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3 Vehicle Subsystems INTRODUCTION At the time of the Phase 1 review of the FreedomCAR and Fuel Partnership, the Partnership had been under way for a relatively short time, although it did have the advantage that a number of the technologies under development were part of the Partnership for a New Generation of Vehicles (PNGV) program, which had been initiated in 1993. Since the Phase 1 report was issued, there have been significant changes in some external influences, such as a large increase in the price of gasoline and heightened interest in carbon dioxide (CO 2) contributions to global warming. These changes could make achieving the program goals even more beneficial in the long term and, consequently, more important to the nation. Since the program objectives are obviously in the national interest, and since most of the high-risk activities would not be undertaken without governmental support, DOE involvement is clearly justified. The long-range goals of the Partnershipâto transition to a transportation system that uses sustainable energy resources and produces minimal criteria or net carbon emissions on a life-cycle or well-to-wheels basisâare extremely ambi- tious. The difficulties are compounded when the additional constraints associated with the Partnership are imposed: energy freedom, environmental freedom, and vehicle freedom. These goals and associated constraints effectively eliminate the continued simple evolution of the gasoline-fueled internal combustion engine (ICE) vehicle as a possible answer. âSustainable energy resourcesâ and âenergy freedomâ both suggest non-petroleum-based alternative fuels. The emphasis on ânet carbon emissionsâ and âenvironmental freedomâ suggests that CO 2 and other emissions from the production and consumption of alternative fuels should 48
VEHICLE SUBSYSTEMS 49 be reduced, through highly efficient processes, to minimize adverse environmen- tal effects. Finally, âvehicle freedomâ implies that the fuel and onboard energy conversion systems should not limit the options and choice that buyers expect to have available in their personal vehicles. These goals, if attained, are likely to require new transportation fuel(s) utilized in more efficient power plants in lighter vehicles having reduced power requirements and equivalent utility and safety. DOE envisions that the path to achieving the long-term goals of the Freedom- CAR and Fuel Partnership involves improvements in ICEs, a transition from improved gasoline- and diesel-fueled ICE vehicles to a greater utilization of gasoline- and diesel-fueled hybrid electric vehicles (HEVs), the development and implementation of plug-in hybrid electric vehicles (PHEVs), more utilization of hydrogen-fueled ICEs and HEVs, andâfinallyâhydrogen-fueled fuel cell vehicles (FCVT, 2004). For this transition to take place, the industry will require enhanced technology in many areas so that it can develop new vehicle subsys- tems and vastly improved vehicles. The DOE-sponsored activities described in this section are intended to provide understanding that will enable the needed technologies to be successful. The scope of the technologies needed is broad and the timescales for implementation are short. Competitive pressures dictate that if a technology appears to be promising it will be rapidly integrated into industryâs implementation plans. Consequently, continued close collaboration between DOE and industry is necessary to allow these technologies to transition into the indus- trial laboratories and development programs and then to identify new critical areas where enhanced understanding will be most beneficial. An example of technology that has progressed from concept demonstration stage to implementation is exhaust gas aftertreatment from lean-burn engines. Various engine manufacturers and original equipment manufacturers (OEMs), both domestic and foreign, have or are planning to introduce lean oxides of nitrogen (NOx) traps, selective catalytic reduction, and diesel particulate filters to their production models. Therefore, it is appropriate that DOE funding for these activities should be curtailed and redirected to areas where fundamental understandings are lacking. This observation was made in the Phase 1 report and recommended that the Partnership redirect its pursuit of novel emission control technologies and plan for, analyze, and seek solutions for emission problems associated with emerging fuels, fuel infrastructure, and propulsion systems (see Recommendation 3-3 in Appendix D). In response to the recommendation, DOE initiated a solicitation (DE-PS26_ 07NT43103) to address (1) E85-optimized engines, (2) enabling technologies for fuels and lubricants, and (3) efficiency of clean combustion and fuels develop- ment. Since some of these technologies are in production (e.g., flex-fuel vehicles), it is important that the Partnership carefully coordinate with industry to maintain programs that contribute most to a new understanding of the physical, chemical, and thermal processes impacting performance of the engine, the fuel, and the aftertreatment system.
50 review of the freedomcar and fuel partnership The most direct way to enable near-term reductions in fuel consumption and emissions is by improving ICEs. Specifically, better understanding of the ICE combustion process and how emissions are produced could both increase efficiency and decrease engine-out emissions. Higher thermal efficiency reduces the fuel needed to produce a given power output, and lower engine-out emissions will allow the use of a simpler, probably less expensive exhaust aftertreatment system. Such improvements in ICEs, which could be implemented quickly, would benefit both conventional vehicles and HEVs. The fuel cell subsystem is an energy converter with the potential to be more efficient than an ICE. However, the only fuel cell systems currently appropriate for transportation systems use hydrogen as fuel. The hydrogen can be stored onboard the vehicle in pure form or it can be extracted from hydrocarbon fuels and water using an onboard fuel processor. However, DOE effectively eliminated the latter alternative from its R&D portfolio after years of research determined that there was little prospect of meeting essential cost and performance targets within the program time frames. This means that sufficient pure hydrogen must be carried onboard the vehicle to meet range requirementsâa very challenging task given the space and weight limits of typical light-duty vehicles. This, in turn, places a high premium on reducing the mass of the vehicle and maximizing the efficiency of the energy converter. Current experimental hydrogen-fueled fuel cell systems demonstrate efficien- cies approaching 50 percent over a fairly wide range of operation. Further, such systems produce zero criteria emissions (occasional discharges of small quantities of hydrogen may occur). FreedomCAR and Fuel Partnership programs are ad- dressing the performance, durability, and cost issues that need to be resolved so that fuel cells can become a viable option for personal transportation vehicles. HEVs require compact, efficient, and low-cost power electronics and energy storage systems as well as other advanced electrical components to make vehicle costs and weights competitive with conventional vehicles. Many of these same technologies are applicable to fuel cell vehicles and PHEVs. Consequently, ad- vances in the power electronics and electrical subsystems are critical for improved viability of both the midterm as well as the longer-term vehicles envisioned by the Partnership. It is possible for HEVs and fuel cell vehicles to reduce fuel consumption by capturing some of the vehicle kinetic energy during deceleration and stopping. This requires some form of energy storage capable of accepting this energy and returning it to the drive train for propulsive power (called regenerative braking). The most likely form of such energy storage is electrochemical (batteries), but ultracapacitors are also being investigated. For such relatively small-scale energy storage, the most important parameters are cost per kilowatt ($/kW), specific power (kW/kg), cycle life, and calendar life. With increased electric energy storage onboard, the vehicle could run for a significant distance without using the fuel cell or engine. This would add design
VEHICLE SUBSYSTEMS 51 flexibility to HEVs and reduce some of the performance requirements for fuel cells (e.g., start-up time and power ramp-up rate). Further increases in onboard energy storage capacity could enable PHEVs (vehicles whose batteries could be recharged by plugging them into a source of electricity while it is parked) and even all-electric vehicles. Both plug-in hybrids and all-electric vehicles would shift some transportation energy demand from petroleum-based fuels to the elec- tric grid, which is mostly non-petroleum-based but not emissions free. The most important goals for research on these energy storage systems are to improve their cost per kilowatt-hour ($/kWh), specific energy (kWh/kg), cycle life, and calendar life. These storage systems also have to maintain adequate specific power (kW/kg) even at low states of charge. Irrespective of the propulsion technology, reducing the mass of a vehicle for a given mission will, with no other design changes, have the effect of reducing fuel consumption and increasing acceleration performance. However, to achieve the vehicle goals of the Partnership, any such mass reduction must be accomplished without compromising safety or overall vehicle utility. To accomplish significant weight reductions, several materials, including aluminum, high-strength steel (HSS), and carbon-fiber-reinforced polymer composites have been considered for replacing a large part of the (mostly) mild steel currently used. Other mate- rial substitutions, such as cast magnesium, in other vehicle components could further decrease vehicle weight. The challenge for all of these potential material substitutions is to reduce their cost. The following sections discuss in more detail the research approaches and issues associated with each of these technologies. ADVANCED COMBUSTION, EMISSIONS CONTROL, AND HYDROCARBON FUELS Introduction Even the most optimistic scenario for introducing fuel cell vehicles into the market requires several decades before market penetration becomes sufficient to have a measurable impact on petroleum consumption and CO2 emissions. During this transition the dominant powerplant for mobility systems will continue to be ICEs fueled with a hydrocarbon (gasoline, diesel fuel, or biofuel). Consequently, it is important to maintain an active R&D program at all levels of industry, aca- demia, and government. The near-term introduction of such technologies could reduce the rate at which petroleum consumption for transportation grows during the transition to alternative powerplants and powertrain configurations. Adding electric components to a vehicle powertrain opens new ways to im- prove fuel economy. HEVs are being marketed today, and PHEVs, which offer greater vehicle range from the electricity stored in the onboard battery and can benefit from off-peak battery recharging, are being actively pursued. In hybrid
52 review of the freedomcar and fuel partnership vehicles, the ICE can be operated more efficiently than it is with conventional mechanical or hydromechanical transmissions. Obviously, any improvements to the ICE will carry over directly into incremental improvements of these electri- fied vehicles. Maximizing efficiency under the constraint of meeting stringent emission standards complicates engine-powertrain systems. Efficiency improvements re- quire understanding and precise control of every aspect of the engine operation as well as optimization of every component and its interaction within the powertrain system. The technologies currently being pursued with the intent of introducing them to the market for both diesel- and gasoline-fueled vehiclesâfor example, low-temperature combustion (LTC) and lean exhaust aftertreatmentâtax the limits of the engine and powertrain communityâs fundamental understanding of the controlling thermochemical processes. A greater knowledge of the controlling thermochemical phenomena will accelerate the introduction of these technologies into the marketplace. The urgent need to get vehicles with lower fuel consumption to market has spurred the effort to incorporate new technologies such as LTC or new lean ex- haust aftertreatment systems into vehicle powertrains. After research is completed, system optimization through prototyping and the development of manufacturing procedures can take several years before the new technology reaches production. This time pressure has unified the traditionally separate pursuits of âresearchâ and âdevelopment.â Researchers are now pursuing enhanced fundamental under- standing of the controlling thermochemistry at the same time as engineers are investigating concept systems. Sophisticated research tools such as laser-based optical diagnostics, the detailed identification of chemical kinetic mechanisms and their subsequent simplification, and the implementation of advanced three- dimensional computational fluid dynamics (CFD) are being used to expand the fundamental knowledge base and also being applied to potential configurations for prototype engines and powertrains. To successfully conduct such a program requires close coordination among industry, government laboratories, and academia. In the opinion of the committee, the advanced combustion and emission control technical team is doing a good job with this close coordination. The organizational structure of their activities involves memoranda of understanding (MOUs) between companies and govern- ment labs, working group meetings, regular intergroup reviews, and an annual peer-reviewed research meeting. The committee is pleased with the responses of the technical team to the recommendations made in the Phase 1 report. In particu- lar the team has succeeded in involving the energy companies in its programs. The energy companies are now actively engaged, and a program known as Fuels for Advanced Combustion Engines has been organized under the Coordi- nating Research Council. This program has the objective of providing a set of research fuels to discern fuel effects on LTC. The technical team is making good use of its resources. Requests for proposals (RFPs) have been issued for an E85-
VEHICLE SUBSYSTEMS 53 optimized engine, for enabling technology for fuels and lubricants, and for clean combustion and fuels co-development. Funding FY07 funding for the advanced combustion and emission control technical team was $20.7 million, with the same amount requested for FY08. A breakdown of how the funding was dispensed to different organizations and technologies is shown in Figure 3-1. Support Support HC 11% 11% Company Combustion University 25% Enabling 48% 8% 4% Aftertreatment 22% H2 Combustion National Labs 6% Energy Recovery 56% 9% Recipients Technical Area FIGURE 3-1â Distribution of DOE FY06 funding for the advanced combustion and emis- sion control technical team. SOURCE: R. Peterson and K. Howden, DOE, âAdvanced combustion and emission control,â Presentation to the committee on March 1, 2007. Goals and Targets The technical targets and roadmap remain the same as reported previously (NRC, 2005; DOE, 2004). To briefly summarize, the Partnership expects to achieve by 2010 an engine thermal efficiency of 45 percent, with a cost under $30/ kW, while meeting Tier 2, Bin 5, emissions. These are very challenging targets. The technical team is working hard to achieve them and is making progress. Figure 3-1 The focus of the research continues to be lean-burn, direct-injection engines for both diesel- and gasoline-fueled vehicles. Within this broad area, specific research areas include the following:
54 review of the freedomcar and fuel partnership â¢ Low-temperature combustion âControl, âExpanding the load range, âCoupling to fuel characteristics, âTransient operation, and âCombustion mode switching. â¢ Aftertreatment âModeling of a diesel particulate filter, âLean NOx traps, âSelective catalytic reduction (SCR) NOx reduction, and âIdentification of a potential catalyst for hydrocarbon NOx catalysis. â¢ Tool development âImproved CFD capabilities, âImproved diagnostics capabilities, and âComparison of CFD and experimental results. Within each of the research areas discernable progress has been made. High- lights are documented in âFreedomCAR and Fuel Partnership 2005âHighlights of Technical Accomplishmentsâ and can be found at the USCAR Web site: <www. uscar.org/commands/files_download.php?files_id=95>. Significant Barriers to Achieving Success The technologies being pursued by the advanced combustion and emission control technical team are very sophisticated. Making these technologies work in an engine-powertrain system under a range of operating conditions is very challenging. It pushes all the fundamental boundaries of understanding within the combustion and powertrain community. For example, trying to expand the LTC operating condition from an optimal operating point quickly leads to excessive unburned HC and carbon monoxide (CO) emissions, with an attendant reduction in combustion efficiency. The increase in HC and CO poses an additional prob- lem because the exhaust temperatures during LTC are usually below the typical light-off temperatures of current catalysts. Extended-range catalytic converters to facilitate engine operation approaching the edge of the combustion stability regime may solve this problem. Expanding the LTC operating range of an engine will require optimal match- ing of the fuel, its distribution within the cylinder, the fluid mechanic mixing, and the temporal and spatial evolution of thermodynamic states within the cyl- inder. Combustion mode switching between regular spark or diesel combustion and LTC may affect emissions, and the emission behavior of the engine during transient operation within LTC operation is not well understood and could be a serious issue. Similar statements about the technical complexity of the problems can be
VEHICLE SUBSYSTEMS 55 made for virtually all the technologies being investigated by the advanced com- bustion and emission control technical team. A critical prerequisite for achieving success is expanding the knowledge base of the processes that influence the performance of advanced combustion and emission reduction technologies and their interaction with the fuel being used as the energy carrier. Conclusions and Recommendations In light of the FreedomCAR and Fuel Partnership objectives, the funding and work allocation for continued development of the ICE and vehicle electrification seem appropriate. The advanced combustion and emission control technical team is doing a good job of maintaining a close and constructive working relationship with the stakeholders in the auto and energy communities. Since the distinction between research and development has blurred, it is critical for the technical team to maintain this collaboration and make it even stronger. The international competition is fierce, so maintaining a presence within that community and an awareness of technological developments outside the United States continue to be important to establish benchmarks and grow the knowledge base. The largest barrier to implementing advanced combustion, aftertreatment, and fuel technologies is an insufficient knowledge base. Not only topic-specific understanding but also understanding the system-level interactions between the energy carrier, the energy release process, and the final emission cleanup is critical to continued improvement of the ICE powertrain. Continued close collaboration between DOE and industry is necessary to allow these technologies to transition into industrial laboratories and to identify the areas where enhanced understand- ing will be most beneficial. Recommendation.â The Partnership should formulate and implement a clear set of criteria to identify and provide support to ICE combustion and emission control projects that are precompetitive and show potential for improvements well beyond those currently being developed by industry. Recommendation.â DOE should actively encourage collaborations among the national laboratories, industry, and academia to more effectively direct research efforts to areas where enhanced fundamental understanding is most needed. Transient LTC engine operation and combustion mode switching between conventional combustion and LTC could have significant impact on total vehicle drive cycle emissions and the necessary operating domain for catalytic exhaust treatment systems. This could also be relevant to the emissions for PHEVs, where the engine may be off for long periods of time before being started and engaged into the vehicleâs powertrain.
56 review of the freedomcar and fuel partnership Recommendation.â The Partnership should investigate the impact on emissions of combustion mode switching and transient operation with LTC. As the engine is made more efficient and exhaust thermal energy is used for advanced turbocharging and the aftertreatment systems, the final exhaust temperature will become lower. This will reduce the theoretical maximum ther- mal efficiency of heat engine exhaust recovery systems. Given the projected conversion efficiency of the exhaust heat recovery systems under investigation, the committee questions how much exhaust energy can actually be recovered. In addition, it seems likely that the cost per kilowatt of the heat recovery systems will be high. Recommendation.â The Partnership should perform a detailed analysis of the potential improvement in efficiency and the cost effectiveness of the exhaust gas heat recovery effort and make a go/no-go decision about this work. FUEL CELLS Introduction Hydrogen-based fuel cell powerplants promise to be one of the most ef- ficient and least polluting way to power personal transportation vehicles while providing the potential for meeting the Partnershipâs major goals. Consequently, the advancement of fuel cell technologies to the point where performance and costs can be compatible with mass-manufactured automobiles is a key element of the FreedomCAR and Fuel Partnership. Over the course of the Partnership, DOE-sponsored fuel cell activities have contributed to solid advances in many of the performance and engineering metrics as well as reductions in projected costs as described in the following section. Current projects are focused on advancing the science and engineering of the high-risk technical challenges that remain, including performance, durability, and lifetime. Initiatives that can lead to cost reductions through materials advancements, new concepts, or simplification of the engineering are also under way and are expected to eventually lead to a mass- manufactured product. Current Status of Key Parameters Fuel cell stack life currently limits the overall demonstrated powerplant dura- bility to only about one fourth of what is needed to meet the performance targets set forth by the Partnership. A major reduction in stack life occurs in actual vehicle applications because of the many stops and starts and transients with vehicle operations, fuel composition, and related phenomena when compared to what is observed with the testing methods and conditions in laboratory development work.
VEHICLE SUBSYSTEMS 57 In addition, as laboratory fuel cell stack lifetimes lengthen, new failure modes are surfacing and must be better understood and resolved. One such example is platinum catalyst dissolution, which impairs long-term performance. The prompt resolution of these and new failure modes, as they are discovered, is critical to achieving 2010 and 2015 targets. Projected costs for high-volume (500,000 units/yr) fuel cell powerplant pro- duction are currently approximately $100/kW for relatively proven technologies and about $67/kW for a newer technology compared to the 2015 target of $30/kW (see Figure 3-2; also see James and Kalinoski, 2007; Lasher, 2007). The latter estimate includes recent advances by 3M (Debe, 2007) in membrane and electrode technology that result in lower projected costs. These new technologies are quite promising, yet there is still a need to demonstrate that laboratory performance can translate to similar results in full stacks and then, ultimately, in vehicle tests. It should also be noted that the manufacturing and supply chains have not been fully established to date because the technology continues to evolve. The numer- ous assumptions that underlie the aforementioned cost projections may have to change as the development process proceeds. The cost of the platinum catalyst used in the membrane electrode assembly (MEA) represents approximately 57 percent of projected stack costs (Lasher, 2007). The platinum metal contained in the electrode alone accounts for most of DTI Fuel Cell System 80 kW Direct H 2 TIAX Fuel Cell System 80 kW Direct H 2 Cost = $118/kW (net), $9,412 Cost = $97/kW (net), $7,760 Assemble, Test, and MEA Assembly, MEA Misc., Condition, without Pt, $436 without Pt, $527 $979 $1,200 Fuel $790 Misc. System, $888 $340 Fuel System, Air System, $445 $1,085 Platinum, Platinum, Air System, $2,876 Cooling $2,956 $1,055 System, $340 Cooling Humidity System, Humidity Stack Stack System, $383 System, Balance, $640 Balance, $639 $467 $1,105 FIGURE 3-2â Two estimates of 2006 costs for fuel cell systems. The differences between the DTI and TIAX estimates are (1) the cost of the MEA and seals in stack balance of plant and (2) DTI included test and conditioning in its estimate. The 2015 cost target is $30/kW, for a total cost of $2,400. SOURCE: D. Tran and K. Epping, FreedomCAR fuel 3-2.eps cell tech team, Presentation to the committee on March 1, 2007.
58 review of the freedomcar and fuel partnership the cost of the catalyst, and the price of precious metals has risen substantially in recent years. The spot market price was approximately $1,300 per troy ounce in June 2007, 18 percent higher than the price used for estimating stack costs as reported at the 2007 DOE Merit Review. It must be noted that this price is set by market forces and will not be impacted by the Partnershipâs research program. Even though the fuel cell stack is the core of a fuel cell power generation system (and its most discussed element), it must be part of a carefully integrated system to achieve performance goals. The design, performance, and integration requirements of the ancillary components of the system depend heavily on the performance and engineering specifications of the stack, which means that the developmental progress of the entire system is highly dependent on the uncer- tainties and risks associated with meeting the long-term targets for each of these ancillary components. Of these components, onboard hydrogen storageâeven though it does not affect power plant performance directlyâis probably the most challenging goal. Major issues associated with this goal are discussed in detail in the next section of this report. The Partnership has achieved a significant improvement in the power density of the fuel cell stack without storage over the years: 440 W/l (2004), 500 W/l (2005), 580 W/l (2006) vs. the DOE target of 650 W/l in 2010 (Epping and Tran, 2007). Progress in power density, including the storage subsystem, has also been achieved (160 W/l in 2006) and is steadily progressing toward the 2010 target (220 W/l). The DOEâs Office of Basic Energy Sciences (BES) sponsors activities and programs at national laboratories and academic institutions that have used solid state and polymer sciences to study the atomic and molecular structure of catalysts and new polymers. These efforts have improved the knowledge base and could result in new and improved materials and processes for fuel cell components (e.g., membranes and electrocatalysts). The impact of these important efforts will most likely not be realized until after 2010. Lastly, water dynamics still remains challenging in that, if water distribu- tion is mismanaged, it can reduce stack performance and lifetime. The neutron scattering in situ water imaging technique available at the National Institute of Standards and Technology (NIST) has yielded exceptionally valuable insights into water behavior in an operating fuel cell. With the detection equipment installed in the spring of 2007, it is possible to âseeâ the water not only in the plates but also under dynamic conditions in the MEA and the gas diffusion layer (Jacobson, 2007). DOEâs support for the development of new laboratory techniques such as these is commendable. K. Epping and D. Tran, FreedomCAR Fuel Cell Tech Team, Presentation to the committee on March 1, 2007.
VEHICLE SUBSYSTEMS 59 FY 2007 Funding Funding/Request ($M) 14 FY 2008 Request 12 10 8 6 4 2 0 on As s er ing la nes n ts gy an s s y Q t ad is t/O ent r io te pt lit ge spo ys v ME er ra ess te Ro ua at la ce a n al En br iz rP po at ff- c em /C Pro om C n d H r Tr C ct po M C D or bu no e l ro Bi Ev ue ha at /P P tri yd In BO F W x Au al FIGURE 3-3â Fuel cell R&D funding, allocated and requested. SOURCE: Communication Technology Area between the committee fuel cell subgroup and Kathi Epping and Terry Payne, EERE, on August 28, 2007. Program Direction and Management The FreedomCAR and Fuel Partnershipâs overall requirements (cost, reli- ability, and performance goals) for the fuel cell system are well established and very challenging. DOEâs support is crucial for meeting these requirements. DOE has been actively engaged in funding high-risk R&D for existing programs on a 3-3.eps continuing basis and has been able to increase its multiyear development funding for a broad spectrum of technologies and new activities. The budgetary difficul- ties of FY07 (continuing budget resolution) appear to have abated, and FY08 funding requests have been increased (see Figure 3-3). The potential benefits of this technology and the progress to date justify current spending and increased future spending levels. The DOE fuel cell program is addressing the high-risk technical elements, and managers have proactively refined some of the near- and longer-term targets that needed refinement. If the 2010 and 2015 goals of the program are to be met, some recently funded R&D initiatives will have to contribute to the timely reso- lution of many of the remaining technical challenges. Since DOE awarded about $100 million in the fall of 2006 for such development, the research direction and priorities have already been set for the next few years. To gain further valuable See <http://www1.eere.energy.gov/hydrogenandfuelcells/mypp/pdfs/fuel_cells.pdf>.
60 review of the freedomcar and fuel partnership insight into the resolution of engineering issues, DOE funded and supported the Learning Demonstration Program using on-road, fuel-cell-powered vehicles sup- plied by the automotive partners. This program will help to further identify and quantify state-of-the-art capabilities and deficiencies of fuel cell power generation systems (see Chapter 2). Assessment of Progress and Key Achievements Steady progress in fundamental research on polymers and catalysts has been demonstrated. However, it is difficult to assess this progress in terms of the program targets until such time as the technologies are demonstrated on-board a vehicle or in a laboratory situation where vehicle operation can be accurately simulated. The 2010 goal for power system density includes the fuel cell power plant as well as the complete hydrogen storage and delivery subsystems. For this reason and because of the apparent difficulty in meeting storage density targets, it seems unlikely that power system goals can be met, even with substantial progress on the fuel cell power plant. Although the cost estimates for high volumes (500,000 units/yr) show steady progress, the accuracy of these estimates is limited, because many of the final technologies and manufacturing processes are still evolving or are unproven. Even with such uncertainties, however, the estimates allow benchmarking and assessing progress. The accuracy of these cost estimates will improve as advanced technologies move out of the laboratory, complete systems are better defined, and performance is demonstrated. BES materials R&D has started to yield fundamental knowledge about the membrane and electrodes. Such work should continue in force. The delay in ini- tiating funding of selected aspects of the BES program (see, for example, Kung, 2007) may have a negative impact on the program in the longer term. Significant Barriers and Key Issues On the technical front, a number of barriers remain that were addressed in the Phase 1 review. Membrane and catalyst lifetimes, reliability, and durability remain problematic, as do barriers within other subsystems. Water management is still a challenging operating parameter as it impacts membrane conductivity, freeze protection, and electrode performance, and ultimately balance of plant complexity. Too little or too much water can cause drying out or flooding. Platinum loading needs further reduction, especially as platinum spot market costs remain high and unpredictable. In addition, new issues have started to emerge and will have to be addressed, including catalyst loss due to platinum dissolution into the membrane. Others include the possible impact on performance and system costs associated with intake air quality and coolants; at the same time, electrode composition is being reevaluated with respect to durability.
VEHICLE SUBSYSTEMS 61 The technical approaches should be reviewed in light of recent knowledge and advancements gained from earlier funded efforts and vehicle testing. Sensi- tivity studies should be conducted to determine the consequences of variability in operating parameters on performance, cost, and system design, as well as the programmatic issues of not meeting various targets. To meet the 2015 goals, the currently funded and newly awarded programs must come up with viable technical solutions in the next 3 to 5 years. Funding must remain intact, and delays in funding certain critical efforts must be mini- mized. Allocated budgets should be reassessed and reallocated as necessary, with the emphasis on the highest priorities. For example, the possibility of making up for the delays in funding new membrane research (Kung, 2007) at the expense of less critical programs should be considered. There can be value in funding stationary programs, which could help establish the supply chain vendor base and contribute to solving key technical issues. Nevertheless, stationary opportuni- ties and markets are still emerging, and stationary and vehicle technologies are often significantly different, so overlap may be minimal. Funding for stationary programs under the Partnership should be reassessed to ensure that it is used only for technologies that have a clear value to vehicular applications. With membrane and electrode technology still under development and stack designs still being enhanced, it is difficult for the supply base or systems develop- ers to build manufacturing operations and invest in fixed assets at this time. It is commendable that the DOE has identified component and stack manufacturingâin particular, the development of manufacturing models and processesâas areas that will need to be addressed later on. With the design uncertainties that exist, how- ever, any funding for manufacturing initiatives must be restricted to generalities at this time rather than applied to specific component designs and materials. The purity of the hydrogen fuel entering the stack remains a significant factor for both fuel cell performance and durability and is currently being addressed. The same should be done for impurities in the air entering the stack. Recommendations Recommendation.â The Partnership should conduct sensitivity analyses on key fuel cell targets to determine the trade-offs and tolerances in engineering specifica- tions allowable while still meeting fuel cell vehicle engineering requirements. Recommendation.â The Partnership should reassess the current allocation of funding within the fuel cell program and reallocate it as appropriate, in order to prioritize and emphasize R&D that addresses the most critical barriers. In par- ticular, the Partnership should give membranes, catalysts, electrodes, and modes of operation the highest priority. In particular, it should also
62 review of the freedomcar and fuel partnership â¢ Place greater emphasis on science and engineering at the cell level and, from a systems perspective, on integration and subcomponent interactions; â¢ Reduce research on carbon-based supported catalysts in favor of develop- ing carbon-free electrocatalysts; â¢ Ensure that BES funding of membranes, catalysts, and electrodes re- mains a high priority of the program; and â¢ Apply go/no-go decision making to stationary fuel cell system initiatives that are not directly related to transportation technologies. ONBOARD HYDROGEN STORAGE Background Storing enough hydrogen on board the vehicle to provide a 300-mile driving range while simultaneously meeting weight, volume, and cost targets continues to be very challenging. At this time, the only demonstrated complete, workable storage systems use highly compressed hydrogen gas or liquid, but they are unlikely to meet the 2010, much less the 2015, targets. The committee therefore believes that the research activities of the FreedomCAR and Fuel Partnership are appropriate in view of the need for new materials, reduced cost, and thermally integrated processes for efficiently storing and releasing clean hydrogen onboard the vehicle. Until a no-go decision was made in 2003, DOE focused on R&D for onboard fuel processors to produce hydrogen from stored-onboard liquid feedstocks, es- pecially methanol or gasoline. As an alternative, DOE recently initiated a broad- based R&D program on the storage of hydrogen, which can be utilized onboard the vehicle. Hydrogen storage had been explored in the past, but mostly for niche applications. This DOE-sponsored program is the first-ever effort with so many researchers pursuing alternative technologies simultaneously with cost and perfor- mance targets. As this effort began only recently, hydrogen storage technologies lag other technologies for hydrogen fuel cell vehicles. This delay could impact the overall schedule for the program. The targets and the time line for technology development included in the Hydrogen Storage Technologies Roadmap are aggressive, particularly when one considers that all targets must be met simultaneously. These include targets for volumetric and gravimetric storage, cost, thermal management (hydrogen flow rate requirements and energy efficiency targets), and a minimum number of fill/discharge cycles. The initial strategy is to explore a diverse portfolio of candidate materials that could potentially lead to acceptable complete storage systems. Thus, appropriate materials are necessary but not sufficient to resolve the storage issue. The hydrogen storage program is currently organized around three hydrogen
VEHICLE SUBSYSTEMS 63 storage centers of excellence (COEs) and a number of independent projects. The COEs and independent projects include work by 40 universities, 15 companies, and 10 federal laboratories. The budget for hydrogen storage activities was $26 million for FY06 and $34.6 million for FY07. The requested budget for FY08 is $43.9 million. Lack of earmarks in the FY07 Continuing Resolution has ben- efited the program. BES funding for hydrogen storage was approximately $11 million and $12 million for FY06 and FY07, respectively; the request for FY08 was about $17 million. Current Status of Hydrogen Storage with Respect to the Targets The OEMsânamely, the automotive companiesâare currently and presum- ably for the foreseeable future using compressed gas storage in their demonstra- tion vehicles, even though the volumetric storage densities (as well as costs) will not meet the 2010 or 2015 targets. Liquid hydrogen storage and 700-bar (10,000- psi) high-pressure storage have the highest volumetric and gravimetric storage densities demonstrated, respectively, but fall significantly short of the 2010 and 2015 targets for both performance and cost. In addition, liquid hydrogen is stored at â253Â°C (â423Â°F), which introduces many additional problems. The compressed gas tanks being utilized by the automobile OEMs are made from carbon fibers wound around either metal liner tanks (type 3) or high-density-polyethylene liner tanks (type 4), which are bonded with resin. The carbon fibers make up more than half of the system weight and costs. Further, the maximum allowable temperature (85Â°C) limits refill rates for storage at 700 bar (10,000 psi). Therefore, one DOE activity is an effort to reduce carbon fiber costs. From 2004 to 2006, the hydrogen storage COEs made significant progress in identifying materials with increased hydrogen storage capacity. Yet the materials identified to date are still far below the target levels for net (usable hydrogen, accounting for all energy losses during filling and release) storage of hydrogen onboard the vehicle. The DOE targets for onboard hydrogen storage are 6 and 9 weight percent for the entire system (Satyapal, 2007) for 2010 and 2015, respec- tively. This goal is often confused with the chemical weight percent of hydrogen in the material. Given that the balance of plant for the system will be at least 50 percent of the system, the material weight percent of hydrogen should be halved in order to judge it against the 2010 and 2015 system goals. Of the 24 sample materials presented at the Hydrogen Program Merit Review (Satyapal, 2007), 16 are equal to or more than 6 weight percent, while 8 materials fall below this value for the material alone. Accounting for the balance of plant for the system, only one material will meet the 2010 goal, but this material will not meet the 2015 goal. The target for 2015 was set to provide a driving range equivalent to 300 miles between fill-ups and make the hydrogen storage system approximately the same size and weight as a gasoline system. Even if materials are identified that meet the weight require-
64 review of the freedomcar and fuel partnership ment, they may be incompatible with other targets due to energy or temperature requirements and/or absorption/release rates that are too low. Furthermore, few if any have progressed to the point of complete system design and evaluation. Driving ranges of 300 miles can be achieved with weight fractions of less than 9 percent given innovative overall vehicle designs that decrease the hydrogen stor- age capacity requirements or increase the space available for fuel storage. Many of the initial round of projects (normally 3- to 5-year contracts) will be up for renewal or discontinuation within the next year. Projects focused on materials not having the potential for meeting targets need strong justification for renewal. Assessment of Progress and Key Achievements The three broad classes of materials for hydrogen storage being screened are sorbents, chemical hydrides, and metal hydrides. During the past 2 years several very promising approaches to hydrogen storage have been pursued, including (1) hydrogen storage in engineered metal organic frameworks with very high surface areas that adsorb significant amounts of hydrogen at cryogenic temperatures, (2) progress in lowering the temperature of hydrogen release from ammonia borane with the addition of lithium amide, (3) exploration of hydrogen spillover as a route to ambient temperature storage, and (4) the development of computational techniques/methodology for predicting the thermodynamics of complex, mul- ticomponent hydride systems. Additionally, organic liquid systems are being designed that minimize energy losses. DOE should be commended for sponsoring a demonstration of a hydrogen storage system with a prototype based on NaAlH4. A significant finding was that the balance of system weight was about 50 percent of the total system weight. This finding provides information on what may be required in a practical system for heat exchangers, vessels, manifolds, and other components. Significant Barriers and Issues That Need to Be Addressed It is not clear at this time that a suitable hydrogen storage material will be identified that can meet program goals and timing targets. Without a suitable hy- drogen storage material, widespread deployment of a hydrogen fuel cell vehicle for transportation would be a market risk. The hydrogen storage targets for 2010 and 2015, set at the start of the FreedomCAR and Fuel Partnership, were chosen based on attaining a 300-mile vehicle driving range and making assumptions about overall powerplant and vehicle characteristics. Storage of liquid hydrogen or hydrogen at high pressure can apparently meet the 300-mile range target but not other targets. Alternative storage materials identified to date have not been shown to meet any of the storage system capacity targets. The committee believes that the stringent storage targets should be kept for approximately 4 more years (until 2011). At that time, (1) the progress toward
VEHICLE SUBSYSTEMS 65 the 2010 system goals will be known (and they will probably not be met), and the realism of the 2015 goals can be reassessed; (2) perhaps all of the major goals (not just storage) should be reexamined to see how the vehicle optimizes; and (3) the Partnership will be able to make trade-offs between storage, structural materi- als, batteries, fuel cells, and other major subsystems of the vehicle. Delaying the assessment of targets to 2011 will also allow a second round of 3-year contracts to be completed. Thermal management is also important. For all the materials considered, energy is required to either absorb or release the hydrogen, with rates for these processes depending on temperature and pressure. Ideally, the waste heat from the fuel cell (currently around a temperature of 85Â°C) would be used in the fueling process, since otherwise additional fuel would be consumed, lowering overall ef- ficiency. Accordingly, systems must be thermally compatible as well as carefully integrated to allow both hydrogen rates and efficiency targets to be realized. A proposed new hydrogen storage COE on systems analysis was noted in the presentations to the committee. This COE should help with downselection (go/no- go). It should also model and evaluate conceptual systems to ensure that system targets are met and materials and thermal balance and dynamics are compatible with the fuel cell stack and subsystems. The hydrogen storage program organized in BES is also of critical importance given the need for the discovering new materials and for understanding material properties that might lead to the improvement of current promising candidate materials. New starts in the BES program were severely hampered by funding limitations under the 2007 Continuing Resolution. The Partnership should en- dorse a robust program in the basic sciences. The committee is disappointed that BESâs request for increased FY07 basic hydrogen research funding was not fully authorized under the joint congressional for FY07. Response to Recommendations on Hydrogen Storage from the Phase 1 Report Communicating the status of suitable hydrogen storage materials and systems to those who set policy is essential in view of the criticality of hydrogen storage to the long-term goals of the Partnership. In the Phase 1 report, Recommendation 3-9 recommended reporting the status of the technology annually to all program participants, DOE, and the Congress. The following were published during the last 2 years of the program: (1) reports to all the technical teams, (2) a report to the Fuel Operating Group (high-level company managers), (3) report to the Executive Strategy Group (automotive company vice presidents and DOE Undersecretary David Garman), and (4) reports to Congress on the state of the research program in hydrogen storage (in the form of testimony). There was also participation in the International Partnership for the Hydrogen Economy. The committee is satisfied with these reporting and other activities.
66 review of the freedomcar and fuel partnership In view of the size of the hydrogen storage program and the diversity of investigative approaches, participation in many technical conferences and in the yearly contractorsâ program review meeting are critical means for communicating progress and evaluating the work across the program as a whole. These report opportunities focus dialogue on the most promising approaches and foster the generation of new ideas and discoveries. Recommendation 3-7 recommended checking progress in terms of go/no- go decisions. Accordingly, DOE established a go/no-go process for determin- ing which materials are worthy of continued R&D. The process entails criteria development, data gathering, and review of results, followed by evaluation and final decisions by DOE. It ensures that time and resources are devoted to materi- als that exhibit the most promise, and it enables new materials to be cycled into the program for study and evaluation. This evaluation procedure is judged by the committee to be adequate. Certainly the screening out of unworthy candidate materials should be an ongoing process requiring little formality. A go/no-go decision was conducted on pure single-wall carbon nanotubes. The hydrogen storage capacity of pure carbon nanotubes was judged to be far short of the storage targets, so work was, appropriately, discontinued following a no-go evaluation. Cryocompressed storage was assessed, and a go/no-go deci- sion was planned for fall 2007. A go/no-go decision on the NaBH4 is planned for the same time frame; in addition, a downselection is expected on a reversible metal hydride. When the Phase 1 report was issued, the hydrogen storage component of the FreedomCAR and Fuel Partnership was just being established. The COE approach for project organization and project management had not been tested. Now, 2 years into the research, three COEs for hydrogen storage ($5 million to $6 million per year each) have been established. The current centers, which are planned for 5 years (to FY10) are as follows: the metal hydride center, the hydrogen sorption center, and the chemical hydrogen center. The Phase 1 review committee asked in Recommendation 3-8 that the existing COEs be evaluated before extending the approach to other areas. During the past year the program benefits and difficul- ties have been identified in a self-evaluation process that elicits responses from center members. Benefits identified include a critical mass of researchers with similar interests, collaborations and sharing of equipment, common methods for evaluation of new materials, with testing done at the Southwest Research Insti- tute, rapid communication, and best safety practices. Participants are aware of hydrogen storage targets and criteria. The oversight of the program provided by DOE sets a standard for communicating progress through contractor meetings. One downside was limited flexibility of research. Also, university partners found it somewhat difficult to adapt to milestone-driven work. Based on this analysis, the committee finds that the COE system is working well.
VEHICLE SUBSYSTEMS 67 Appropriate Federal Role Sponsorship of the hydrogen storage component of the FreedomCAR and Fuel Partnership is an appropriate role for the federal government. Work on hydrogen storage has been advanced significantly through the large increase in the number of qualified researchers, the sharp focus on common goals, enhanced communication among participants, and accountability for results. Recommendations The hydrogen storage program has reported significant progress during the past 2 years, yet results reported to date are still far short of the 2010 and 2015 system targets. Recommendation.â The hydrogen storage program should continue to be sup- ported by the Partnership at a high level since finding a suitable storage material is critical to fulfillment of the vision for the hydrogen economy. Both basic and applied research should be conducted. At the beginning of the hydrogen storage program a wide net was cast in search of suitable hydrogen storage materials. It is now becoming clear that many approaches and materials may not be worth pursuing, even at a basic level. Recommendation.â The Partnership should rebalance the R&D program for hy- drogen storage to shift resources to the more promising approaches as knowledge is gained. The new systems engineering center of excellence should look at all of the system requirements simultaneously, not just the system weight percent storage goal, and guide this rebalancing. Recommendation.â In the event that no onboard hydrogen systems are found that are projected to meet targets, the Partnership should perform appropriate studies to determine the risks and consequences of relying on pressurized hydrogen storage. They should include production and delivery issues as well as effects on vehicle performance, safety, and costs. Recommendation.â The Partnership should pursue research leading to lower costs for high-quality carbon fibers and bonding materials that would allow higher operating temperatures for compressed hydrogen gas storage. Recommendation. The Partnership should maintain a strong basic research activ- ity on hydrogen storage. New hydrogen storage concepts should continue to be supported by the Office of Basic Energy Sciences.
68 review of the freedomcar and fuel partnership ELECTROCHEMICAL ENERGY STORAGE Introduction Electrochemical energy storage technologies are critical to the develop- ment of HEVs, which would play at least a key transitional role in achieving the FreedomCar and Fuel Partnershipâs long-term goal of clean and sustainable energy for transportation systems and may become central to achieving these goals if development of fuel cells and fuel cell vehicles is not sufficiently successful to result in their large-scale commercial introduction. For a long time, the Freedom- CAR and Vehicle Technologies (FCVT) program has supported the development of advanced batteries and ultracapacitors for lightweight and heavy-duty vehicles, with particular focus on advancing the development and commercialization of HEVs, hybrid fuel cell vehicles (HFCVs), and battery electric vehicles (EVs). In response to the Presidentâs Advanced Energy Initiative, which he announced in his 2006 State of the Union address, the FCVT began the development of components for plug-in hybrid vehicles (PHEVs), including advanced batteries for this application. Currently HEVs are a small but growing part of the U.S. automotive market. In 2006 HEV sales accounted for about 1.5 percent of new vehicle sales, and hy- brid technology has continued to penetrate across a variety of vehicle platforms. In 2006, 10 different models of HEVs were available, and another 8 models are expected to be introduced by 2009. In addition, a hybrid version is being provided as an option in several existing models. All the HEVs available at present use a nickel metal hydride battery, and DOE has been involved in the advancement of this technology since the 1990s. However, the nickel metal hydride battery will not meet the long-term FreedomCAR and Fuel Partnership electrochemical energy storage goals for HEVs of 15-year life with 25 kW pulse power and $20/kW by 2010. Thus the FCVT is primarily focused on the development of Li ion batteries for HEV, HFCV, and EV applications. FCVT has expanded the electrochemical energy storage activity to include PHEVs, with a goal of developing vehicles that can travel about 40 miles on electric energy stored in the battery, which represents about 70 percent of the daily commuting mileage in the United States. PHEVs operate in both electrical and mechanical (as in HEVs) and electric only (as in EVs) modes, and the battery can be recharged from a standard electric outlet. The FCVT efforts are directed at developing PHEV components and systems that could be commercialized some- time between 2016 and 2020. At present, analytical and benchmarking activities are being conducted to determine the benefits and requirements for PHEVs. In February 2007 FCVT released an external draft of the PHEV R&D plan, which was modified and rereleased in June 2007. In April 2007 a request for proposal information (RFPI) was announced by the United States Advanced Battery Con- sortium (USABC) for the development of advanced high-performance batteries for PHEV application; the RFPI was expected to be awarded later in 2007.
VEHICLE SUBSYSTEMS 69 In addition, BES plans to increase its basic research on energy storage tech- nologies. BES held the workshop âBasic Research Needs for Electrical Energy Storageâ in March 2007, published an R&D plan in July 2007, and is planning to fund projects in 2008. It will focus on long-term needs, such as basic understand- ing of materials, interfacial charge transfer, and tools and processes to design new materials. Although the BES mandate on energy storage is broader and longer term, it recognizes the importance of working closely with FCVT on energy stor- age needs for automotive applications. FCVT, in collaboration with USABC, manages the technology for electro- chemical energy storage. The technology is being developed by battery manufac- turers, DOE national laboratories, and universities and through awards under the Small Business Innovation Research (SBIR) program. The effort comprises three subactivities: (1) battery technology development is involved in battery system module development, technology assessment, and benchmark testing; (2) applied battery research focuses on understanding failure and the life-limiting parameters of the Li ion system, which is currently closest to meeting the technical goals; and (3) long-term battery research addresses fundamental understanding of specific electrochemical systems for Li ion batteries. Over the last few years, just under 20 percent of the FCVT budget has been directed at electrochemical energy stor- age technologies. In FY06, of the $24.4 million total budget, $17.4 million were directed at battery development, $1.4 million at applied battery research, and $4.5 million at long-term research. The total funding for FY07 is $40.8 million, and the FY08 request is $41.8 million; this significant increase over previous years is for the development of PHEV batteries. Program Status and Assessment All the HEVs on the market use a nickel metal hydride battery; however, because this electrochemical system has an inherently low specific energy density and uses expensive materials, it will not meet the performance or cost targets of the Partnership. Thus FCVTâs focus on the development of a Li ion battery is cor- rect since it has the best potential to meet the long-term goals of the Partnership. The Li ion battery has a higher voltage (>3 V vs. 1.3 V for nickel metal hydride), which is an advantage in building higher-voltage (up to 400 V) automotive power systems, and a higher specific energy density (demonstrated 120 Wh/kg vs. 75 Wh/kg for nickel metal hydride), and the technology is capable of further growth. Tests of the entire battery system show that the Li ion battery will exceed the FreedomCAR and Fuel Partnership 2010 battery system weight and volume goals at the minimum pulse power rating of 25 kW. It is expected that with further improvements the Li ion battery will also meet the weight and volume goals at the maximum pulse power rating of 40 kW. Significant improvements have also been demonstrated over the last 2 years in other performance parameters of the Li ion battery. The battery meets the cycle
70 review of the freedomcar and fuel partnership life requirement of at least 300,000, and progress has been made in meeting the calendar life target of 15 years (more than 10 years has been demonstrated). Fur- thermore, the battery will operate over a wider temperature range, and its cold cranking power has been improved. FCVT and the larger battery community have recognized that safety issues are an important part of battery development, and safety-related issues are being worked on by all subgroups of the Li ion battery development program. This involves understanding the thermochemical and electrochemical stability of the individual materials and single cells and the abuse testing of battery modules. (Extensive testing of the battery component and systems are conducted not only within the window of operation of the battery, such as the voltage, current, tem- perature, and so forth, but also outside this window, and such testing is called âabuseâ testing.) Over the last few years the abuse tolerance of the battery has continued to improve. Many abuse-related issues can also be addressed by external electronic control; however, it is imperative that researchers continue to look for battery chemistries that are resistant to voltage or thermal abuse. The recent rash of fires in laptops using Li ion batteries may have left the public with the idea that these batteries cannot be made safe. This perception should be balanced against the reality that such failures are very rare and Li ion batteries are still in the early stage of development. In the past, generally during early development, todayâs safe lead acid and nickel metal hydride batteries were perceived to have safety issues. A safety concern has also been raised about the scale-up of Li ion batteries from the AA type cells used in cell phones and laptops to the larger cells used in automotive applications. Large Li ion batteries and other lithium-metal-based batteries have been safely deployed in military and space applications and, in Japan, in some trucks. The FCVT should continue to be forth- right and transparent about all safety-related concerns, tests, and results, not only by making technical improvements but also by correcting any misperceptions. Performance improvements and the abuse tolerance issues of Li ion batteries are being addressed at all levels of development. Similar systems (nickel/cobalt oxideâcarbon or manganese oxideâcarbon) are being investigated at the level of the entire battery system by the battery technology development subactivity; single-cell performance is being investigated by the national laboratories as a part of the applied battery research subactivity; and a basic understanding of compo- nents and materials is being sought at universities in the long-term research sub- activity. Similarly, more stable anodes, such as lithium iron phosphate (LiFePO 4), and alternative cathodes, such as nano lithium titanium oxide (LiTi12O5), which prevents the deposition of metallic lithium, are being investigated to improve the abuse tolerance of the Li ion battery system. Again, this investigation is being conducted at the materials level in the long-term battery research subactivity and as cells and batteries in the advanced battery research subactivity. There appears to be coordination of efforts in investigating similar and related materials and systems issues across all three subactivities of the Li ion battery development
VEHICLE SUBSYSTEMS 71 effort, and it is hoped that there is close communications between groups to ac- celerate progress. Although significant progress has been demonstrated in the performance of the Li ion battery, the cost of this battery remains a major barrier to its introduc- tion in HEV applications. Currently, the cost for the HEV battery in volumes of 100,000 units per year is estimated to be between $750 and $900, which is almost twice the FreedomCARâs 2010 target of $500. However, in comparison to the 2004 cost estimate of $1,200, there has been significant reduction in cost. Cost is a critical factor in the introduction of Li ion batteries in HEV applications since they will replace existing and presumably lower cost nickel metal hydride bat- teries. Going forward, it is generally expected that the cost of the mature nickel metal hydride battery will be tied to the commodity price of nickel, while the evolving Li ion battery technology, which can use a variety of lower cost materi- als, will eventually become much cheaper. In fact the main improvement in the cost of the Li ion battery over the last 2 years comes from replacing the expensive LiCoO2 by cheaper LiMn2O4 or LiFePO4 for the cathode in the battery. Another expensive material in Li ion batteries is the microporous separator, and FCVT has funded two programs to reduce the cost of the separator by half, to about $1/m 2. FCVT should be commended for recognizing that cost reduction will primar- ily be achieved by investigating alternative low cost materials and aggressively pursuing various combinations of materials for the Li ion battery. Furthermore, the performance and abuse tolerance of these potentially lower cost materials are being simultaneously studied by the various subactivities at all levels, from basic research on understanding the materials themselves to research at the level of cells to determine their life-limiting processes. The fact that Li ion batteries can be made from a variety of materials is at one and the same time both the strength of this technology and its difficultyâ namely, developing a viable commercial product. On the one hand, the variety of materials that can be used to make a battery suggest that there is significant room for increasing the batteryâs energy density, improving other performance characteristics, and reducing cost. On the other hand, the development of the battery is made more difficult by the wide choice of materials, since not only do the individual materials have to be characterized but each electrochemical couple has to be characterized for its performance, abuse tolerance, and cost at the cell and battery module levels. Replacing expensive cobalt (LiCoO2) with low-cost manganese (LiMn2O4) or iron (LiFePO4) could significantly reduce the cost of the battery, but it would still be much higher than the target cost of $500 per battery. These estimates have a wide window ($750 to $900) at a production rate of 100,000 units per year. Thus, larger production volumes may be required to reduce the price of the battery, and a detailed study of the effect of production rate on battery cost should be undertaken. In fact, the cost study should be carried out to at least 500,000 units per year to allow a meaningful comparison against fuel cell production costs. It may also
72 review of the freedomcar and fuel partnership be necessary to revisit the cost target established for the battery and substitute a more realistic target. It is possible that the initial assumptions, both market and technical, may have to be refined to reflect the present market conditions such as gasoline prices. In addition, the greater base of knowledge about materials and processing gained over the last few years should be factored in to obtain a more realistic cost target for these batteries. In any case, the impact of higher battery cost on the cost of an HEV should be determined. The cost of the battery will play a large role in the eventual success (or oth- erwise) of the PHEV, which operates in both the HEV mode, requiring high pulse power, and the electric mode, like an EV, where the increase in electric energy required is proportional to the electric mileage requirements. Thus, while an HEV requires a battery delivering only 1.5 to 2 kWh, a PHEV with a 10-mile electric range will require 5-7 kWh of energy from the battery and a PHEV with a 40- mile electric range will require 10-15 kWh (the energy and power requirements can depend on the charge depleting and sustaining modes chosen for the PHEV application). The FCVTâs cost goal for the high-power HEV battery is $250/ kWh; its goals for high-energy EV batteries are $150/kWh in the short term and $100/kWh in the long term. Since the PHEV battery needs both high power and high energy and the ratio of the power to energy changes with the desired electric range, a new normalized cost requirement needs to be established for PHEVs. Although the PHEV cost goal has not been finalized, the draft short-term goal is a 10-mile electric range at a battery cost of $300/kWh and the draft long-term goal (2016) is a 40-mile (or more) electric range at a battery cost of $200/kWh. The energy and power required from the battery for the PHEV application depend on the electric range and the relative charge-depleting and charge-sustaining modes. Some performance and cost goals that may be under consideration are listed in Table 3-1. The recognition of the potential benefit of PHEVs, a reduction in petroleum consumption, has led to growing support from the government and, in 2007, to $27.5 million in funding for the development of PHEV-related components and systems. However, progress has been extremely slow, and although the first dis- cussions on a PHEV program began in May 2006, FCVT and its partners were unable to finalize the PHEV R&D plan by fall 2007. The latest draft plan states that the PHEV program goal and the development targets are expected to be completed sometime in 2008. There is a serious lack of urgency in executing this important plan, and the reasons for the delay are not clear. Furthermore, DOE is delivering inconsistent messages. On the one hand, the PHEV program has been presented as one of the elements in the transition to hydrogen-driven vehicles that are to be ready for a commercialization decision in 2015. On the other hand, the June 2007 draft plan for PHEVs calls for commercialization between 2016 and 2020. These mixed messages can only cause confusion among the interested parties. It is very important that DOE present a single and consistent R&D plan for PHEVs immediately.
VEHICLE SUBSYSTEMS 73 TABLE 3-1â USABC Goals for Advanced Batteries for PHEVs High Energy/ Characteristics at High Power/Energy Power Ratio End of Life Unit Ratio Battery Battery Reference equivalent miles 10 40 electric range Peak pulse discharge kW 50/45 46/38 power at 2 sec/10 sec Peak Regen pulse power kW 30 25 (10 sec) Available energy for CD kWh 3.4 11.6 mode, 10 kW rate Available energy for CS kWh 0.5 0.3 mode Minimum round-trip % 90 90 energy efficiency (USABC HEV cycle) Cold cranking power at kW 7 7 â30Â°C, 2 sec-3 pulses CD life/discharge cycles/MWh 5,000/17 5,000/58 throughput CS HEV cycle life, cycle 300,000 300,000 50 Wh profile Calendar life, 35Â°C year 15 15 Maximum system weight kg 60 120 Maximum system volume liter 40 80 Maximum operating Vdc >.55 * Vmax >.55 * Vmax voltage Minimum operating Wh/day 50 50 voltage System recharge rate at kW 1.4 (120 V/15 A) 1.4 (120 V/15 A) 30Â°C Unassisted operating and Â°C â30 to +52 â30 to +52 charging temperature range Survival temperature Â°C â46 to +66 â46 to +66 range Maximum systems $ 1,700 3,400 production price, 100,000 units/yr NOTE: CD, charge depleting; CS, charge sustaining. SOURCE: USCAR Request for Proposal Information for Advanced High Performance for Plug-in Electric Vehicle Applications. Available on the Web at <http://www.uscar.org/guest/publications. php>.
74 review of the freedomcar and fuel partnership Recommendations Recommendation.â The Partnership should conduct a thorough analysis of the cost of the Li ion battery for each application; hybrid electric vehicles (HEVs), PHEVs, battery electric vehicles (EVs), and hydrogen-fueled fuel cell HEVs. The analysis should re-examine the initial assumptions, including those for both market forces and technical issues, and refine them based on recent materials and process costs. It should also determine the effect of increasing production rates for the different systems under development. Recommendation.â The Partnership should significantly intensify its efforts to develop high-energy batteries, particularly newer, higher specific energy electro- chemical systems within the long-term battery research subactivity and in close coordination with BES. High-energy batteries provide the surest way to successful batteries for PHEVs. Recommendation.â The Partnership should move forward aggressively with com- pleting and executing its R&D plan for plug-in hybrid electric vehicles. ELECTRIC PROPULSION, ELECTRICAL SYSTEMS, AND POWER ELECTRONICS Introduction The scope of the FreedomCAR and Fuel Partnership includes R&D aimed at commercial advancement of HEVs, fuel cell HEVs, EVs, and PHEVs. Electrical systems in all these types of vehicles consist of electric propulsion systems and power electronics systems, along with appropriate electronic controllers. Electric propulsion systems convert electrical energy from the fuel cell and/or electro- chemical energy storage device (e.g., a battery) into propulsive force interfaced to the wheels through appropriate drive trains and vice versa. Power electronic systems are used to convert the electrical energy among various forms (current, voltage, dc, ac, frequency) for energy flow between a fuel cell, and electrochemi- cal energy storage device, a rotating electric machine, an internal combustion engine, and the electric utility. Electric machines and power electronic systems thus form an enabling technology critical for achieving the Partnershipâs goal of clean and sustainable energy for transportation systems, cutting across the various approaches in both the near term and the long term. The relatively recent em- phasis on PHEVs has raised additional technological concerns about interactions between the electric grid and the vehicle. Concomitantly, the budget appropriation for these activities has been essentially steady in recent years (for FY07, $15.6 million; for FY06, $13.6 million). HEVs are gradually becoming established and noticeable in the marketplace, spurred by increasing gasoline prices. Although the share of new vehicles sold
VEHICLE SUBSYSTEMS 75 accounted for by HEVs is small, their absolute numbers are growing rapidly, and they are the segment with the fastest growth. The electric propulsion and power electronics technologies in these vehicles continue to improve, with new models introduced every year. The technologies of permanent magnet electric motors and power electronic converters are showing aggressive design and rapid progress in their performance. In recognition of the critical nature of these enabling technolo- gies, there has been an increase in activities focused on them. A majority of the technical activities are being conducted by DOE national laboratories, by universities, and by automotive equipment vendors. During 2006, a comprehensive solicitation aimed at developing advanced technologies was issued and research awards were announced in May 2007. The projects include a significant amount of cost share from industry focused in four areas: (1) high- temperature, three-phase inverters, (2) high-speed motors, (3) integrated traction drive systems, and (4) bidirectional dc-to-dc converters. The goal in all four areas is to reduce the cost, weight, and package size of electric drive and power con- version devices while increasing vehicle efficiency. These projects represent are spending about $33.7 million, including the 50 percent cost sharing by industry. Program Status The current generation of HEV devices uses a permanent magnet ac motor, along with insulated gate bipolar transistor (IGBT)-based inverters and dc-dc power converters to manage the power flow among various energy sources and loads, with an appropriate cooling system. Improvements in the cost, weight, and volume of these systems are projected to come from developments in (1) the high- temperature operation of materials, components, and subsystems; (2) high-speed electric machines; (3) novel power converters that minimize the use of capacitors and magnetic elements; and (4) the integration of subsystems and components. Higher Temperature Operation Current-generation power conversion devices utilize a secondary coolant loop that operates at a lower temperature than the primary engine coolant loop. Advances in the technology to operate the devices at higher temperatures would lead to improvements in cost, reliability and power density. A variety of projects aimed at this include phase change cooling, compressed air cooling, spray cool- ing, high-temperature capacitors, high-temperature insulation, high-temperature packaging, wide band-gap materials such as silicon carbide power devices, high- temperature gate drives, high-temperature magnets, and thermal interface materi- als. While these projects are broadly aligned with the goals of the program, it is unclear whether there is a clear, quantifiable impact on meeting the performance and cost goals of the program.
76 review of the freedomcar and fuel partnership High-Speed Electric Machines The current generation of permanent magnet electric machines for vehicle propulsion operate at about 15,000 rpm. For a given power level, the general scaling laws of rotating electric machines lead to a proportionate reduction in the weight of the active materials, copper and iron, as the operating speed is increased. However, the accompanying design trade-offs involved in increasing the speed are related to various electrical and mechanical parameters such as voltage, current, losses, shear stress, fault tolerance, manufacturability, etc. The series of projects in progress that are aimed at high-speed machines include the development of design and optimization models, control without sensors, magnet materials, prototyping, and testing. An Oak Ridge National Laboratory technical report prepared by Unique Mobility indicates that the cost, volume, and mass goals for the Partnership are realizable with projected design developments and manufacturing improvements. Novel Power Converters Current-generation power electronic systems in HEVs include three-phase inverter modules to interface between the dc bus and the electric machine and possibly dc-to-dc converters between the battery and the dc bus. The capacitors at the dc bus and the inductor of the dc-to-dc converter represent major volume and cost elements as do the silicon power devices. Various projects are being conducted that are aimed at reducing the size of the dc-to-dc converter through high-frequency switching, integrated converters that incorporate the battery in- terface and the machine interface into one converter, and the use of switched capacitor converters, among other things. While progress and success in these projects are expected to lead to incremental improvements in the size and cost goals for the converters, their impact on meeting the goals of the Partnership in terms of performance and cost is unclear. Integration of Subsystems and Components The current generation of electrical systems, including electrical propulsion subsystems, power electronic subsystems, and thermal management subsystems, is packaged as discrete and separate elements and assembled together to realize the overall functional objectives. From a systems point of view, integrating these subsystems into a single package and specifying it as a single component can drive their cost and size lower and their reliability higher as the designs continue to evolve. However, the disparate constituent technologies and manufacturing involved in each of these subsystems cause such integration to be a significant challenge. Selected projects are aimed at various degrees of integration: the con- verter with the motor, the converter package with the thermal management, and so forth. Together, these integration projects are perhaps the riskiest projects in the
VEHICLE SUBSYSTEMS 77 portfolio. Successful realization of their ambitious goals may lead to significant improvements in the electrical propulsion system performance across various measures. Summary Assessment The activities of this program have been multidisciplinary, and its portfolio is diverse: (1) materials development (thermal interfaces, high-temperature in- sulation, wide band-gap semiconductors, magnetic materials), (2) components development (high-temperature capacitors, silicon on insulator gate drives), (3) converter topologies (multilevel converters, switched capacitor converters), (4) manufacturing (high-temperature packaging), (5) machine control (sensorless operation, optimizing efficiency), and (6) design optimization and modeling (motor design and modeling tools, thermal modeling). Program review reports from 2005 and 2006 indicate a dispersed effort with diverse perspectives (Rogers, 2005; Wall and Rogers, 2006). By contrast, the recent solicitation and its selected projects with specific demonstration goals are aimed at realizing manufacturable engineering prototypes and designs by the selected technology vendors. Overall, these projects are aimed at incremental improvements relative to the state of the art in each of the constituent technologies. Recommendations Recommendation.â The Partnership should conduct a meta-analysis and develop quantitative models to identify fundamental geometric limitations that ultimately set bounds on and lead to the realization of the size, mass, and cost of power converters and electric propulsion systems in relation to the physical properties of materials and processes such as dielectric strength, magnetic saturation, thermal conductivity, etc. This will allow the various ongoing and future efforts to be benchmarked against the theoretical boundaries of what is possible and enable the establishment of appropriate directions in research goals. Recommendation.â In general, the Partnership should focus on the projects that address specific performance and cost goals of the program on the basis of the results of the meta-analysis recommended above. Specifically, it should (1) intensify packaging efforts; (2) commit additional resources to high-temperature electronics, including wide band-gap semiconductor devices such as SiC; and (3) redirect research on higher speed electrical machines to improve torque density. STRUCTURAL MATERIALS Substantial weight savings are a critical and key requirement of the Freedom- CAR and Fuel Partnership. The vehicle weight reduction target has been set at
78 review of the freedomcar and fuel partnership 50 percent, with the added criterion of cost parity (i.e., no increase in structural materials cost). This weight target is critical to vehicle design because the pow- erplant and fuel storage requirements are based on it. Any failure to meet the vehicle weight goal would necessitate a larger powerplant, increased fuel stor- age capacity, and larger components to achieve the overall vehicle functional goalsâfor example, driving range and acceleration. As noted in the Phase 1 report (NRC, 2005), the majority of the materials technical programs have been under way for some time, going back to the Partnership for a New Generation of Vehicles (PNGV) before the initiation of the FreedomCAR and Fuel Partnership (NRC, 2001). Thus detailed descriptions of the individual material studies would be superfluous here, and readers interested in specific details are referred to the earlier reports. In this report, the committee concentrates on reviewing the overall objectives and recommending some changes in the program targets and focus that appear to be more appropriate based on the progress to date. Assessment of the Program The lightweight materials programs have continued unabated, with only very small modifications to the activities described in the Phase 1 report. Thus the main structural weight savings are anticipated to be achieved through the widespread application of advanced high-strength steels, aluminum alloys (both sheet stock and castings), and cast magnesium. Lesser overall weight savings are also ex- pected from specialized use of glass-fiber-reinforced plastics (GFRPs), titanium alloys, metal matrix composites, and stainless steel. From a technical perspective, all these materials are more than adequately covered in the current programs, from both an application viewpoint and an innovative manufacturing viewpoint. In addition to the above activities, there is a significant effort on carbon-fi- ber-reinforced plastic (CFRP) composites. While these materials potentially offer greater weight savings than any of the other candidate materials, the formidable challenges involved in meeting both cost and manufacturing requirements appear to be insurmountable in the time frame of this program, if indeed ever! In par- ticular, the cost barrier is so great that the cost modeling results of the materials technical team apparently confirm the conclusion that CFRP composites will not be economically viable within the time frame of the Partnership. This is not to imply that some research activity in CFRP is not justified, but it does mean that the Partnership should not include such composites as part of its main program objectives and projections for vehicle design. By far the biggest question mark in the drive to achieve 50 percent weight reduction is the cost penalty for such a massive reduction. There is essentially zero possibility that such a reduction can be achieved at cost parity. However, failure to achieve the 50 percent goal would require redesigning the fuel cell to have a larger capacity; this would be accompanied by a significant increase in the size of the fuel storage system, not to mention an increase in the size and weight of
VEHICLE SUBSYSTEMS 79 other components such as brakes and suspension. Such enlargements of the fuel cell powerplant and hydrogen storage capability would involve extraordinarily expensive materials and major cost increases, allowing the cost penalty for the structural materials to likely pale by comparison. Thus in the committeeâs opin- ion, the 50 percent weight reduction is mandatory even with the associated cost penalty, because the alternative is likely to involve significantly greater cost! Overall, it seems clear that while the technical challenges to the successful application of lightweight materials are not trivial, a reduction in the associated large cost penalty is by far the bigger obstacle. Minimizing this cost penalty is primarily a matter of reducing the feedstock cost and is influenced to a much lesser extent by component manufacturing improvements, etc. This clearly gets into individual company proprietary matters (e.g., the cost of aluminum sheet stock), so cost modeling of structural materials in the context of the Partnership is unlikely to produce reliable information. However, it is the committeeâs opinion that some realistic cost estimating to achieve the 50 percent weight reduction is needed if the Partnership is going to obtain anything close to a realistic evaluation of the overall cost/functionality trade-offs. Recommendations The technical programs are making good progress, and the team members are extremely competent and interacting very well. The main recommendation of the committee in the Phase 1 report is still pertinentânamely, that the funds support- ing materials research should largely be diverted to higher priority areas such as fuel cells, hydrogen storage, high-energy batteries, and infrastructure transitions. The committee believes that the proportion of funding going to materials is still exceedingly high given the urgency of many of the other R&D areas (see Chapter 5). The committee also wants the materials effort to focus on what appears to be the most difficult issue for the materials program: recognition that while a 50 percent weight reduction not only must but also probably can be achieved, it will involve a significant cost penalty but, nonetheless, be the most cost-effective way of achieving the overall vehicle program objectives. Recommendation.â Based on the goal of 50 percent weight reduction as a critical goal and the near-certainty that some (probably significant) cost penalty will be associated with it, the Partnership should develop a materials cost model (even if only an approximation) that can be used in a total systems model to spread this penalty in an optimal way across other vehicle components. Recommendation.â The materials research funding should largely be redistrib- uted to areas of higher potential payoff, such as high-energy batteries, fuel cells, hydrogen storage, and infrastructure issues. However, materials research for proj- ects that show a high potential for enabling near-term, low-cost mass reduction should continue to be funded.
80 review of the freedomcar and fuel partnership REFERENCES Debe, M. 2007. Advanced Cathode Catalysts and Supports for PEM Fuel Cells. Annual Merit Re- view Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www. hydrogen.energy.gov/pdfs/review07/fcp_25_debe.pdf>. Department of Energy (DOE). 2004. FreedomCAR and Vehicle Technologies Multi-Year Program Plan. Washington, D.C.: U.S. Department of Energy, Office of Energy Efficiency and Renew- able Energy. Available on the Web at <http://www.eere.energy.gov/vehiclesandfuels/resources/ fcvt_mypp.shtml>. Jacobson, D. 2007. Neutron Imaging Study of the Water Transport in Operating Fuel Cells. 2007 An- nual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/pdfs/review07/fc_2_jacobson.pdf>. James, B.D., and J.A. Kalinoski. 2007. Mass Production Cost Estimation for Direct Hydrogen PEM Fuel Cell System for Automotive Applications. 2007 Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/ pdfs/review07/fc_28_james.pdf>. Kung, H. 2007. Update on DOE Basic Hydrogen Research. 2007 Annual Merit Review. Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy. gov/pdfs/review07/pl_0_kung.pdf>. Lasher, S. 2007. Direct Hydrogen PEMFC Manufacturing Cost Estimation for Automotive Applica- tions. 2007 Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available on the Web at <http://www.hydrogen.energy.gov/pdfs/review07/fc_27_lasher.pdf>. National Research Council (NRC). 2001. Review of the Research Program of the Partnership for a New Generation of Vehicles, Seventh Report. Washington, D.C.: National Academy Press. NRC. 2005. Review of the Research Program of the FreedomCAR and Fuel Partnership, First Report. Washington, D.C.: The National Academies Press. Rogers, S.A. 2005. Annual Program Report for the Advanced Power Electronics and Electric Ma- chines Program (November). Washington, D.C.: U.S. Department of Energy, Office of Freedom- CAR and Vehicle Technologies. Satyapal, S. 2007. Hydrogen Storage Session Review. 2007 Annual Merit Review Proceedings, May 15-18, 2007, Arlington, Virginia. Available online at <http://www.hydrogen.energy.gov/pdfs/re- view07/pl_3_satyapal.pdf>. Wall, E., and S.A. Rogers. 2006. Annual Program Report for the Advanced Power Electronics Tech- nology Area. Washington, D.C.: Department of Energy, Office of FreedomCAR and Vehicle Technologies.