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Valeo Developing Supercapacitor-Based Energy Storage for Regenerative Braking with StARS

Configuration of the StARS + X system with start-stop and regenerative braking. Click to enlarge.

Valeo is developing a supercapacitor-based extension to its award-winning StARS stop-start system (earlier post) to support regenerative braking and thus enable a greater reduction in fuel consumption than is possible with the stop-start system alone.

By itself, the start-stop system delivers a reduction in fuel consumption of 4-5% (although Valeo has measured reductions of up to 25% in real-world testing in congested traffic in Paris). The new StARS + X system with regenerative braking can deliver a 10-15% reduction, according to Valeo.

The StARS + X system uses a slightly different architecture with different motor for starting and regen, and support for voltage between 14V and 30V. The floating voltage enables extended torque for diesel or large engine cold cranking, 4 kW generation for regenerative braking and extra power supplies for peak loads.

Valeo is working with multiple supercapacitor technologies with capacitance values of 200 farads with nominal voltage between 20V and 30V, depending upon the technology. The company is using different size powerpacks—12-, 10- and 6-cell—to support a range of powertrains and internal space constraints.

The powerpacks must last for the lifetime of the vehicle, deliver reliability in the harsh thermal environment created by being close to the engine, and be safe and environmentally friendly. Valeo is specifying 600,000 stop-starts, 1 million regeneration events, and 200,000 boost events for the system.

Testing in partnership with INRETS (French National Institute for Transport and Safety Research) on the new systems is currently underway. The main goal of the current testing is to observe the failure of the cells.



Out of such small steps shall European cars hit 130 gms Co2 / km.
If people can afford them.


These smaller s-caps will provide the needed buffering for surge demands until supercap/battery integration is fully functional. Another good transitional technology and our hats are off to the international effort.

Rafael Seidl

The beauty of electricity is that the UC banks do not in fact need to be under the bonnet at all. They can be squirreled away underneath the passenger seats.

Valeo's approach looks sound: start with microhybrids and work your way up, keeping a close eye on the price-performance ratio. In terms of fleet average fuel economy/CO2 emissions, it's much more effective to deploy this type of system in millions of cars than to bring just a few hundred thousand fully hybrids to market.

An important aspect for the European market is that microhybrid systems are pretty much the only ones that car makers can afford to mate with diesel engines, especially in cars designed to be city runabouts.

The ultracaps, possibly in combination with combustion-assisted "direct start" technology, should deliver very smooth and efficient restarts of the engine. It should also deliver some extra torque to a manual transmission in first gear, something otherwise only available with a less efficient and expensive AT.


This system sounds like an excellent step forward, unless it is only used to boost acceleration power and therefore not add much to fuel economy. I hear the Lexus SUV hybrid is basically a power booster, not a gas saver. A puny motor saves gas only because you can't stomp on the gas any more than it already is usually (I owned a 2 cyl honda ...around 45mpg in 1988) Stands to reason that a regular sized motor and electric power boost would equal be used for nitrious like power boosting.


Stan Peterson


I agree with your comments about micro-hybrids appearing on millions of vehicles is something to be desired, especially while the full hybrids still have a price component disadvantage.

Another beneficial side effect is that the widespread adoption of stop-start systems and regenerative braking systems will drive the cost of hybrid and full hybrid componentry down by manufacturing volume efficiency.

That will bring the day closer when full hybrids will no longer suffer a sales price disadvantage.

I never understood why micro-hybrids were so derided when they first appeared in limited numbers.

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