Activity. Hydrogen for Transportation? Overview. Background Information

Transcription

1 1 Activity 1 2 class sessions Hydrogen for Transportation? Overview A PowerPoint presentation and a short video introduce this module s focus on the development of hydrogen and fuel cell technology as one potential solution to transportation energy concerns. Students analyze tabulated data to investigate several potential options for powering vehicles. Students are introduced to various fuels and consider some of the trade-offs of using them. Materials For the class Alternative Energy Vehicles PowerPoint presentation (on DVD) Get on the Bus video (on DVD) DVD player and TV or projector and computer with DVD player* For each student Student Sheet 1.1, Advantages and Disadvantages of Various Buses Concepts, Processes, and Issues (with NSES 9 12 Content Standards Correlation) 1. Decisions involve assessment of alternatives and are made based on perceptions of benefits, risks, and trade-offs. (Perspectives: 6) 2. Many factors influence environmental quality, including materials from human societies that induce hazards. (Perspectives: 4, 5) 3. Students use evidence, apply logic, and construct an argument for proposed explanations. (Inquiry: 1) 4. Technological designs have constraints, benefits, risks, and trade-offs. (SciTech: 2; Perspectives: 6) 5. Progress in science and technology can be affected by social issues and challenges and have a direct effect on society. (SciTech: 2; Perspectives: 6) *Not supplied in kit Background Information Fuels 2011 Regents of the University of California TEACHING SUMMARY Step 1. Introduce vehicle fuel and engine options. Step 2. Analyze data on several vehicle fuel and engine options. Step 3. Discuss advantages and disadvantages of several vehicle fuel and engine options. Our current transportation system is dependent on petroleum-based fuels, such as gasoline and. Unfortunately, there are many problems associated with the use of these fuels. The price of petroleum can change drastically. Fossil fuels are finite, and as they get scarcer they will become more expensive. Even if this doesn t happen for a long time, there are more short-term concerns related to the use of fossil fuels. Most of the petroleum consumed in the United States comes from other parts of the world. This makes us dependent on other countries for our transportation fuel, which can create political and economic problems. Finally, there are numerous environmental impacts associated with the use of these petroleum fuels, including global climate change, acid rain, smog, and localized air pollution. These environmental problems are a serious concern, even if fossil-fuel supplies were more abundant. For these reasons, there are many alternative transportation fuels being explored, including hydrogen, ethanol, and bio. Electricity is also being considered as an energy source for powering vehicles. 1

2 2 Investigating Alternative Energy: Hydrogen & Fuel Cells A fuel is a substance that releases usable energy during a chemical reaction involving the fuel and oxygen gas. Most vehicles rely on exothermic combustion reactions where the fuel is exploded inside the engine, releasing thermal energy. These engines are called internal combustion engines (ICE). In contrast, fuel cells convert the chemical energy of the fuel directly into electrical energy without combustion and with less heat generated, which allows for higher energy conversion efficiencies. The following factors are important to consider when comparing transportation fuels: Availability, cost, and environmental impact of obtaining the fuel Amount of energy required to collect and process the fuel so that it is ready for use Amount of energy released per unit mass (or volume) of fuel Safety of handling, storing, transporting, and using the fuel Type and amount of reaction products In this exercise students investigate the trade-offs associated with using various vehicle fuels (petroleum, bio, hydrogen, and electricity), as well as various vehicle-engine technologies for powering buses. A brief discussion about the various fuels and engine technologies students will consider is given here. Diesel Engine Burning Petroleum Diesel or Bio Diesel internal combustion engines are very similar to gasoline internal combustion engines and are commonly used to power large trucks and buses. The main difference between and gasoline engines is that engines use the heat of compression to ignite the fuel-air mixture in the cylinder, whereas gasoline engines use an electric spark from a spark plug. Diesel engines require higher compression ratios, and this leads to higher efficiencies. Peak thermal efficiencies for engines range from 40% 45% compared to gasoline ICE peak efficiencies of 25% 30%. (Note: As will be discussed later, vehicles achieve much lower average efficiencies.) Old engines were very dirty and emitted a lot of air pollutants, whereas newer engines using ultra-low sulfur fuel and advanced pollution control technologies emit much less pollutants. As of 2010, clean vehicles have lowered pollutant emission levels by up to 90% compared to typical vehicle emissions in Over 99% of fuel in the United States is currently produced from petroleum. Petroleum, or distillate fuel oil, accounts for approximately 20% of the transportation fuel energy used annually in the United States (whereas gasoline accounts for about 60%). Diesel fuel is readily available at gas stations throughout the U.S. and is priced comparably to gasoline fuel. Diesel fuel can also be made from animal and vegetable oils, and is then referred to as bio. Bio can be made from used plant-based oils (e.g., used oils from restaurants); however, the majority of bio is produced from oil extracted from crops grown for making fuel. In the United States, bio is primarily produced from soybean oil. Currently, U.S. soybean feedstocks for bio production are grown primarily on prime agricultural land in the Midwest. This creates competition between growing food and growing feedstocks for biofuels on prime arable land. To produce bio, raw vegetable oil is chemically treated in a process called transesterification. Bio is similar to petroleum and can be used in the same applications, but it has specific chemical, handling, and combustion characteristics. It can be blended with petroleum in any fraction and used in engines, as long as the fuel system that uses it is constructed of compatible materials. Frequently, a blend of 20% bio and 80% petroleum is used, and this mix generally does not require any vehicle modifications. One important difference for end users is that bio becomes too viscous at low temperatures and needs to be preheated or blended with petroleum. Hybrid Diesel-Powered Vehicle Burning Petroleum Diesel or Bio Hybrid vehicles use an internal combustion engine and an electric motor plus a battery bank to provide motive power. Hybrid vehicles are significantly more

3 activity 1 / Hydrogen for Transportation? 3 efficient than their ICE vehicle counterparts. This results in reduced emissions of carbon dioxide, nitrogen oxides, and sulfur oxides as well as reduced fuel costs per mile driven. For these reasons hybrid vehicles are becoming more popular. The increase in efficiency is attributable to two key features. First, the efficiency of an ICE varies with the amount of power it produces. Due to a constantly varying load on the engine as the vehicle changes speed or climbs hills, a standard ICE vehicle engine does not operate near its peak efficiency most of the time. This results in average efficiencies that may be only half the engine s peak efficiency. A hybrid vehicle, on the other hand, is designed to keep the internal combustion engine operating near its peak efficiency. This is accomplished by running the engine at a nearly constant load while using the electric battery to absorb or supply energy as needed. When the ICE, operating near its peak efficiency, produces excess power, that power is used to charge the battery bank. When the power from the ICE is insufficient to meet vehicular demands, then power is drawn from the battery bank. The electric power from the battery bank drives an electric motor, which assists the ICE in providing motive power. The second reason that hybrid vehicles are more efficient is that they are able to recapture some of the vehicle s kinetic energy when the vehicle slows or stops. This is referred to as regenerative braking. When fuel is burned to provide motive power, the fuel energy is effectively converted into kinetic energy. When slowing or stopping, this kinetic energy can be recaptured. The kinetic energy is used to turn a generator, producing electrical energy that charges the battery bank. Although regenerative braking is not what defines a hybrid vehicle, most modern hybrids use this technology. Both - and gasoline-powered vehicles can be configured as hybrid vehicles, and hybrids can use either petroleum or bio as a fuel. Electric and Fuel Cell Using Hydrogen Fuel A hydrogen fuel cell vehicle is an electric vehicle. It uses an electric motor to provide motive power. However, instead of storing electrical energy in a battery, a fuel cell vehicle stores energy in the form of hydrogen fuel. Most fuel cell vehicles store hydrogen as a compressed gas in very strong tanks. When hydrogen is provided to the fuel cell it combines with oxygen in the atmosphere and produces electric power, heat, and water. Fuel cells are typically 40% 50% efficient at converting chemical energy (in the form of hydrogen) into electrical energy. Most of the major automobile manufacturers are working on fuel cell vehicles, but these cars are not yet widely commercially available. Many nations, including the United States, Canada, China, Europe, and Japan are introducing hydrogen power for buses and other fleet vehicles. If hydrogen vehicles are to become commonly used, there will need to be a substantial infrastructure investment to build a network of hydrogen fueling stations. There are hundreds of hydrogen fueling stations throughout the world, including 58 operating stations in the United States as of Numerous regions in the United States are working to develop hydrogen highways where strategically located hydrogen fueling stations will allow people to drive long distances in hydrogen vehicles. Hydrogen vehicles can refuel in a matter of minutes, just like gasoline- and -powered vehicles do. While fuel cell vehicles are very clean (the emissions are pure water), pollution may still be created when hydrogen fuel is produced. Hydrogen is the most abundant element in the universe; however, on earth it is bound with other elements. The main sources of hydrogen are hydrocarbon fuels and water. Currently, over 90% of the hydrogen produced in the U.S. comes from natural gas, or methane (CH 4 ). The hydrogen is stripped from the methane molecule in a process called reformation. The main byproduct from this process is carbon dioxide. Hydrogen can also be made by using electrical energy to split water in a process called electrolysis. If the electricity comes from a clean, renewable energy source like solar or wind power, then there is essentially no pollution generated. However, if the electricity comes from a power plant that burns coal or natural gas, then some pollution and CO 2 will be emitted from these power plants. Electric and Rechargeable Battery Using Electricity Battery-powered electric vehicles are similar to fuel cell vehicles in that they utilize an electric motor to provide motive power. However, energy is stored on-

4 4 Investigating Alternative Energy: Hydrogen & Fuel Cells board the vehicle as chemical potential energy in an electric battery. When needed, electrical energy is drawn from the battery to power the electric motor. In order to recharge the battery, it must be plugged into an electrical outlet. Like fuel cell vehicles, battery electric vehicles are very clean; they produce no emissions. However, similar to fuel cell vehicles, there may be some pollution emitted in order to generate the electricity needed to charge a battery for an electric vehicle. No pollution is generated if the electricity used to recharge the battery comes from a clean, renewable energy source like solar or wind power. However, pollution and CO 2 will be emitted if the electricity comes from a power plant that burns coal or natural gas. Battery electric vehicles have been available on a limited basis for many years, but they have never really caught on as a common mode of transportation. Two of the biggest issues with battery vehicles are the limited range they can travel on a single battery charge and the amount of time it takes to recharge the battery. New battery technologies, such as lithium ion batteries, offer greater range. Battery electric vehicles are typically heavier than their petroleum-powered counterparts. For this reason, battery energy storage is more practical in personal passenger vehicles rather than large commercial trucks or buses. A potential niche market for battery electric vehicles appears to be compact cars for local commuting. Scientists and engineers continue to work on improving battery technology with the hope of placing practical electric vehicles on the road in the near future. Note: There are additional technologies and potential transportation fuels that are being considered; however, their consideration is beyond the scope of this exercise. These additional technologies include, but are not limited to plug-in hybrid vehicles, hydrogen internal combustion engine vehicles, ethanol-fueled vehicles, natural gas-fueled vehicles, and propane-fueled vehicles. Teaching Suggestions GETTING STARTED Step 1. Introduce vehicle fuel and engine options. Ask students, Think about the vehicle you ride in the most what kind of fuel does it use? Compile a list of responses, making a tally if desired. Students will likely mention various grades of gasoline,, and possibly even electricity, natural gas, or bio. Next, ask, Why do you think manufacturers make vehicles that use a variety of fuels? And why do people buy them? Have students share their thoughts, and if desired, compile a list of responses. At this point don t elaborate or augment student responses or encourage student debate or discussion. Finally, ask, Has anyone heard of a car or other vehicle that runs on any other type of fuel than those already listed? Add any new suggestions to the list, and if no one mentions hydrogen gas, introduce students to this as a fuel, both in internal combustion engines and in fuel cells. Briefly describe a fuel cell as an electricity generator that continually produces power as long as hydrogen and oxygen gas are available. Like a battery, it is an electrochemical cell. However, unlike a battery it does not have to be recharged. Explain that for the next few class periods, they will be studying hydrogen fuel cells, and that in today s activity they will begin comparing fuel cells to other vehicle engine options. Have students read the Introduction and Challenge for Activity 1 and briefly respond to any questions or comments. Explain that the activity will provide several, but not all, important pieces of information about specific fuels and engines for them to consider. To give students more background about various energy options for vehicular transport, show the PowerPoint presentation Alternative Energy Vehicles. INVESTIGATING Step 2. Analyze data on several vehicle fuel and engine options. Encourage students to complete the Procedure Steps 1 through 3. If necessary, demonstrate how to complete Student Sheet 1.1 for the first bus option. Circulate among the groups and provide guidance where needed. Possible student answers are provided at the end of this activity. When groups have finished, have them share their responses to Procedure Step 3 with the class and compile a list of factors, tallying how many times they appeared.

5 activity 1 / Hydrogen for Transportation? 5 SsYNTHESIZING Step 3. Discuss advantages and disadvantages of several vehicle fuel and engine options. Show the first segment (approximately 2 minutes) of the Get on the Bus video (the teaser segment). Then have students respond to Analysis Questions in their science notebooks. After students have had ample time to respond to the Analysis Questions, hold a class discussion to review their responses. When discussing the questions, emphasize the need to consider the long-term consequences and costs, in both environmental health and in real dollars spent on counteracting negative environmental and health effects associated with obtaining and using the fuels most commonly used today. Note: It may be desirable at the end of this exercise to discuss the quality of the data presented in Table 1, Comparing Buses. There is a lot of complexity in the data, and many assumptions had to be made when compiling this information. The numbers can vary significantly depending on what assumptions were made. For example, when hydrogen is generated using electricity we must consider where the electricity came from and how it was generated. If it was generated via burning coal, then a significant amount of air pollution may have been emitted; but if it was generated using a wind turbine, then essentially no air pollution was emitted. It is good to think critically and ask questions about data like these. Are the comparisons valid? What are the underlying assumptions? Who is presenting the data and might they be biased by their own agenda or vested interests? Sample Responses and Discussion of Analysis Questions 1. Which factors are most important to you in evaluating the bus types in this activity? Why? Answers will vary. Possible student responses include: cost of fuel, types and amount of polluting emissions, whether or not the fuel is renewable, the cost of the vehicle, the mileage the vehicle gets, and vehicle performance. 2. Which factors are least important to you? Why? Answers will vary. A possible student response is cost of the vehicle, because some students will value factors related to the environment more heavily, or for some students the long-term cost of fuel will outweigh the short-term cost of the vehicle. 3. Based on the information you have so far, what s your initial impression of the promise of hydrogen powered fuel cell buses? Of the buses that you ve analyzed, which two buses do you think are most promising for future investigation? Explain your answer using evidence from this activity. Answers will vary. Some students will show enthusiasm for fuel cell vehicles, based on their emissions-free potential. Other students might prefer hybrid -electric as a more practical and short-term way to reduce pollution and fuel consumption. Emissions-free electric buses might be the favorite of many students, despite these vehicles short range and limited passenger capacity. Encourage students to share their ideas in groups and then to have groups share their favorite choices with the class. Make sure that everyone hears the reasoning behind students choices. EXTENSIONS The values in Table 1 are generally averages for the United States and may vary in your local area. Some students may be interested in looking into whether there are other options available in your area, such as compressed natural gas or plug-in hybrid vehicles, as well as whether the prices for fuels are significantly lower or higher where you live when compared to the national averages provided. The CO 2 emissions estimates in Table 1 are based on well-to-wheels analyses. This accounts for not only the emissions from the tailpipe of the vehicle, but also all the upstream emissions associated with obtaining, processing, transporting, and delivering the fuel. This is a complicated topic, but it is critical to a valid comparison between various vehicle fuel and engine options. Some students may like to research the concept of a well-to-wheels analysis and share their findings with the rest of the class. Also, students might want to consider additional upstream impacts that might be associated with various fuel options, such as water-use or land-use impacts.

6 6 Investigating Alternative Energy: Hydrogen & Fuel Cells Table 1. Comparing Buses Engine or Fuel CO 2 Emissions (kg/mile) Air Pollution (grams/mile) Vehicle Cost Fuel Cost ($/mile) Range (miles) Diesel Engine (ICE) a Hybrid Diesel (ICE, Battery, and Electric ) Electric Powered by a Hydrogen Fuel Cell Electric Powered by a Rechargeable Battery d (from petroleum) bio (from petroleum) bio hydrogen (e.g., reformed from natural gas) Renewable hydrogen (e.g., from water using solar, hydro, or wind power) electricity (e.g., fossil fuels used to make electricity) Renewable electricity (e.g., from solar, hydro, or wind power) : : : : 4.28 $320,000 $532, b 0 b $0.963 : 0 b $2,275,000 c 0 0 : e 0 e : 0 e $295, : 0 $ $ $ $ $1.31 $0.200 $ a ICE = internal combustion engine b Pollution and greenhouse gases are totally avoided when using hydrogen only if it is generated with a renewable energy source such as wind, hydroelectric, or solar. There are never any tailpipe pollutants from a fuel cell vehicle, but there will be upstream generation of pollutants and greenhouse gases if a nonrenewable feedstock, such as natural gas, is used. This is also true for battery electric vehicles. c The $2,275,000 price results from hydrogen fuel cell buses being in a prototype phase. If these buses move into widespread use, their cost should fall dramatically. d Data for all buses are based on standard 40-ft passenger buses with one exception. Values for the battery electric bus are based on data for a 22-ft bus because battery electric buses are not typically made in the full size 40-ft format. Consequently, the electric bus will hold far fewer passengers. Also, the all electric battery powered bus will not perform well in hilly terrain and is only appropriate for use in flat areas. Maximum speed is 40 miles per hour. e Emissions are not produced by the battery electric bus. Low to moderate emissions of CO 2, particulate, and are produced by the power plant that produces the energy to recharge the bus battery.

7 Hydrogen for Transportation? 7 Suggested answers to Student Sheet 1.1, Advantages and Disadvantages of Various Buses Engine or Diesel Engine (ICE) a Hybrid Diesel (ICE, Battery, and Electric ) Electric Powered by a Hydrogen Fuel Cell b, c Electric Powered by a Rechargeable Battery b Fuel Advantages Disadvantages (from petroleum) bio (from petroleum) bio hydrogen (e.g., reformed from natural gas) Renewable hydrogen (e.g., from water using solar, hydro, or wind power) electricity (e.g., fossil fuels used to make electricity) Renewable electricity (e.g., from solar, hydro, or wind power) Readily available, fuel distribution system in place, inexpensive fuel and technology, good vehicle range Vehicles need little or no alterations to accept new fuel, domestically produced renewable fuel Moderate reduction of emissions, lower fuel cost per mile, fuel distribution system in place Moderate reduction of emissions, lower fuel cost per mile, vehicles need little or no alterations to accept new fuel, domestically produced renewable fuel Ample supply of natural gas (currently), although it is nonrenewable No pollution or greenhouse gases, domestically produced renewable fuel Large reduction in emissions, emissions confined to individual power plants so emission controls are easier to implement, large reduction in fuel cost per mile Elimination of emissions, domestically produced renewable fuel, large reduction in fuel cost per mile High emissions, fuel costs vary, most supplies from overseas, inefficient engine (15% 20%) Small reductions of some emissions and small increases in others, still contributes to greenhouse gas production, land-use competition between fuel and food crops More expensive than ICE, nonrenewable fuel Still contributes to greenhouse gas production, competition between fuel and food crops Fuel cells are currently expensive, very little hydrogen fueling infrastructure currently exists, lower vehicle range, slightly more expensive fuel Hydro and wind power can face environmental opposition due to threats to habitat, fuel cells are currently expensive, very little hydrogen fueling infrastructure currently exists, lower vehicle range, more expensive fuel Still produce air pollution and greenhouse gas emissions, much lower vehicle range, full size electric buses not available, limited speed, limited to flat terrain Hydro and wind power can face environmental opposition due to threats to habitat, much lower vehicle range, full size electric buses not available, limited speed, limited to flat terrain, slightly higher energy costs (compared to electricity generated from fossil fuels) a ICE = internal combustion engine b Pollution and greenhouse gases are totally avoided when using hydrogen only if it is generated with a renewable energy source such as wind, hydroelectric, or solar. There are never any tailpipe pollutants from a fuel cell vehicle, but there will be upstream generation of pollutants and greenhouse gases if a nonrenewable feedstock, such as natural gas, is used. This is also true for battery electric vehicles. c Although the energy density of hydrogen is very high per unit of mass, the energy density is very low per unit of volume. This makes it challenging to store enough hydrogen on board a vehicle the size of a passenger car to get the desired driving range we are accustomed to. In order to store it more densely, it is typically compressed to very high pressures (5,000 psi or even 10,000 psi), or it is liquefied. Compression and liquefaction of hydrogen require substantial energy input, reducing the overall energy efficiency of a hydrogen energy system.