UC Davis Researchers Suggest the “Battery Problem” Seen to Be Slowing Electric Drive Commercialization Is Perceptual as Well as Technological
|Distribution of battery requirements for consumer-selected PHEV designs (shaded circles) compared to USABC, MIT and EPRI performance requirements. Source: Axsen et al. Click to enlarge.|
Addressing the widely held notion that battery technology and cost remain as barriers to the initial commercialization of electric-drive passenger vehicles, researchers from the Institute of Transportation Studies at UC Davis are suggesting that part of the “battery problem” is a mismatch between established performance goals and what consumers may initially seek from electric-drive vehicles.
In a paper published in the journal Transport Policy, Jonn Axsen, Ken Kurani and Andrew Burke explore two aspects of the “purported problem” in the context of starting a market for plug-in hybrid vehicles (PHEVs): performance goals, and the abilities of present and near-term battery chemistries to meet those goals.
We contend that potential solutions to the battery problem are not just a matter of technology development and cost reduction, but instead involve a concurrence between battery technology and appropriate PHEV performance goals. The present analysis explores both, with a particular emphasis on the latter—challenging untested assumptions regarding consumer valuation of PHEV capabilities.
—Axsen et al.
Goals set forth by government, industry and academic sources considered in the study include:
The US DOE (2007) draft PHEV R&D plan sets a mid-term (2012-2016) goal of commercializing PHEVS with an all electric charge depleting (CD) range of 20 miles (AE-20) and/or a blended charge depleting range of 40 miles (B-40), progressing towards long-term commercialization (2016-2020) of AE 40 or B 60.
The USABC specifies two PHEV designs to guide its battery requirements: an AE-10 crossover and AE-40 mid-sized car.
MIT proposes a B-30 mid-size car, with a more aggressive driving cycle simulation.
EPRI assumes PHEVs to be AE-20 and AE-60 mid-size cars.
|Influential PHEV Performance Goals (as summarized by Axsen et al.)|
|Body type||Type||Cross-over SUV||Mid-size car||Mid-size car||Mid-size car||Mid-size car|
|Depth of discharge||Percent||70||70||70||80||80|
|Drive schedule||Type||UDDS||UDDS||UDDS, HFWET,
|UDDS, HFWET||UDDS, HFWET|
To explore whether are not those are the right goals for consumers, the research team created a design space in which consumers could create their own designs, and thus set their own PHEV goals. Parameters of the design space included all-electric (AE) or blended (B) operation, and CD ranges of 10, 20 or 40 miles. The design space was presented to a sample of 2,373 new-vehicle buying households in the US.
Our design space approach differs from a common approach to estimating consumer demand for alternative vehicles: eliciting consumer preferences or willingness-to-pay [WTP]. There are several reasons why we implemented the design space approach.
First, we were not willing to assume what a PHEV “should” be. Second, in order to derive consumer-driven battery requirements to compare to experts’s assumption-driven requirements we need consumers complete vehicle designs—it is neither necessary nor sufficient to estimate partial-attribute values or overall WTP.
...Third, constructive design processes are consistent with theories of constructed preferences that view consumer preferences as outcomes of, not inputs to, decision contexts and processes. Willingness-to-pay presumes consumers have preferences about the attributes available in a given choice. However, research suggests that most consumers have little experience or understanding of electric drive, and have difficulty quantifying their valuation of fuel economy.
—Axsen et al.
The analysis simplified the results into two categories: cars and trucks. The majority of the potential early market respondents (69%) selected the based B-10 design—i.e., the PHEV design with the lowest battery power and energy requirements. Using the results of the design study (and using only the more aggressive US06 cycle) the team assessed the resulting battery requirements for power, energy, longevity, cost and safety.
They found that the requirements derived from prospective consumers are within the capabilities of several lithium-based battery chemistries, and even that some NiMH batteries can meet energy density, ir not peak power density, requirements of most PHEV designs created by new car-buying households interested in PHEVs. They note that other requirements may make NiMH unsuitable for PHEV applications.
However, the research reported here indicates that more important than concerns about technology development per se is the perceived problem: the previously untested assumptions regarding the types of PHEVs to be commercialized.
...in contrast to statements by battery researchers indicating that accelerated PHEV development may be a misguided “detour” due to the large gap between present battery performance and performance requirements for PHEVs, we are saying that appropriate batteries may be closed for commercially viable PHEVs than often realized and that the battery problems to be solved for those batteries are radically different from the power/energy/life/cost/safety issues implied by the USABC and others.
—Axsen et al.
These findings have significant implications for policymakers, Axsen et al. say. For example, the individual federal tax incentive of $2,500 to $7,500 for the purchase of an electric-drive vehicle only applies to vehicles with a battery pack larger than 4.0 kWh in capacity.
The 4.0 kWh lower limit on battery size is difficult to reconcile with the fact that of the people in this study who designed a PHEV for themselves in the high cost design game, over 90 percent designed a PHEV that requires a battery smaller than 4.0 kWh and nearly 75% designed a PHEV that requires a battery smaller than 2 kWh.
—Axsen et al.
Jonn Axsen, Kenneth S. Kurani, Andrew Burke (2010) Are batteries ready for plug-in hybrid buyers? Transport Policy 17 173–182 doi: 10.1016/j.tranpol.2010.01.004