Period 26 Solutions: Using Energy Wisely

Transcription

1 Period 26 Solutions: Using Energy Wisely Activity 26.1: Comparison of Energy Sources for Generating Electricity 1) Comparison of energy sources a) Fill in the table below to describe the advantages and disadvantages of the various energy sources. Fossil fuels have the advantage of currently being cheap and rather plentiful. On the other hand, supplies are believed to be limited, mining and drilling for coal, oil and gas can be environmentally destructive, burning fossil fuels releases carbon dioxide, burning coal also releases sulfur and nitrogen oxides that produce acid rain. Generating electricity from fossil fuels results in thermal pollution when the water used to cool the operation is released into lakes and rivers. Nuclear power plants do not release greenhouse gasses or give off atmospheric pollution. They do produce thermal pollution. There is a safety problem with older nuclear power plants. All nuclear power plants generate radioactive waste, a problem for which there is yet no feasible solution. Tidal, hydroelectric, geothermal, wind, and biomass energy sources do not produce pollution but can still harm the ecosystem (damming rivers can kill off fish which spawn upstream, wind tubines are dangerous for birds, and drilling geothermal wells may threaten ecosystems.) When burning biomass, we assume that the amount of carbon dioxide emitted is equal to the carbon dioxide ingested by the biomass plants as they grew; thus, biomass is considered carbon neutral. Solar energy seems to be the most environmentally friendly energy source. However, the manufacture of solar cells can involve CFCs, which destroy the ozone layer. In many applications, solar energy is too expensive to be cost effective. This is the result of high manufacturing costs and low efficiency of solar cells. Research into solar cells is improving efficiency and lowering costs. 1

2 Energy Fossil Advantages Plentiful (at least for now) and inexpensive Disadvantages greenhouse gases, acid rain, soot. Nonrenewable Biomass plentiful, inexpensive, renewable Soot. (No net carbon dioxide is released.) Wind Inexpensive to operate, renewable Expensive to install, noisy, affects scenic vistas, can harm birds Tidal Renewable. No atmospheric pollution Limited locations. Can change aquatic ecosystem Hydroelectric Renewable. No atmospheric pollution Dams can change the aquatic ecosystem Nuclear No atmospheric pollution Thermal pollution. Nuclear accidents. Storage of radioactive waste. Geothermal Limited atmospheric pollution. Large quantities available only in areas with hot rock close to the surface. Solar No atmospheric pollution. Renewable Low efficiency, expensive, not always available. b) Which of these energy forms are ultimately forms of solar energy? All of the above energy sources are ultimately forms of solar energy except nuclear, tidal, and geothermal. Hydroelectric (solar energy drives the water cycle), wind (solar energy produces uneven heating of the Earth s surface that causes winds), biomass (plants and the animals that eat them rely of the Sun s energy for photosynthesis), fossil fuels (fossilized plant and animal materials), and, of course, solar energy. 2

3 Activity 26.2: Comparison of Vehicle Fuels 2) Comparison of energy sources for vehicles a) How do hybrid vehicles increase gasoline mileage? Most hybrid vehicles use a gasoline-powered internal combustion engine in combination with batteries to store the electrical energy generated by the motor. As the car coasts or brakes, energy from the moving wheels is used to generate electricity that is stored in the batteries. b) What advantages are there to bioethanol and biodiesel fuels? Bioethanol is ethyl alcohol that has been distilled from plant material, such as corn, sugar cane or switchgrass. Biodiesel is produced from vegetable oil or animal fats. Biofuels reduce our dependence on oil. In many cases, biofuels burn more cleanly than fossil fuels. Because the plants that produce biofuel ingest carbon dioxide, biofuels can be considered carbon neutral with no net emissions of carbon dioxide c) What are CNG and LNG fuels? Natural gas consists primarily of methane. CNG is compressed under high pressure. LNG is very cold liquified natural gas. Most gasolinecombustion engines can be retrofitted to run on CNG or LNG d) How can hydrogen be used to power vehicles? Hydrogen gas can be used in vehicles with adapted engines as an alternative to gasoline. Energy can also be obtained from hydrogen by a fuel cell that converts the energy from hydrogen into electricity to power electric motors. A hydrogen-oxygen fuel cell converts hydrogen and oxygen continuously into electrical energy and water. e) What are the advantages of flex-fuel vehicles? Flex-fuel vehicles have the advantage of operating on ethanol, biodiesel, or gasoline. E85 vehicles use 85% ethanol and 15% gasoline. f) What is the future of electric vehicles? It s a rather positive future based on this clip from the U.S. Department of Energy Minimizing Thermal Energy Transfer 3) Heat flow through a surface a) What factors determine how much heat flows through a surface, such as a glass window? the thickness of the window (L) 3

4 the thermal conductivity of the glass (K) the area of the window (A) the difference in temperature between the two sides of the glass (T hot T cold ) b) Write an equation for heat flow through a surface. E t K A ( Thot Tcold ) L c) How much heat flows through a glass window that is 2 meters by 2 meters in area and 1.5 cm thick if the outside temperature is 10 0 C and the inside temperature is 25 0 C? (The thermal conductivity of glass is 0.84 J/s m 0 C ) E t K A ( Thot Tcold ) L (0.84 J/s m 0 C) x (4 m m 2 ) x ( 15 0 C) 3,360 J/s 4) Insulation to Reduce Heat Flow R-value of insulation Examine a piece of home insulation. The R-value of a material is a ratio of two variables: the thermal conductivity of the material K and its thickness L. a) Use ratio reasoning to write an equation for R so that good insulating material has a larger R-value than poor insulating material. The thicker the material, the less heat flows through it. Therefore, R and L are directly proportional. The larger the thermal conductivity, the greater the heat flow. Therefore, R and K are inversely proportional. R = L / K b) Rewrite your equation for heat flow from part 3.b, using R instead of L and K. E t A ( Thot Tcold ) R c) What would happen to the heat flow through a wall if you increased the thickness of the insulation from 2 inches to 6 inches? Assuming the other variables are not changed, the heat flow would be 1/3 of what it was with 2 inches of insulation. 5) Energy efficiency and insulation Your instructor will demonstrate radiant energy from light bulbs directed at panels made of wood, aluminum, and plexiglass. 4

5 a) The thermometer that shows the most rapid increase in temperature is attached to which panel? Prediction: Answer:_The thermometer attached to the plexiglass shows the most rapid temperature increase, followed by the aluminum and then the wood b) This panel was heated by which of the three types of thermal energy transfer? The clear plexiglass allows for the transfer of heat by radiation. Heat is transferred through the metal and wood panels by conduction. The metal has a high thermal conductivity and the wood has a lower thermal conductivity. c) Your instructor will demonstrate a model room with and without insulation. What is the temperature increase inside the room when it is covered with insulation? d) To retain the most heat inside of a home, should you choose insulation with a high or a low R-value? a high R-value e) Group Discussion Question: Is home insulation necessary in warm climates? Yes because on hot days insulation is needed to prevent the flow of heat into the home Minimizing the Cost of Electricity: Payback Time 6) Conserving Electricity Your instructor will demonstrate a compact fluorescent and an incandescent bulb. Compare the brightness of the bulbs. a) How many watts of power does each bulb use? Compact fluorescent Incandescent b) If electricity costs $0.10 per kilowatt-hour, how much money does the compact fluorescent bulb save compared to the incandescent bulb when used for 1,200 hours? Suppose that the compact fluorescent used 15 watts and the incandescent used 60 watts. Find the difference between the cost to operate each bulb per hour. Compact fluorescent (15 watts): Convert watts to kilowatts: 1 kw 15 watts x 1000 watts kw 5

6 Multiply kw by hours: kw x 1,200 h 18 kwh $0.10 Multiply kwh by cost/kwh: 18 kwh x $1. 80 kwh Incandescent (60 watts): Repeat the steps shown above for the 15 watt bulb. Or, notice that the 60 watt bulb has 4 times the watts of the 15 watt bulb (60/15 = 4). So the cost of operating the 60 watt bulb will be 4 times greater than the 15 watt bulb: $1.80 x 4 = $7.20 The amount saved over 1,200 hours is $ $1.80 = $5.40. The incandescent bulb costs four times as much to operate as the compact fluorescent bulb because its wattage is four times greater. c) Explain why the compact fluorescent requires less energy to produce the same amount of light. Both bulbs convert electrical energy into radiant energy in the form of visible light and infrared radiation. The compact fluorescent bulb converts a larger fraction of the energy into visible light and wastes less energy heating the light bulb glass with infrared radiation What Can I Do to Save Energy? You may think that your small energy savings will not make a difference to our planet s energy problems. This isn t true! The energy-savings steps you take can be multiplied by those of billions of people. Your instructor will give you ideas for energy savings. Make a list of the energy saving steps you will take. 6