No matter what the manufacturer, all electric cars slowly lose range as their battery packs age due to the chemical changes that take place in a battery pack with continued charge and discharge cycles.
With early examples of modern electric cars like the Nissan LEAF and Chevrolet Volt more than 4 years old, there’s a growing interest in the automotive industry and the mainstream press on how healthy the battery packs of those cars are after tens or even hundreds of thousands of miles.
Some of that attention has been focused on the cost of eventually replacing battery packs as they age and lose capacity. Some of it has been focused on how useable those vehicles are as daily drivers after losing ten or twenty percent of their original capacity.
Thanks to companies like Nissan, which now offers LEAF and e-NV200 electric van drivers the option of buying a replacement battery pack for a set cost (€5,000, $5,500) when their car’s battery packs have lost significant capacity, the former is less of a concern than it once was.
Now a study from the Department of Energy’s Lawrence Berkeley National Laboratory has proven quantitatively that the latter shouldn’t be a big concern either for the majority of Americans in a study which it says is the first of its kind.
As it detailed yesterday in a blog post on its website, scientists at the Lawrence Berkeley National Laboratory analysed the effects of battery loss on electric car battery packs and plotted it against real-world driving patterns across the U.S.
Its discovery? Even in an aged, limited-range electric car like a 2011 Nissan LEAF — whose new EPA-approved range was just 73 miles per charge — a battery capacity loss of 20 percent still means that it can meet the daily travel needs of more than 95 percent of all U.S. drivers.
Even with a capacity loss equivalent to 50 percent of the original battery pack, more than 80 percent of U.S. daily travel needs — both weekday and weekend — could be met. This disproves the old theory held by many non-electric car drivers that electric car battery packs would become useless for everyday use once they had lost more than 30 percent of their original battery capacity.
“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 Samveg Saxena, leader of a vehicle powertrain research program at the lab and coauthor of the study. “We show that, even after substantial battery degradation, the daily travel needs of most people are still going to be met.”
In total, more than 160,000 real-driving itineraries taken from the National Household Travel Survey by the Department of Transportation were studied and analysed. The data set covered 24-hour periods and included tracking when the car was parked or driving over both weekend and weekday periods.
Assuming those itineraries were travelled in a vehicle similar in specifications to a Nissan LEAF, a car with about 24 kilowatt-hours of on-board battery storage, the researchers then fed the data into its custom-built simulation tool V2G-Sim. As the name suggests, V2G-Sim is designed to model and quantify second-by-second energy use and charging capabilities for a plug-in vehicle, and allowed the researchers to plot battery draining and recharging for any given moment in each 24-hour period. In total, more than 13 million daily state-of-charge profiles were computed, taking into consideration different charging profiles and usage scenarios, including driver speed, weather conditions and weather the air conditioning was on or not.
The results speak for themselves.
“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.”
Here at Transport Evolved, we’ve owned and operated several Nissan LEAFs in our staff fleet, with Hiro — the Gordon-Bloomfield family LEAF — having covered more than 72,000 miles since new four years ago. Even with an estimated capacity loss of around 20 percent, it is still happily handling a 100 miles per day round commute, with a top-up charge during the day at a public type 2 charging station.
While range is certainly less than it was when new, it can easily drive more than the 40 miles of an average daily commute on a single charge.
If you’d like to read the report for yourself, there’s an abstract available with open access at Sciencedirect, or you can view the report in full in Volume 282 of the Journal of Power Sources, which is published on 15 May.
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