Chapter 10 Energy for Tomorrow: Solar and Other Renewable Energy Resources Copyright ©2019 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.

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

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

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

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

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.

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

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

Figure 10.4: Schematic Diagram of Solar Two

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

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.

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

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

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

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

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

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

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?

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:

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

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

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

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

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

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.

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

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

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

Figure 10.11: Generation of Electricity Page number 275.

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

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