacturing solar-energy devices creates some pollution
Some regions are not sunny enough to provide much solar power
Solar equipment is expensive

37. Wind turbines convert wind’s kinetic energy into electrical energy
Harnessing Wind Power
Wind turbines convert wind’s kinetic energy into electrical energy
People have used wind power for thousands of years with windmills
A wind turbine is a device that converts the wind’s kinetic energy into electrical energy
Wind blowing into a turbine turns blades that connect to a gearbox which connects to a generator that produces electricity.

38. Wind turbines are often built in groups called wind farms
Average wind speeds are approximately 20% greater over water than over land
Offshore wind turbines are becoming more common even though costs to erect and maintain wind turbines in water are higher.

39. Benefits and Costs of Wind Power
Wind power is nonpolluting and efficient, but its supply is unpredictable and it may damage the landscape and wildlife.
Benefits
Does not cause pollution
Highly efficient
Wind farms are less expensive than fossil fuel power plants once they are up and running

40. Costs
Wind farm startup costs are generally higher than those of fossil fuel power plants
We have no control over when wind will occur – unpredictable
Some areas are windier than others
When wind farms are proposed near communities, the people living in the area often oppose them
Clutter the landscape
Too noisy
Birds and bats can be killed

41. Lesson 4: Energy From Hydrogen

42. Producing Hydrogen Fuel
Hydrogen fuel can be produced from the breakdown of water or other hydrogen-containing compounds
In electrolysis, water molecules are broken down into oxygen gas (O2) and hydrogen gas (H2) by an electric current that runs through the water
2H2O → 2H2 + O2
Does not emit greenhouse gases or pollutants
A costly process

43. Hydrogen can be extracted from the breakdown of methane in natural gas.
CH4 + H2O → 4H2 + CO2
Less expensive
Produces a greenhouse gas

44. Scientists are investigating other ways to obtain hydrogen
The heat given off by a nuclear reactor may be used to split water into hydrogen and oxygen
Algae may be used to produce hydrogen

45. Benefits Hydrogen is the most abundant element in the universe
Produces few greenhouse gases or pollutants
Water and heat may be the only waste products generated
Can be stored and transported

46. Costs Can catch fire if not stored properly Requires energy inputs
Expensive to produce
To be useful in a motor vehicle, hydrogen needs to be compressed

47. Fuel cells are used to generate electricity
Hydrogen gas can be used to produce electricity within fuel cells
A fuel cell has a positive electrode and a negative electrode and reactions in a fuel cell result in an electric current
Uses the reverse of the reaction for electrolysis
2H2 + O2 → 2H2O

48. Hydrogen gas enters the side of the cell with the negative electrode and each molecule then splits into two positively charged hydrogen ions (H+)
Oxygen gas enters the cell on the side with the positive electrode
A series of reactions cause an electric current to flow from the negative terminal to the positive terminal and while this happens the oxygen and hydrogen ions combine to form molecules of water

49. A fuel cell can be used in many ways such as powering vehicles and producing electricity.