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Green Wheels: EV performance melts in boiling heat

If blistering heat is to be a feature of our summers, its effects on batteries are things to consider.

  • Detail of an automatic gear shifter in a new, modern car. Modern car interior with close-up of automatic transmission and cockpit background

This summer?s heatwaves put some electric vehicle owners in a sweat.

In sweltering temperatures, they said, their cars? range dropped dramatically.

The problem was centred on the southwest U.S., which has been broiling for weeks. And it seemed to be confined to Nissan Leafs.

Since Leafs are, for now, the only EVs on the road in significant numbers, that?s not surprising. Still, some analysts say the car?s air-cooled battery pack contributed to the reduced distances between charges and that a water-cooled system would work better.

Cause and effect haven?t been established.

Nissan says only five of the 400 Leaf owners registered in Arizona ? the focal point of the issue ? have complained about heat-related battery problems.

?We want to learn more about what?s going on,? Mark Perry, the company?s director of product planning, said in a local television interview. ?We?ve just been made aware of the problem so we have not made any conclusions yet.?

Still, if blistering heat is to be a feature of our summers, its effects on batteries are things to consider.

Canadians might, in fact, get a double whammy since cold weather also shrinks lithium-ion battery range.

To the rescue ? maybe ? rides Germany?s Fraunhofer Institute for Environmental, Safety and Energy Technology, which describes itself as: ?Europe?s largest application-oriented research organization.?

The institute just unveiled a coolant, CryoSolplus, which it says is three times more effective than water in keeping EV batteries comfortable ? no cooler than 20C, no warmer than 35C.

Fraunhofer says the product would increase hot-weather range, in part because less battery energy would be required for cooling. More important ? since ?operating a battery at 45C instead of 35C halves its service life? ? it would extend longevity. ?That is the motivation for cooling the battery, because the battery price is about half the price of the complete car at this time,? says researcher Tobias Kappels.

The company estimates CryoSolplus would add about $120 to the cost of an EV, or a tiny fraction of a battery pack?s price.

These are early days, though. Fraunhofer says the coolant needs further development and won?t be ready for several years. The next step is field trials in an experimental vehicle.

So, this is more about the complexities of a new technology than a guaranteed solution.

CryoSolplus has four ingredients: Its base is water. And floating in it are tiny ?droplets? of paraffin. A detergent-like substance known as tensides keeps those bits evenly dispersed, rather than clumping or floating to the surface. Finally, there?s a dash of glycol antifreeze.

Fraunhofer says the coolant is very efficient at conducting heat from the battery. As it does, the droplets ? solid at the start ? melt and store the heat until it?s dissipated in the coolant tank. At that point, the droplets return to their solid form and make another trip through the battery cooling channels.

The new product not only cools more effectively but is also more compact, which saves space: Battery cells can be closer together and the coolant tank made smaller than in a conventional water-cooled system.

The main challenge was keeping the droplets properly and consistently dispersed, Kappels says.

The tensides do that job by coating each droplet. Researchers had to find a type that could withstand long storage as well as mechanical stresses such as being pumped through pipes, and thermal stresses as the droplets repeatedly ?freeze? and ?thaw.?

The potential range extension from using the new coolant ?would depend on the ambient temperature and driving style,? Kappels says. ?I only can say, it would be significant.?

And in case winter ever returns here, he says the stuff would also keep a battery cosy, since the droplets would ?store heat from the battery as long as possible, to keep it warm.?

We?ll see.

  • Green Wheels: EV performance melts in boiling heat

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