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4
Heavy-Duty Hybrid Vehicles
INTRODUCTION
The objectives for introducing hybrid architectures into the powertrains of heavy-duty trucks and buses are much the same as those for introducing them into passenger vehicles and light-duty trucks. More specifically, the introduction of either electric or hydraulic propulsion equipment makes it possible to operate the diesel engine at or near its conditions for maximum efficiency and/or lowest emissions to spend more of its operating time while under conditions of reduced fuel consumption and emissions. In addition, the electric/hydraulic equipment is used for acceleration and the recovery of braking energy, making it possible to reduce the required engine rating and, in some cases, to turn the engine off during idling conditions. In addition to the opportunities for improved fuel economy, heavy-duty hybrid trucks also are capable of delivering significant reductions in emissions (Barker and Hitchcock, 2003).
The architectures developed for hybrid heavy-duty vehicles (HHV) have much in common with the configurations adopted for passenger vehicles and light-duty trucks. For hybrid-electric powertrains, both parallel and series hybrid configurations have been developed for different applications. In parallel hybrid systems, the electric or hydraulic motor is coupled to the same driveshaft as the engine so that the motor can add torque when needed to assist with acceleration. The motors can also act as generators or as hydraulic pumps in the case of hydraulic systems to provide regenerative braking force that recovers energy to help recharge the system batteries or as accumulators respectively. In series hybrid architectures, all of the mechanical power from the engine is converted to electricity or pressurized hydraulic fluid which is then delivered to one or more electric or hydraulic motors that drive the wheels.
During the past several years up to and including FY2007, funding has been dedicated to the development of hybrid truck components and systems as part of the 21CTP initiative. This investment has resulted in the completion of several prototype heavy-duty hybrid vehicles in a variety of classes for a range of applications. Tests to date with these vehicles have confirmed that these trucks are capable of delivering significant improvements in fuel economy falling predominantly in the range of 40 to 60 percent depending on the truck class and the specific technologies that have been applied (Table 4-1). The reports straddle the 21CTP target of 60 percent fuel economy improvement that will be discussed in more detail later in this chapter. However, larger increases in fuel economy exceeding 100 percent have already been demonstrated in some special applications such as the Class 6/7 hybrid utility trucks that are particularly good candidates for this technology1 (van Amburg, 2006).
Funding agencies for hybrid truck projects under the 21CTP umbrella have included DOE, DOD, and EPA.2 The DOE-funded projects have focused on trucks with hybrid-electric powertrains, while the EPA-funded effort has been devoted to hybrid-hydraulic configurations as shown in Table 4-1. The DOD-funded projects are distinguished from the DOE and EPA projects by the special requirements associated with military vehicles, often including significant amounts of auxiliary electric power.
In the face of changing priorities in the larger FCVT program, DOE has diverted nearly all of its hybrid-electric technology investments to light-duty vehicles since FY2006. As a result, the requested R&D budget for heavy-duty hybrid development in the DOE budget for 21CTP activities was reduced to zero in both FY2007 and FY2008.3 The only remaining research projects on heavy hybrid propulsion systems are two congressionally directed activities (DOE, 2006b). The committee was advised that this termination
1
Kevin Beaty, Eaton Corp., and V.K. Sharma, International Truck, “Hybrid Technology Program Review,” Presentation to the committee, Washington, D.C., February 8-9, 2007.
2
Ken Howden, DOE, FCVT, “21st Century Truck Partnership,” Presentation to the committee, March 28, 2007, Washington, D.C.
3
Ken Howden, DOE, FCVT, “21st Century Truck Partnership,” Presentation to the committee, March 28, 2007, Washington, D.C.
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TABLE 4-1 Reported HHV Fuel Economy Improvements
Developer and Vehicle
Fuel Economy Improvement (percent)
Eaton Electric Hybrid
UPS P100 Delivery Vana
36 (in field)
Adv. Technology HEVb
47 (on dynamometer)
HTUF Utility Truckc
67-150 (in field)
Oshkosh Electric Hybrid
AHHPS Refuse Truckd
36 (in field)
EPA Hydraulic Hybrid
Urban Delivery Vane
39-74 (in field)
aData from Kevin Beaty, Eaton Corp., and V.K. Sharma, International Truck, “Hybrid Technology Program Review,” Presentation to the committee, Washington, D.C., February 8, 2007, Slide 5.
bData from Beaty and Sharma presentation, Slide 20.
cData from Beaty and Sharma presentation, Slide 8.
dData from Nadr Naser, “Oshkosh Truck Corporation–AHHPS,” Presentation to the committee, Washington, D.C., February 8, 2007, Slide 16.
eData from Charles Gray, Jr., “EPA’s Transportation R&D,” Presentation to the committee, Washington, D.C., March 28, 2007, Slide 24.
of funding was necessitated by the sharp reduction in the total 21CTP initiative funding that was enforced beginning in FY2007, requiring deep cuts in even successful project areas. In contrast, funding has continued for hybrid truck projects supported by DOD and EPA, although this hybrid work apparently falls outside of the 21CTP initiative.4
The 21CTP Roadmap (DOE, 2006a) identifies the major challenges for hybrid truck commercialization to be:
System reliability
System cost
System integration into the vehicle.
Based upon these commercial issues, it identifies the top priority areas for HHV funding to achieve the 21CTP goals as:
Drive unit reliability
Drive unit cost
Energy storage system reliability
Energy storage system cost
Demonstrated ability to meet heavy-duty 2007 emission standards
Demonstrate 60 percent improvement in fuel economy, compared to current production heavy duty vehicles.
The 2012 goals stated in the 21CTP 2006 Roadmap for heavy-duty hybrid vehicles are as follows:
Develop a new generation of drive unit systems that have higher specific power, lower cost and durability matching the service life of the vehicle. Develop a drive unit that has 15 years of design life and costs no more than $50/kW by 2012.
Develop an energy storage system with 15 years of design life that prioritizes high power rather than high energy, and costs no more than $25/kW peak electric power rating by 2012.
Develop and demonstrate a heavy hybrid propulsion technology that achieves a 60 percent improvement in fuel economy, on a representative urban driving cycle, while meeting regulated emissions levels for 2007 and thereafter.
However, summary presentations by government staff have shown significant changes in program goals over time. Skalny presented information which showed that the original fuel economy improvement targets when 21CTP was established, following the earlier Review of the DOE Office of Heavy Vehicle Technologies (National Research Council, 2000) were between 100 and 200 percent improvements for heavy-duty hybrid vehicle demonstrations, depending upon the application.5 Rogers reported a goal of “up to a 100 percent improvement” in fuel economy without reference to a driving cycle.6 The current official 21CTP goal of demonstrating 60 percent improvement in fuel economy on a representative urban driving cycle neither defines the cycle nor does it identify the vehicle class or intended use. This gradual reduction in the fuel economy improvement target during the past seven years has the effect of aligning the goal more closely with what available electric or hydraulic hybrid technology can achieve in Class 5/6 urban delivery vehicles, as summarized in Table 4-1.
Some insight into the background of these changing program objectives was provided by the 21CTP management in response to a question posed by the committee. The committee was informed that “the change in goals is mainly attributable to a change in focus at the government level soon after the development of the 2000 roadmap, in which government agencies (DOE in particular) were encouraged by the Administration to focus more on component technologies and less on vehicle/system technologies.”7
The timetable for hybrid truck development is very brief (truncated beyond 2007) as a result of the decision to terminate further research in the heavy hybrid propulsion area.
4
Charles Gray, Jr., “EPA’s Transportation R&D,” Presentation to the committee, March 28, 2007, Washington, D.C.; Paul Skalny, “Briefing to the National Academies’ Committee to Review the 21CTP,” Presentation to the committee, March 28, 2007, Washington, D.C.
5
Paul Skalny, DOD (U.S. Department of Defense), U.S. Army Tank Automotive Research and Development Command, “Briefing to the National Academies’ Committee to Review the 21CTP,” Presentation to the committee, March 28, 2007, Washington, D.C.
6
Susan Rogers, DOE, FCVT, “Heavy Hybrid Propulsion Overview,” Presentation to the committee, February 21, 2007, Washington, D.C.
7
DOE, FCVT, Response to committee query on “Partnership History, Vision, Mission, and Organization” section of “Responses to NAS Queries on 21CTP Management and Process Issues,” transmitted via e-mail by Ken Howden, March 27, 2007.
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FIGURE 4-1 Network chart for heavy hybrid propulsion. SOURCE: DOE, 2006b, Figure 3.1-4.
The Heavy Hybrid Propulsion Network Chart (Figure 4-1) for the heavy-duty hybrid truck program provided in the FreedomCAR and Vehicle Technology (FCVT) Multi-Year Program Plan (MYPP) document (DOE, 2006b, Fig. 3.1-4) shows that heavy-duty hybrid R&D efforts supported by DOE are being brought to a close in early 2008.
GOAL 1:
DEVELOP A NEW GENERATION OF DRIVE UNIT SYSTEMS
This goal’s full title is “Develop a new generation of drive unit systems that have higher specific power, lower cost, and durability matching the service life of the vehicle. Develop a drive unit that has 15 years design life and costs no more than $50 kW by 2012.” Goal 1 and Goal 3 (60 percent improvement in fuel consumption) are identified by 21CTP as separate goals, but they are closely interrelated. That is, the achievement of a commercially-viable hybrid truck for any application depends on achieving significant improvements in both fuel economy and emissions at a cost that is low enough to justify the associated cost premium. In addition, the equipment must be sufficiently rugged and durable to perform reliably during the full design life of the truck in adverse environmental conditions.
Demonstrating the cost-effectiveness of a heavy-hybrid vehicle within a specific period (typically, the objective is a payback period less than two years) is a major factor in determining the commercial success of heavy-duty hybrid trucks. Key obstacles to achieving cost effectiveness include (1) high costs of the non-optimized, hybrid components used in the demonstration vehicles to date; (2) the large variety of potential low-volume applications (buses, garbage trucks, delivery trucks, etc.) that result in high initial development and investment costs; and (3) the lack of a recognized procedure/standard for demonstrating the fuel savings, which are highly dependent on the vehicle duty cycle.8
Meeting the aggressive cost target of $50/kW is proving to be one of the most difficult challenges for the developers of heavy hybrid propulsion systems. On the positive side, information presented to the committee indicates that 21CTP funding has helped manufacturers to reduce the produc-
8
Arthur McGrew, GM Allison Transmission, “AH2PS: Motor and Power Electronics Development,” Presentation to the committee, February 8-9, 2007, Washington, D.C.; Kevin Beaty, Eaton Corp., and V. K. Sharma, International Truck, “Hybrid Technology Program Review,” Presentation to the committee, February 8, 2007, Washington, D.C., Slide 20; Nadr Naser, “Oshkosh Truck Corporation—AHHPS,” Presentation to the committee, February 21, 2007, Washington, D.C.
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tion cost of the hybrid propulsion equipment. For example, a representative of Allison Transmission reported to the committee that the company’s DOE-supported project had yielded component improvements that could achieve a 40 percent decrease in electric machine costs and a 50 percent reduction of power electronics costs, yielding an aggregate cost reduction of 14 percent for the hybrid-electric drivetrain system. Furthermore, it is likely that increases in the annual production of hybridized versions of passenger vehicles and light-duty trucks will help to bring the cost of hybrid-electric drivetrain equipment down the learning curve in ways that will directly benefit heavy-duty truck hybrid powertrain equipment as well.
Despite this progress, the 21CTP management reported to the committee that, as of 2006, industrial partners working on electric-based hybrid propulsion systems “had achieved costs of between $600 and $1,000 per kilowatt with the energy storage system as the major cost item.”9 This same document reports that “… industry may be able to achieve a target of $300 per kilowatt by 2012” and that the threshold for achieving high-volume sales is expected to be “in the range of $100 to $200 per kilowatt.” If this threshold is correct, it suggests that the official 21CTP goal of reaching $50/kW may be more ambitious than necessary to achieve commercial success. Regardless of the ultimate cost objective, it is clear that significantly more progress is required in the area of cost reduction in order to achieve dollar-per-kilowatt values that would make hybrid powertrains attractive to buyers of heavy-duty trucks in the absence of direct subsidies or appropriately targeted tax credits.10
One notable exception to the cautious pronouncements about the cost of heavy-duty hybrid truck technology was the more optimistic outlook articulated by representatives of Eaton Corp. and International Truck and Engine indicating that series hydraulic hybrids can be sufficiently low in cost to achieve a payback period of two to three years.11 EPA has indicated that the cost premium for installing a hydraulic-hybrid drivetrain into a Class 6 urban delivery van on a mass production basis could be as low as $600 (Nikkel, 2006). However, this promising news is tempered by the fact that the limited energy storage capacity of hydraulic accumulators constrains the usefulness of hybrid-hydraulic technology in heavy-duty trucks primarily to those with significant start-stop duty cycle requirements, such as refuse trucks.12
Looking beyond the cost targets, DOE contractors have reported progress toward achieving substantial increases in the power density of the hybrid-electric drivetrain hardware. For example, Allison Transmission reported that their engineers had succeeded in improving the power of their Dual Power Inverter Module (DPIM) by 200 percent compared to the previous generation of power electronics. A 30 to 40 percent improvement in the motor power density was also reported in the same presentation.
Very little evidence was presented to the committee to substantiate any significant progress made by 21CTP-funded researchers toward achieving the desired reliability target of 15 years design life for the hybrid propulsion powertrain equipment. In fairness, the number of prototype heavy hybrid trucks currently in the field is very low, making it particularly difficult to gather any meaningful reliability data. However, there are promising reports indicating that hybrid powertrain equipment can be designed to operate reliably over long periods of time under adverse environmental conditions. For example, a 2006 NREL-funded study of the maintenance records of hybrid passenger buses used in regular revenue service in New York City indicated that the hybrid buses delivered approximately 5,000 Miles Between Road Call (MBRC), exceeding the New York City Transit minimum requirement of 4,000 MBRC (Barnitt and Chandler, 2006).
GOAL 2:
DEVELOP AN ENERGY STORAGE SYSTEM WITH 15 YEARS OF DESIGN LIFE THAT PRIORITIZES HIGH POWER RATHER THAN HIGH ENERGY, AND COSTS NO MORE THAN $25/KW PEAK ELECTRIC POWER RATING, BY 2012
Current State of Electrical Storage Technology for Transportation Use
The ideal electrical energy storage system for heavy-duty hybrid trucks would have the following characteristics:
High Volumetric Energy Density (energy per unit volume)
High Gravimetric Energy Density (energy per unit of weight, Specific Energy)
High Volumetric Power Density (power per unit of volume)
High Gravimetric Power Density (power per unit of weight, Specific Power)
Low purchase cost
Low operating cost
Low recycling cost
Long useful life
Long shelf life
Minimal maintenance
High level of safety in collisions and rollover accidents
High level of safety during charging
9
DOE/FCVT, response to question 1 in “Additional Hybrid System Questions” section of “Responses to NAS Queries on 21CTP,” transmitted via e-mail by Ken Howden, August 28, 2007.
10
DOE, FCVT, Response to committee query on “Partnership History, Vision, Mission, and Organization” section of “Responses to NAS Queries on 21CTP Management and Process Issues,” response to committee query, transmitted via e-mail by Ken Howden, March 27, 2007.
11
Kevin Beaty, Eaton Corp., and V.K. Sharma, International Truck, “Hybrid Technology Program Review,” Presentation to the committee, February 8, 2007, Washington, D.C.
12
Charles Gray, Jr., “EPA’s Transportation R&D,” Presentation to the committee, March 28, 2007, Washington, D.C.
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Ease of charging method
Minimal charging time
Storable and operable at normal and extreme ambient temperatures
High number of charge-discharge cycles, regardless of the depth of discharge
Minimal environmental concerns during manufacturing, useful life, and recycling or disposal
Unfortunately, every commercially viable battery technology being pursued must trade off compromises of these attributes. The optimal electrical energy storage system for a given application will highly depend on the weighted values of these attributes as they relate to the specific application.
Trading Off Attribute Priorities for an Application
Battery-only electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in HEVs (PHEVs) have somewhat distinct requirements. An EV developer might place the highest priority on an energy storage system that has the highest energy density or specific energy, to assure maximum range between charges for a given size of system. The instantaneous power available would likely be less important than mileage or range to the EV developer, but the relative priorities would be reversed for the HEV developer. However, systems with higher energy capacity also tend to have higher available power for acceleration but with more mass than is desired for HEV applications.
The EV developer might also interpret system safety and environmental concerns somewhat differently from an HEV developer. Because a battery-only vehicle usually has a much larger battery than an HEV, and because it carries more electrical energy and caustic chemicals on-board, it may carry higher battery-related safety risks than an HEV with a smaller battery. However, the HEV includes an internal combustion engine (ICE) that carries additional safety risks associated with its energy storage system (i.e., gasoline fuel tank) that drivers of conventional ICE-based vehicles have lived with for many years.
An HEV seeks to recover as much of the braking energy as possible to recharge the battery. If the battery system has insufficient ability to be rapidly charged, the friction brakes will be used and significant energy will be lost to heat. Because regenerative braking is a primary method to charge the battery in an HEV, the efficiency is critically important to an HEV’s performance characteristics. Because the electric motor is also used significantly to assist the internal combustion engine during acceleration, specific power and power density will become important considerations. PHEVs have battery energy storage characteristics that can have more in common with either typical EV or HEV requirements, dependent on whether the PHEV powertrain design is dominated by the electric motor or by the internal combustion engine.
Comparing Published Energy Storage Data
Metrics for energy storage components vary quite significantly in published data, making accurate comparison of energy storage technologies difficult. For example, capacity specifications, often expressed in ampere-hours (Ah), vary with the interval used to discharge the battery during testing. Testing with longer intervals typically exhibits much higher capacities than with shorter intervals for the same battery. The interval used for a capacity test is usually expressed by the time used during testing to discharge the battery, and is often expressed as a “C-rate.” 1C represents discharge of the rated energy capacity in one hour, 2C corresponds to discharge in 0.5 hours, and 0.5C (or C/2) corresponds to discharge in two hours. For example, if a battery is rated with an energy capacity of 5 Ah, the 1C rate would be 5 amps, the C/2 rate would be 2.5 amps, and 2C would be 10 amps.
In addition to the inconsistencies associated with the C-rate, the amp-hour rating does not usually allow easy analysis of the instantaneous power available for acceleration or the ability of the battery to store energy quickly to recover braking losses.
Power density specifications are suitable for comparison of the short-term power delivery capability for an energy storage system, as a function of its mass or volume. In contrast, energy density specifications are suitable for comparison of long-term available stored energy capacity of an energy storage system, as a function of its mass or volume. However, even these metrics (when provided) possess variability in how they are derived, particularly the percentage and rate of discharge over the measurement interval. This measurement renders the task of comparing energy storage device technologies difficult at best, based upon the information provided to the committee.
Appendix F of this report reviews the state-of-the-art in batteries for light-duty vehicles.
Battery Technology for Heavy-Duty Applications
Unique challenges exist for the application of energy storage components in heavy-duty hybrid trucks, including batteries, ultra-capacitors, hydraulic accumulators, or flywheels. Light-duty EVs and HEVs focus on energy capacity for long battery range, or rapid power charging and discharging capabilities for acceleration and braking energy recovery, or a combination of both. It is currently impractical for heavy-duty vehicles and trucks to carry sufficiently large battery packs or electric power sources (e.g., fuel cells) to provide the required power levels for an all-electric powertrain (without ICE). Therefore, vehicle manufacturers and researchers are focusing on hybrid powertrains based on diesel-electric architectures that require batteries with high power capability to assist in vehicle acceleration, rapid charging, and efficient recovery of braking energy.
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TABLE 4-2 Current Status of FreedomCAR Energy Storage Goals and NRC Evaluation
FreedomCAR Energy Storage Goal (units)
2010 Goal (end of life)
2005 NRC Review
Current Status
Discharge Power (kW)
25 (18 sec)
25
25
Available Energy (Wh)
300
300
300
Calendar Life, years
15
10
10-15
Cost Goal (at 100,000 units/year)
500
1,200
750-900
Regen Pulse, kW
20 (10 sec)
20
20
Cycle Life, cycles
300 k
300 k+
300 k+
Maximum System Weight, kg
40
32
25
Maximum System Volume, liter
32
33
20
Cold Cranking Power, kW at −30°C
5 for 2 sec
3-5
3-5
Operating Temperature Range, °C
−30 to +52
+10 to +40
−10 to +40
SOURCE: National Research Council, 2005.
The charge rate and level of charge acceptance needed to maximize the capture of braking energy in a heavy-duty vehicle is much greater than the comparable requirements for a light-duty vehicle, due to the difference in vehicle mass and inertia. A popular way to reach the higher power capacity required for heavy-duty truck applications is to over-size the battery. For light-duty hybrid vehicles there are storage systems available with sufficiently high charge rates that avoid the need to over-size the battery. Over-sizing the energy storage system to obtain the necessary power capacity is undesirable in several regards including the unnecessary expenses of additional mass, volume, and heightened environmental and safety concerns.
The additional mass in the heavy-duty vehicle makes them less practical as battery-only EVs due to the required battery size for reasonable performance, given the current state of the art, while battery-only power remains more viable for the light-duty vehicle.
21CTP Goals
During meetings with DOE and 21CTP management, the committee was informed that essentially all DOE-sponsored effort associated with batteries and other forms of energy storage is focused on light-duty vehicles under the Freedom-CAR and Fuel Partnership.13
Based upon materials submitted to the committee (Howell and Habib, March 2007), the FreedomCAR Program charter related to energy storage is to:
Research and develop electrochemical energy storage technologies which support the commercialization of (light-duty) hybrid and electric vehicles, with the following target applications:
HEVs (power-assist hybrid electric vehicles)
PHEVs (plug-in hybrid electric vehicles)
FCVs (fuel cell hybrid vehicles)
EVs (battery electric vehicles)
The stated 2010 FreedomCAR research goals associated with energy storage (Table 4-2) are intended to enable reliable HEVs that are durable and affordable, with an electric drivetrain energy storage system that exhibits:
15 year life
Capacity of 300 Wh
Discharge power of 25 kW for 18 seconds
Cost of $20/kW
100 Wh/kg by 2012
150 Wh/kg by 2015
The DOE PHEV battery goal is focused on cost reduction with a target of $200 to $300 per kWh by 2014.
TARDEC Program Goals and Activities
TARDEC Program Goals.14 The energy storage program goals established by the US Army Tank-Automotive Research, Development and Engineering Center (TARDEC) are to:
Reduce the current $115,000 per 30 kWh pack cost to $58,000
Accelerate the technology and automate the manufacturing process
Improve the temperature stability and safety
Develop enhanced materials
Produce affordable battery packs for HEV dash mobility, silent watch, and pulse power for weapons
13
Personal communication, Rogelio Sullivan, Ken Howden, and Ed Wall, DOE, FCVT, during committee meeting, August 28, 2007.
14
DOD, TARDEC (U.S. Army Tank-Automotive Research, Development, and Engineering Command), “Energy Storage Research Projects, TARDEC Ground Vehicle Power & Mobility,” received by the committee from Ken Howden, DOE, FCVT, August 31, 2007.
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>3 kW/kg by 3/2009
150 Whr/kg by 3/2009
TARDEC ManTech Objective (MTO) Program. Within the MTO program, TARDEC is pursuing opportunities to encourage battery technology suppliers, especially Li-ion cell and battery manufactureres, to produce safer, more reliable, lower-cost cells and batteries for heavy-duty HEB applications. Included in these goals is earlier demonstration of higher energy capacity compared to that currently being demonstrated under the FreedomCAR program.
TARDEC desires to achieve the goal of 150 Wh/kg by March 2009, whereas the FreedomCAR goal is to achieve 150 Wh/kg by 2015. TARDEC reports that it has demonstrated more than 100 Wh/kg in FY2008,15 whereas the FreedomCAR program has targeted the demonstration of 100 Wh/kg by 2012.
FreedomCAR Electrochemical Storage Program
The FreedomCAR program appears to be exploring a greater breadth of technologies than the Army TARDEC program. Because the focus is light-duty vehicles, all of the stated goals seem to be extremely cost-driven, because the energy storage system remains a significant percentage of the cost of an HEV, and an even higher percentage of PHEV and EV cost.
15 Year Life. Battery life is critically important to avoid the replacement of the energy storage system before the end of the useful life of the vehicle which would represent a very significant repair/replacement cost and increase the recycling challenges. The need to replace the energy storage system once in a vehicle’s life would more than double its effective cost. Therefore, the goal of achieving battery lifetimes that match or exceed that of the vehicle may be necessary for owner acceptance in large volume production.
Capacity Goals. The FreedomCAR energy capacity goals of 300 Wh and power capability goal of 25 kW for 18 seconds may be appropriate for the anticipated battery-only range of a light-duty HEV, but they may fall short of the needs for heavy-duty HEVs, unless two or more of the target battery packs are used for the application.
Costs. The targeted energy storage system for 2010 has a cost target of $20/kW pack so the battery pack would cost $500, making the cost reasonable for a light-duty HEV. The achievement of this goal opens the door for energy storage packs with peak power ratings higher than 25 kW. However, if the light-duty HEV industry adopts a 25 kW, 300 Wh storage pack as a standard, economy-of-scale would suggest the opportunity to further reduce cost by using multiple 25kW packs for heavier-duty vehicles. However, the shift in focus toward technologies that favor high power over high energy is not currently a high priority in the light-duty segment where cost reduction and reliability are the driving factors at this time. In principle, a shift toward higher power capability would not detract from the normal use of battery pack in full hybrid light-duty applications.
However, for PHEVs, the DOE target of $200-300 per kWh re-emphasizes the need for energy capacity optimization, as expected for PHEVs. The market expectation for battery-only range with a PHEV will be much higher than 2010 expectations for HEVs. Although these cost goals are founded on reasonable market expectations, they may prove to be difficult to achieve by the targeted dates.
Specific Energy. Specific Energy goals of 100 Wh/kg by 2012 and 150 Wh/kg by 2015 seem achievable, considering the rapid pace of development, the high levels of public and commercial business interest, and that TARDEC has already achieved the 2012 goal.
Shift to High Power from High Energy. During the period when California initially imposed its zero emission vehicle standards, battery-only EVs received significant development attention by the auto industry. In those cases, gravimetric energy density was a primary concern because acceptable vehicle range was one of the most important EV attributes being addressed, due to the battery limitations at the time. Advancements in Ni-metal-hydride battery technology in the late 1990s allowed light-duty EVs such at the electric-powered Toyota RAV4 to achieve reasonably acceptable range. Gravimetric power density is a focus of light-duty HEV electrical storage system. Heavy-duty HEVs require even higher power so the shift in priority for improved gravimetric power density for such applications is quite appropriate.
Higher power density will support further improvements in light-duty HEV fuel efficiency as less reliance on the internal combustion engine for transient power is achieved, enabling further engine downsizing. As power density increases, the maximum charging rate and charge acceptance tend to increase as well, facilitating greater ability to recover brake energy. Therefore, progress made toward higher power density, which is necessary for efficient heavy-duty HEV applications, will also benefit light-duty HEVs. Li-ion technology appears to be the leading candidate for significant progress in energy storage system power density, but significant cost, durability and safety issues exist.
Durability and Safety Issues for Li-ion Battery Systems. Safety remains a significant issue for Li-ion battery systems. Overcharging, fast charging, fast discharging, crushing, projectile penetration, external heating, or external short-circuiting, can cause the battery pack to heat up. If heat gen-
15
DOD, TARDEC (U.S. Army Tank-Automotive Research, Development, and Engineering Command), “Energy Storage Research Projects, TARDEC Ground Vehicle Power & Mobility,” received by the committee from Ken Howden, DOE, FCVT, August 31, 2007.
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eration exceeds heat dissipation capability, thermal runaway can occur. Elevated temperatures can cause leaks, gas venting, smoke, flames, or even “rapid disassembly” to occur.
Intelligent monitoring and control of the charging and discharging processes is being developed to manage many of the concerns associated with thermal runaway. However, vehicle collisions and projectiles that can cause the battery case to be breached are inspiring the need for new construction materials that are less prone to mechanical and thermal issues.
Other battery technologies, such as LiFePO4 and Lititanates, are also being pursued because they offer some advantages over Li-ion approaches, but have other features which render them less attractive than Li-ion. Some new technologies are becoming available that offer promise for greater safety with fewer environmental concerns.
Future Development Trends. There are several promising new technologies which are currently under development and will be evaluated to determine the extent to which they can provide improvements over conventional Li-ion approaches. The features that allow these technologies to be directed toward higher power density for use in heavy-duty hybrids should be explored.
Lithium Nano Titanate. Altair Nanotechnologies, Inc., is marketing a battery called NanoSafe® that offers extremely fast charging without thermal runaway, along with other safety improvements. NanoSafe® is a lithium nano titanate battery system. Altair Nanotechnologies recently demonstrated a 10-minute charge cycle for an 18-kWh pack, using a 125-kW-rated, high-voltage charging station from AeroVironment, Inc.
50°C lithium titanate batteries under development by the company Enerdel are identified in the FreedomCAR summary.
Ultracapacitors. Ultracapacitors represent an alternative way to achieve the desired power density levels in combination with other batteries. Ultracapacitors are inherently high in instantaneous power availability, compared to batteries. Currently, ultracapacitors are very expensive, but the technology is advancing quickly and production costs are continuing to decrease.
Ultracapacitors offer more than 10× the power density of today’s batteries, but far less energy density, making them unsuitable as battery replacements. However, hybrid energy storage packs containing both batteries and ultracapacitors are under development. Practical production vehicle systems must trade off the associated costs of system with both high energy density and high power density. However due to the high factor of fuel in the operational cost of heavy-duty vehicles, the use of ultracapacitors may prove to be cost effective. Ultracapacitors have extremely long useful life and are inherently safer than most practical batteries.
Enhanced Lead-acid Batteries. Enhanced Lead-acid batteries are also under development. The company Firefly® Energy, Inc., is introducing a new carbon-graphite foam-based construction that significantly reduces the volume, mass, and cost of a lead acid battery, while reportedly improving its cycle life, durability, recycle ability, and temperature range. TACOM is currently evaluating this advanced lead-acid solution for potential heavy-duty hybrid applications.
Assessment of 21CTP Energy Storage Research Programs
FreedomCAR Light-Duty Energy Storage Effort. Review of the material provided by DOE on the ongoing FreedomCAR research and development effort for light-duty vehicles suggests that the program is addressing the needs, goals, and sizing for light-duty HEVs. However, it is clear that the capabilities needed for heavy-duty use may differ significantly from light-duty applications. Therefore, a clearer assessment by DOE as to how the technology may be transitioned from light- to heavy-duty is needed.
TARDEC Energy Storage Research Projects. TARDEC’s Energy Storage Research Projects appear to be focused on incremental improvements in lead-acid, Ni-metal-hydride, Li-ion, and Ni-Zn batteries that can be introduced into planned military-specific hybrid electric applications. Power density and energy density trade-offs appear to be appropriately considered. The near-term focus is to address durability and safety issues related to Li-ion batteries, due to the specific requirements of military applications. The urgency of this matter as well as the need for Li-ion-type energy and power density characteristics for next-generation military combat and tactical vehicles underscores the need for significant financial support in the future.
Allison and Eaton Heavy-Duty Hybrid Programs under 21CTP. The Allison Two Mode Hybrid Bus Program and the International/Eaton Advanced Technology HEV were identified as examples of successful developments conducted under the 21CTP programs. The Allison Two-Mode system incorporates a lead-acid battery system and the International/Eaton system uses a 70 kW NiMH battery. Based upon materials provided to the committee, it appears that the successful development effort was targeted more toward advanced motor, drive and power electronics systems, although early Eaton plans call for Li-ion batteries. However, future cooperative programs have identified the desire for Li-ion battery systems.
Energy Storage Funding
The annual energy storage funding under the DOE Freedom-CAR budget has been fairly stable (~$17 million) in FY2005, FY2006, the FY2007 request and the FY2008 request, related to High Power Energy Storage. However, significant increases
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in Advanced Battery Development have been requested for FY2007 ($7.6 million, up from $1.4 million in FY2006) and FY2008 ($18.2 million, up from $1.4 million in FY2006). These increases are targeted toward higher energy storage capacity systems that would be necessary for PHEVs.
No information was provided to the committee concerning the funding allocations that have been directly attributable to the energy storage system development under the TACOM budget line items.
Appropriateness of the 21CTP Research Areas of Focus
The committee agrees that the following issues need to be addressed to advance the state of the art in energy storage systems for heavy-duty vehicle applications:
Cost, both procurement and life cycle
Weight and space claim
Life expectancy in a specific heavy-duty drive cycle
Energy and power capacity for a heavy-duty hybrid application
Suitability for the heavy-duty vehicle environment and cooling techniques
Architecture/modularity
Safety/failure modes
Maintainability
Supplier base for the energy storage components.
Continued focus on solving the cost, durability, safety, battery management system, and reliability issues associated with Li-ion batteries appears to be appropriate. However, due to the unique requirements for very high power capacity for certain heavy-duty applications, additional focus on ultracapacitors or other very high power capable technologies seems appropriate.
Although the stated intent for transfer of technology from light-duty to heavy-duty appears logical, the unique requirements for heavy-duty application may require significantly different trade-offs. This appears to be the focus of the TACOM programs, but the cost issues for military acceptance may be significantly different than commercial heavy-duty service.
Progress Toward Achieving the Stated Goals. TARDEC appears to have established more aggressive technical goals than those stated in the 21CTP 2006 Roadmap. For instance, TARDEC reports that it has already achieved and exceeded the 2012 FreedomCAR goal of 100 Wh/kg. However, the cost and durability targets have not yet been confirmed.
The Roadmap stated goal is to develop an energy storage system with 15 years of design life that prioritizes high power rather than high energy, and costs no more than $25/kW peak electric power rating by 2012. It is difficult to extrapolate the progress made in the light-duty sector with respect to the achievement of goals in a heavy-duty environment. In general, it appears that as a minimum, lithium-ion technology is necessary to achieve the stated heavy-duty roadmap goals. However, until sufficient effort is conducted to truly evaluate the light-duty progress in a commercial heavy-duty environment, the committee cannot gauge the real progress.
Findings and Recommendations
Finding 4-1. Challenges with lithium-ion anode/cathode materials and chemical stability under high power conditions will likely preclude achieving the 15-year durability targets by 2012.
Recommendation 4-1. Much closer interaction between military and commercial suppliers is recommended to identify the highest-priority areas for further research in an attempt to expedite the development of commercially viable battery or battery/ultracapacitor systems that can accomplish the unique high-power needs of heavy-duty vehicles.
Finding 4-2. There are significant differences associated with the use of battery energy storage systems in heavy-duty vs. light-duty applications.
Recommendation 4-2. Due to these differences and the much lower production volumes for heavy-duty applications, it is appropriate to continue funding and conduct sufficient research and development to demonstrate prototypical success in heavy duty applications, or identify areas for continued research.
Finding 4-3. The information exchange between DOD, DOT, DOE appears to be rather casual due to completely separate funding mechanisms, priorities, and testing methods.
Recommendation 4-3. Jointly funded programs that prioritize research, build on the success of each agency’s programs, and thereby necessitate technology transfer between the partners would significantly improve the technology transfer and reduce the chance for “reinventing the wheel” or duplicating others’ mistakes.
Finding 4-4. The metrics used for comparing battery technologies differ from manufacturer-to-manufacturer, agency-to-agency, and even for different evaluations within a given agency. Terminologies also vary in definition. Many existing standards for measuring battery parameters are technology specific, making accurate comparison of different technologies difficult or impossible.
Recommendation 4-4. Metrics should be standardized or modified to enable more accurate comparisons across different battery technologies for transportation use. Universal terminologies should be defined, published, and recommended for adoption by the various battery manufacturers.
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Finding 4-5. Very little data are published about batteries when used in conjunction with ultracapacitors for heavy-duty HEV applications in this program. Recent developments show great promise with this technology, especially for heavy-duty applications requiring high power output for acceleration and fast charging for braking energy recovery.
Recommendation 4-5. Expanded research effort and associated funding focus should be focused on ultracapacitors or supercapacitors as “hybrid” storage systems, in combination with batteries.
GOAL 3:
DEVELOP AND DEMONSTRATE A HEAVY HYBRID PROPULSION TECHNOLOGY THAT ACHIEVES A 60 PERCENT IMPROVEMENT IN FUEL ECONOMY, ON A REPRESENTATIVE URBAN DRIVING CYCLE, WHILE MEETING REGULATED EMISSIONS LEVELS FOR 2007 AND THEREAFTER
The hybrid truck development projects funded by DOE as part of the 21CTP initiative have demonstrated significant progress toward achieving the 60 percent fuel economy improvement target for some specific truck classes and applications. In order to evaluate this progress, it is important to recognize that heavy-duty trucks experience a much wider range of driving cycles than passenger vehicles or light-duty trucks. For example, a Class 6 urban delivery van experiences typical driving cycles that are much different from those of Class 8 long-haul commercial trucks. Because large numbers of accelerations and braking decelerations associated with truck applications such as delivery vans or refuse trucks are well-suited to demonstrating the advantages of hybridization, most of the 21CTP-funded development of hybrid trucks has been focused on these applications.16 In fact, even Goal 3 itself has been formulated in terms of an “urban driving cycle” to highlight these applications.
An example of a heavy-duty hybrid truck that has demonstrated greater than 60 percent improvement in fuel economy is a Class 6/7 utility truck developed using Eaton parallel hybrid-electric drivetrain technology. In tests conducted by the Hybrid Truck Users Forum (HTUF), the prototype hybrid utility truck demonstrated higher-than-expected fuel economy improvement of between 62 and 150 percent on four different mission duty cycles. As a second example, a series hydraulic hybrid system installed in a Class 6 UPS delivery Nader Nasr, Oshkosh Truck Corporation, “Advanced Products–AHHPS,” Presentation to the committee, February 8, 2007, Washington, D.C. van by Eaton and International Truck and Engine achieved an improvement in fuel economy between 60 and 70 percent during lab testing using an EPA city driving cycle.
One of the most aggressively developed applications for heavy-duty hybrid truck technology has been urban transit buses. Tests conducted by the U.S. National Renewable Energy Laboratory (NREL) on the hybrid-electric buses developed by Orion Bus and BAE Systems demonstrated that the buses achieved an average fuel economy improvement of 45 percent compared to conventional diesel engines when driving over the city’s most severe duty cycles (Green Car Congress, 2006).
It is also worth noting that Eaton has reported progress in the development of parallel hybrid-electric powertrains for Class 8 heavy-duty commercial highway trucks that have demonstrated fuel economy improvements of 5 to 7 percent over long-haul routes during independent tests (Eaton Corp., 2006). Although this percentage improvement is not as high as for the other heavy-duty trucks and buses cited above, it is still noteworthy because of the much higher annual fuel consumption associated with Class 8 long-haul trucks compared to any other type of heavy-duty truck (Eaton Corp., 2006). Eaton claims that the fuel savings provided by their hybrid drivetrain can deliver a cost savings of approximately $9,500 per long-haul truck per year. Overall, the progress achieved by truck manufacturers and suppliers toward meeting the 60 percent fuel economy improvement objective in Goal 3 is substantial.
Past DOE-supported heavy-duty hybrid truck development efforts appear to have been almost completely biased toward achieving improved fuel economy with comparatively little attention being given to opportunities for major reductions in emissions. Despite references to emissions reductions in the basic mission of the truck partnership, the briefings that the committee received summarizing the accomplishments of recent hybrid truck development projects made almost no mention of targets or achievements in the area of emissions reductions.
In response to a question about this apparent omission, the committee was informed that “the emissions of heavy-duty vehicles are not measured on a chassis dynamometer and regulated on a grams/mile basis like passenger cars and light trucks.”17 This is unfortunate, because features such as electric creep (movement under electric power alone) are expected to make it possible to turn off engines for extended periods during congested traffic or loading queue conditions, creating opportunities for substantial emission reduction during these conditions. The limitations imposed by existing procedures for certifying truck engines make it difficult to fairly evaluate the full benefits of heavy-duty hybrid trucks,
16
Susan Rogers, U.S. Department of Energy, “Heavy Hybrid Propulsion Overview,” Presentation to the committee, February 8, 2007, Washington, D.C.; Arthur McGrew, Allison Transmission, General Motors Corporation, “AH2PS: Motor & Power Electronics Development,” Presentation to the committee, February 8, 2007, Washington, D.C.; Kevin Beaty, Eaton Corp., and V.K. Sharma, International Truck, “Hybrid Technology Program Review,” Presentation to the committee, February 8, 2007, Washington, D.C.;
17
DOE, FCVT, 21CTP, response to committee query (Question 15 in “Hybrid Electric Vehicle Systems” section), transmitted via e-mail by Ken Howden, March 27, 2007.
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providing the basis for a separate recommendation (4-8) presented later in this section.
In summary, there is an acknowledged risk that heavy-duty truck hybrid propulsion technology will not be successfully commercialized on a broad scale without continuing coordinated governmental support at both the federal and state levels. As stated by the 21CTP management team: “Currently, the development of hybrid technology for various vehicle platforms represents a high technical risk and is cost-prohibitive. Government-industry sharing of these risks and costs may accelerate introduction of these vehicles. This evaluation is consistent with the stated 21CTP “Strategic Approach” that calls for efforts to “promote research focused on advanced heavy-duty hybrid propulsion systems” as well as to “promote the validation, demonstration, and deployment of advanced truck and bus technologies” (DOE, 2006a).
Finding 4-6. R&D on heavy-duty hybrid trucks and buses has demonstrated significant progress, achieving 35 to 47 percent fuel economy improvements in hybrid-electric delivery vans and urban buses, with specialized applications and the hydraulic hybrid delivery van in the 50 to 70 percent range (60 percent is the present 21CTP target). Commercial success has already been achieved with hybrid electric urban buses, albeit with major governmental subsidies. Despite the promising progress, significant hurdles still remain to achieving the fuel economy improvement targets for a broader range of heavy-duty hybrid vehicle (HHV) applications, reducing the cost, and improving HHV reliability sufficiently to achieve broader commercial success. In addition, there are opportunities for achieving significant system-level improvements that would make HHVs more attractive to OEMs and users, such as the merging of hybrid propulsion and idle reduction features, including start-stop operation and creeping under all-electric power.
Recommendation 4-6. Development and demonstration of heavy-duty hybrid truck technology should be continued as part of the 21CTP program in order to reduce barriers to commercialization. These development projects should include efforts to capitalize on opportunities for system-level improvements made possible by HHV technology in order to extract the maximum possible value from any new hybridized propulsion equipment that is installed in future trucks and buses.
SYSTEMS DEVELOPMENT AND PROJECT COORDINATION
The decision by the government to focus 21CTP development efforts on component technologies has resulted in a reduction of emphasis on coordinated systems development. For example, there is little indication that any significant portion of the substantial 21CTP investment in advanced combustion engine development has been directed to optimizing the engine design for integration into a hybrid powertrain.18 This is noteworthy in view of the major impact that engine performance characteristics have on the achievable fuel economy and emissions of heavy hybrid trucks and buses.
Progress toward the successful development of hybrid truck technology would benefit from improved coordination among the governmental agencies that are funding this work—DOE, DOD, and EPA—as well as among the national labs, universities, and subcontractors who are carrying out this R&D. Although it has been pointed out to the committee that some communication and technical interactions already occur as part of 21CTP activities and technical conferences,19 the overall development program would benefit from closer technical coordination among the various projects. In light of the limited resources that are available to support R&D projects in this area, the importance of gaining the highest value from these investments by sharing information wherever possible and avoiding unnecessary duplication takes on added urgency.
Looking elsewhere among the 21CTP programs for best practices in developing system approaches, the idle reduction program reviewed in Chapter 6 deserves special attention. In particular, the nighttime idle reduction initiative has been particularly successful in demonstrating how several agencies and stakeholders can coordinate their activities to aggressively move new technology developments out of the laboratory and into marketplace.20 This has been accomplished using an effective combination of technology development, field validation, certification testing, and tax credit incentives. In addition, this initiative has included customer education and incentive programs that have involved governmental agencies at both the state and federal levels working together with equipment manufacturers.21
The considerable progress achieved in the idle reduction area deserves to be studied to determine whether its success can be replicated in other areas such as hybrid trucks using some of the same techniques. This approach makes particular sense for the hybrid truck area because hybrid drive and idle reduction technologies directly overlap in some key areas such as creep idle.
There is also a need for this coordination to extend beyond the agencies to Congress itself. For example, the tax credits
18
Gurpreet Singh, DOE, FCVT, “Overview of DOE/FCVT Heavy-Duty Engine R&D,” Presentation to the committee, Washington, D.C., February 8, 2007.
19
Ken Howden, DOE, FCVT, “Partnership History, Vision, Mission, and Organization,” Presentation to the committee, February 8, 2007, Washington, D.C.
20
Mitchell Greenberg, EPA (U.S. Environmental Protection Agency), “EPA SmartWay Transport Program: Overcoming Technology Deployment Challenges,” Presentation to the committee, March 28, 2007, Washington, D.C.
21
Glenn Keller, Linda Gaines, and Terry Levinson, DOE, Argonne National Laboratory, Center for Transportation Research, “Idle Reduction Technologies,” Presentation to the committee, February 8, 2007, Washington, D.C.
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specified for hybrid trucks in the Energy Policy Act of 2005 (Public Law 109-58, August 8, 2005) are due to expire on December 31, 2009. There is a high likelihood that the timing of this expiration and uncertainty about its renewal will complicate the market acceptance of hybrid trucks introduced by manufacturers during the coming years unless early action is taken to clarify renewal plans. A very similar problem has afflicted the wind power industry because of the series of expirations and renewals of tax incentives in that industry, creating a “feast-or-famine” market environment (Pellerin, 2005). Closer coordination between the agencies and Congressional offices would help to prevent this problem from harming the hybrid truck market in a similar fashion.
Industry also has an important role to play in order to ensure that an appropriate systems perspective is maintained in the 21CTP programs. In 2006, DOE established a subgroup activity named the Validation Working Group made up of 21CTP member volunteers. The purpose of this subgroup is to focus attention on vehicle system technologies that are evaluated as having the greatest potential for positive impact on fuel economy and emissions combined with high cost effectiveness. The Validation Working Group is intended to actively seek out opportunities to conduct in-service demonstrations of these promising technologies in order to encourage their commercial adoption. The Hybrid Truck Users Forum (HTUF) established with the support of the U.S. Army National Automotive Center (NAC) and the Hewlett Foundation is playing a similar role.22
Finding 4-7. Progress in the development of HHV technology under the 21CTP program has been hindered by the decision to focus on component-level technology rather than systems. Successful development and commercialization of HHV technology requires coordinated, customized development of the combustion engine, electrical/hydraulic drive equipment, mechanical powertrain, and controls as components of an integrated system, in order to realize its full potential. In addition, the coordination of HHV project activities among the 21CTP’s federal partners (DOD, EPA, and DOE) has not matched the level achieved in other 21CTP programs such as nighttime idle reduction, making it more difficult to achieve ambitious HHV technology targets.
Recommendation 4-7. Coordination of all 21CTP heavy-duty hybrid truck development and demonstration activities should be strengthened across components, programs, and agencies to maximize the system benefits of this technology and to accelerate its successful deployment in commercial trucks and buses. In addition to improved cross-agency coordination, HHV stakeholder-based organizations including the Validation Working Group and the Hybrid Truck Users Forum should be engaged more aggressively to assist in identifying and overcoming key hurdles to the successful commercialization of HHV technology.
HHV CERTIFICATION TEST PROCEDURES
Lack of fuel economy and emission certification test procedures for heavy-duty hybrid trucks has been a deterrent to their commercialization. Although the U.S Energy Policy Act of 2005 provided direct tax credits for hybrid trucks that deliver improved fuel economy, there was no practical way for truck purchasers to derive these direct tax credits until mid-2007.23
EPA is aware of the lack of fuel economy and emissions test and certification procedures for heavy-duty hybrid trucks. Currently, EPA is developing a procedure to directly measure fuel economy and emissions of complete heavy-duty vehicles, including hybrids; when finalized, this procedure is expected to provide a measurement method and certification procedure for obtaining tax credits for heavy-duty hybrid trucks.24 Unfortunately, EPA’s development of fuel economy and emissions test procedures for heavy-duty hybrid trucks is expected to be a time-consuming process, requiring vehicle-level testing on heavy-duty chassis dynamometers. This process is particularly challenging because the number of large chassis dynamometers available in the United States that are suitable for heavy-duty trucks is quite limited.
EPA, in response to a U.S. Supreme Court ruling in a lawsuit brought by the state of Massachusetts in April 2007, is developing programs to utilize its experience with fuel economy and CO2 measurement protocols as part of its ongoing deliberations on potential greenhouse gas regulations for vehicles under the Clean Air Act. Whether this program will accelerate the development of fuel economy and emissions test procedures for heavy-duty hybrid trucks is not known at this time.
22
HTUF is available at http://www.calstart.org/programs/htuf/. Accessed June 2, 2008.
23
Note added in proof—Following the public release of this report, the following information came to the committee’s attention: In 2007, the Internal Revenue Service set forth interim guidance that provides a means to obtain tax credits for new qualified heavy-duty hybrid motor vehicles, based on their improved fuel economy. Internal Revenue Service Notice 2007-46, issued June 4, 2007, and entitled “Credit for New Qualified Heavy-Duty Hybrid Motor Vehicles,” provides procedures for a vehicle manufacturer to certify to the IRS that the city fuel economy of a heavy-duty hybrid vehicle was measured in a manner that is substantially similar to the manner in which city fuel economy is measured under 40 CFR (Code of Federal Regulations) Part 600 (in effect August 5, 2005). This notice allows the manufacturer to use any procedure that the manufacturer reasonably determines to be substantially similar to procedures under 40 CFR Part 600. In addition, the IRS will not challenge a manufacturer’s determination of city fuel economy. A manufacturer following this procedure still needs a certificate of conformity that the vehicle’s internal combustion engine meets the EPA emission standards for heavy-duty engines. Therefore, no credit is available for possible reductions in actual vehicle emissions with hybrid operation. As a result, simplified emission control systems cannot be considered for hybrid heavy-duty vehicles.
24
Note added in proof—The committee was unaware of this fact at the time of the report’s public release.
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Finding 4-8. Emissions of heavy-duty trucks are currently measured and certified by EPA for each engine type rather than for any truck as a complete unit. Current procedures do not allow either the fuel economy or emissions of complete hybrid propulsion systems to be certified, and so neither the fuel economy improvements nor emissions reductions of hybrid trucks are appropriately recognized. Prior to mid-2007, these procedures served as deterrents to commercialization of HHV technology since there was no practical way for truck purchasers to derive any direct tax credits for buying hybrid trucks as called for in the U.S. Energy Policy Act of 2005, which expires in 2009. Developing the necessary test procedures is expected to be a complex and lengthy process, and EPA has not been able to devote sufficient resources to developing such procedures in a timely manner.25
Recommendation 4-8. Since tax credits for hybrid trucks established in the Energy Policy Act of 2005 expire at the end of 2009, and there are not established engineering test procedures, DOE should work with EPA and stakeholders to accelerate the development of fuel economy and emissions certification procedures for heavy-duty hybrid vehicles so that the actual benefits of hybridization can be recognized and rewarded to further encourage commercial adoption.
HYBRIDIZATION OF LONG-HAUL TRUCKS
21CTP investments in heavy-duty hybrid truck development activities have been predominantly focused on truck types other than Class 8 long-haul trucks because stakeholders originally identified long-haul trucks as poor candidates for significant fuel economy improvements in comparison to other truck types and classes.26 However, as noted earlier in this chapter, recent statements by some truck manufacturers and OEM suppliers are suggesting that the potential fuel economy benefits of hybridization for Class 8 long-haul trucks may be much larger than previously expected (Eaton Corp., 2006).
Some opportunities for fuel-economy improvement in long-haul trucks can be derived from engine-off operation under idle and low-speed creep conditions, as well as energy recovery from regenerative braking. Additional improvement has been proposed using waste heat recovery (WHR) from a Rankine cycle using a turbine generator to provide electric power to supplement the main engine shaft power, providing a predicted fuel efficiency boost of 15 to 20 percent to the diesel engine (Regner et al., 2006).
As discussed in Chapter 3, Cummins engineers have reported that, in addition to the WHR technology, a revision of the entire heavy-duty vehicle propulsion system and its accessories could potentially yield significant fuel savings from the following techniques beyond those achievable with WHR alone. These revisions include the following:
Application of the basic hybrid-electric vehicle concept, allowing the main diesel engine to be downsized and peak power demands to be supplied by the electric motor and battery storage system.
Extensive use of high-voltage, electrically driven accessories on an on-demand basis.
Elimination of a separate engine-driven alternator.
In light of these developments, the 21CTP management has made statements indicating that they are reconsidering some of their earlier conclusions about the benefits of hybridization for heavy-duty Class 8 long-haul trucks.27 However, there is no indication that any documented study is yet available in the public literature to prove that opportunities for significant fuel economy/emissions improvements in hybrid Class 8 long-haul trucks really exist.
Finding 4-9. Recent statements by representatives of some heavy-duty truck OEMs have reported that there are opportunities for fuel economy improvements between 5 and 7 percent in hybridized versions of Class 8 long-haul trucks, yielding annual fuel cost savings exceeding $9,000 per year. This result runs counter to generally-held opinions about the low potential of hybrid versions of Class 8 long-haul trucks for substantial fuel savings, and no documented study results have been made available to the committee to firmly substantiate the recent claims.
Recommendation 4-9. The committee recommends that the potential benefits of hybrid Class 8 long-haul trucks be evaluated as part of the 21CTP program by conducting a documented study using a combination of analytical simulation and experimental data. If the results of the study confirm the recent claims of substantial fuel economy opportunities in hybrid long-haul trucks, the 21CTP program management is encouraged to find ways to contribute directly to the accelerated development of the necessary hybrid technology and its successful demonstration in prototype vehicles.
REFERENCES
Barker, W., and D. Hitchcock. 2003. Potential Emissions Reductions of Diesel/Electric Hybrid Pickup/Delivery Vehicles in the Houston/ Galveston Region, Presented at Hybrid Truck Users Forum, San Antonio, Tex., Oct. 23. Available at http://files.harc.edu/Projects/Transportation/FedExTechnicalBriefing.pdf (accessed May 12, 2008).
25
Note added in proof—Currently, EPA is developing a procedure to directly measure fuel economy and emissions of complete heavy-duty vehicles, including hybrids.
26
DOE, FCVT, 21CTP, response to committee query (Question 2 in “Hybrid Electric Vehicle Systems” section), transmitted via e-mail by Ken Howden, March 27, 2007.
27
DOE, FCVT, response to Question 14 in “Hybrid Electric Vehicle Systems” section of “Responses to NAS Queries on 21CTP Idle Reduction, Hybrid Vehicles, and Parasitic Losses,” forwarded via e-mail by Ken Howden, 21CTP program director, March 27, 2007.
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Barnitt, R., and K. Chandler. 2006. New York City Transit (NYCT) Hybrid (125 Order) and CNG Transit Buses: Final Evaluation Results, Golden, Colo.: NREL (National Renewable Energy Laboratory). Rep. no. NREL/TP-540-40125, Nov.
DOE (U.S. Department of Energy). 2006a. 21st Century Truck Partnership Roadmap and Technical White Papers. Doc. No. 21CTP-003. Washington, D.C. December.
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Eaton Corp. 2006. News release: Eaton Announces Plans to Develop Heavy-Duty Hybrid System for Trucks, June 23. Available at http://truck.eaton.com/news_19.htm. Accessed May 13, 2008.
Energy Policy Act of 2005 (Public Law 109-58, August 8, 2005). Available at www.doi.gov/iepa/EnergyPolicyActof2005.pdf. Accessed May 13, 2008.
Green Car Congress. 2006. NYC Hybrid Buses Improve Fuel Economy 45 Percent Over Diesel, 100 Percent Over CNG, Feb. 27. Available at http://www.greencarcongress.com/2006/02/nyc_hybrid_buse.html. Accessed May 13, 2008.
Nikkel, Cathy. 2006. EPA Innovates Hydraulic Hybrid System, Aug. Available at http://www.automedia.com/EPA_Innovates_Hydraulic_Hybrid_System/dsm20060801eh/1. Accessed May 13, 2008.
NRC (National Research Council). 2000. Review of the U.S. Department of Energy’s Heavy Vehicle Technology Program. 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.
Pellerin, C. 2005. Wind Power World’s Fastest-Growing New Electricity Source; Financial incentives, technology critical for further development. Washington, D.C.: U.S. Dept. of State, International Information Programs, April 23. Available at http://usinfo.state.gov/xarchives/display.html?p=washfile-english&y=2005&m=April&x=20050423130541lcnirellep0.9051172 . Accessed May 13, 2008.
Regner, G., H. Teng, and C. Cowland. 2006. A Quantum Leap for Heavy-Duty Truck Engine Efficiency—Hybrid Power System of Diesel and WHR-ORC Engines, AVL Powertrain Engineering. Paper presented at DEER (Diesel Energy Efficiency and Emissions Research) Conference, Detroit, Aug. Available at http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2006/session6/2006_deer_regner.pdf. Accessed May 13, 2008.
van Amburg, Bill. 2006. Hybrid Truck Users Forum, HTUF Utility Working Group: Utility Hybrid Truck Project Update, January. Available at http://www.calstart.org/programs/htuf/. Accessed May 13, 2008.