Mazda i-ELOOP regenerative braking system with capacitor storage

Mazda i-ELOOP regenerative braking system with capacitor storage

Ultracapacitors have been the next big thing in energy storage for well over a decade.

And while automakers have been hung up on their far greater price (per energy stored), and prices haven’t decreased all that significantly, there are some indications that automakers are softening in their resistance.

Part of the reason is that for engine stop-start systems, they make a lot of sense. As they can store energy quickly—energy that can then be released as needed—ultracapacitors are great choices for those arrangements, as well for hybrid (and fuel-cell) vehicles, to get better efficiencies as part of rapid braking or acceleration.

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Existing stop-start systems typically employ heavier glass-mat lead-acid batteries that tend to need replacing more often than other car batteries—sometimes at intervals of less than two years.

Ultracapacitors also last far longer, aren’t as temperature-sensitive (they’ve been used in F1 racing, after all), and don’t lose capacity as they age. They’re also about 95 percent recyclable and can be shipped without hazardous-materials precautions. And in a stop-start application, an ultracapacitor paired with a conventional lead-acid battery would last ten years or more.

The potential to make stop-start systems more effective

According to a representative of Ioxus, an ultracapacitor supplier, swapping an ultracapacitor for an underperforming lead-acid battery in a start-stop battery could boost fuel-economy savings from the 1-2 percent range up to 5-7 percent—simply because the engine would then be able to shut off more often.

Such a deployment of an ultracapacitor system might cost $200, the supplier says.

So far, however, there are few vehicles that employ ultracapacitors. The only application we’re aware of is the i-ELOOP system that’s offered in the Mazda 3 and Mazda 6 (we’ve tested it in both models). Other than a stop-start system for the Lamborghini Aventador, WardsAuto points to systems in the Japanese Honda Fit and various overseas PSA Peugeot Citroen vehicles.

i-ELOOP in the 2014 Mazda 6

i-ELOOP in the 2014 Mazda 6

In the Mazda models, i-ELOOP serves a function essentially a heightened version of the so-called ‘smart’ alternator systems of recent years—by storing away as much energy as possible, with an ultracapacitor, when decelerating and braking, and then using it to effectively eliminate alternator load in some conditions when accelerating.

Mazda uses them already, but it's cautious on cost

Yet cost comes into play in those Mazdas as well. To get those cars with that i-ELOOP technology, you need to get the optional Technology Package—essentially the icing on what’s already the top Grand Touring models.

Those Mazdas don’t even have engine start-stop; to enable that would require some component upgrades—and possibly that larger ultracapacitor.

Is that $200 well spent on a single component, where every little bit counts in putting together a new vehicle? We tend to think so. But it’s a matter of priorities, for sure, and we’ll soon see whether it’s the 2-3 years that supplier anticipates...or yet another decade being the next big thing.


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