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Tuesday, October 03, 2006


I happened across an interesting post on the promise of ultracapacitor startup EEstor at Ezra Klein's site. Guest poster John raises a few interesting questions and a commenter gets the last word in. The latter reminds us that 1/2 the energy stored in a capacitor eventually gets wasted. I rolled this assertion around in my head for a bit and essentially come to the same conclusion. If you consider that any power source has an internal resistance (R1=r) that must eventually get balanced by an external resistive sink (R2=R), the most efficient power transfer occurs when r=R.


dP/dR = 0 when r=R
Reduce r and you have to reduce R to get the current up. Increase r and you have to increase R to generate a significant voltage drop. And since equal amounts of power get consumed internally and externally when r=R, only 1/2 becomes usable for an application.

The same principle follows from audio amplifiers having an internal impedance designed to match that of your typical speaker (8 ohms). Half the power gets lost as heat emanating from your amplifier.

Another reminder that energy storage devices by themselves do not save us from dealing with the real issue at hand:
But these are all forms of energy storage, not sources of energy on their own. The primary form of energy for the United States would still, even if every car had one of these EEStor capacitors in it, still be coal and oil. (We could use a lot less, but still.) The objective still has to be reducing the amount of oil we use to avoid Peak Oil (whenever it happens, better to prepare early.) Quite aside from Peak Oil, climate change requires that we stop using fossil carbon altogether. Storage technologies, exciting as they are, are not by themselves the answer.

Update: The anonymous commenter has a good point, but consider that big-money military rail gun development and other directed energy weapons has predominantly funded the development of ultracapacitors. Here, and in other applications (like the Tesla Roadster racing) where you need huge amounts of instantaneous power, power extraction efficiency remains important. All those fast discharge losses add up. But I'm happy to see designs get above 80% efficiency (charge+discharge). I have to admit that I must have retained little from the switching power supply class I took in grad school circa 1986.



Professor Anonymous Anonymous said...

No, no, no. This is the 21st century.

You will charge and discharge the capacitor through a switching power supply - the same as you would charge and discharge the battery in a notebook computer. Since the capacitor voltage is not constant, the supply characteristics are slightly different, but good circuitry should get you at least 90% efficiency in and out (=81% overall). Of course, that's on top of losses in the capacitor or battery. We hope those are fairly modest, or the technology isn't worth talking about.

The most efficient power transfer idea was necessary for vacuum tube amplifiers, which have many problematical electrical characteristics. Audio amplifiers these days often have an impedance of a fraction of an ohm, and speaker impedance is usually mostly simply a matter of electrical loading (the lower the impedance the more power it draws, and some amount is too much.)

Generally load resistances are much higher than internal impedances, these days. Typical ultracapacitors that you can go out and buy will discharge in a few seconds if you match their internal impedance. This is unnecessary and possibly dangerous; you usually intend to discharge an energy storage device much more slowly than that.

Now, as to whether EEStor is for real, that's another matter. Technologies like this are often sold in small sizes first, because there is a large market for energy storage in all sorts of infrastructure applications. (Things like sodium sulfur batteries that can't easily be built small are exceptions fof course.) That seems not to be happening with EEStor. Could be business strategy, could also be the technology is simply not very practical yet, or is not as good as it seemed at first.

4:52 PM  
Professor Blogger step back said...

The 1/2 lost concept comes from a physics book problem: You have 2 identical capacitors, one charged (say to 10 volts) and the other not charged. The initial energy in cap#1 is 1/2 CV^2. Let's pretend C=2 so that E=100. You hook the two caps in parallel. Voltage balances out and you end up with 5 volts across each. The enrgy in each is now v^2=25. 25 plus 25 is a total of 50. You started out with 100 energy units. Now you only have 50 stored. Where did the other 50 disappear to?

6:50 PM  
Professor Blogger WHT said...

This site goes into all the details,

And how about this stupid brain teaser:

" Clive (Max) Maxfield
EE Times
(07/10/2006 10:00 AM EDT)

Some of these were old chestnuts, such as the perennial "Splitting a bill into three parts," which appears in many forms. For example:

Three couples check into a hotel late one night. The manager charges each couple $10 to stay the night. They all pay in cash. Sometime later, the manager realizes he's made a mistake and the couples were overcharged, so he gives the bellboy five $1 bills to distribute between the couples.

The bellboy realizes that it will be hard to split $5 three ways; so he decides to give each of the couples $1 and keep the remaining $2 for himself.

The conundrum is this; the couples each ended up paying $9 to stay at the hotel (their original $10 less the $1 returned by the bellboy). Now, $9 x 3 = $27, plus the $2 the bellboy has in his pocket = $29. But the couples originally paid $10 each, and $10 x 3 = $30. So what happened to the other dollar?

7:28 PM  
Professor Blogger head lem said...

Thanks for the link.

And oh ... about the missing dollar ... that's too easy, it's still in the manager's pocket.
Actual price= $8/room
change=$6 but manager takes 1 for himself, bell boy takes 2; leaving 3 for the couples

5:17 AM  
Professor Blogger Engineer-Poet said...

(aside:  that unsolicited popup is annoying!)

You're confusing energy transfer with power transfer.  Power transfer is maximum when the source and load resistances are the same, and this does indeed result in half the power being lost in the source.  However, the source resistance of most sources is so low that operation at that level would seriously overload or even destroy them.

Energy transfer asymptotically reaches 100% as the load impedance tends towards infinity.  For most purposes, 95-99% is good enough.  If the EEStor unit operates at 3 kV and you want 150 kW out, you'll need to pull 50 amps; your load impedance would be about 60 ohms, and a source impedance of an ohm or less would lose less than 2% in the capacitor itself.

7:47 AM  
Professor Blogger WHT said...

(aside: that unsolicited popup is annoying!)

WTF are you talking about?

9:04 PM  
Professor Anonymous Anonymous said...

arghhhh!, there is no missing dollar. and they didn't pay $8 per room. they ended up paying $9 per room x3 =$27, the manager got $25, and the bellboy kept $2. 27 MINUS 2 is 25, (not 27 + 2). i have been following eestor articles for some time now. so much speculation. i am waiting impatiently for more info from feel good cars or eestor itself. nothing yet.

8:23 PM  
Professor Anonymous Anonymous said...

A breakthrough like this will not eliminate the use of oil and coal by itself, it's true.

The other half of the equation is energy generation through renewable means such as solar and wind. With thin-film solar technology, solar power will be cost-competitive with power sold from the grid.

Picture your house running on solar during the day, with the excess power being stored in your home ultracapacitor.

At night you draw on the ultracapacitor (although even then, it might be receiving a charge from a home wind turbine). Also, you recharge your car from it after arriving home.

Very tidy and beautiful.

9:46 AM  
Professor Anonymous JimJohnson said...

I saw a very interesting post on this site that shows how EEstor's technology cannot work and is a result of a miscalculation.


11:16 AM  
Professor Blogger WHT said...

Non-linear dielectric response, aha, thanks.

10:54 PM  
Professor Blogger aaron said...

I find the whole eestor thing very unlikely as Weir has made the claim that there is a production facility currently under construction in the Cedar Park area.
A PI was hired to dig into this and found absolutely nothing, kind of hard to hide a factory on 200 to 300 acres.

Also, I've discovered that Richard S. Wier, the son of Richard D. Weir runs an internet marketting company, well what more would you need to start a pump and dump internet scam than an internet marketting professional? I tried pointing this out on www.theeestory.com but they quickly tried to erase all evidence that I was member on the site. my motto was find the building, find the proof. I suspect that the admin of www.theeestory.com with their anonymous dns hosting information and anonymous contact info and eestor are one in the same entities.
Its a shame that so much attention has been given to this snoke oil technology, when legitimate science like the silicon nano-wire battery holds a much greater promise.

7:39 AM  
Professor Blogger WHT said...

Nice digging, Aaron!

5:35 PM  
Professor Blogger Andreya said...

Hi Nice Blog .Setting the backlight to “always on” will significantly reduce your ipod battery life. Only use the backlight when necessary.

11:29 PM  
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5:43 PM  

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