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4 Alternative Technologies ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ fï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ or Light-Duty Vehicles In keeping with its statement of task, the committee Recent History considered âwhether other technologies would be less Before discussing evolutionary vehicle technologies, it expensive or could be more quickly implemented than fuel is useful to review the evolution of some key automotive cell technologies to achieve significant reductions in carbon technologies since the 1960s. These changes were driven in dioxide emissions and oil imports.â After considering a range part by two major sets of regulations: of alternative technologies and the budget constraints of the study, the committee chose to evaluate in depth two options 1. Corporate average fuel economy (CAFE) standards. that received increased emphasis in the Energy Independence These provisions were established by Congress in 1975. The and Security Act of 2007 (EISA 2007): (1)Â evolutionary near-term goal was to double new car fuel economy by model improvements in internal combustion engines (ICEs) and year 1985. hybrid electric vehicles (HEVs) and (2) a biofuel option 2. The Clean Air Act of 1970. The act (as amended in (i.e., fuel derived from biomass). Many of these vehicle 1990) for the first time set federal limits on vehiclesâ emis- technologies will be needed through 2020 to meet the sig- sions of so-called criteria pollutants (such as lead, particu- nificantly higher fuel economy standards required by EISA lates, carbon monoxide, volatile organic compounds, and 2007. These are not the only technologies that could make a nitrogen oxides [NOx]). contribution to improved fuel economy and reduced carbon dioxide (CO2) emissions, but they are the ones for which the Industry responded to this pair of regulatory challenges committee felt confidence in projecting technology avail- with a âtotal-systemsâ approach to optimize the spark- ability, costs, and consumer acceptance. Others are discussed ignition engine vehicle and its fuel. That approach yielded briefly below. numerous important changes in major components, includ- The ultimate goal of this chapter is to estimate the extent ing switching to unleaded fuel, addition of the catalytic to which continuing evolution of light-duty vehicle technolo- converter, engine computer control, port fuel injection, the gies, increased use of improved hybrid electric vehicles, and four-speed automatic transmission with torque-converter the use of biofuels can reduce oil imports and greenhouse lock-up, and approximately 1,000 pounds of weight reduc- gas emissions through 2050. tion due to platform and material changes. Even though Evolutionary Vehicle Technologies The Energy Policy Conservation Act, enacted into law by Congress in 1975, added Title V, âImproving Automotive Efficiency,â to the Motor Over the past 25 years, oil consumption in the light-duty Vehicle Information and Cost Savings Act and established CAFE standards vehicle fleet has grown because of an increase in the number for passenger cars and light trucks. The act was passed in response to the of vehicles in the fleet and the annual miles driven, along with 1973-1974 Arab oil embargo. An overview of these regulations is available a shift to light-duty trucks for personal use, including sport at http://www.nhtsa.dot.gov/cars/rules/cafÃ©/overview.htm. Title II, Part A of the act covers motor vehicles. It gives the administra- utility vehicles (SUVs). To meet todayâs environmental and tor of the Environmental Protection Agency the duty âto prescribe (and energy challenges, there is a need to markedly improve the from time to time revise) in accordance with the provisions of this section, fuel efficiency of the light-duty fleet in order to lower both standards applicable to the emission of any air pollutant from any class or CO2 emissions and oil imports from their current upward classes of new motor vehicles or new motor vehicle engines, which in his trajectories. judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.â 44
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 45 Adjusted Fuel Economy by Model Year Weight and Performance (Three-Year Moving Average) (Three-Year Moving Average) FIGURE 4.1â U.S. light-duty vehicle fuel efficiency and performance trends from 1975 to 2005. NOTE: Three-year moving average, used to Figure4-1.eps smooth curves, means that for each year, what is shown is the average of that year with the two previous years. SOURCE: EPA (2006). 2 BITMAP IMAGES (vector heads re-aligned) there were major increases in the use of plastics and alu- efficiency, leading to reductions in oil imports and CO 2 minum, the highest percentage new material introduction emissions. was high-strength steel. Since 1980, vehicle efficiency During the same period in Europe, major advances have has continued to improve even as air pollution laws and been made in compression-ignition (diesel-fueled) engines; regulations have tightened, forcing vehicle designers to today, such engines form a major part of Europeâs CO 2 accommodate a multiplicity of goals. Engines, transmis- reduction efforts. There is concern about NOx and particulate sions, drivetrain components, and vehicle aerodynamics emissions from diesel engines, and the standards for these have all improved remarkably, with these improvements emissions have been tightened, as have the specifications on spread among emissions reduction, improved performance, diesel fuel to enable effective emission control technologies. greater weight, and more power-consuming accessories in This activity has resulted in the development of new after- the cabin (EPA, 2005). treatment devices for NOx and particulates for diesel engines. Since 1987, only a small fraction of these improvements These technologies continue to improve. have been directed to fuel economy, as shown in Figure 4.1 In 1997, the hybrid electric vehicle was introduced in (EPA, 2006). After an initial marked drop in average vehicle Japan and, in 2000, imported to the United States. In 2006, weight and a significant fuel economy increase, most of the 364,845 HEVs (with 254,545 in the United States) were sold continuing improvement in power train technology went to worldwide out of 68,727,429 total global vehicle sales. The overcome a steady increase in vehicle weight and to provide National Research Council (NRC) report on the hydrogen enhanced performance, particularly faster acceleration. The economy and fuel cell vehicle, which was released in Febru- baseline case projects this trend to continue into the future ary 2004 but had access only to actual year-end 2002 HEV because it is driven by consumer choices similar to those sales numbers, projected that 2006 HEV sales in the United that have been made over the past 20 years. Although some States would represent 2Â percent of the market and would changes in motorist attitudes can be expected, driven by increase 1Â percent annually thereafter for the next 9Â years and higher fuel prices and an enhanced environmental conscious- 5Â percent per year for the next 10Â years (NRC, 2004). The ness, they are unlikely to produce radical improvements in actual 2006 U.S. sales were 1.5 percent. As shown in Figure light-duty vehicle fuel efficiency. However, suitable poli- 4.2, even though gasoline prices have fluctuated dramatically cies promoting fuel efficiency could change vehicle design from 2004 to the present, the actual increase in sales was less priorities and result in significantly improved vehicle fuel in 2006 than in 2005 (DOE, 2007).
46 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen â¢ Efficiency improvements â¢ Transmission evolution â¢ Vehicle weight reduction â¢ Aerodynamic improvements, reduced rolling resistance Efficiency ImprovementsâSpark-ignition Engine.â Technical improvements that can be applied to spark-ignited internal combustion engines include the following: â¢ Variable valve timing (VVT) and variable valve lift offer improvements in part-load engine efficiency. Engines only operate at full load during hard acceleration and hill climbing; the remainder of the time, engine operation is at part load, when much less power or a smaller engine is all FIGURE 4.2â U.S. hybrid Figure4-2.eps electric vehicle sales through 2006. that is needed. VVT and lift allow the engine to supply the Note that the order of vehicles in the key matches the order indi- BITMAP reduced power requirement with improved fuel efficiency. cated in the bars of the graph from top to bottom. SOURCE: DOE The next major change is camless valve actuation (CVA), (2007). Available at http://www1.eere.energy.gov/vehiclesandfuels/ which can vary lift and timing and also allow strategies such facts/2007_fcvt_fotw462.html. as cylinder deactivation at light loads while simultaneously reducing valve-train friction. â¢ Cylinder deactivation (also called cylinder cut-out) can also reduce fuel consumption under part-load vehicle operation. Efficiency is improved by having fewer cylinders Potential for Reducing Oil Use in working at higher load. This technology is already being Conventional Light-Duty Vehicles implemented, especially in V8 engines, but constitutes a This section examines options for improving fuel econ- small fraction of the market to date. Application to four- and omy in conventional gasoline, diesel, and hybrid power train six-cylinder engines is more difficult because of noise and vehicles. Although not discussed explicitly in this chapter, vibration problems. CO2 reductions directly follow improvements in fuel effi- â¢ Gasoline direct injection (GDI) and GDI combined ciency in these types of vehicles. CO2 estimates are presented with turbocharging allow higher compression ratio operation in Chapter 6. Various transportation demand reduction efforts because of the cooling effect of in-cylinder fuel evapora- are under way, but are not considered in this report. tion, which protects against knock. Raising the compres- Gasoline and diesel power train vehicle technologies are sion ratio increases efficiency (which is why diesels are considered mature, but they will continue to advance and relatively efficient), but conventional spark-ignition engines improve for the foreseeable future. The following material are susceptible to pre-ignition (knock) if the compression reviews the areas in which improvements can be expected is too high. With GDI, the cooling effect counters the heat to continue, evaluates the potential extent of these improve- from the high compression. This technology benefits from ments, and projects their impact on fuel economy. Potential variable-geometry turbines for turbo boosting and variable cost increases are also estimated, although these are more compression ratio. This produces more horsepower from a qualitative. For improved vehicle technology to have a smaller engine, allowing weight reduction and fuel savings. significant effect on CO2 emissions of the light-duty fleet This technology option is in limited production in Europe and on oil imports, it must be directed to fuel efficiency and Japan and is on a few models in the United States. improvements and must be included in a large fraction of all â¢ Homogeneous-charge compression ignition (HCCI) vehicles manufactured and sold in a given year; then it, or enabled by CVA might decrease fuel consumption more than further improved versions, must continue to be manufactured GDI with turbocharging. HCCI involves the introduction of a for the time required to turn over a majority of the vehicles homogeneous air-fuel mixture, where the fuel is a gasoline- in the existing fleet. This is a decadal process. range hydrocarbon, into the cylinder. HCCI uses the same kind of âchargeâ as a spark-ignition engine but with higher compression, whereas a classical compression-ignition Technical Improvements in Gasoline and Diesel-Powered engine uses a stratified charge with a higher-boiling fuel that Light-duty Vehicles is injected directly into highly compressed air in the cylinder. The approaches to improving the fuel economy for gaso- Although HCCI has typically been considered a separate line and diesel vehicles are well understood. Each of these technology, its components will most likely be implemented areas offers considerable potential fuel efficiency benefits. as engine technology advances providing additional reduc- The methods considered here include the following: tions in fuel consumption.
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 47 â¢ Other changes that would result in improved fuel matic transmission and the automated manual transmission, consumption include reduced friction in the engine and which will soon be offered on some European models, will drivetrain via new materials or better lubricants; intelligent be almost as efficient as manual transmissions. With these start-stop with enhanced starter and battery, which involves technologies, transmission efficiency should be about 93 per- engine shutoff when the vehicle stops (e.g., at a red light); cent, a significant gain over typical automatic transmissions variable compression ratio technology; improved lean-NOx today (Kasseris and Heywood, 2007). In addition, transmis- catalyst technology; and improved engine controls and sions with more speeds allow the engine to operate closer integration. to its optimum efficiency, reducing fuel consumption. Con- tinuously variable transmissions (CVTs) allow the vehicle to Normally aspirated spark-ignition engine efficiency is vary the gear ratio continuously as it goes through its driving expected to improve significantly as these technologies are cycle for even greater power train efficiency (Nishigaya et successfully applied. Collectively, their application can be al., 2001; Burke et al., 2003). expected to increase peak engine efficiency by about 7 to 9 percent by 2030. For turbocharged spark-ignition engines, Vehicle Weight Reduction.â Reducing vehicle weight is a the efficiency gain could be better than that projected for the significant factor in improving vehicle fuel economy. Weight normally aspirated spark-ignition engine by 2030 (Kasseris reduction reduces the energy required to move the vehicle. and Heywood, 2007). Turbocharged gasoline direct-injection In doing so, the power plant may be reduced in size and engines with variable valve lift and timing could approach the weight itself, further improving fuel efficiency. Weight can efficiency of todayâs diesel engines (see discussion below), be reduced by using advanced materials such as advanced, which will also see efficiency improvements during this time. high-strength steel, aluminum, magnesium, carbon fiber Turbocharging is used commercially in a small fraction of composites, and plastics or by redesign to reduce the weight light-duty vehicles today, mainly to enhance performance. without using advanced materials. Estimates of potential These engine efficiency gains can be translated into reduc- weight reductions range from 10 to 33 percent (Weiss et al., tions in fuel consumption and CO2 emissions. 2000; An et al., 2001). Although weight reductions in the upper end of this range are technically possible, reductions in Efficiency ImprovementsâCompression-ignition (Diesel) the range of 5 to 10 percent by 2025 are probably achievable Engines.â Significant improvements to diesel engines have at a reasonable cost (Duleep, 2007), although some automak- been made over the past 20 years, but further gains can ers are already planning to go further. be expected. The several technologies that will add to this include improved fuel injection, higher boost levels, series Other Improvements.â Vehicle aerodynamics, as measured turbocharging, more advanced engine control technology, by a reduction in the coefficient of drag (Cd), has improved and variable valve train control. Although the major issue recently by at least 1 percent per year (Hucho, 1998; Weiss with dieselâemissionsâhas largely been resolved, current et al., 2000; An et al., 2001). If this trend continued for the emission control technology to meet U.S. emission laws is next 25 years, it would provide a significant reduction in fuel complex and costly. Several currently produced European consumption if car size remains the same. Reduction in car diesels have met the Environmental Protection Agencyâs size (frontal area) would result in added fuel consumption (EPAâs) Tier 2 and Californiaâs LEV (low emission vehicle) benefits because total resistance would be reduced. Vehicle 2 emissions standards, although doing so subtracts from their rolling resistance has historically undergone an estimated overall efficiency. The dieselâs fuel consumption is 18 to 25 reduction of 1.1 to 1.6 percent annually. An NRC committee percent better (lower) than that of a normally aspirated spark- recently concluded (NRC, 2006) that a 10 percent reduction ignition engine, and it is robust across all driving conditions. in rolling friction is possible for todayâs replacement tires, Diesel engines offer tremendous low-end torque and are well and further improvements are possible. suited to towing and cargo hauling. With the application of the technologies noted above, diesel engine fuel consumption Summary of Evolutionary Conventional Vehicle can be expected to be reduced further by about 30 percent Improvements over typical diesel fuel consumption today after subtracting for emissions control (Kasseris and Heywood, 2007). A summary of the reductions in fuel consumption for spark-ignition powered vehicles from the technology Transmission Evolution.â Transmission type and operation advances reviewed above for the periods 2006-2015 and also have a significant effect on fuel consumption. U.S. driv- 2016-2025 is given in Table 4.1, based on Duleepâs work ers have favored automatic transmissions, which have been (Duleep, 2007). These technology-driven fuel-consumption less efficient than manual transmissions. New transmission improvements must be focused on delivering efficiency gains technologies provide the user-friendliness of automatic (versus providing more performance or motorist comforts) transmissions with the efficiency of a manual transmission. and have to be broadly incorporated into the light-duty fleet Developments, such as the conventional 6/7/8 speed auto- if they are to have the desired impact on reducing fuel con-
48 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen TABLE 4.1â Potential Percentage Reductions in Fuel in 2030 compared to a conventional spark-ignition gasoline Consumption (gallons per mile) for Spark-ignition engine in a 2005 midsized sedan from Heywoodâs work. Vehicles Expected from Advances in Conventional Vehicle The Heywood fuel consumption improvements result Technology by Category, Projected to 2025 from changes in the engine and transmission and include 2006-2015 2016-2025 appropriate vehicle weight reductions as well. It is assumed that the improvements are entirely dedicated to reduced fuel Engine and transmission 12-16% 18-22% Weight, drag, and tire loss reduction 6-9% 10-13% consumption. The 2030 spark-ignition gasoline-powered Accessories 2-3% 3-4% vehicle, with automatic manual transmission and weight Idle stop 3-4% 3-4% reduction included, is projected to have a 38 percent reduc- NOTE: Values for 2016-2025 include those of 2006-2015. SOURCE: tion in fuel consumption from the 2005 version of the gaso- Duleep (2007). line vehicle technology. Spark-ignition gasoline-powered vehicles with turbocharger, automatic manual transmission, weight reduction, and parasitic-loss reductions are projected to be capable of a 44 percent reduction in fuel consumption sumption and CO2 emissions. Combining the projections for versus todayâs spark-ignition gasoline vehicle and an 11 improvements in engine, transmission, weight, parasitic loss percent improvement over the 2030 spark-ignition gasoline (including friction losses, rolling resistance, and air drag), vehicle. Heywood also concludes that CVT technology accessories, and idle-stop components suggests reductions could reduce fuel consumption further, reaching a 48 per- in fuel consumption, relative to todayâs vehicle and perfor- cent reduction in fuel consumption compared to today. The mance, of 21 to 29 percent (average = 25 percent) by 2015 turbocharged version of the gasoline vehicle would have an and 31 to 37 percent (average = 34 percent) by 2025. estimated $500 cost premium compared to the 2030 gasoline Heywood and colleagues at Massachusetts Institute vehicle. of Technology (MIT) have carried out a series of studies Also shown in Figure 4.3 is the projected fuel consump- focused on light-duty vehicle fuel efficiency (Heywood, tion of a 2030 compression-ignition diesel-powered vehicle. 2007; Kasseris and Heywood, 2007; Kromer and Heywood, The 2030 diesel-powered vehicle, with weight reduction, is 2007). Their studies rely on many of the technologies dis- projected to have 47 to 50 percent lower fuel consumption cussed above but include more aggressive reductions in than the 2005 spark-ignition gasoline vehicle on a gasoline weight and rolling resistance and aerodynamic drag. Figure energy-equivalent basis. It also has a projected 15 percent 4.3 summarizes the projected fuel consumption improve- lower fuel consumption than the 2030 spark-ignition gaso- ments for combinations of technology for gasoline- and die- line vehicle on a gasoline energy-equivalent basis. On a fuel sel-powered light-duty vehicles and hybrid electric vehicles volume basis (kilometers per liter of diesel fuel), the 2030 diesel engine shows an additional 15 percent benefit over the 2030 gasoline engine because of the greater energy density of diesel fuel. The diesel-powered vehicle is projected to have a cost premium of about $1,200 over the 2030 gaso- 10 liters/100km of Gasoline Equivalent line-powered vehicle. If diesels achieved significant market Automatic/Manual penetration, they could increase the potential reduction in 9 8.8 fuel consumption to 3 percent per year. However, the com- 8 CVT mittee was too uncertain of the cost penalty for diesels that 7 meet emission regulations to be willing to include increased 6 5.5 penetration in the scenarios of Chapter 6. 5 4.6 4.7 4.9 Based on the work reviewed above, and assuming a base- 4 4.1 4.0 3.7 line of 25 mpg (miles per gallon) and fuel increases starting 3 3.1 in 2010, Duleepâs projections correspond to a 2.3 to 2.9 2 Improvement over 2030 Gasoline 15% 11% 20-45% percent compounding annual reduction in fuel consumption 1 through 2025, or an average of 2.6 percent per year. This Cost premium over 2030 Gasoline $1200 $500 $1800-2500 results in the average value from Duleepâs analysis, a 34 0 2005 Gasoline 2030 Gasoline 2030 Diesel 2030 2030 Gasoline percent fuel consumption reduction, being applied by 2025. Engine Turbocharged Hybrid Gasoline This estimate assumes the diesel improvements discussed above, but the diesel percentage of the fleet remains constant Figure4-3.eps FIGURE 4.3â Fuel consumption of light-duty vehicles with differ- over time. While the data from Heywood suggest that this ent power trains using projected 2030 technology compared to a pace could continue through 2030, the committee judges, typical 2005 gasoline-powered vehicle. NOTE: To convert to gal- based on the discussion in the recent NRC review of the lons per 100 miles, multiply liters per 100 km by 0.426. SOURCE: FreedomCar Fuel Partnership (NRC, 2008), that continued Heywood (2007). weight reductions beyond 2025 would be slower to enter the
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 49 fleet, delaying Heywoodâs potential for gasoline vehicles by Potential for Reducing Oil Use in Hybrid Electric Light- about 5 years and slowing the pace of vehicle fuel consump- duty Vehicles tion reduction to about 1.7 percent per year between 2025 Hybrid electric vehicles and plug-in hybrid electric and 2035. This leads to a 44 percent reduction in fuel con- vehicles (PHEVs) provide increased energy efficiency by sumption compared to 2009, which is Heywoodâs projection mating a battery-powered electric motor with a conven- for the turbocharged spark-ignition gasoline vehicle with tional gasoline engine. The engine can be smaller than in automatic manual transmission. conventional vehicles, and therefore more economical, but Further, a 0.5 percent per year reduction in fuel consump- acceleration can be just as great because additional power is tion was assumed from 2035 to 2050. At this pace, a 48 supplied by the electric motor. The batteries can be charged percent reduction in fuel consumption would be achieved in part by regenerative braking, which captures the energy by 2050. This improvement could be reached if Heywoodâs that otherwise would be lost in braking. In addition, the more aggressive projections for turbocharged spark-ignition electric motor allows the engine to be operated at or near its gasoline vehicles with continuously variable transmissions optimum efficiency a greater fraction of the time. are realized. Alternatively, the fuel consumption reductions The two hybrids are similar, except that future PHEVs shown in Figure 4.3 do not define the limit to how far con- would have much larger battery packs that are anticipated ventional fuel economy can go. Heywoodâs analysis looks to be able to operate the vehicle for as much as 40 miles at a 20 percent weight reduction, relying mainly on higher- without the gasoline engine. When the battery charge is strength metals, but future carbon composites could lead to low, the engine kicks in and operates normally, recharging weight reductions of one-third or more. Even limited use the batteries and providing power. The batteries for PHEVs of carbon composites to achieve a 25 percent total weight can also be charged from the electric grid. Thus, for some reduction would boost Heywoodâs spark-ignition vehicles to driving patterns, no gasoline at all would be needed. PHEVs a 46-48 percent reduction in fuel consumption, up from 44 are not available commercially yet because the advanced bat- percent. Weight reductions through changes in the fleet mix, teries that would make them viable are not ready. As battery rather than changes in materials would have similar effects. technology improves and costs decrease, both of these hybrid A 10Â percentage point shift from trucks to cars (i.e., increas- power trains will become more effective and have a smaller ing car share to 60 percent) would increase Heywoodâs cost differential relative to conventional engine vehicles. spark-ignition vehicles to a 45-48 percent reduction in fuel All-electric vehicles would use no gasoline, but they are consumption. In conclusion, the spark-ignition internal even more dependent on improved battery technology than combustion engine vehicle can produce marked reductions PHEVs. All-electric vehicles will have CO2 emissions that in fuel consumption and CO2 emissions in the intermediate are determined by the emitted CO2 content of the electricity and long term at little additional cost. Policy initiatives may on the power grid. be necessary to help speed additional weight reduction and associated fuel consumption reductions. Thus, the committee judges that evolutionary vehicle Hybrid Electric Vehicles technologies could, if focused on vehicle efficiency, reduce When HEVs were first developed, the technology was fuel consumption by 2.6 percent per year through 2025, 1.7 dedicated almost exclusively to improving fuel economy. percent per year in the 2025-2035 time frame, and 0.5 percent However, as with other power trains, as HEV technology per year between 2035 and 2050. has begun to mature, the benefits of hybrid electric vehicles Increased penetration of diesel engines into the light-duty have shifted to now represent a blend of fuel efficiency, vehicle fleet was limited in the projections made here (and in performance, and larger vehicles. Still, HEVs presently are Case 2 in Chapter 6) because of the poor public perception of the most efficient light-duty vehicles. Continued improve- diesels in the United States and concerns over meeting future ment relative to conventional vehicle technology is likely tailpipe emission specifications. However, advanced diesel to occur. These improvements are expected to arise largely power trains could offer an additional 15 percent reduction from improved vehicle integration, allowing tighter, more in fuel consumption and a similar level of CO2 emissions optimized control of the engine operating points. Due in part reductions over advanced conventional spark-ignition power to scale economies and in part to significant reductions in the trains without turbochargers and have cost advantages over cost of high-power batteries, the incremental cost of HEVs hybrid electric vehicles (Kromer and Heywood, 2007). In a relative to conventional technology vehicles is expected to high-fuel-cost environment, diesels could become a growing decrease. Furthermore, HEVs will benefit from continued fraction of the light-duty vehicle fleet promoted by some technological development in terms of vehicle weight and shifts in government positions on diesels and a positive accessory loads, as well as improvements in engine technol- public relations program. ogy. CO2 emissions from hybrid electric vehicles are reduced as fuel consumption decreases, and current models, such as the Ford Escape Hybrid, the Honda Civic Hybrid, Nissan
50 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen TABLE 4.2â Comparison of Projected Improvements in Vehicle Fuel Consumption from Advances in Conventional Vehicle Technology From Kromer and Heywood (2007) From Weiss et al. (2000) Fuel Consumption Relative to 2005 Relative to 2030 Relative to 2005 Relative to 2030 (liters/100 km) Gasoline Gasoline Gasoline Gasoline 2005 Gasoline ICE 8.8 1 2005 Diesel 7.4 0.84 2005 Turbo 7.9 0.9 2005 Hybrid 5.7 0.65 2030 Gasoline 5.5 0.63 1.00 2030 Diesel 4.7 0.53 0.85 0.61 1.00 2030 Turbo 4.9 0.56 0.89 0.45 0.77 2030 Hybrid 3.1 0.35 0.56 0.54 0.88 2030 Plug-In 1.9 0.21 0.34 0.38 0.615 Altima Hybrid, the two-wheel drive Chevrolet Tahoe Hybrid, vide a 29 percent reduction in fuel consumption relative to and the Toyota Camry and Highlander hybrids, achieve fuel comparable evolutionary ICEVs. This assumes that hybrids consumption reductions of 26 to 34 percent, with a simple will have reached their peak in terms of fuel consumption average of about 29 percent. reductions relative to conventional vehicles by 2009 and As indicated in Figure 4.3, analysis from MIT indicates future improvements in hybrid fuel economy will be due, that CO2 emissions and fuel consumption could be as much primarily, to the same technologies used to improve conven- as 37 percent lower than those from a competitive 2030 tional vehicles. As a result this analysis assumes that hybrid spark-ignition gasoline vehicle (Kromer and Heywood, vehicles reduce fuel consumption by 2.6 percent per year 2007). Table 4.2 compares the results of Kromer and Hey- from 2010 through 2025, 1.7 percent per year in 2025-2035, wood (2007) and those of an earlier study, âOn The Road in and 0.5 percent per year between 2035 and 2050, the same 2020,â by Weiss et al. (2000). The Kromer and Heywood as for evolutionary ICEVs. (2007) study projects that HEVs will improve at a rate signif- icantly faster than conventional gasoline vehicles. This may be expected in the earlier years because they are relatively Plug-in Hybrids new and should enjoy a steeper learning curve, but hybrids PHEVs are designed to be charged from the power grid should be a mainstream technology before 2020. and to have a significant range without requiring operation While the committee acknowledges the significant of the internal combustion engine or only using the engine potential for hybrids outlined in Kromer and Heywood, it under higher-power driving conditions. This range is depen- concluded that most advances in hybrid technology are likely dent on the availability of economic, high-energy battery to lower the cost of battery packs (which will increase their technology. Cost-effective battery technology for even a 20- appeal to consumers relative to conventional vehicles, and mile trip is not available today. PHEVs could become com- thus their market share) rather than increase fuel economy. To mercially available within a few years if battery performance simplify the analysis in this report, the committee assumed and costs continue to improve rapidly. that hybrids achieve a constant 29 percent fuel consumption PHEVs will be significantly more expensive than HEVs. reduction compared to conventional vehicles (which also For a 30-mile-range plug-in hybrid, which is not considered improve each year) in each year. While this is conservative viable with existing battery technology, the incremental cost compared to Kromer and Heywood, it still leads to a 60 mpg is estimated to be between $3,800 and $4,300 over an HEV, average for new spark-ignition hybrids by 2050. the largest component of which is the battery, estimated to Thus, the committee judges that hybrid electric vehicles be about $2,500 (Kromer and Heywood, 2007). could, if focused on vehicle efficiency, consistently pro- PHEVs could save more oil than HEVs. Table 4.2 shows an improvement of 1.2 liters per 100 km (about one-half gal- Weiss et al. (2000) did not consider plug-in hybrids. Otherwise, the lon per 100 miles), but the actual savings would be highly results of these two studies agree reasonably well. dependent on driving patterns and the frequency with which
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 51 the vehicle is plugged in. However, the plug-in hybridâs fuels can also be made from biomass using thermochemical CO2 emissions reduction will not be nearly as large as sug- conversion of the biomass to syngas followed by catalytic gested by their lower fuel consumption because of the CO2 synthesis of a range of products, including gasoline and emissions associated with power generation. Today about diesel. These are also biofuels because they are derived from two-thirds of our electricity is generated from fossil fuels biomass. (mainly coal and natural gas, none of which employs car- Biofuels provide the opportunity to sustainably produce bon capture and sequestering because of the expense). Still, liquid fuels for the U.S. transportation system, reduce oil PHEVs offer a potential path for incremental CO2 emissions imports, and reduce carbon dioxide emissions from the savings through increased decarbonization of the power sec- transportation sector because the CO2 emitted from their torâan opportunity that does not exist for HEVs. combustion is captured in the next plant growth cycle. The The committee chose not to include PHEVs in the alterna- true impact of biofuels on CO2 emissions and oil use requires tive vehicle case even though they have significant long-term a full life-cycle analysis because fossil fuels, including oil, potential. The main issue for the committee was predicting are used in growing and collecting biomass and, in the case the rate of battery advancement to achieve significant driving of grain-based ethanol, in processing biomass into biofuels. distances. This, in the committeeâs view, and as presented in Also, CO2 and other greenhouse gases can be released if land the recent FreedomCar Fuel Partnership review, is more than use and land management practices change in conjunction evolutionary technology (NRC, 2008). In addition, consum- with the production of biomass for energy. When land use ersâ acceptance of the additional cost relative to HEVs and changes result in a reduction in soil carbon, that carbon is their willingness and ability to plug the vehicle in essentially released and emitted as CO2. This is a major concern. Proper every day are uncertain. land use changes could result in storage of more carbon in the soil, decreasing net CO2 emissions. Biomass-based biofuels are an emerging area that is expected to see much change in Conclusion on Evolutionary Technologies the next several decades. CONCLUSION: Continued advancements in conven- This section first discusses biomass availability and some tional vehicles offer significant potential to reduce oil use of the associated issues. It then reviews the production and CO2 emissions through improved fuel economy, but technology for those biofuels that are commercial or close policy measures and/or significant long-term increases to commercialization. It also briefly discusses biofuel tech- in fuel costs probably will be required to realize these nologies that have longer-term potential but are today in the potential fuel economy gains in a significant number of research stage. The primary biofuels for transportation con- on-road vehicles. sidered here include ethanol from corn grain, ethanol from cellulose, biobutanol from starch and sugars, and biodiesel from plant oils. At the end of the biofuels section, gasifica- Impact of Biofuels tion of biomass to produce synthesis gas is discussed briefly; this can be converted into diesel and gasoline. It represents Overview a parallel route to biofuel production. Today, it is not clear By definition, a biofuel is any fuel that is produced from which route to biofuels (biochemical or thermochemical) plant- or animal-based materials, generically referred to as will be the most economic. biomass. The biofuel that is receiving the most attention An important biofuel driver in the United States is politi- today is ethanol, which can be produced from the starch and cal. The Energy Policy Act of 2005 mandates 7.5 billion sugar in grains using fermentation and is referred to as grain gallons per year of ethanol and/or biodiesel in the nationâs ethanol. More than 6 billion gallons of grain ethanol were fuel supply by 2012. The Presidentâs State of the Union produced for vehicle fuel in the United States, primarily from Address in January 2007 increased the target volume of corn, in 2007 (RFA, 2008). Ethanol can also be produced renewable and alternative fuels to 35 billion gallons per year from the cellulosic material in plants using biotechnology by 2017. (Then in December 2007, EISA 2007 was enacted and is referred to as cellulosic ethanol. Cellulosic ethanol with a goal of 36 billion gallons per year by 2020.) These production technology is evolving today and is not yet fully initiatives are acting to drive production and demand for commercial. Higher alcohols, such as butanol, which can biofuels, particularly ethanol, in the United States. Note that use the gasoline infrastructure directly, can also be produced the energy content of ethanol is approximately two-thirds from biomass by biological routes. Fuels that can substitute that of gasolineâthus, 35 billion gallons replaces about for diesel fuel, referred to as biodiesel, can be produced 24 billion gallons of gasoline. However, if engines can be from plant oils and animal fats by esterification. A range of optimized to operate on ethanol instead of gasoline (e.g., a higher compression is possible with ethanol), they will be A 40-mile PHEV driven 40 miles every day and plugged in every night more efficient, somewhat compensating for the lower energy would use essentially no gasoline at all, saving as much as 365 gallons per content of the fuel. year relative to a 40 mpg HEV. The same vehicle driven 20 miles every day or 80 miles every other day would save exactly half that.
52 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen Biomass Availability technologies. However, there are significant uncertainties as to how much biomass would actually be available at this Biomass is anything that grows, and since it is renewable price and whether it could be converted into fuel at a close- if grown responsibly, it represents a sustainable source of to-acceptable cost. feedstocks for energy, fuels, and petrochemical production. More recently, Milbrandt (2005) estimated the current For the present time, easily processed agricultural crops, amount of biomass that is technically available (meaning such as corn, will likely be the major biomass feedstock to without considering costs) in the United States to be 466 the emerging biofuels industry. Low- or even negative-cost dry tons (423 million dry tonnes) per year using a state- materials such as waste greases and cooking oils will also by-state geographic information system (GIS) buildup. The be used to the extent available. In the mid term, agricultural major components are 184 million dry tons (132 million dry crop residues, forestry residues, and short-rotation trees tonnes) per year of forest, mill, and urban wood residues; will likely provide the feedstocks to an expanding biofuels 173 million dry tons (157 million dry tonnes) per year of industry. However, in the longer term, energy crops including crop residues (estimated using a 35 percent recovery of total perennial grasses and algae will probably have to be added crop biomass residue); and 99 million dry tons (84 million to the mix to supply the amount of feedstock needed to meet dry tonnes) per year of switch grass on Conservation Reserve national bioenergy goals. Program (CRP) lands. Perlack et al. (2005) estimated that the Current annual U.S. grain production includes about 11 technically available sustainable annual forest resource was billion bushels of corn, 2.9 billion bushels of soybeans, 2.0 about 368 million dry tons per year, of which 142 million billion bushels of wheat, and significantly lesser quantities dry tons was currently being used, leaving about 226 million of sorghum, rapeseed, oats, and barley (Perlack et al., 2005). available for conversion to fuels or energy per year. They Higher corn prices and increased interest in ethanol resulted estimated that about 194 million dry tons of biomass per in an increase in corn acreage from 78 million acres in 2006 year could be sustainably removed from agricultural lands to 93 million acres in 2007 (Achenbach, 2007). Much of this today. This number includes 15 million dry tons of grains to increased corn acreage came at the expense of other grains, biofuels. They do not include energy crops in the currently mainly soybeans. However, most of the grain grown in the available number. United States has traditionally been dedicated to food and Table 4.3 summarizes the committeeâs estimate of the livestock feed supply and as such has high societal economic main components that make up the non-feed and food crop value. The result is that a maximum of about 25 percent of biomass available in the United States in the near term any grain is likely to be available for production of transpor- (today) at less than about $68 (2007 dollars) per ton, deliv- tation fuel. This observation is based on recent experience ered to the processing plant. Also included in the table are in which corn prices rose sharply when ~20 percent of the other estimates for comparison. Crop residues are readily grain was diverted to ethanol production. The U.S. Depart- estimated (~60 percent recovery) and are available annually. ment of Agriculture (USDA) estimates that in the mid term, Energy crops are estimated at 3 dry tons per acre per year on the United States can meet food, feed, and export demand ~30 million acres of CRP land (which could be available in for corn and not seriously disrupt markets with less than 20 the near term). Forest residue is estimated at less than half percent of the corn crop being diverted to ethanol (USDA- of that projected to be available from logging residues and OCE, 2005). fire suppression (Perlack et al., 2005). Wood waste estimates In comparison, the amount of non-grain biomass in the are from Walsh et al. (2000) and Perlack et al. (2005). More United States is potentially significantly larger. Walsh et al. than 95 percent of mill wastes are used internally already. (2000) estimated the amount of biomass currently available Biomass costs, including transportation distance and cost, in the United States at less than $50 per dry ton (in 1995 dol- remain major uncertainties. lars) to include 135 million dry tons per year of forest and With future technology, Perlack et al. (2005) projected mill residues and 150 million dry tons per year of agricultural that todayâs technically available biomass amount could be crop residues. However, most of the mill residues are already increased to more than a billion dry tons per year within 35 being used for heat and power in the lumber, pulp, and paper to 40 years through a combination of technology changes industry. The total estimated biomass available at this price (e.g., higher crop yields and improved residue collection in the United States increases to 510 million dry tons per technology), full adoption of no-till cultivation, and changes year when municipal wood wastes (37 million dry tons) and in land use to accommodate large-scale production of peren- dedicated energy crops (188 million dry tons) are included. nial crops. Forest residues were projected to increase by more This is an estimate of the biomass that was projected to be than 225 million dry tons per year from todayâs use level, economically available in 2000 for less than $50 per dry ton and by 88 million dry tons per year from todayâs estimated in 1995 dollars (Walsh et al., 2000). This would be about $68 forest biomass availability to 368 million dry tons per year, per dry ton in 2007 dollars. The cost of biomass supplied through a combination of recovering wood wastes produced to an ethanol production plant would have to be less than through traditional and improved logging operations, forest about $65 per ton to be economical with future production thinning for fire suppression, and increased productivity and
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 53 TABLE 4.3â Estimated Primary Solid Biomass Components Available in the United States in the Near Term and 2030 for Less Than About $65 per Ton (2007 dollars) Biomass Amount (million tons per year) NRC ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ï¿½ Walsh et al. Milbrandt Perlack et al. ï¿½ï¿½ï¿½ NRC Source Estimatea (2000) (2005) (2005) 2030 Crop residues 160 50 173 179 315 Forest residues 55 44 62 136 55 Mill wastesa 5 90 88 106 Urban wood waste 30 37 34 37 30 Energy crops 85 188 99 â 100 â Total 335 509 456 458 490 aNRC estimate includes only that fraction that is estimated as not already being used. use of forest growth beyond lumber requirements. Agricul- numbers in their high-yield version of this case. For example, tural biomass availability increased even more than forest corn stover increases to 256 million dry tons (versus 172 mil- residue availability. Under their moderate-yield growth case, lion) per year, and most other agricultural biomass sources crop residue yields were assumed to increase up to 50 percent increase similarly. Without perennial crops, the projected for corn and 100 percent for soybeans, and the efficiency of amount of sustainable agricultural-based biomass production recovery increases from 60 to 75 percent over the next 40 ranges from 425 million to almost 600 million dry tons per years. Thus, recoverable corn stover today is estimated at 75 year (including 56 to 97 million tons each year of grains to million dry tons per year at 50 percent recovery. Total sto- biofuels) by 2050, assuming the high-technology changes ver biomass is therefore 150 million dry tons per year. This summarized above (Perlack et al., 2005). Perennial energy increases by 50 percent to 225 million dry tons of total stover crop production is assumed on 60 million acres and woody produced, and when 75 percent of this is recovered, corn energy crop production is assumed on 5 million acres, with stover available for biofuel production is 170 million dry tons significant yield increases for each included. These peren- per year. Estimates for small grains and soybeans increase nial energy crops contribute between 156 million and 377 from 6 million dry tons per year (many current residue levels million dry tons of biomass per year. Their high-technology are too low to recover economically) to 26 dry tons per year. case involves significant land use changes raising questions Recoverable wheat straw was estimated to increase from of storage or loss of carbon from the soil, which could affect 11 million dry tons per year to 35 million dry tons. Grain the CO2 impacts of biofuels (see below). Figure 4.4 shows quantities for biofuel production increase about 70 percent. the projected maximum technically available biomass in the Perlack et al. (2005) project even more aggressive growth United States in 2050 under the high-technology scenario Figure4-4.eps FIGURE 4.4â Projected sustainable biomass technically available in the United States by 2050, with aggressive energy crops. SOURCE: Perlack et al. (2005). BITMAP
54 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen with aggressive production of energy crops (Perlack et al., for the majority of 23 locations across the United States 2005). Although these numbers are for the technical amount (McLaughlin and Kszos, 2005; Perlack et al., 2005). The available from the listed sources, the cost can be assumed committee judges that the combination of changes to achieve to be as high as $100 per dry tonne (2007 dollars) for some these production levels appears achievable. portion of this supply. Most studies, including that of Perlack Beyond 2030, if the sustainable amount of biomass et al., estimate technically available biomass as a function obtainable from forest lands, estimated at 200 million dry of cost per tonne, typically to about or exceeding $100 per tons per year, is added to the estimated sustainable biomass dry tonne, and different biomass types have different cost available from agricultural lands (~500 million dry tons per profiles. At these prices, particularly by 2050, both algae year), the total annually available biomass for biofuels by and alternative crops for biodiesel, which can be grown on 2050 is estimated to be about 700 million dry tons per year. land unsuitable for food crops, may add to available sources. This is less than the 1.3 billion dry tons estimated by Perlack However, at $100 per dry ton for feedstocks, biofuels are et al. (2005) because of other energy uses for biomass such as unlikely to be competitive with other options as long as power generation and expected cost and water limitations. As carbon emissions are cost-free. noted earlier, the quantities of biomass available as a function Environmental issues are also associated with massive, of price remain unclear. intensive production of biomass, particularly via more traditional agriculture. These are not well quantified today Production: Grain- and Sugar-based Ethanol but could involve increased depletion of soil nutrients and micronutrients and potential reduction of soil carbon, result- Most of the ethanol produced in the United States today ing in increased CO2 emissions, significantly increased soil is produced from corn via either dry milling or wet milling erosion, reduction in habitat and biodiversity, and increased production processes. In dry milling, corn is ground into a stress on available water resources. Today, agriculture fine powder, and the resulting meal is mixed with water and accounts for about 13 percent of greenhouse gas emissions, the enzyme alpha-amylase, which breaks down the starch and land use changes account for about 19 percent (WRI, into its individual sugar (glucose) components. The mixture 2008). Land use changes frequently result in a loss of soil is then heated to kill undesirable bacteria, the mash is cooled, carbon; agricultural practices on cropland can either increase and a second enzyme, glucoamylase, is added to convert or decrease the amount of soil carbon (Tilman et al., 2007; the glucose into dextrose. Yeast is added and ferments the Fargione et al., 2008). Thus, significant soil carbon loss can dextrose to ethanol and CO2. The resulting mixture has a result in biofuels being a significant CO2 emissions source. relatively low ethanol concentration in water because the The above issues will become increasingly important as the yeast is inhibited when the ethanol content reaches a certain amount of biomass directed to energy and biofuel produc- level (~13 percent ethanol). Ethanol is separated from water tion increases. by distillation, which consumes a large amounts fossil fuel, After reviewing significant research on the major issues typically natural gas, to distill off the water. The unconverted with biomass supply for biofuels including water avail- solid material consists of the cornâs protein and nutrients, ability, cost, and avoiding significant land use changes, the which upon drying makes good animal feed. Wet milling is committee estimates that about 500 million dry tonnes per similar to dry milling except that the corn kernels are soaked year of biomass could be sustainably produced in 20 years in weak sulfurous acid for about 48 hours before grinding. at reasonable cost. This involves using crop residues at twice The ground mixture is then separated into solid and aque- current levels (see Table 4.3); using switchgrass, mixed prai- ous components. The starch-containing liquor is hydrolyzed rie grasses, and other energy crops at what is considered a enzymatically, then fermented, and finally distilled as in dry conservative yield on CRP lands (about 3 tons per acre per milling. Wet milling is somewhat more expensive because year on 30 million CRP acres); and using forest or wood of the additional processing but it is amenable to larger- wastes at a moderate level at a level projected to be available scale plants. Typical fermentation times are about 48 hours; today (Table 4.3). fermentation times beyond 72 hours typically experience an More specifically on the basis for the increases in Table increased failure rate because of contamination with bacteria, 4.3, corn yields, both grain and stover, have been increas- acetogens, or other contaminants. ing at nearly 1.2 percent a year recently (Arkebauer et Ethanol production in Brazil starts with sugar cane. The al., 2004), and if this continues at 1 percent per year, with sugar is pressed out of the cane and fermented. The crushed increased recovery efficiency, stover recovery will double. cane left over from the sugar removal (called bagasse) pro- Less aggressive increases for the remainder of the crop resi- vides heat for the process and the distillation, effectively dues, increased recovery efficiency, a <10 percent increase eliminating the need for fossil fuels in the manufacturing in acreage planted, and other agricultural residues produce process and the resultant net CO2 emissions. Sugar cane can the projected biomass amount. The energy crop estimate is be grown much less expensively in Brazil and other tropical considered conservative in light of recent data showing an countries than in the United States, and Brazilian sugar-based average of 5.5 to 8 dry tons of biomass pre acre per year ethanol has the lowest production cost of any biofuel, with
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 55 costs running from $0.80 to $1.40 per gallon on a gasoline- per gallon, the cost of ethanol ready to blend is $1.95 per equivalent basis (Paustain et al., 2006). gallon. If the $0.51 per gallon excise tax credit is applied, One bushel of corn can yield about 2.8 gallons of ethanol. the apparent cost of ethanol at the blending terminal is $1.44 To produce 3 billion gallons of ethanol per year requires per gallon. Since ethanol contains 80,000 Btu per gallon, about 1.1 billion bushels of corn, which in turn requires versus about 119,000 Btu per gallon for unleaded gasoline, about 8 million acres. The United States currently produces the cost of ethanol on a gasoline energy-equivalent basis is about 11 billion bushels of corn annually on about 85 mil- about $2.90 per gallon. If the excise tax credit is applied, lion acres. Thus, production of 3 billion gallons of ethanol the apparent cost of ethanol per gallon at the blending ter- per year consumes about 10 percent of our current corn minal on a gasoline energy-equivalent basis is about $2.15. crop. Increasing ethanol production to 6 billion, 9 billion, In April 2007, unleaded gasoline on the Nymex was about or 12 billion gallons per year would consume 20, 30, or 40 $2.00 per gallon (crude price was about $65 per barrel). As percent of our current corn crop, respectively. In view of the a consequence, due in part to the rise in corn prices attendant fact that we currently consume about 150 billion gallons of on higher demand, higher oil prices have not made ethanol gasoline per year in our light-duty vehicle fleet, it is clear competitive economically. Thus in 2007, the Nymex selling that corn ethanol cannot significantly impact oil imports for price of ethanol was about $2.05 per gallon. The higher cost gasoline production, especially since ethanol contains less can be justified on the basis of the high blending octane value energy per unit volume, and much of that energy is in fact of ethanol, but there are volume limits on this. In other words, from fossil fuel. It seems unlikely that we could devote more once the required octane rating of the blended gasoline is than about 25 percent of our corn crop to ethanol because of reached, it is not justified economically to blend more of the the substantial cost increases in corn prices that would result higher-cost material into the pool because it only increases and the impact of these higher prices across our economy and the cost of the fuel. economies worldwide. Current experience is that the price of corn doubled when ~20 percent of the crop was directed Cellulosic Ethanol to ethanol production. The U.S. Department of Agriculture (USDA) states that with projected increases in yield and corn To address the ethanol volume issue as well as greenhouse acreage the United States should be able to produce about gas emissions, biomass cellulose is a more attractive route 11 billion gallons of ethanol per year while meeting food, because of its larger volume potential and because most of feed, and export demands first (USDA-OCE, 2005). Thus, the feedstock is not in the food or feed chain. The stems, even with a 60 percent increase in corn production (increased stocks, and leaves of plants and the trunks of trees (wood) yield and increased acreage), to move beyond 10 billion to 12 are all composed of hemicellulose, cellulose, and lignin. billion gallons of ethanol per year would require substantial Hemicellulose is a polymer of several sugars. Cellulose is a ethanol imports, which could come from Brazil currently and polymer of the six-carbon sugar glucose. These sugars can be in coming years potentially from a wide range of countries fermented if the individual sugar units can be broken out of in Africa, Asia, and South America. Ethanol imports are cur- the hemicellulose and cellulose polymer chains. This is the rently discouraged by an import duty of $0.54 per gallon on challenge that must be overcome for cellulose- and hemicel- ethanol for fuel use. This would most likely have to change lulose-based biofuels to reach commercial viability via the if imports are to make substantial contributions to our biofuel biochemical route. Lignin is a highly cross-linked polymer supply. Furthermore, today there are only limited volumes of that does not contain any sugar components but can be used ethanol available globally, and many countries are bidding as a renewable fuel for energy needed in processes used to for it. Planning on large volumes of imports raises the issue convert the biomass to a liquid fuel. of large land use changes in other countries, which carries Relevant biomass that could be a feedstock for cellulosic with it other environmental issues, including the potential for ethanol production can be essentially anything that grows. increased CO2 emissions. However, every biomass type is different and would be In 2002, with corn at $2.36 per bushel, natural gas at expected to offer different challenges for conversion. For $3.00 per million British thermal units (Btu), and electricity illustrative purposes, consider the biomass associated with at $0.04/kWeh, the cost of corn ethanol production was esti- corn, with the exception of the grain. This biomass includes mated at about $1.20 per gallon of ethanol, including return corn stocks, leaves, husks, and cobs and is referred to as corn on capital (Whims, 2002). Unleaded gasoline on the Nymex stover. The corn stover is available only about one month per in that time frame was about $0.80 per gallon. In 2007, due year and must be collected, bailed, and delivered to a central in large part to demand for ethanol, corn prices rose above processing site. It must undergo washing and grinding for $4.00 per bushel. Natural gas prices have also risen and are size reduction before it is introduced into the process. currently over $8.50 per million Btu. At $4.00 per bushel of The cellulose-based process is more complex than that corn and $8.50 per million Btu of natural gas, the cost of for ethanol production from grain, particularly because of producing ethanol is about $1.70 per gallon of ethanol. If the need for acid hydrolysis (or another processing step) to the total transportation cost to the blending terminal is $0.25 break up the complex cellulose-hemicellulose-lignin struc-
56 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen ture before enzymes can free sugar molecules from the cel- corn stover. This is a similar number of plants to that in place lulose for fermentation, which is effectively the third major for grain ethanol. step. Each of these steps typically involves separate vessels. From the total estimated currently available crop residue Further, the total residence time in the process is about twice of 160 million dry tons per year (see Table 4.3), including as long as for grain ethanol production. These add capital and corn stover, and a yield of 60 gallons of ethanol per dry ton, operating cost to the process. The increased hydrolysis and it would be possible to produce about 10 billion gallons of fermentation times can also lead to increased contamination ethanol per year. If process improvements increase the con- and fermentation problems and to increased cost. Although version efficiency to 90 gallons of ethanol per dry ton, 14 the costs of the hydrolytic enzymes have been reduced ten- billion gallons of ethanol could be produced per year. If by fold or more over the last decade, this remains the key area 2030, crop residues total 315 million dry tons per year and in need of R&D attention. Cellulase is currently estimated to sufficient forest residues and perennial crops are added to cost between $0.10 and $0.30 per gallon of ethanol produced reach a total sustainable annual biomass production of 500 (DâAquino, 2007). A major development required for cellu- million dry tons, the ethanol production potential from cel- losic ethanol to become competitive with grain ethanol and lulosic materials could reach about 40 billion gallons per year potentially with oil-based fuels is the development of new, at an average yield of 80 gallons per dry ton. Producing 35 more robust organisms that can hydrolyze cellulose and fer- billion gallons of biofuels by 2017, the current administration ment the freed sugars in the same vessel at acceptable rates. and legislative target, is a large stretch that is probably not This would reduce capital and operating costs. At this point achievable (see Case 3 in Chapter 6) without major biofuel there is no clear evidence that such robust organisms have imports. Further, without the development of new organisms been developed. Organisms that could operate at higher con- that can simplify the cellulose conversion process, reduc- centrations of ethanol would also reduce cost. Furthermore, ing capital costs and residence time, cellulosic ethanol will different improved, more robust hydrolysis and fermentation remain significantly more expensive to produce than grain cultures also require development. ethanol, requiring significant subsidies to be economically attractive. Costs Biobutanol Although the plant equipment can currently be specified and designed, a relatively large uncertainty in the produc- Biobutanol is another potential entrant into the automotive tion cost and the technical readiness will remain until the biofuel market. Biobutanol is a four-carbon alcohol (versus technology has been demonstrated on a commercial scale. the two-carbon alcohol ethanol). Several technologies to Furthermore, the increased complexity, greater number of produce it are in the R&D phase. The one receiving the most vessels, and longer residence times associated with cellulosic attention is the acetone-butanol-ethanol (ABE) process. As ethanol, compared to grain ethanol, production means that currently envisioned, this process involves the bioconver- the cost of ethanol via the cellulosic route would signifi- sion of sugars or starches from sugar beets, sugar cane, cantly exceed that for the grain-based route. Using the above corn, wheat, or cassava into biobutanol using a genetically parameters, the estimated ethanol production cost is around engineered microorganism, Clostridium beijernickii BA101. $2.50 per gallon. Paustain et al. (2006) estimate the cost of a The midterm goal is to start with cellulose, but this awaits the gallon of ethanol to be $1.95 Â± 0.65 for biomass costing $35 success of the economic conversion of cellulose and hemicel- per dry ton. While DOE targets for âmatureâ cellulosic bio- luloses into sugars. Biobutanol has many attractive features mass conversion technology project parity with fossil fuels as a fuel. Its energy content is close to that of gasoline; it for transportation, achieving such parity represents a large has a low vapor pressure; it is not sensitive to water; it is less stretch for the technology, which is yet to be demonstrated hazardous to handle and less flammable than gasoline; and commercially. it has a slightly higher octane than gasoline. Thus, it can go directly into the existing distribution system and substitute directly for gasoline. Its main drawback to date is its cost. Production Volumes To attack the cost and initiate market entry, DuPont and BP The potential ethanol production from corn stover can be have joined forces to retrofit an existing bioethanol plant to estimated from the expected yield per ton of biomass of a produce biobutanol using DuPont-modified biotechnology cellulosic ethanol plant. Using the Perlack et al. (2005) esti- (Chase, 2006). An improved next-generation bioengineered mate of 75 million dry tons of corn stover currently available organism is projected to be available within a few years. The per year and 60 gallons of ethanol per dry tonne leads to 4.5 promise of biobutanol is to start with cellulosic biomass as billion gallons of ethanol from corn stover per year. For a a feedstock. The cellulose approach is being studied but is typical plant size of 2,000 dry tons per day, 110 plants would far from commercial. be required to produce this amount of cellulosic ethanol from
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 57 Biodiesel $2.10 per gallon. In spring 2008, soybean oil rose to about $4.20 per gallon (Brasher, 2008). The current viability of the Biodiesel is a renewable fuel produced from vegetable industry depends on government incentives, which are about or animal oils and fats. It is made by the transesterification $1.00 per gallon (Brasher, 2008), and programs. of these feedstocks, typically with methanol. The reaction is catalyzed by a base such as sodium hydroxide (NaOH). The main products are a methyl ester, which is referred to Production of Biodiesel as biodiesel, and glycerol, which has a variety of other uses U.S. production grew from about 500,000 gallons per (see Figure 4.5). If ethanol is used instead of methanol, year (33 barrels per day [bbl/d]) in 1999, to 2 million gal- the product is an ethyl ester; methanol has been preferred lons per year in 2000, to 250 million gallons per year in because it is cheaper than ethanol. Biodiesel has about 93 2006, and 450 million gallons per year in 2007 (Brasher, percent of the energy content per gallon of oil-based diesel 2008). This compares with 690 million gallons per year in fuel and has a cetane number between 50 and 60, with 55 Germany and about 200 million in France in 2006. For most being typical. of the period up to 2006 in the United States, the utilization rate of installed capacity was less than 25 percent. In 2006, Cost of Biodiesel 250 million gallons were produced from an installed capac- ity of about 580 million gallons per year (about 45 percent Driven by the feedstock cost, which is about 80 percent capacity utilization [Hofman, 2003]). In Europe, the industry of a plantâs operating cost, the cost of biodiesel has been sig- has grown rapidly, with capacity expanding in step with nificantly higher than the cost of conventional diesel. Operat- demand. The United States is also in the process of building ing costs (excluding feedstock costs) are $0.40 to $0.45 per massive additional capacity, with 57 plants under construc- gallon. The variable cost (operating + feedstock, excluding tion or in the planning stages as of January 2008 (Brasher, capital) of producing biodiesel has been in the range of 2008). Further, South America and Asia are building excess $2.50-$2.80 per gallon for the last decade, with soybean oil capacity in expectation of large export markets (Weirauch, around $2.00 per gallon (Hofman, 2003). This cost is for the 2006). Countries in these regions are studying new plants use of methanol for esterification; if bio-based ethanol were such as jatropha, which can be grown in areas unsuitable to used, the cost would be higher, but net CO2 emissions would traditional crops. be reduced. The largest cost component in this is for the To produce 1 billion gallons of biodiesel from soybean feedstock, which for soybean oil has been around $2.00 per oil would require about 690 million bushels of soybeans, gallon of biodiesel. Increasing grain prices have increased 22 percent of our recent annual soybean crop of about 3.1 the cost of soybean oil also. Yellow grease (used cooking oil) billion bushels per year. As with corn ethanol, an expansion is about $1.00 per gallon but is limited in volume. Outlays in soybean oil use for biodiesel beyond perhaps 35 percent to cover capital and other fixed costs and returns to investors of our soybean production is likely to cause significant eco- are likely to be more than $0.20 per gallon, bringing the total nomic ripples through food and agricultural markets. If we cost of biodiesel to around $3.00 per gallon for traditionally are to go beyond the level of 1.5 billion gallons of biodiesel priced soybean oil (Hofman, 2003). Wholesale diesel fuel per year, we will most likely need to depend substantially during this period was about $1.80 per gallon, which means on imports. Yellow grease availability will limit biodiesel that biodiesel was not competitive. However, biodiesel from production from this material to about 100 million gallons yellow grease was cost competitive. In 2007, soybean oil rose per year (Radich, 2004). In the case of biodiesel, current to $3.00 per gallon, and the cost of biodiesel was about $3.50 technology is relatively straightforward and well proven. per gallon, whereas the cost of conventional diesel was about Because of the simplicity of the process, there is not much to be gained in terms of economies of scale or process opti- mization. Forward projections are fairly linear and depend on the availability of animal and vegetable oils. The major issue is cost. The other option involves producing diesel fuel via biomass gasification, pyrolysis, or Fischer-Tropsch synthe- sis. This is considered in âGasification Routes to Biofuelsâ below in this chapter. Biodiesel has the advantages that it has good requisite diesel fuel properties (excluding low-temperature properties) and can be blended into the fuel supply, where desired, to utilize the existing infrastructure. Because production is sim- pler and less energy intensive than for corn ethanol, the use of biodiesel, on an energy-equivalent basis, can reduce CO2 FIGURE 4.5â Transesterification of vegetable oils. emissions per gallon by about 10 to 50 percent, depending Figure4-5.eps BITMAP
58 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen on the plant oil source and the amount of fossil fuels used CO2 emissions, and if gasification is combined with capture in growing, harvesting, and producing the biodiesel com- and sequestration of CO2 emissions, such processes should pared to a gallon of conventional diesel on a life-cycle basis have a negative CO2 emission footprint. They should also (UK Department for Transport, 2008). For soybean oil the result in an equivalent reduction in oil use. CO2 reduction is about 30 percent. Biodiesel can reduce oil Gasification is carried out under a variety of pressure and consumption by 90 to 95 percent relative to oil-based diesel temperature conditions. When relatively low pressures are usage (Radich, 2004). used, the process is basically rapid pyrolysis. Under low- pressure rapid pyrolysis conditions, primary products are a mix of hydrogen, CO, light hydrocarbons, bio-oil, and char. Future Biosynthetic Biofuels The heating is usually indirect and operation is at lower Over the last 25 years significant research efforts have pressure, avoiding the need for an expensive air separation focused on algae for biofuel production. Algae can be grown unit. The mix of primary products can be separated into in both salt- and freshwater environments, in shallow ponds, several fractions for upgrading. Bio-oil, which is a complex tubes, or raceways utilizing waste nutrients. One area of mixture of organic compounds, can theoretically be refined research is the development of algae that have high lipid further under process conditions that resemble oil refining. productivity (Briggs, 2004; Pacheco, 2006). The oil would If this can be done commercially, it would provide an avenue be extracted from the collected algae. Progress was made to biomass-based liquid transportation fuels that would sub- early in the period, but efforts have slowed greatly. Recent stitute directly for their oil-based counterparts. However, reevaluation suggests that current costs are well over $4.00 the requisite refining technologies need to be developed and per gallon, and much more progress is needed if this technol- demonstrated. In addition to deriving products from the bio- ogy is to have an impact in the foreseeable future (Pacheco, oil, the full set of gaseous and liquid pyrolysis products can 2006). Alternatively, algae can be grown as a source of cel- be gasified, the gas stream can be compressed, the CO shifted lulose for biofuels. to the appropriate CO-to-hydrogen molar ratio, and the CO2 With the rapid growth of synthetic biology and the removed. The resulting synthesis gas can be converted to increasing ability to engineer organisms to produce specific transportation fuel (e.g., diesel fuel via Fischer-Tropsch syn- chemical or fuel products, the area of genetic engineering of thesis). Another option is to produce methanol from CO and biomass has witnessed significant renewed interest (Savage, hydrogen. Methanol can then be converted to dimethyl ether 2007). Microbes that produce and excrete specific hydro- (DME) or to gasoline using methanol-to-gasoline (MTG) carbons minimize the energy-consuming separation costs technology, which has been commercially demonstrated in a that are the key issue with ethanol formation. Furthermore, 14,000 bbl/d plant in New Zealand that operated successfully properly designed hydrocarbon products in either the diesel from 1985 to 1996. MTG appears to be the most likely route range or the gasoline range could fit into the existing infra- because MTG gasoline blends directly into the gasoline pool structure without requiring new infrastructure as needed for and fully uses the existing infrastructure. DME would require ethanol at larger scales. Although no specific processes can a separate or greatly expanded infrastructure. be considered for commercial evaluation at this point, the Gasification using direct firing with oxygen at higher pres- rate of change and potential specificity that can be expected sures produces a relatively pure stream of CO and hydrogen, could produce rapid changes in the not-too-distant future. It with some CO2 and other gases. This syngas mixture is easily is difficult to project future developments; thus, this technol- shifted to the desired CO-to-hydrogen molar ratio and, after ogy is not considered further here, but it deserves careful CO2 removal, can be converted to diesel fuel by the Fischer- tracking in the future. Tropsch synthesis or to methanol and then to gasoline by MTG. This approach would have the highest capital cost but, because of the simplicity of fuel production and a high yield, Gasification and Pyrolysis Routes to Biofuels could be competitive. Biomass gasification involves the conversion of biomass Several U.S. and European groups are developing to a mixture of carbon monoxide, hydrogen, carbon dioxide, advanced biomass gasification technologies, and there are methane, and other organics including bio-oils and tars, ash, about 10 different biomass gasifiers with a capacity greater and small char particles. The concentration of these gases and than 100 tonnes per day operating in the United States and other materials depends on the process design and operating worldwide. There are more than 90 installations (most are conditions of the gasifier. Gasification has the advantage small) and 60 manufacturers of gasification technologies that it can convert essentially any biomass to clean synthesis (BTG, 2004). For example, at the McNeil Generating Sta- gas from which a broad range of products can be derived. tion in Vermont, a low-pressure wood gasifier, which started Biomass gasification exhibits many similarities to coal operation in August 2000, is converting 200 tons of wood gasification including a significant number of gasifier types chips per day into fuel gas for electricity generation. Many and different approaches to gasification technology. Fuels of the gasification technologies have technical or operational produced via gasification of biomass should have low net challenges associated with them, but most of these problems
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 59 are probably resolvable or manageable with commercial cost associated with biomass gasification, combined with experience. The most persistent problem area appears to the higher cost of biomass feedstock supply, will make it be biomass feed processing and handling, particularly if a difficult to compete with coal if carbon capture and storage gasifier operates at high pressure and/or must contend with (CSS) is not required. different biomass feeds. DOE has funded five other advanced biomass R&D projects (DOE-EIA, 2007). Impact of Biofuels on Oil Imports and Greenhouse Gas Although several of the available gasification technolo- Emissions gies have been demonstrated commercially, the technology is not yet commercially proven for biomass gasification and the In part due to competition with the food and feed needs production of biofuels. The technology is still on a relatively of the United States and the world, corn ethanol has severe steep learning curve, and the integration of gasification, gas limitations with respect to its potential volume and impact cleanup, and biofuel synthesis or bio-oil refining is yet to be on oil imports and on reductions of CO2 emissions from the commercially established. The same can be said for biomass transportation sector. Corn production in the field is energy gasification for hydrogen production. A major difference with intensive, using fossil fuels for fertilizer production, cultiva- biomass gasification is that it will involve smaller units than tion, and harvesting. The production of ethanol also requires coal gasification and will not see the economies of scale of large amounts of energy, which typically comes from natural coal gasification. This will increase the cost per unit product gas, with the result that net energy and net CO2 reductions unless major process simplification and capital cost reduction are limited. Life-cycle estimates of the net energy of corn can be achieved. The primary approach to this is to eliminate ethanol range from a loss to a more than 30 percent energy the air separation unit, which is typically required with most gain over the energy in the fossil fuels used in its production, high-severity gasification technologies, and its cost. This depending on the assumptions made in the studies and on the leads to gasification by indirect heating, which could more system boundaries (i.e., what is included in and not included appropriately be considered biomass pyrolysis, as discussed in the analysis). Figure 4.6 shows the range of results found above and typically produces bio-oil, tar, and gases. in the literature. The specifics of the studies leading to these Several economic studies of biomass gasification have results are referenced and discussed by Farrell et al. (2006). been reported, at times combined with demonstration proj- A reasonable conclusion for grain ethanol is 18 to 25 percent ects. A Finnish company has estimated that its biomass gas- energy gain over fossil inputs (Wang, 2005) and a similarly ification technology, which is operating at the 150 kWth feed sized net CO2 emissions reduction relative to gasoline. scale, can produce diesel fuel for $2.50 to $3.10 per gallon Figure 4.7 shows the primary energy inputs of fossil and (VTT, 2006). Jensen (2004) from Shell estimated the cost of other energy sources in megajoules of primary energy and Fischer-Tropsch diesel from biomass gasification to be about the estimated greenhouse gas emissions in kilograms CO2 $1.80 per gallon. Using a consistent basis for comparison, equivalent per megajoule of fuel for gasoline production rapeseed methyl ester biodiesel was estimated at about $4.50 and per megajoule of product energy for ethanol production, per gallon. These two sets of estimates are for large-scale also from the work of Farrell et al. (2006). This shows that plants. Choren Industries is in the early operating phases of the use of dry-mill ethanol reduces CO2 emissions by about a gasification process coupled with Fischer-Tropsch technol- 25 percent over the use of gasoline on an energy-equivalent ogy from Shell to produce high-quality diesel from a 50-50 basis. mixture of wood chips and wood waste in Germany (Choren Total fossil fuel use is also reduced by 20 to 25 percent Group, 2008). This facility will demonstrate the gasifica- (for dry-milled ethanol), but since most of the fuel used in tion, syngas cleanup, and synthesis technologies integrated growing, harvesting, and producing ethanol is natural gas together. and coal, the reduction in oil use that ethanol can produce The World Bank (2007) made a series of estimates for is much greater (see Figure 4.7). Thus, dry mill ethanol use biomass-based integrated gasification combined cycle could reduce the petroleum requirement by about 0.95 gallon (IGCC) plants that were about one-fifth the size of typi- per energy-equivalent gallon of ethanol used. cal coal-based IGCC plants. The size was limited by the Net CO2 reductions improve when biomass, such as maximum distance at which it was economic to harvest and bagasse or lignin, supplies the energy needed for the con- transport biomass fuel. The estimated total plant cost was version and separation. Thus, ethanol from cellulosic feed- $2,150/kWe (1997 dollars) for a 100-MWe wood gasifica- stocks can produce a roughly 88 percent reduction in net tion-combined cycle power plant. For a 32 MWe wood gas- CO2 emissions on a fuel energy-equivalent basis (see Figure ification-IGCC demonstration plant in Brazil the total plant 4.5) (Wang, 2005; Farrell et al., 2006). Estimated emissions cost was about $2,900/kWe (1997 dollars). This compares to from todayâs conventional vehicles are shown in Table 4.4. an estimated total plant cost of $1,300/kWe (1997 dollars) Because the cellulosic ethanol process is self-sufficient in for a 500 MWe coal-based IGCC. These results demonstrate terms of energy, the oil reduction achieved when cellulosic that biomass gasification suffers from diseconomies of ethanol is used to displace a gallon of gasoline is about 0.93 scale because of feedstock limitations. The higher capital gallon of oil on an energy-equivalent basis.
60 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen Net GHG (g CO2 eq/MJ-ethanol) FIGURE 4.6â Published estimates of range of impacts on net greenhouse gas (GHG) emissions (A) and oil inputs (B) for grain-based ethanol. For additional discussion and information, see http:www.sciencemag.org/cgi/content/full/sci;312/5781/1748b. SOURCE: Farrell et al. (2006). Reprinted with permission of the American Association for Figure4-6.eps Science. the Advancement of BITMAP Figure4-7.eps FIGURE 4.7â Primary energy inputs and net greenhouse gas (GHG) emissions for gasoline and ethanol (primary energy inputs are in mega- joules per megajoule of product energy; GHG emissions are in kilograms of CO 2 equivalent per megajoule of fuel). SOURCE: Farrell et al. BITMAP (2006). Reprinted with permission of the American Association for the Advancement of Science. TABLE 4.4â CO2 Emissions from Todayâs Conventional Production Potential of Biofuels Light-duty Gasoline and Diesel Engines in a Typical Production of ethanol from grain is fully commercial. Fig- Family Sedan and from Fuels from Less Conventional ure 4.8 shows the corn-ethanol production capacity growth Sources from 1990 to 2007. U.S. production capacity grew from 4.3 Vehicle Technology or Well-to-Wheels CO2 billion gallons annually at year-end 2004, to 5.9 billion gal- Fuel Source Emissions (g CO2/km) lons annually by year-end 2006, and about 7 billion gallons Conventional gasoline 2005 165 annually by year-end 2007. Considering only current plant Conventional diesel 2005 143 construction under way, ethanol capacity will be at least 8 Ethanol from corn 131 Ethanol from cellulose 15 billion gallons per year by year-end 2008 and could be as much as 10 billion gallons per year if all proposed projects SOURCE: Heywood (2007). are completed. This is a doubling of capacity in 4 years and
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 61 7000 TABLE 4.5 Key Assumptions and Parameters Used in Biomass-to-Biofuels Scenarios 6000 Probable Upper-bound Million gallons per year 5000 Case Case 4000 Biomass potentially available in the near-term (dry tons/yr)a 335b 335b 3000 Biomass available in 2050 (dry tons/yr) 500 700 2000 Average ethanol yield on biomass, 2008 to 2030 (gallons/dry ton) 60 60 1000 Average ethanol yield on biomass, 2030 to 2050 (gallons/dry ton) 90 90 0 aBiomass use starts with crop residues (corn stover) and then adds other 1990 1993 1996 1999 2001 2004 2007 sources including energy crops as they become available, driven by cost. Year bSee Table 4.3 for primary biomass components that make up this number. FIGURE 4.8 Growth in production of corn-based ethanol in the United States. SOURCE: Courtesy of Renewable Fuels Figure4-8.eps Association. is well ahead of mandated biofuel levels. However, the 10 about two to four times that of ethanol plants. For the rest billion to 12 billion gallons per year probably represents the of this discussion, the committee assumes that cellulosic limit with respect to corn availability, assuming that corn ethanol is commercially demonstrated by 2010 and capac- yields and acreage increase modestly. Production of ethanol ity begins to grow. Two cases are considered; both assume from grain is not likely to see significant additional process that cellulosic ethanol is economically competitive or there cost reduction. Further, costs are not subject to economies of are sufficient fuel subsidies to make it competitive with oil- scale because current plant size is about at the limit and water based fuels so that production capacity is built with private use limitations will probably increase costs in future plants. capital. One case is considered to be a measured response to Based on the previous analysis in this chapter, a forward the need to replace oil-derived liquid transportation fuels and projection of grain ethanol production is as follows: is called the probable case. The other case involves a more aggressive application of the technology to generate liquid â¢ 8 billion gallons in 2008, transportation fuels and is called the upper-bound case. Table â¢ 10 billion gallons in 2010, and 4.5 summarizes the key assumptions and parameters used â¢ 12 billion gallons in 2015. for the two cases. The probable case assumes a more measured pace of Production of ethanol from cellulose is yet to be dem- application of the technology in view of all the issues includ- onstrated at a commercial scale, and significant questions ing process cost, water availability, biomass cost, other com- remain about the economic and commercial viability of petitive uses of biomass and the ability to build plants and the technology. Within the next 3 to 5 years, four to five to increase biomass availability. For this case, the capacity commercial demonstration plants are expected. These will build followed the grain ethanol capacity build experience, provide valuable information on cost, technology robustness, in which over a several-year period about 1 billion gallons and particularly, commercial viability at the scale required of capacity was added per year. For this case (see Table 4.5 to achieve large-scale cellulosic ethanol production. This for details), the key assumptions are that the technology is information should be available by 2010. The committee commercially ready and there are 335 million dry tons of expects the commercial and economic viability of cellulosic biomass available in the near term, increasing to 500 mil- ethanol to remain a key issue for some time. lion dry tons available per year for conversion to biofuels by Cellulosic ethanol or other alternatives (e.g., biomass 2050. The upper-bound case also starts with 335 million dry gasification, liquid-fuel synthesis) will be required to meet tons of biomass available per year and assumes that by 2050, biofuel demand beyond levels achievable with grain ethanol. If commercially successful, cellulosic ethanol production The DOE roadmap on cellulosic ethanol is âto accelerate cellulosic could approach the growth experienced for grain ethanol. ethanol research, helping to make biofuels practical and cost-competitive Cellulosic ethanol plants are similar to grain ethanol plants by 2012.â The three to five demonstration plants that DOE is funding should although somewhat more complex, and because of the have achieved that goal by the end of 2010 or have identified the key remain- ing issues. If an economic business case can be made by that time, there is dispersed nature of biomass, they will be limited in size to capital ready to build forward.
62 TRANSITIONS TO ALTERNATIVE TRANSPORTATION TECHNOLOGIESâA focus on hydrogen 700 million dry tons of biomass are available per year and Biobutanol should be commercially demonstrated in 2 to converted to biofuels (ethanol). It assumes that many of the 3 years with the BP-DuPont plant noted above, but the main constraints are resolved, that sufficient additional biomass is issue will be cost. It will probably require about a decade to available, and that once sufficient experience is gained, plant define the extent to which costs can be reduced, for next-gen- capacity build exceeds the grain ethanol experience. It is eration microbe technology to be developed and applied, and consistent with the aggressiveness of the Hydrogen Success for technology developed to convert cellulosic biomass to scenario (Case 1) discussed in Chapters 3 and 6 and, thus, biobutanol. This is when commercial viability will be clearer. is the most logical case for comparison with the hydrogen Biobutanol is included in the scenario by assuming that it is cases. It also shows the maximum impact that biofuels can produced at 10 percent of the cellulosic ethanol production have on oil import reduction and on greenhouse gas emission level and is offset by 5 years. Thus, 0.1 billion gallons per reductions from light-duty vehicle transportation. year could be available in 2015, 0.5 billion gallons per year Biomass for biofuel production starts with agricultural in 2020, and so forth. crop residues, which are readily available today and then Biodiesel production from plant and animal oils is fully double over time. Grown-for-purpose energy crops and forest commercial, and the technology is considered mature. The residues contribute later in the period, driven by price, loca- production cost is mainly in the plant oil cost, and the yield tion, and local availability. Because of the issues of gathering of oil per acre is low for crops suitable for the United States. and transporting biomass, conversion plants will be limited in This suggests that it will not be a major player in the U.S. size, potentially two to four times as large as corn-based etha- light-duty vehicle fuel market. U.S. production costs are nol facilities and will not be able to gain further economies of about $3.00 per gallon. The technology is simple and mature, scale. Ethanol yield is assumed to improve from 60 gallons and there has been no problem building plant capacity to per dry ton early in the build to 90 gallons per dry ton about date, with recent utilization of installed capacity at less than mid period and beyond. Water will become a major issue as 50 percent. the production grows. For forest residues and energy crops Projected annual production volumes are as follows: grown on less desirable land, the areas where plants will be built will likely be dryer, and water is expected frequently â¢ 250 million gallons per year today, to become a major issue. This and other factors, including â¢ 600 million gallons in 2012, and the cost of biomass per dry ton, will limit full utilization of â¢ 1.5 billion gallons in 2020 (maximum production). the technically available biomass. The upper-bound case removes or limits many of these restrictions The 1.5 billion gallons of production per year would The infrastructure build for rapid growth in cellulosic consume about 30 percent of the soybean crop and probably ethanol production should be similar to that experienced cannot be increased. Corn and soybeans compete for the for corn ethanol. The primary difference is that cellulosic same land, limiting soybean production. ethanol plants will cost two to three times as much as corn Because the manufacture of biodiesel is much less energy ethanol plants due to greater complexity and increased mate- intensive, the estimated impact on CO2 emissions is a 30 rial and construction costs. The infrastructure for delivery to 35 percent reduction per gallon of biodiesel used, and of the product to blend plants would be expected to remain the impact on oil consumption is about a 90 to 95 percent largely the same as for grain ethanol, but it would have to be reduction relative to use of a gallon of regular diesel fuel. expanded to meet the greater production. Since the plants are CO2 emissions include those associated with the methanol relatively small and widely scattered, truck and rail would used in esterification. The energy contents of biodiesel and probably pick up most of the growth. Dedicated pipelines regular diesel are roughly the same. connecting areas of substantial production with large blend plants would be expected to develop in specific instances. Conclusions on Biofuels Costs can be expected to decrease but will remain a signifi- cant issue. The estimated build-out and projected annual cel- CONCLUSION: Although use of corn- and oil-based lulosic ethanol production for each case are given below: biofuels can provide some benefits in reducing U.S. oil use and CO2 emissions, cellulosic biofuels will be required Probable Case Upper-bound Case for such benefits to be significant. Lower-cost biofuel â 1 billion gallons in 2011 â 1 billion gallons in 2011 production methods and conversion processes will have â 5 billion gallons in 2015 â 6 billion gallons in 2015 to be developed for large-scale commercialization, but 12 billion gallons in 2020 16 billion gallons in 2020 the initial high costs of biofuels, together with other 18 billion gallons in 2025 28 billion gallons in 2025 barriers, may limit their market potential, absent policy 32 billion gallons in 2035 44 billion gallons in 2035 interventions or significant oil price increases or supply 45 billion gallons in 2050 63 billion gallons in 2050 disruptions.
ALTERNATIVE TECHNOLOGIES FOR LIGHT-DUTY VEHICLES 63 Biofuels offer the potential to reduce oil imports because States will be able to meet the biofuels target of 35 billion they can replace a fraction of the liquid fuels needed for gallons per year by 2017. U.S. light-duty vehicle transportation. They can also reduce CO2 emissions because they use carbon that was captured OVERALL CONCLUSION by plants in their last growth cycle, not carbon stored during previous millennia, and the repeated growth cycles recapture CONCLUSION: The committeeâs analysis indicates that the CO2 emitted during combustion of the fuel. Biofuels from at least two alternatives to HFCVsâadvanced conven- different sources will have a different impact on oil imports tional vehicles and biofuelsâhave the potential to pro- and on net CO2 emissions. vide significant reductions in projected oil imports and Grain ethanol has a 20 to 25 percent energy gain over the CO2 emissions. However, the rate of growth of benefits fossil fuel inputs used for its production and, on average, from each of these two measures slows after two or three reduces CO2 emissions by 18 to 25 percent over the use decades, while the growth rate of projected benefits from of gasoline on an energy-equivalent basis. Grain ethanol fuel cell vehicles is still increasing. The deepest cuts in oil production is fully commercial but is constrained by grain use and CO2 emissions after about 2040 would come from availability because it competes with the use of grains for hydrogen. See Chapter 6. food and animal feed. Much more biomass is available from non-grain sources. Bibliography The technology for cellulosic ethanol has not yet been dem- onstrated for commercial production. It should be signifi- Achenbach, J. 2007. So Whatâs So Bad About Corn? 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