[clett]

Todays capacitors are almost the ideal energy back-up system for hybrid-electric vehicles. They are capable of enormous power outputs (and inputs) making them ideal for capturing large amounts of regenerative energy. They are also very safe, but most significantly in terms of car lifespan, economics and consumer confidence, they can be charged and discharged from 0 to 100% and back again for millions of cycles without appreciable degradation.

In fact, to date the only problem has been that capacitors do not store nearly as much total energy as chemical batteries. By way of example, the NiMH pack in the Prius can contain about 46Wh per kilogram of battery mass, while the best ultracapacitors, until recently, were only about 6Wh/kg.

But a company in Japan has just announced that they may have finally cracked this last stumbling block in ultracapacitor technology. They claim that their new capacitors have energy densities from 30 to 75 Wh/kg! :shock:

http://www.jeol.co.jp/english/newsroom/2003/031003.htm
http://www.okamura-lab.com/ultracapacitor/ecsnews2Eng.htm


What could this mean for future hybrids?
The pack in the '03 Prius contains about 1.8kWh of energy, but as the computer limits the available state of charge from between ~60% minimum and 80% maximum (to extend battery life), this means that only 360Wh of energy is actually available.

This much energy (360Wh) could be stored in only 6kg of JEOL's new ultracapcitors! That could be easily placed under the front bonnet, freeing up room from where the larger NiMH battery pack was. As they claim to make these ultracapacitors from "aluminium and coal", there is even the possibility that these capacitors may end up relatively inexpensive.

The 30Wh/kg version has a power output of 8kW per kg! :shock: You could get an extra 200bhp of shove with just an 18kg capacitor!


Fingers crossed everyone....

 

[RSnyder]

IIRC, cost was another issue vs. batteries. Any breakthrough there?
There was also the issue of overnight storage, though I suppose a conventional 12 volt battery+starter could be used (eewww!).

It's great that the goals of hybrids are now widely accepted and we're into the phase of figuring out how best to reach them.

 

[clett]

IIRC, cost was another issue vs. batteries. Any breakthrough there?

The guy who develops them says on his website that there is in principle no reason why capacitors should be any more expensive to make than batteries - the process and materials are similar. The reason they are so expensive right now he says is because of the extremely low volume almost bespoke nature of the products. With decent manufacturing volumes he reckons they will come down to a cost similar to that of batteries. At the equivalent of todays NiMH prices, therefore, a 6kg pack for the Prius could cost as little as $160! That could really get hybrids moving.

PS the earlier version of this capacitor is already in use in a commercially available hybrid - a Nissan diesel truck, and they claim improvements in fuel economy of 50%!

 

[efusco]

Interesting post Clett...thanks for the info. It'll be interesting to see if the 3rd generation Prius will incorporate this. Personally, I'd like to see a 25kg or so capacitor and be able to fully use it's potential.

 

[Guest]

As far as I know (but I'm very probably not as well informed as you, Clett), ultracapacitors suffer also from a relatively fast self-discharge rate : they can deliver huge power when necessary but don't keep energy as long as batteries do. In other words, they don't work on the same timescale. I'd bet future hybrids will include both ultracapacitors and batteries, the former being good for storing or delivering bursts of power and the latter for long-term storage and relatively low power supply. Kind of a new synergy... 8)

I think I've read somewhere that Toyota already had some patents about using ultracapacitors for hybrids... am I right ?

 

[frenchie]

sorry... the "guest" above, is just me :wink:

Fran�is

 

[clett]

Hi Frenchie! I was concerned about this too, but there is an interesting interview with the Senior Vice President of Maxwell Technologies, another ultracap company, who says that their capacitors, if you leave them on the shelf at full voltage will take a whole 45 days to discharge to half-voltage! That's some advance on the traditional 24hrs expected of normal capacitors and not far off some types of NiMH. Not sure if the JEOL's would be the same. Another interesting point from the interview is how much interest GM are taking in their products, suggesting that there may soon be mild-hybrid cars from GM using ultracaps.

But as you say, I also think that future hybrids will have both a large storage battery and an ultracapacitor. In fact, Solectria did an experiment on one of their electric cars like this, just using the ultracapacitor to capture more energy on the regen and to buffer against enormous changes in current drain from the battery. Just by adding the ultracap they got 30% better range from the same battery! They also claim that the ultracap allows the battery to last much longer as it's much less stressed.

8)

 

[clett]

I think I've read somewhere that Toyota already had some patents about using ultracapacitors for hybrids... am I right ?

Not heard this - but the original Insight was always going to be ultracap driven, until the last minute when they switched to NiMH. Honda were also seriously considering ultracaps for the new NSX hybrid, on the basis of the stupid power outputs possible, but scrapped it again at the last minute. I think the only ultracap powered vehicle on sale and on the road today is the Nissan diesel hybrid truck, which gets 50% (alledgedly) improved fuel economy.

 

[clett]

Ultracapacitor news update

Just read that 4 companies are getting together to put ultra-caps into production! By starting with large scale production, they hope to be able to compete with NiMH on a cost basis. Amazingly, they're claiming to be able to sell 40Wh/kg caps by the end of this year, and 60Wh/kg caps by 2005!

As I've said before, if Toyota replaced the NiMH pack in the Prius with these, the pack would be more or less immortal (ie millions of discharges with no degradation) thereby allaying all concerns of potential buyers over battery lifespan. At the same time, because ultracaps can charge and discharge so quickly, it would allow much more energy to be captured on the regen thereby improving economy while simultaneously allowing battery pack outputs of up to 150bhp (would knock a fair bit off the 0-60!)

They've also finally published technical details of how they've managed to make their ultracaps so much better than the opposition:


(taken from website)

There are two types of ECaSS, each based on a different technology.

(1)Activated carbon capacitor (porous carbon type, energy density:6-12Wh/kg)
Fine pores, which absorb the electrically charged ions, are formed on the electrode of the activated carbon capacitor by breaking down the carbon at high temperature. The activated carbon capacitor is characterized by high output density, but there is a limit to the increase of energy density due to the inability of some of the fine pores formed during the production of the electrode to contribute to the capacity. However, the technology is complete, and focus is being placed on mass production of this type in hopes of spreading its use.

(2)Nanogate capacitor (non-porous carbon, energy density:20-60Wh/kg)
The electrode of the nanogate capacitor is formed by making pores in the carbon with the ions themselves in the electrolyte solution. A nanogate capacitor is different from an activated carbon capacitor and is characterized by the fact that the ions form the fine pores themselves, and thus the pores unable to contribute to the capacity are not formed. Furthermore, it is possible to form the fine pores that perfectly match the ion size, to obtain higher energy density. However, because an advanced level of technology is necessary for the production of the electrodes, focus is being placed on further improvement of energy density and technical development for the purpose of mass commercialization.

8)