The ZEV Program. Created in 1990, the ZEV program required that 10% of new vehicle sales by large auto manufacturers have zero emissions, beginning with 1998 model-year vehicles. This ZEV requirement was included to catalyze efforts to commercialize sustainable transportation.

Manufacturers originally planned to meet the ZEV requirements with battery electric vehicles. The board modified the program in 1998 and 2001 to allow up to 60% of the requirement to be met with vehicles having extremely low emissions and specific attributes. In 2009, up to 85% of the requirements may be met with these vehicles. The most recent change in 2003 revised the percentage of ZEVs required to 11% starting in 2009, increasing to 16% in 2018. (An alternate path allows the requirement to be met by the production of specified numbers of fuel cell vehicles.)

The Expert Panel on PHEVs. The ZEV panel convened by ARB is chaired by Michael Walsh, and includes Dr. Fritz Kalhammer;  Bruce Kopf; Vernon Roan, Jr.; and David Swan. The panel’s work consisted primarily of extensive data collection followed by a critical assessment.

Overall, the panel determined that plug-in hybrids (PHEVs) are the most likely technology to reach large volume production the soonest.

It is the Panel’s opinion that PHEVs have the potential to provide significant direct societal benefits and are likely to become available in the near future. They may foster future mass market BEVs by stimulating energy battery development and conditioning mass market customers to accept plugging in...

The Panel’s projection is that PHEVs with modest energy storage capacity will be derived from HEVs and will proliferate rapidly, stimulating further development and cost reduction of energy batteries and leading to commercially viable PHEVs and, in the longer term, FPBEVs [Full Power Battery Electric Vehicles].

While PHEVs will continue to grow rapidly, as they have no functional limitations, FPBEVs will grow more slowly due to customer acceptance of limited range and long recharge time. NEVs [Neighborhood Electric Vehicles] are commercially viable now and will continue to grow, but will grow slowly due to limited functionality. CEVs [City Electric vehicles] will become commercially viable in Japan and Europe in the not too distant future due to lower hurdles for BEVs to overcome. CEVs may be offered in the US as energy batteries continue to mature, but growth will be slow due to functional limitations of BEVs in general, and the specific limitations of CEVs, especially urban freeway driving.

The intense effort on FCEVs [Fuel Cell Electric Vehicles] will result in technically capable vehicles by the 2015 to 2020 time frame, but successful commercialization is dependent on meeting challenging cost goals and the availability of an adequate hydrogen infrastructure. If that happens, FCEVs will grow rapidly, followed by some H2ICVs [Hydrogen Internal Combustion engine Vehicles], and some H2ICVs with FCAPUs [Fuel Cell Auxiliary Power Units].

As a long term ZEV outcome, the Panel can envision plug-in hybrid FCEVs, powered by sustainable electricity for shorter trips and sustainable hydrogen for longer trips.

The panel concluded that the major technical issue faced by PHEVs—in addition to the same issues faced by conventional hybrids—is the ability of the energy battery to endure the large number of deep cycles the battery must deliver over the life of the vehicle. (The largest overall issue is battery cost.)

A PHEV battery can operate in four primary modes:

1. Grid-charging mode, which occurs when the vehicle is parked, is plugged into the grid and is charging the battery.

2. Charge-Depleting EV only mode (CD-EV), which consists of discharging the battery during driving after being charged by the grid from a full state-of-charge (SOC) to a predetermined low SOC, allowing regenerative brake charging but not ICE charging.

3. Charge-Depleting HEV mode (CD-HEV), which consists of discharging the battery during driving after being charged by the grid from a full SOC to a predetermined low SOC, allowing regenerative brake charging but not ICE charging (the ICE does supply power to the wheels when needed – similar to a HEV).

4. Charge-Sustaining mode (CS), which consists of continuously varying the battery SOC between an upper and lower limit during driving, allowing both regenerative brake charging and ICE charging, the same as with a HEV, but around a much lower average SOC.

Battery cycle life when first operating in a charge depletion mode and then switching to operation in a charge sustaining mode around a relatively low average SOC is not completely known at this time. However, in the first laboratory tests, both NiMH and Li Ion medium energy/medium power batteries are approaching 2000 deep cycles when cycled in this mode.

Because a PHEV has an ICE to meet a portion of the vehicle’s range requirement and power demand, its battery can be smaller than a FPBEV, thus reducing the battery cost, weight and volume issues. However, because of their lower capacity, PHEV batteries are more likely to be fully discharged daily than FPBEV batteries, making cycle life requirements more severe...

Other technical issues for PHEVs flagged by the review panel include:

• Definitions and standards for testing emissions and fuel economy.

• Vehicle emissions if the internal combustion engine in the PHEV is forced to perform a cold start under high load.

• Evaporative emissions if EV mode All-Electric Range (AER) is used.

The panel also considered a series hybrid plug-in configuration—i.e., similar to what GM proposed with its first Volt powertrain. The series PHEV can avoid the cold start emissions problem, but it requires a relatively large energy battery and a large, full performance, electric drive propulsion system, similar to a FPBEV or FCEV, according to the panel.

Compared to a FPBEV, it can use a smaller, more affordable battery and it does not have the driving range limitation issues. Compared to a parallel PHEV, it can operate the ICE at the optimum combination of speed and load necessary to achieve maximum efficiency (except for a short time for warm up), however, this efficiency advantage is reduced to some degree by a combination of generator, battery charging, battery discharging, and electric drive system efficiency losses before reaching the wheels. Compared to some other parallel hybrid systems, it is probably not suitable for vehicles intended for trailer towing.

Potential of battery technologies for HEV, PHEV and EV applications. Click to enlarge.

Battery Chemistries. The panel focused on three main ZEV enabling technologies: energy storage, hydrogen storage and fuel cells. On the energy storage side, the panel focused on batteries as the only viable energy storage option for zero and near-zero emission vehicles, at present and in the foreseeable future. The emphasis was on li-ion technologies because of their rapid technical progress and excellent potential to meet the energy storage requirements for full (including fuel cell) hybrid, plug-in hybrid, and full performance battery electric vehicles.

The panel also covered NiMH  batteries because of their near term importance for HEVs (including fuel cell HEVs) and their potential for PHEV applications. Finally, it examined the status of ZEBRA (sodium-nickel chloride) and lithium-sulfur batteries because of their near and, respectively, longer term potential for FPBEV applications.

...it seems very likely that full exploitation of presently known and yet to be discovered advances in materials, chemistry and manufacturing techniques will result in Li-Ion battery technologies that combine substantially higher performance with longer life and yet more robust safety at lower costs. In mass production, these costs should permit payback through fuel cost savings for PHEVs and HEVs but also for FPBEVs, especially if fuel costs continue at high levels and vehicle technologies keep advancing.

However, realization of the ultimate performance and cost potential of the Li Ion “family” of battery chemistries for ZEV and near (including partial) ZEV applications is likely to take another decade.

Potential ARB Impact. Given that there is growing technical and market momentum towards PHEVs, there still remains the question specific to ARB as to how to categorize a PHEV for the ZEV program. The category selected makes a difference in the credits a manufacturer receives toward meeting the overall target specified by ARB.

Following the changes of 1998 and 2001, there are three categories of vehicles in the ZEV program:

• Zero-Emission Vehicles (ZEV). Zero tailpipe emissions: battery electric vehicles, and hydrogen fuel cells.

• Advanced Technology Partial Zero Emission Vehicles. (AT PZEV). These are vehicles certified to PZEV standards and employing ZEV-enabling technologies: e.g. hybrids or compressed natural gas vehicles.

• Partial Zero Emission Vehicle (PZEV). Conventional vehicles certified to the most stringent tailpipe emission standards, zero evaporative emissions, and extended warranty.

ARB staff is recommending against allowing PHEVs in the pure ZEV category, preferring to place them in the AT PZEV group.

This recommendation is based on the original concern that PHEVs are not zero emission. Additionally, uncertainty exists regarding how PHEVs will be used (will they be plugged in consistently and throughout their life? Will all electric range be maximized under a wide variety of driving cycles? etc.).

...PHEVs being discussed today have more of a blended approach to using the battery pack. Like a conventional hybrid, the battery is used off and on throughout the driving cycle to assist the engine or drive in an all electric mode. Staff needs to learn more about how these blended PHEV strategies would be implemented and how they might impact air quality before recommending how they be treated in the ZEV regulation. For these reasons, staff does not recommend opening up the pure ZEV category as an incentive to bring PHEVs to market.

...however, that there are good reasons why manufacturers will produce PHEVs and there are adjustments to the regulation that could be explored that would facilitate this.

Resources:

• ARB ZEV Technology Review

• Status and Prospects for Zero Emissions Vehicle Technology: Report of the ARB Independent Expert Panel 2007

• ARB Staff Report

• CalCars Assessment