Electric cars more useful than thought: study

Electric vehicle batteries have a more useful life than believed and will meet the daily travel needs of drivers longer than commonly assumed, a new study led by an Indian-origin scientist has found.
Many drivers and much prior literature on the retirement of EV batteries have assumed that EV batteries will be retired after they has lost 20 per cent of energy storage or power delivery capability.
The first study of its kind by scientists at the Lawrence Berkeley National Laboratory (Berkeley Lab) 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, analysed real-world driving patterns and found that batteries that have lost 20 per cent of their originally rated energy storage capacity can still meet the daily travel needs of more than 85 per cent of US drivers.
He and his research team also analysed 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.

"We show that, even after substantial battery degradation, the daily travel needs of most people are still going to be met," Saxena said.

With today's EV batteries, "end of life" is commonly defined as when the storage capacity drops down to 70 to 80 per cent of the original capacity.
As capacity fades, the vehicle's range decreases. The researchers took nearly 160,000 actual driving itineraries from the National Household Travel Survey conducted by the US 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 US.

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.
"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 per cent of their battery's energy storage capabilities," said Saxena.