1. Chapter 10 Energy for Tomorrow: Solar and Other Renewable Energy Resources
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2. The Sun: Earth’s Ultimate Energy Source
Fusion reactions that occur in the Sun produce 1026 watts (W) of power, which constantly radiates into space
If energy can be captured and stored by even 0.01% of the energy represented by a dollar, 1/100 of one penny, energy problems would be solved

3. The Sun: Earth’s Ultimate Energy Source (continued)
Obstacle to using solar energy
Low concentration
Amount of solar energy available varies with geographical location and weather
Fossil fuels are hard to beat for concentrated energy content
Solar energy is expensive

4. Hydroelectric Power Considered to be an indirect form of solar energy
Hydropower is a clean, efficient, and renewable energy source
Figure 10.3; page 265

5. Disadvantages of Hydroelectric Power
Small number of dammable rivers in the United States
Threats to marine life
Potential dam failure

6. Wind Power Another indirect form of solar energy
The Sun heats air, which expands and rises; cooler air rushes in to fill the void, creating wind that can turn a turbine
Wind turbines near Palm Springs, California; page 266.

7. Disadvantages of Wind Power
Unattractive
Lots of land required
Winds are intermittent and uncontrollable
Secondary energy source or storage mechanism is necessary

8. Solar Thermal Energy
Obtaining energy from concentrating and focusing the Sun’s rays with mirrors to generate electricity
Three designs
Solar power towers
Parabolic troughs
Dish/engine
Cost of generating electricity is currently about 12 to 18 cents per kilowatt-hour

9. Figure 10.4: Schematic Diagram of Solar Two

10. Parabolic Troughs
Use large troughs to track and focus sunlight onto a receiver pipe through which synthetic oil flows
In a heat exchanger, water is heated to steam to turn a turbine
Figure 10.5; page 267

11. Concept Check 10.1
A parabolic trough with an active area of 30.0 m2 produces 3.5 kW of power. The solar power falling on the active area was measured at 1.0 × 103 W/m2. Calculate the percent efficiency of the trough.

12. Concept Check 10.1 Solution
First, calculate the solar power falling on the solar trough.
Calculating the efficiency as follows:

13. Dish/Engine
Dish-shaped reflectors focus sunlight onto a central receiver, which becomes the heat source for a conventional engine or turbine
Can be hybridized to use other fuels when sunlight is insufficient for operation

14. Photovoltaic (PV) Energy
Ultimate energy source (besides the Sun)
There are no moving parts, no noise, and no pollution during PV cells operation
PV cells found on watches and calculators are the most familiar of solar technologies

15. Photovoltaic (PV) Energy (continued)
PV cells are made of semiconductors, materials whose electrical conductivity is controllable
Common semiconductor is silicon
n-type
p-type
Figure 10.7 (left); page number 269
Figure 10.8 (right); page number 269

16. PV Cell: Method of Operation
An n-type silicon sample is brought in contact with a p-type sample in what is called a p-n junction
Light excites electrons and allows them to flow from the n-type side to the p-type side
These mobile electrons when forced to travel through an external wire, produce an electric current
Figure 10.9; page 269

17. PV Cell: Method of Operation (continued)
PV cells are currently expensive
Cost is dropping dramatically, and several commercial applications have been found

18. Concept Check 10.2
Suppose you are installing a 2500-W heat pump to cool and heat your house and want to use PV cells to provide the power. The average solar power is 1.0 × 103 W/m2, and the PV cells are 15% efficient. How many square meters of PV cells are needed?

19. Concept Check 10.2 Solution
2500-W heat pump is installed.
The average solar power is 1.0 × 103 W/m2.
PV cells are 15% efficient.
Input power needed is based on 15% PV efficiency:

20. Concept Check 10.2 Solution (continued)
The total area of PV cells required is:

21. Solar Energy Storage
Solar sources must be supplemented or hybridized with fossil-fuel sources or must have a mechanism for energy storage
Short time duration of the storage period is a disadvantage
Battery is a permanent storage option
Quickly increases the cost of the energy production method

22. Solar Energy Storage (continued)
Energy can be stored in chemical bonds
Solar energy can be used to decompose water, and the resulting hydrogen and oxygen gases are stored
Combustion of hydrogen can be used at a later time to liberate the energy
Nature’s heat tax will take some of this energy

23. Biomass
Nature efficiently captures and stores the Sun’s energy through photosynthesis
sunlight + 6CO2 + 6H2O → C6H12O6 + 6O2
Energy contained in living plants can be harvested two ways
Direct way is to burn the plants and use the heat to produce electricity
Second way is to produce liquid fuel, such as ethanol from plants

24. Biomass: Advantages and Disadvantages
Exact balance between CO2 absorbed while the plant grows and the CO2 emitted when burned
Plants can be burned directly or converted to ethanol, a fuel that is easily transported and burns cleanly
Disadvantages
Large land areas required
Most cropland is used to grow food; the switch to growing fuel would be difficult
High consumption of energy

25. Geothermal Power
Produced by the high temperatures present in Earth’s interior
Steam emitted from Earth’s interior is used to turn turbines and produce electricity
In rare cases, steam from the Earth is used directly
Disadvantages
Limited availability
Spent-steam disposal
Contains sulfurous gases and ammonia
Geothermal power plants, such as this one, generate electricity by using steam emitted from Earth’s interior; page 273.

26. Advantages and Disadvantages of Nuclear Power
No smog production
No CO2 emissions
Breeder reactors increase reserves by 100 times
Reduced energy costs
Disadvantages
Radioactive waste
Need supply of U-235
Public fear of accidents and concerns over waste disposal have halted growth in the United States

27. Breeder Reactors/Fusion
U-238 is bombarded with neutrons to form U-239
U-239 is extremely unstable and undergoes two successive beta decays to form Pu-239

28. Efficiency and Conservation
Energy will likely continue to become more expensive
Conservation efforts coordinated with development of energy technologies will help stabilize energy costs
Table 10.2; page number 274

29. Figure 10.11: Generation of Electricity
Page number 275.

30. The 2050 World
Centralized power exists to provide electricity to urban centers where the concentration of people and corresponding energy need are too high for solar
Efficiency has kept energy costs slightly higher than at the turn of the century
Environment is the real winner from the new energy technologies

31. Chapter Summary Molecular concept Societal impact
Indirect solar energy
Hydroelectric power
Wind power
Fossil fuels are primarily being used currently. People should find alternative sources of energy
Direct solar energy
Sources under development of energy must become cheaper and more convenient
Photovoltaic cells
Some companies provide electricity
generated from only environmentally friendly, renewable energy sources