Nissan Diesel hybrid boosts fuel economy 50% with new capacitor technology

Diesel Fuel News, Feb 3, 2003 by Jack Peckham

Unlike Toyota, Honda or other hybrid-electric cars coming on to the market, Nissan Diesel aims to employ a unique capacitor technology that avoids the very high cost of replacing batteries.

The so-called "SuperPower" capacitor "is expected to provide service for 600,000 kilometers over a 10-year period without replacement," unlike lead-acid batteries that would have to be swapped out at least three times over the same period.

The new technology not only boosts city-drive-cycle fuel economy by about 50%, but also reduces emissions by slashing engine load during acceleration. This could especially aid engine/automaker strategic designs to cut nitrogen oxides (NOx) and particulate matter (PM) to meet upcoming world-wide limits for certain vehicles.

Nickel-based batteries -- a more durable but much more expensive alternative to lead-acid -- have yet to prove their full useful lives in commercial experience. Both Toyota and Honda are using the nickel-based batteries for their mild-hybrids, whereas GM is planning to use cheaper lead-acid batteries because of very high warranty costs for replacing nickel batteries (see Diesel Fuel News 1/20/03, p14).

Until now, capacitors weren't practical for automotive applications because of their relatively low energy density. But breakthrough technology jointly developed by W.L. Gore ("Excellerator" electrode assemblies), Nissan Diesel and Okamura Laboratory doubles energy storage and regeneration, compared to prior capacitors.

The so-called electro-chemical double-layer capacitor (EDLC) technology is "particularly suited for typical city driving conditions, where constant acceleration and deceleration are the norm," according to W.L. Gore.

Like all other hybrids, the Nissan Diesel vehicles will cost a lot more to produce than conventional internal-combustion engine (ICE) vehicles. The new Nissan hybrid (four-to-eight-ton delivery truck) costs about twice as much to produce as a conventional ICE diesel -- even including Japanese government subsidies, explains Gore Capacitor group specialist Robert Sassa.

In future, technology performance upgrades and package-size reduction will be required to slash these costs to a level closer to ICE technology, although ICE always will be simpler and thus cheaper technology, Sassa told us.

Hybrid costs probably should come down by around 2008, he said. If cost-reductions are combined with more government incentives or tougher emissions limits, then it's more likely that robust sales of such vehicles can become feasible. Until then, automakers will sharply restrict hybrid output in order to limit marketplace losses, Sassa predicts.

* Capacitor rationale

Capacitors not only deliver unlimited charge/discharge cycles (unlike batteries), but offer dramatic weight savings (one-third the weight of batteries) and much greater instantaneous power.

The latest EDLC technology delivers tens or hundreds of seconds of power for acceleration, and only requires a few seconds of braking to recharge, unlike conventional batteries. In contrast, batteries take hours to discharge power, but frequent regeneration and discharge means greatly reduced battery life.

Capacitors also don't face hazardous material recycling/disposal issues as with lead-acid or nickel, both of which are toxic materials.

Only months ago, about a half-dozen capacitor units were installed at passenger train stations in Europe, Sassa said. These special trains discharge deceleration energy into the stationary units at stations, then re-tap the capacitor energy for acceleration upon leaving the station. Such technology conceivably could be employed in many other passenger train lines in relatively frequent stop-and-go service.