EV Batteries Get Second Life with Energy Storage
Tom Lombardo posted on June 18, 2015 |
A new life for used EV batteries: commercial energy storage

Whenever I talk about the benefits of electric vehicles (EVs), the common environmental criticism is “What happens to all those old batteries?” Well, here’s a great solution: repurpose them.


While Tesla made a big splash with its announcement of the Powerwall, I think a more important, albeit less flashy, deal is Nissan’s partnership with 4R Energy and Green Charge Networks, who will sell used Nissan EV batteries for use in commercial energy storage systems.




  

Image credit: Nissan and Green Charge Networks



Batteries designed for electric vehicles need high energy density to maximize range while minimizing weight. All rechargeable batteries have a limited life - for Li-ion batteries that are common in EVs, that life is about 1200 charge-discharge cycles. But the batteries don’t die completely, they just have a reduced capacity (and therefore a shorter range), making them unsuitable for EV use.


Rather than recycling them at this point, it makes much more sense to repurpose these “old but not dead” batteries for use in stationary energy storage systems, where weight isn’t as much of an issue as cost. New batteries are very expensive, but if used batteries are relatively cheap, one can simply buy a few extras to make up for the decreased storage. So how much capacity is actually available in these “second life” batteries? Let’s crank the numbers…


A brand new Nissan Leaf battery pack comes with a 24 kWh storage capacity. The battery warranty is 96 months (8 years) or 100k miles. They guarantee at least 90% capacity for 60 months (5 years) or 60k miles. Although the company doesn’t specify exactly when the battery is considered “dead,” 80% capacity is the commonly accepted number, so we’ll go with that.


A 24 kWh battery with 80% of its nominal capacity will hold 19.2 kWh of energy. By comparison, Tesla’s Powerwall contains just over half of that amount, 10 kWh. It’ll be about twice the size and weight of a Powerwall, but if it’s in a utility room, then it probably doesn’t matter.


It’s difficult to do an apples-to-apples cost comparison with the Powerwall because this is a used battery, where the Powerwall is new. So far they haven’t announced the price, specifications, or warranty period. When they release that information, I’ll do a detailed comparison and share it with you. Meanwhile, here is Nissan’s Brad Smith discussing the partnership:



(Note: an earlier version of this article incorrectly said that the batteries were intended for home use. Green Charge Networks later informed us that the batteries are, in fact, intended for commercial use.)

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