Ultracapacitor EV

Ultracapacitor EV

I am trying to crunch the numbers needed to make a super(ultra) capacitor based EV commercially feasible.
Take for example the Model S:
1. For a battery with 85 kWh capacity, it can run a 2.1 ton car for 300 miles.
2. Assuming the specific energy of the Panasonic cells as around 240-260 Wh/kg, the battery weighs approx 700 lb (320 kg) excluding the battery management.
3. The best UCs (Graphene-based) achieved around 85 Wh/kg under laboratory conditions. At this rate, a 85 kWh source for Model-S weighs about 2100 lb (950kg) i.e. making the car 30 % heavier and affecting the range by say 80 miles.
4. As the UCs have high power density, the power electronics can be adjusted to maintain the same performance.
5. The UCs charge extremely fast. Hence, a nationwide network of superchargers can gain further momentum as charging can be dropped to a fraction of the current time. You need not have lunch everytime you charge, listening to a song would suffice :)

As specific energy doesn't seem to be much of a problem, benchmark for UCs must be based on volumetric energy density (Wh/L). What should be the vol. energy density for UCs to get adapted in EVs?

The above analysis has been simplified just to get an idea of the order of magnitude and not the exact values of such technologies. There has been significant improvements in mass production of Graphene and if it can replace silicon in semiconductors, the price would drop even further.

Brian H | 18 January 2013

Start with a truck. Capacitors are BIG. They are lightweight, and take up a lot of volume. Try energy density per cubic meter and see how far you get.

Bellboyrsa | 21 January 2013

Ok people, here goes my 2 c. Maybe I'm stupid, maybe I don't know anything at all but this is what may train of thoughts is... so bear with me and correct me if and where I'm wrong... No problems if people points out dumb thinking processess to me but please refrain from chewing me out or shoot me to pieces etc. I don't like to fight...

Why do we need 85kWh worth of battery power? for the distance correct? The one limitation of quick charging is what the battery can handle. According to what I've picked up on the web this is a total different ball game with supercaps or ultracaps. They can handle massive volumes of charges within seconds but they also due to leakage looses quite a bit of it over a period of time.

This means that while we put back energy into the system by charging with regenerative breaks, the batteries can not handle al the current delivered to it. On the other hand, caps can handle much more than batteries. This results in a battery normally charged for 10 secs allows for more or less 10 secs worth of usage, while a ultra cap after 10 secs of charge allows for about 2 mins worth of usage of the same apparatus.
So by replacing more than 50% of the battery storage with about 20% , ultracaps.40 kWh of battery power combined with about 20kWH supercaps will result in a car with more or less the same weight but do tue bigger current handelig abilities, will allow this car to go maybe as far previously or even further.
With the correct electronics between cap and battery all the energy of regen breaking is caught up in the caps and then eficient been charged into the baterries

Brian H | 21 January 2013

A small buffer would serve to smooth out the spikes, but the 40kWh of supercaps would take as much volume as the whole 85kWh of battery does now, or more. Caps are big and light by comparison to batteries.

ChicagoBob123 | 22 January 2013

I am a software engineer and love cars. I have so many ideas and hopes for the future but understand the engineering limitations that currently exist and the struggle to get new ideas onto the market.
That said if the car is designed to have a shelf under the entire center of the car from front to back you can store quite a few super capacitors in there. This would mean a slighty different look and you would take on more wind drag but after seeing the volts roller skate body I think just raising the passenger compartment up and storing the capacitors underneath it can give you all the storage you need for the caps.

BUT the COST thing comes into play.

Everytime I see an EV and its limited range and expense I shrug my shoulders and move on to see if there is something I can afford.

That is why I hope this post finds someone at Tesla, who seems to have some brass, to do a 4 or 2 cylinder gas electric car using supercaps for accelerations and the engine to maintain current velocity. Using current software tracking of each wheel I think the engine can be used as an efficent generator running at its optimum level, making it more efficent than throttling. Using electric motors in each wheel and some feedback software when the driver wants to accelerate they can call on the stored power from a much smaller and light weight supercapactitor bank.
In my imagination if you used a 2 cylynder light weight low HP (under 50) engine and were constantly throttling it should make it quite a gas saver and much cheaper than a straight up EV. Cheap enough so a regular middle class person can afford it.
As far as batteries have come they are still not an optimum auto
energy source.
They are heavy and not perfect for instant energy discharge or quick charge.
They are not meant to be constantly charged and discharged while caps are perfect for this.
Caps also excell at delivering instant power and quick to charge with regenerative breaking.
I would love to hear from a mechanical engineer or someone at Tesla to tell me why this should be be done. Seems like a no brainer to me but takes someone with resources to create.

ChicagoBob123 | 22 January 2013

Slight correction this should have read..
In my imagination if you used a 2 cylynder light weight low HP (under 50) engine and were NOT constantly throttling it should make it quite a gas saver and much cheaper than a straight up EV.

Brian H | 22 January 2013

You've added at least 3 layers of complexity, and are still burning gas.

Vawlkus | 23 January 2013

Elon's already said that while he's CEO no Tesla will burn gas, which is how it should be IMHO.

Throw this GM or Fisker's way, it seems to run on the road they've picked.

MrB | 24 January 2013

The only way I could see UCs work is if there was a nationwide Ultracharger (UC for ultra cap cars) network of > 1000kw chargers, as in one at every gas station in the country, and cars had say 40 kw Ultracaps and you could charge them in about 3 1/2 minutes.

That said as far as complaints about battery and breaking regen in this thread, you obviously need to go test drive a Model S. My P85 will regen 60kW when off the throttle at highway speeds, and put out 310kW at full throttle, charging at a supercharger at close to 200kW. 60kW is more than enough breaking for anything but emergency stops and for those you want to use the real breaks anyway.

Brian H | 26 January 2013


1 MW chargers require serious hardware. Not human-operable.

Benz | 29 January 2013

Let's wait and see what kind of technology we have at our disposal in 2020. This is just future talk.

The fact that we have the 85 kWh battery, that allows us to have a range of 480 km sounds already very exciting to me. Because it's the reality of today. And add the technology of the Superchargers (solar powered) to that. Then it becomes even better.

I think that some people within the oil and car industry are slowly starting to get nervous. Regarding as to what extent this Tesla technology can lead to.

PRB | 5 February 2013

In the October 1, 2012 Popular Mechanics Breakthru Awards interview with Elon Musk, Mr. Musk mentioned super capacitors, and stated he was aware of a company in Silicon Valley that is working towards a solid state super capacitor, that the company is not EEStor, a stealth capacitor start up in Cedar Park Texas.

That was about 4 months ago. Last Month, on January 28, 2013, EEStor issued a press release that claims heretofore unheard of energy density in a capacitor from a pilot production line, not a lab sample.

Here is a link to the press release.

Super capacitor technology is not ready for prime time as the primary energy storage device, but are certainly ready to capture regenerative braking energy and act as a buffer between regenerative capture and lithium ion batteries. Moreover, they can be used for high energy bursts for quick acceleration rather than stressing the battery pack. Seems likely that battery pack cooling systems would need to be less robust with a few supercaps, and perhaps they are only a few years away now.

Would be nice to have confirmation that Tesla Motors is aware of the EEStor press release.

Benz | 5 February 2013

If I click on the link then I see
"Sorry the page you are looking for cannot be found".

eadolphe | 5 February 2013

EESTOR is not new. Been following them for a while now (since the initial announcements and the incubation phase in Texas). Their primary investor has been Zenn Motors ( There has been a LOT of promises about this technology. If they are able to work out the many technical hurdles, it would be a significant breakthrough (think about charging your EV for 10 minutes and getting a 200 mile range). There are a LOT of hurdles to overcome.

Benz | 6 February 2013

Is this possible in the near future (before 2020)? Or is 2040 more likely?

MRTova | 6 February 2013

Try this link for the January 28, 2013, EEStor PR:

I have been following this story for six years, now. It has been a long slog, but I can say with some confidence that it is most assuredly not a scam.

PRB | 6 February 2013

It is hard to predict if or when the technology will be available for the automotive market. Tyler Hamilton is a technology writer and has a weekly column in the Toronto Star. He has been been following the story since 2006 and posted a column on Feb 1st.

You can visit ( and search for "eestor" to find the press release. Likewise, visit ( and search for "tyler hamilton eestor" and choose the link written on February 1, 2013, or maybe this link will work for you.


If the links don't work, copy and paste into your browser. :)

Mr. Musk is very interested and also uniquely qualified to assess the technology. In fact, he attended Stanford and was part of a team working towards high energy density solid state capacitors in the mid 1990's.

High energy and power density solid state capacitors with low leakage are the holy grail for energy storage. If EEStor delivers, it is a game changer. I sure hope they succeed. If they do, Tesla Motors will be beating a path to Zenn Motors, as Zenn holds exclusive rights to the technology for automobiles.

Brian H | 6 February 2013

Well, the secret of running a good scam is to convince lots of people you're not running a scam.

Timo | 6 February 2013

Brian H +1

EEStor has been promising this "coming soon" for about decade now, seemingly being on verge of breakthrough all of time. That raises whole lot of red flags in my mind.

pilotSteve | 7 February 2013

I was at a financial conference and heard the CEO of Maxwell Technology (a San Diego based ultra capacitor company) speak. Some thoughts from my notes:

(1) think of batteries as a Teapot, and UltraCaps as a Tea Cup. You can only fill/empty the teapot at the rate possible by its spout. The Tea Cup however can be emptied/filled very fast.

(2) UltraCaps are unaffected by charge/discharge cycles and have a much greater operating temperature range. Thats because they store energy in electrostatic rather than electrochemical form.

(3) UltraCaps hold up to 50% of their energy for 30 days, and a single 3000 farad 2.7V UltraCap is about the size of a Coke can. As BrianH noted the weight is much less hence the energy density is low.

(4) ideal application is to pair UltraCaps with Batteries. Lets the UltraCaps absorb/provide the big currents need for acceleration and regeneration and the battery supply the steady state 'cruising' load. Maxwell has shown a DOUBLE of service lifetime in a combined battery/UltraCap solution.

(5) the UltraCap 'protects' the expensive battery from high charge/discharge rates ("power") but the battery provides the kWh need for range ("energy").

They have over 500k units installed in the field with varying applications such as wind turbines, busses and truck batteries. Very interesting technology that I imagine Tesla could include in the future.

Tiebreaker | 8 February 2013

Motor connected to
Ultra Caps <--> Li-Ion battery <--> Li-Air battery
<--- high discharge . . . . . . . high storage --->

When physical volume and economics allow, probably sealed in the same pack. Advanced management needed.... or maybe never, keeping the KISS principle...

Brian H | 8 February 2013

You mean Keep It Sophisticated, Sylvester? ;) :D

SD Supercharger | 8 February 2013

pilot Steve-
+1 nice analysis for us non-engineers. Looks like a combination strategy might work in the near future but I would not want to be in charge of developing the management system.

frmercado | 8 February 2013

Take a look at this technology.

Benz | 9 February 2013

@ polotSteve

That sounds great to me, but wouldn't it be very complicated to build/manufacture/engineer something like that?

pilotSteve | 10 February 2013

Maxwell current sells a battery (lead acid I believe) co-developed with Exide with internal UltraCaps for commercial trucks that does exactly this. They have hundreds of thousands of units installed and have documented 2x life improvement in fleet battery life.

I think Tesla did it exactly right for the Model-S with their temperature managed pack, but I think its likely future batteries will include UltraCaps in some quantity because the life improvements make such compelling economics.

All this is part of the 8%/year compound improvement in battery cost/life/weight/capacity and everybody is factoring in for future pricing and product specs.

Its going to be exciting!

Benz | 11 February 2013

@ pilotSteve

"I think its likely future batteries will include UltraCaps in some quantity"

Do you think that will be before 2020, or after 2020?

Brian H | 11 February 2013

As a buffer, you don't need much.

GuildfordPete | 1 May 2013

Hi all,

I work in the supercap development field and would like to wade in.

1 - In order to swell their group's chances of getting funding a lot of papers quote the carbon-loading performance, not the gravimetric (i.e. cell) performance. Given carbon's quite light you can usually divide cell-loading performance by 5-10 to get actual cell performance. Best I've seen is 12Wh/kg ~ 10KW/kg.

2 - The group that got 80 ish wh/kg used horrifically expensive ionic liquids as electrolyte and low graphene density, all this makes for good papers, but lousy products.

3 - EESTOR = full of ****.

4 - Yes supercaps can handle simple epic amounts of current, we run 60C - 100C charging as part of our standard analytical step. Whilst supercaps might fall down on storage they more then make up for the ability to regen brake charge (pretty much any scenario you can think of).

5 - Unless someone comes up with a cost effective, high ESW low viscosity electrolyte then I'm afraid it's progressive improvement rather then giant leaps for now!


Scott Rankine | 2 May 2013

I thought I would chime in on this as I've not only been following the story of super caps closely for many years but have had discussions with officials at the DOE and senior DC politicians on both side of the aisle about the the issue of solid state versus chemical energy storage.

Suffice to say that a fully scalable high voltage, high capacity solid state electrical storage device with rapid recharging, low energy dissipation (leakage) and energy density equal to that of petroleum would be a total game changer. This would be similar to the quantum jump from vacuum tubes to transistors. This is the type of breakthrough that's desperately needed but hard to predict in terms of timelines.

Such a development would mark the end of the Carbon Age and make all forms of terrestrial propulsion electric based in short order. It would also lead to the development of a truly smart grid characterized by a decentralized storage infrastructure with electrical dispatching. Coupled with high efficiency solar generation it would make RE far more cost effective than any fossil fuel.

So lets hope the bright sparks out there who are working on this technology nail it and soon. Cheers

ober_the_top | 25 February 2014

Long time no updates here...

I personally think that we should recover this topic as the giga factory could actually make ultra cap development again a focus area....

@ PilotSteve: We have been on the same conference, I participated this year again... I think technology is already much further then publicly discussed.

If Tesla is ramping um production efforts, I am sure that they have some little updates for their packs (2015 onwards). They could otherwise just get Panasonic and Samsung to scale their production further (as Panasonic did in Japan from Jan 2014). But I think they are working already on the 2nd gen of their packs. May be already used for the X (but more unlikely).

Would not be surprised to see Maxwell as a partner for the factory. btw. they have already production capacities in San Diego.

Brian H | 25 February 2014

Maybe a small one would be useful for surges. But with a large battery the power density is generally sufficient, and that's most of what supercaps offer. At the expense of much volume.

huzz1970 | 25 February 2014

I think some type of U/C will be adopted in the future to handle the jackrabbit starts, and possibly recapturing a bit more of the regenerated energy, but I do not think they will drive the car for long distances. There is an important point about the capacitors- yes they can charge and discharge at high rates, BUT, the voltage drops as the charge is removed from the capacitor. In EE terms, capacitance*voltage = charge. Current is charge/time. So, if you pull current, the voltage must drop by a proportional amount since the capacitance is fixed by the construction of the capacitor.
A capacitor's size (actually overall volume) is proportional to the maximum voltage that it can handle. The super-caps tend to be on the lower end of the voltage range so the size remains manageable. I have a one Farad capacitor in my watch- a HUGE amount of capacitance, but at only 1 volt. The higher the voltage, the farther apart the internal electrode plates must be placed (for a given dielectric material), and thus the larger the capacitor dimensions. The larger the charge you want to store, the larger the capacitor plate area, and so on. So to directly use a capacitor of any type, you will need some type of active control to either switch capacitor elements to maintain the output voltage or drive the capacitor through some type of voltage convertor/step up. This requires power. Maybe in a good circuit you get about 90+% efficiency (maybe a bit more at about 50% power draw, and lower at lower draw, and a bit lower at high draw due to heating). So the real question is more weight, more complexity, more losses, and switching high voltages and currents quickly (not easy), versus just increasing the battery size with the additional dead weight? Interesting discussion.

grega | 25 February 2014

I had assumed the ultra capacitors would turn up in Hydrogen Fuel Cell cars. The Fuel Cell would produce 30kW, for sustained 70mph driving, but to get the fast starts & regenerate power they'd have an ultra capacitor.

But I believe I was wrong. They seem to be talking about 80kW HFC cars, it's the figure that comes up often. Seems a waste to me - but maybe using UC or even regular batteries is not entering into the manufacturers mindsets (though I hope they're using regenerative braking!!).

Theoretically a partnership between fast charge/discharge and slower charge/discharge would work better... but I suspect that Tesla really wants to charge their cars very quickly, and in creating that battery technology they can also access their battery power easily.

ober_the_top | 28 February 2014

May be Maxwell is soon a subsidiary of Tesla Motors? A few years of development and the pack could be at 2.0... crazy? May be... just wondering why they are starting like a rocket...

Just a thought and a too perfect fit - but no fundamental information on that

What are your thoughts on this?

grega | 28 February 2014

I'm sure tesla will be at the forefront of energy storage technology.

Is this particular development streets ahead of others? | 29 April 2015

Yup, battery and cap are 2 different things. With ultracap, there got to be different way to skin the cat.

How about wireless charger under every road. It takes 10s to charge up a ultracap, cars usually spend much longer time in front of red light.

With this appoach, ev only need to store 5 miles worth of electricity instead of 300 miles. There is no volume issue. Production cost will be much lower.

Tesla's current model is not the future of EV for sure!!!! It can't be. If battery last for a day, many drivers will just charge their cars at home at night. There arn't many choices to get reliable electricity at night for the most part of the world.....coal plant or expensive energy storage.

If we are able to do high speed wireless charging using ultracap. We charge EV while we are using them. For most of us, we use them during the day. Yes, that's when we have sun light. THat's why we have SolarCity.

Brian H | 29 April 2015

That's why depending on renewables is goofy. And blocking economical conventional power is deadly for most of the planet.

Watt fun | 29 April 2015

I always understood that supercaps excelled in high demand, either acceleration or fast regen, whereas batteries excelled at steady demand as in ideal steady speed cruising, to put them both in the context of a car.

Something not specifically a Tesla, with a still sizable battery pack and a smaller front motor for efficient cruising, and a larger rear motor primarily using supercaps in the rear 1/4 of the battery storage area and primarily for acceleration from stop and passing might be the way to go eventually. Of course, supercaps with 'on the fly' or stationary (at lights) induction 10 seconds at a time top ups if required would be interesting as a partial range enhancement when 'batteries' don't have to deal with inertia.

How possible it all is, or realistic, is beyond me, but the concept sounds a bit promising. It might be a way for 'less compelling to drive' cars might creep up to the 200 mile range club, by separating cruise and acceleration functions into the most effective source for each. I'm thinking of Leaf-like cars in particular.

grega | 29 April 2015

Tesla has done very well with big batteries - it provides the power output to get the great acceleration, it allows better regen braking, it adds weight (to the base) which enables traction (and reduces lean etc). Oh, and it gives greater range of course.

They've done smart things, and probably have enough performance to not need a capacitor to boost it further.

I do think that capacitors acting as buffers would allow for some massive acceleration as well as high regen-through-braking, and allow it for lower battery sizes (and for big batteries when running low, which Teslas experience). It would also mean the battery itself is never charged by braking, that goes into the capacitor and gets used again shortly after, which may help battery life.

Above I said that I'd thought Hydrogen fuel cells would do something similar - a SMALLER hydrogen fuel cell while the rest of the car is an EV, and capacitors allow for the high performance. But they're not doing that. Similarly a BMW i3 could have better performance at any charge, but especially when the battery is low and a range extender is being used to keep it going.

So a capacitor seems most useful to me when the battery it is partnered with is smaller, for whatever reason. If some regular cars were altered to use a low power engine and a small battery with a super capacitor and electric motors to get maximum performance, I imagine it'd perform very well. And even though it would still be a petrol car, it'd shift the focus and interest to the electric side too, for this specific audience who don't care about electric, and prepare them for all electric.

Timo | 30 April 2015

Capacitors are large, very large compared to batteries.

If you just decelerate from 60mph to zero and capture 60% of that energy in capacitors you would need 3kWh worth of capacitors. That's using cutting edge ultracapacitors of 10Wh/liter would be 300liter capacitor. In that same space you can fit Model S entire battery pack with plenty of room left.

grega | 30 April 2015

Slightly off topic. .... Does it use 5kWh to get from 0-60Mph?

Seems way too high to me.... But I haven't even vaguely considered the math yet.

DTsea | 30 April 2015

Kinetic energy of 5000 lb car is about 800 kJ or about .23 kWh.

grega | 30 April 2015

Yeah that sounds right DTsea.

I came at it from a different angle. The P85D has 515kW motors. If it could run for an hour at that it'd use 515kWh :). We know it gets to 60mph in 3 seconds. To simplify we'll say it uses all that power, and has no inefficiencies, for 3 seconds (which are not correct assumptions). So 3 seconds instead of 3600 seconds would use 0.43kWh.

I would say that a well managed 0.6kWh capacitor could handle the peak power for acceleration and braking without any trouble. The volume required presently is still an issue.

Brian H | 30 April 2015

Elon reluctantly gave up the idea of using supercaps because a sufficiently large battery achieved the same result without the limitations.

Timo | 3 May 2015

hm, I apparently made some punctuation error somewhere. It did feel like high to me, but I trusted that I calc it right.

1/2mv^2 is formula of kinetic energy.

2650 lbs car at 60mph = 1202kg and ...OK here was my error, I used km/h when I should have used m/s 26.8224 m/s. Stupid mistake.

1/2 * 1202kg * 26.8224 m/s ^2 ~= 432384 kg*m^2/s^2 or joules = 0.1201 kWh.

60% of that is 0.07206 rounded to 72Wh 10Wh/l means 7.2 Liters. Still quite large lump of capacitors just to capture one regen from 60mph.