Theory/How far do we drive?/3. About 'Range Anxiety'

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The fear of getting stranded on the side of the road with an electric car from running out of battery charge has been termed ‘Range Anxiety’. Range anxiety was first introduced when drivers of the General Motors’ EV1 experienced fear to drive distances near the rated EV range of their vehicle (First gen. EV1: 100 miles, Second gen.: 140 miles). Now it is the major concern for people when considering an EV. With range of EVs so important to drivers, it has been added to the list of car specifications like Horsepower, 0-60 in …, etc. In the following, the technological cause of range anxiety will be explained, namely battery energy density and their recharge times. After that, some surveys about EV range requirements will be discussed.

Battery development is key

The low specific energy of the battery pack compared to gasoline (~0.25 kWh/kg vs ~13 kWh/kg) is the most important factor in range limitations. Numerous battery chemistries have been explored for use in EVs, each with their own advantages and disadvantages in cycle life, energy density, specific power and safety. The battery chemistries currently used in electric cars are mostly from the Li-ion family: LiCoO2, LiFePO4, LiMn2O4, Li(NiCo)O2 as well as Nickel-Metal Hydride (NiMH).

To achieve a 200+ miles range, the Tesla Roadster carries 992 lbs of Li-ion batteries (this includes other electrical components), which is more than a third of the total vehicle weight. That same range would take around 58 lbs of gasoline for a 30 mpg ICE car. Battery technology is in great development though, with a ‘technology pull’ force from the consumer electronics industry, demanding longer battery life from lighter and smaller cells. Consequently, the Li-ion energy density for batteries has increased from 88 Wh/kg (1991) to 280 Wh/kg (2011). There is a theoretical limit to the specific energy of all Li-ion battery types (ranges from 1-3 kWh/kg for the common types), but we are still far from that number.

In a recent poll by Deloitte (Deloitte, 2011), 80% of the U.S. participants of the survey want a range of 100 miles or more from an electric car. Around 60% of them want to be able to drive at least 200 miles before a recharge and 37% expects a range of 300 miles or more… In the results presented later, we will show how often people actually drive that far on a single day.

But do people know the range of the gasoline car they are driving today (SolarChargedDriving.com, 2011)? Of course, it only takes 10 minutes to fill up a gas tank, but it would be interesting to compare it to what people expect from electric cars. Table 1 shows the range of the top-10 best-selling cars in the United States (in 2010). Four out of ten vehicles have a range lower than 300 miles, with the Ford Fusion AWD FFV having the lowest range: 223 miles.

Table 1 : Driving range of the 10 best-selling cars in the United States, for the year 2010. In case of multiple models, the version with the shortest range is picked. Source: www.fueleconomy.gov


Ranking
2010 Model Range (miles)
1 Ford F150 Pickup 4WD 374
2 Chevrolet Silverado 4WD 491
3 Toyota Camry 383
4 Honda Accord 383
5 Toyota Corolla 297
6 Honda Civic 285
7 Nissan Altima 378
8 Ford Fusion AWD FFV 223
9 Honda CR-V 317
10 Dodge Ram 1500 Pickup 234

Many people are not affected by the range they get with their gasoline car. After all, refueling is quick, simple and possible virtually anywhere. Electric vehicles however, take longer to recharge: depending on the method, full recharge times range from typically 30 minutes (80% quick-charge (Nissan, 2010)) to 48 hours (slowest wall-outlet charge for Tesla Roadster (Tesla Motors, 2011)).

To illustrate the difference between ‘recharging’ a gasoline car and an electric car, we can make an interesting comparison by deriving the rate at which energy is transferred into the vehicle during refueling/recharging:

A full 13.5 gallon tank of a 2009 Ford Focus holds about 1.7 GJ of calorific energy in the form of gasoline. Assuming you fill it up in 2 minutes, that’s a rate of 14,000 kW. Believe it or not, that is the peak electricity consumption of almost 2,500 households. Electric cars are different: the several charging methods provide power ratings anywhere between 1.92 kW (standard US household outlet) and 62.5 kW (DC fast-charging) for the Nissan LEAF. An innovative charging method procured by the company ‘Better Place’, swaps batteries instead of recharging them. According to the firm, the batteries are swapped in little over a minute (BetterPlace.com, 2011). Assuming 25 kWh batteries, that is a recharge rate of 1,500 kW (see Figure 1).


Comparing Charging Power (Gasoline vs EV)
Figure 1: Energy transfer during refueling/recharging in kW. For fuel, the calorific energy transfer of a 2-minute, 13.5 gallon fill-up was assumed. Note that the y-axis has a logarithmic scale.

Because gasoline cars waste a much higher proportion of the energy that was transferred to them, it would be more interesting to see how many miles are ‘recharged’ per unit of time. Figure 2 shows the ‘effective charging rate’ in miles per minute for different charging methods. Of course, the number of miles driven from 1 kWh or 1 gallon of gasoline depends on where those miles are driven (highway or city) as will be shown later, but for now we can assume the single EPA rating for the EV range.

Effective charging rates (EV vs Gasoline)
Figure 2 : Effective charging rates in miles per minute for the different methods.

Surveys on Range Anxiety

Surveys have been conducted around ‘range anxiety’ and the implementation of (PH)EVs. The statistical correctness of this type of studies should be carefully reviewed, as same-topic questions from multiple studies show very different answers. Causes of this could be a selection bias (people who do not care about EVs are less likely to take the survey), the use of cluster sampling (surveys spread through networks like Facebook are likely to cover younger age-groups) or simply the way questions and perhaps multiple choice answers are formulated. From a pool of seven surveys, the two below were selected as the best-described and reported. Their results are briefly summarized below.

Accenture (PH)EV survey 2011
Accenture conducted a survey on consumer preferences regarding electrified vehicles in 13 countries, during December 2010 and January 2011 (Accenture, 2011). Random participants were chosen, representing gender, age and income groups according to the general populations’ distributions (n = 7003). Very interesting from this particular study was the observed difference in opinions on the subject between countries.

For example, the question: ‘Are you in favor of electric vehicles (plug-in hybrid electric vehicles and full electric vehicles) replacing conventional cars over time?’ was answered with: ‘Yes, I am very much in favor of this’ by 86% of Chinese participants (highest of all) and only 41% of the Dutch (lowest of all). Average over all countries was 60%.

The question: ‘Would you consider electric vehicles (plug-in hybrid electric vehicles or full electric vehicles) as an option for your next car purchase?’ was answered with ‘Certainly’ or ‘Probably’ by 95% of Chinese and 41% of Dutch respondents, again the two extreme countries (average: 58%).

When asking about the favored range of an EV: ‘How many kilometers would you like to be able to drive with a fully charged battery in order to consider an electric vehicle for your next purchase?’, people responded that they require at least 272 miles (437 km) of range on average. This is a very interesting figure, compared to their self-estimated average driven distance of 32 miles. As will be shown later, the 272 miles is even beyond the full-tank range of some of the top-10 sold conventional cars.

Miles required from EV

Another interesting finding is that only 30% of the participants regard their understanding of (PH)EVs as ‘enough’ to consider electric cars when making a decision on their next car purchase. This figure ranges from 20% to 44% over all countries.

Understanding of EVs by country

This shows that there is a lot to be done in terms of public education on the topic of electric cars. Accenture even states that their interpretation is that some people in this category overstate their level of knowledge.

Mini-E consumer study (UC-Davis)
The Mini E Consumer Study led by UC Davis, investigated consumers’ opinions after a year-long trial of driving BMW’s Mini E in Los Angeles and New York City (Turrentine et al., 2011). As can be expected, the survey sample is by no means representative for the general U.S. population, as the only eligible people were the ones that signed up for the EV trial (a total of 235). The data was collected using online surveys, driving diaries and maps, and by interviews (by phone and in person). Some of the survey questions covered specific aspects about the driven vehicle, like the regenerative braking system. Other questions, more applicable for this study, covered range issues and daily driven miles with the vehicle.

In interesting finding is that all 72 participants of the BMW-survey agreed that electric vehicles are suitable for daily use, of which 60% agreed very strongly. In the End-of-Lease survey (n = 102) however, when asked: ‘Are there any locations you would like to be able to access in your Mini E but can’t or prefer not to because of range issues?’, 81% answered ‘Yes’. And it appears that almost all (94%) participants relied on their second car, when (likely range or person-seating) limitations had to be overcome. This is an important conclusion: Even though users are content with their EV for daily use, a second car is almost a must-have in order to deal with range limitations (the seating-limitations is specific to the Mini E as it only has two seats; the rear seats are taken up by the battery). In order to get a better picture on this, the number of cars in households is taken into account in the analysis of the NHTS datasets.

Mini EV daily useMini EV limitations

On the next page, we will show why EV ranges are so variable, and what factors play a role in this.

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References

Deloitte. (2011). Gaining traction: Will consumers ride the electric vehicle wave?, (April). Retrieved from http://www.deloitte.com/assets/Dcom-Global/Local Assets/Documents/Manufacturing/Deloitte EV Survey Summary Findings China US Europe Japan April 2011 _ Final.pdf

Turrentine, Thomas S., Dahlia Garas, Andy Lentz, Justin Woodjack (2011) The UC Davis MINI E Consumer Study. Institute of Transportation Studies, University of California, Davis, Research Report UCD-ITS-RR-11-05. Retrieved from: http://pubs.its.ucdavis.edu/publication_detail.php?id=1470


 

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