Goodbye, range anxiety? Electric vehicles may be more useful than previously thought

March 30, 2015 by Julie Chao, Lawrence Berkeley National Laboratory
Credit: Lawrence Berkeley National Laboratory

In the first study of its kind, scientists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) quantitatively show that electric vehicles (EVs) will meet the daily travel needs of drivers longer than commonly assumed. Many drivers and much prior literature on the retirement of EV batteries have assumed that EV batteries will be retired after the battery has lost 20 percent of its energy storage or power delivery capability. This study shows that the daily travel needs of drivers continue to be met well beyond these levels of battery degradation.

Samveg Saxena, who leads a vehicle powertrain research program at Berkeley Lab, analyzed real-world driving patterns and found that batteries that have lost 20 percent of their originally rated energy storage capacity can still meet the daily travel needs of more than 85 percent of U.S. drivers. He and his research team also analyzed battery power fade and found that even after substantial loss in battery power capabilities performance requirements are still met.

"There are two main reasons people are hesitant to buy an EV: first, they're unsure it will satisfy their mobility needs, and second, they're afraid the battery won't last the whole life of the car and they'll have to replace it for a lot of money," said Saxena, who has a PhD in mechanical engineering. "We show that, even after substantial battery degradation, the daily travel needs of most people are still going to be met."

The analysis of battery life was published online recently with open access in the Journal of Power Sources, "Quantifying EV battery end-of-life through analysis of travel needs with vehicle powertrain models," which Saxena co-authored with Jason MacDonald of Berkeley Lab and Caroline Le Floch and Scott Moura of UC Berkeley.

With today's EV batteries, "end of life" is commonly defined as when the storage capacity drops down to 70 to 80 percent of the original capacity. As capacity fades, the vehicle's range decreases. The Berkeley Lab researchers decided to investigate the extent to which vehicles still meet the needs of drivers beyond this common battery retirement threshold.

To conduct the study, the researchers took nearly 160,000 actual driving itineraries from the National Household Travel Survey conducted by the Department of Transportation. These are 24-hour travel itineraries showing when a car was parked or driving, including both weekend and weekday usage by drivers across the United States.

This chart shows the fraction of U.S. drivers whose daily travel needs are no longer met as a result of energy capacity fade for each level of capacity fade down to 30% remaining capacity.

The researchers then assumed all itineraries were driven using a vehicle with specifications similar to a Nissan Leaf, which has about 24 kilowatt-hours of energy storage capacity, similar to many other EVs on the market, and 400 kW of discharge power capability, which was based on battery cell-level measurement data for the chosen vehicle.

This data was fed into the team's unique simulation tool, V2G-Sim, or Vehicle-to-Grid Simulator. Developed by Saxena and other Berkeley Lab researchers, V2G-Sim quantifies second-by-second energy use while driving or charging for any number of different vehicle or charger types under varying driving conditions.

Then for each of the itineraries, they changed different variables, including not only the battery's energy storage capacity, but also when the car was charged (for example, level 1 charger [standard 120V outlet] at home only, level 1 charger at home and work, level 2 charger [240V outlet] at home and level 1 charger at work, and so on), whether it was city or highway driving, whether the air conditioner was on, and whether the car was being driven uphill. More than 13 million individual daily state-of-charge profiles were computed.

"People have commonly thought, 'if I buy an EV, I'll have to replace the battery in a few years because I'll lose the ability to satisfy my driving needs, and it's not worth it,'" Saxena said. "We have found that only a small fraction of drivers will no longer be able to meet their daily driving needs after having lost 20 percent of their battery's energy storage capabilities. It is important to remember that the vast majority of people don't drive more than 40 miles per day on most days, and so they have plenty of reserve available to accommodate their normal daily trips even if they lose substantial amounts of battery capacity due to degradation."

As the battery continues to degrade down to 50 percent of its original capacity, the research found that the daily travel needs of more than 80 percent of U.S. drivers can still be met, and at 30 percent capacity, 55 percent of drivers still have their daily needs met. "Even if a driver has a long, unexpected trip beyond the normal daily travel, an EV battery with substantial capacity fade can often still make the trip," Saxena said.

The Berkeley Lab scientists also analyzed power capacity fade, or the declining ability of the battery to deliver power, such as when accelerating on a freeway onramp, as it ages. They modeled the impact of power fade on a vehicle's ability to accelerate as well as to climb steep hills and complete other drive cycles. They found that power fade for the chosen vehicle does not have a significant impact on an EV's performance, and that a battery's retirement will be driven by energy capacity fade rather than by power fade.

"In fact, our analysis showed that the battery pack we studied, the Nissan Leaf, has a large margin of extra power capability," Saxena said. "Energy capacity fade is really the limiting factor for this vehicle, not power fade."

The researchers thus conclude that "range anxiety may be an over-stated concern" since EVs can meet the daily travel needs of more than 85 percent of U.S. drivers even after losing 20 percent of their originally rated . They also conclude that batteries can "satisfy daily mobility requirements for the full lifetime of an electric vehicle."

Given these results, the authors propose that an EV 's actual retirement may be delayed to when it can no longer meet the daily travel needs of a driver, leading many EV batteries to have a longer lifetime than is commonly assumed. Future work will involve providing personalized EV information for drivers, which takes into account an individual's driving behavior.

"In sum, we can lose a lot of storage and capability in a vehicle like a Leaf and still meet the needs of drivers," Saxena said.

Explore further: Understanding the life of lithium ion batteries in electric vehicles

More information: Journal of Power Sources, www.sciencedirect.com/science/ … ii/S0378775315000841

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gkam
3.4 / 5 (5) Mar 30, 2015
I wonder how the goobers will like driving really good cars made by the sons and daughters of California Hippies?
MR166
1 / 5 (4) Mar 30, 2015
"It is important to remember that the vast majority of people don't drive more than 40 miles per day on most days, and so they have plenty of reserve available to accommodate their normal daily trips even if they lose substantial amounts of battery capacity due to degradation."

So let me get this straight, say you have to drive 60 miles one day are you supposed to rent a car?
gkam
2.4 / 5 (5) Mar 30, 2015
No, silly, you get a car that can go that far. They all can.

On second thought, I think you would rent a car.
rocket77777
5 / 5 (3) Mar 30, 2015
MR166. If you don't have friend or relative to borrow from, renting can be like $20 so even if you do it 10 times a year, that's only $200. There is no reason for people that need more frequent long distance to own low range car. Other than that, battery with same size/weight will have double or more range in next 5 years.
howhot2
4 / 5 (4) Mar 30, 2015
There is no reason to fear EVs. The new cars are just amazing technology on wheels and certainly are capable of city travel for nearly everyone. If you get an EV car, can I recommend you get a grid tied solar panel system with it (~$6000). Then it's like you have instant free transportation (at least free for your carbon footprint) with no maintenance except for typical wear and tear.

A friend of mine has a Chevy Volt that he plugs into his solar car port. He tells me that driving his car actually pays him and with a 30 mile commute back and forth each day.
acronymous
5 / 5 (1) Mar 30, 2015
"It is important to remember that the vast majority of people don't drive more than 40 miles per day on most days, and so they have plenty of reserve available to accommodate their normal daily trips even if they lose substantial amounts of battery capacity due to degradation."

So let me get this straight, say you have to drive 60 miles one day are you supposed to rent a car?


Use the other car? Defer the trip? Recharge during lunch? There are endless workarounds.
thebobs
1.3 / 5 (3) Mar 31, 2015
my problem is not range. its charging. my commute is 80 miles round trip. I don't like the idea of charging every night. With my gas guzzler, I only fuel up once per week. and when I have to fuel, it only takes about 10 minutes. if EV manufactures can get the charge time down to 10 minutes and only where I have to charge it once per week, then I will buy an EV. until then, no.
MR166
1 / 5 (1) Mar 31, 2015
"Use the other car?"

That was my point, EV only make sense if you own a second car.
MR166
5 / 5 (1) Mar 31, 2015
"If you get an EV car, can I recommend you get a grid tied solar panel system with it (~$6000). Then it's like you have instant free transportation (at least free for your carbon footprint) with no maintenance except for typical wear and tear."

Exclusive of subsidies, I really doubt that you can get a grid ties system that can do this for $6,000.
Eikka
4 / 5 (2) Apr 01, 2015
They forgot to mention that after about 30% capacity loss, the breakdown of the battery accelerates because the cycle frequency and depth of discharge, as well as the charge/discharge rate (C) increases with falling battery capacity.

That's why lithium batteries are considered "dead" when they reach 63% capacity. After that point the capacity plummets towards zero over a very limited number of cycles. Then there's also the shelf-life of the batteries which is less than 10 years, so you are going to need to replace it anyways.

The other fallacy is that drivers always drive the average distance. The actual driving habits of an individual fall on a normal distribution, and pretty much everyone drives more sometimes, so they should rather measure the percentage of trips the car can satisfy for the average driver. In the UK for example, the average driver may expect to need a rental car once every 1-2 months if they were to rely on the 73 mile range of the Nissan Leaf.
Eikka
4 / 5 (2) Apr 01, 2015
Use the other car?


Thank you for the advice, Mr. "let them eat cake then".
Defer the trip?

The entire point is that people don't want to buy cars that cannot do the distance.

Recharge during lunch?


There's no point in stopping for lunch if you're only travelling a hundred miles or so. Would be just a waste of time, and again people don't want cars that force them to stop and wait for extended periods.

There are endless workarounds.


Few of them are very good.

Range anxiety is also not only about the distance you can drive in a single trip, but also about whether you have sufficient margin without the need to consider whether you can make it. Small EVs with only just enough charge to get you to work and back are stressfull to drive, because you know you'll run out if you suddenly realize half-way in that you forgot your wallet and have to turn back.

It only works in a perfect world.
antialias_physorg
5 / 5 (1) Apr 01, 2015
Use the other car?"


That was my point, EV only make sense if you own a second car.

There are a lot of households with two cars (you know: couples, families, ...). There's no reason why one of them cannot be replaced with an EV. It is very unlikely that both need the huge range on the same day.

Even for singles this is viable. Unless you have a very long commute the number of times when you need long ranges is pretty low. There are such things as public transportation (at least in most developed countries where EVs are an option).
Eikka
5 / 5 (1) Apr 01, 2015
An example of lithium battery cycle life:

http://batteryblo...les2.jpg

The cell starts at 2,500 mAh and degrades down to ~63% by cycle number 1100. Then after the following 200 cycles, the capacity falls to 10% and then gradually towards zero.

This battery was discharged at C/2 which means it's emptied at a rate of 2 hours. That is a similiar discharge rate you can expect from a Nissan Leaf battery. If this were a Leaf battery, it would start out at 73 mi range initially, drop down to 46 miles over the next 65-75,000 miles, and then break down completely over the next 5,000 miles.

Eikka
5 / 5 (1) Apr 01, 2015
There are a lot of households with two cars (you know: couples, families, ...). There's no reason why one of them cannot be replaced with an EV. It is very unlikely that both need the huge range on the same day.


Not very. Mom takes one car to town, teenage kid wants to drive to soccer practice. Whoops, can't go, no charge because dad just came home from work. It's just extra hassle and juggling to deal with a car that has a teacup for a fuel tank and needs 4-8 hours to fill it up. That's why people don't want them - which is the point.

Even for singles this is viable. Unless you have a very long commute the number of times when you need long ranges is pretty low.


In my experience, a single person is one who isn't settled down with a steady job and a family, so their lives will be more varied with higher chance of long commutes in search of work and visiting new places, moving to new cities etc. etc.

And they can rarely afford an EV anyways.
Eikka
5 / 5 (1) Apr 01, 2015
Besides, one of the main points of a car is that you can just pick yourself up and go. The freedom to relocate yourself a thousand miles a day makes quite a difference.

If we are going to drive around in Nissan Leafs and Citroen Berlingo Electriques, a lot of the economy is going to change. Take ski resorts for example. Just last week I drove for 2 hours, spent a wonderful evening and the next day having a day off, then 2 hours back.

And all it took was about €40 in gasoline. Renting a car overnight would have been 90-150€ AND they expect you to pay the fuel as well, taking a bus would take a week of coordination to get there and back, a taxi would be ludicurously expensive...

And I'm not a rich man. I drive a car that cost me 2000€. If I had to choose an EV, I would be forced to choose not to drive, and that would mean no day-trips to ski resorts, no seeing friends and family, no work, no livelyhood.
MR166
not rated yet Apr 01, 2015
Also EV suffer range problems in the cold.

http://www.forbes...an-half/

50% loss
gkam
2.3 / 5 (3) Apr 01, 2015
Whine all you want, kiddies. You are LOSING, and will soon be showing off your own electric vehicles. Eikka could have done that in a Tesla, and been a celebrity. And MUCH safer.

Made practical by California Hippies.
MR166
not rated yet Apr 01, 2015
"Whine all you want, kiddies."

So it is "Whining" when people point out the shortcomings of a product and why it is not being adopted on a wider basis.

Here in my state electricity costs 22 cents/KWH at my meter. At that price there is not much cost savings per fill up, if any, vs. $2.50/gal gas. I know, gas is very cheap at this point in time and I do not expect it to remain there for long.
gkam
3 / 5 (4) Apr 01, 2015
It is not just the price, but the pollution, and the politics of having to get our stuff from folks who hate us. How much does it cost us for the two carrier groups we need for the oil routes?

What kind of disruptions can we take with the oscillating price of energy, subject to the whims of others?
Eikka
5 / 5 (1) Apr 04, 2015
Whine all you want, kiddies. You are LOSING, and will soon be showing off your own electric vehicles. Eikka could have done that in a Tesla, and been a celebrity. And MUCH safer.


Yes. The pre-requisite is though that I should already be a celebrity to afford such a car. Call me back when EVs show up at the second hand lot... oh wait, they won't because the batteries go bust under 10 years and the replacement costs more than the value of the car.

They've got a long way to go before the bottom 80% of people can afford to drive electric.

The cost of a regular car is typically spread over 20 years and 2-3 owners, while the full cost of the EV is left with the first owner because they can't sell it for any appreciable value after the battery has to be replaced. That alone makes them uneconomical to own.
gkam
1 / 5 (2) Apr 04, 2015
Eikka, I love it. They are not going to show up yet because they will not wear out like reciprocating nonsense. Ever see a hundred-year-old electric motor still spinning along, 24/7? Not many cars can to that. No motor oil, no greases, no pollution, no noise, . . . why would anyone want a stinky ICE over electricity?
MR166
not rated yet Apr 04, 2015
Gkam I will agree that the engine and transmission of a modern ICE powered car is limited to say 200K miles or so before major repairs are needed. Well what will it cost to replace battery packs over that mileage period in an EV car? Also, here in the north east it is not at all uncommon to have power failures of a week or more in the winter. How does one get to work during that period with an electric powered car.
gkam
2.3 / 5 (3) Apr 04, 2015
PV and wind, when the utility fails.

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