Monday, October 31, 2011

Batteries for Electric Vehicles

Advances in battery technologies over the past few years have been absolutely remarkable. When I was working on the section devoted to batteries and electric cars in 2008, nickel metal hydride (NiMH) batteries were the batteries available for cars like the Toyota Prius.  They used to cost about $1.00/Wh capacity.  All-electric car manufacturers like Tesla and Fisker (Fisker is a series hybrid not an all-electric car), who were making vehicles targeted for the high-end market, were offering lithium ion batteries.  Li-ion batteries have a higher energy density and are more durable, and they were the battery of choice for many personal electronic devices such as cell phones, PDAs, and laptop computers.  However, they tended to be very expensive.  I estimated their cost to about $2.50/Wh based on the information available at that time for smaller systems.  The price of the Li-ion batteries has dropped dramatically in the last few years—to about $0.40/Wh, and are now the battery of choice for electric vehicles. 
The all-electric Nissan Leaf has a 24 kWh Li-ion battery pack and has a base price of $33,000 (before tax credits); for reference Toyota Prius has a 1.4 kWh battery pack.  Clearly, the batteries cost a lot less that $1,000/kWh.  Likewise, the new gas-electric hybrid Chevy Volt has 16 kWh Li-ion battery, and sells for $41,000.   It is sized to allow users a driving range of about 35 miles on electric power alone.  The battery lifespans have also improved significantly, and they are expected to last 10 years and guaranteed for 100,000 miles.  
These improvements have changed the economics of driving electric vehicles.  According to the US EPA, Nissan Leaf consumes 34 kWh for 100 miles. At grid electricity cost of $0.10/kWh, driving the 100 miles would only cost $3.40.  A comparably sized gasoline engine car giving 33 mpg would cost about $12.00 at the current price of gasoline ($4.00/gallon).  If we add the amortized cost of the battery ($9,600), the cost for 100-mile drive would increase to about $13.00, still comparable to the gasoline case, and not substantially higher as was the case a few years ago.

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