Can capacitors in electrical circuits provide large-scale energy storage?

December 2, 2014 by Lisa Zyga feature
(a) and (b) The charging/discharging curves for various resistor-capacitor combinations. (c) Three-dimensional funnel-shaped surface contour displaying energy-rich discharging after complete charging. Credit: Fukuhara, et al. ©2014 AIP Publishing LLC

(Phys.org)—Capacitors are widely used in electrical circuits to store small amounts of energy, but have never been used for large-scale energy storage. Now researchers from Japan have shown that the right combination of resistors and capacitors can allow electrical circuits to meet two key requirements of an energy storage device: quick charging and long-term discharging. Using capacitors as energy storage devices in circuits has potential applications for hybrid electric vehicles, backup power supplies, and alternative energy storage.

The researchers, Prof. Mikio Fukuhara, Tomoyuki Kuroda, and Prof. Fumihiko Hasegawa, at Tohoku University in Sendai, Japan, have published their paper in a recent issue of Applied Physics Letters.

Developing efficient methods of is a major topic of research, with a strong focus on batteries, fuel cells, and electric double-layer capacitors (EDLCs) when not incorporated in circuits. So far, no research has been performed on the use of capacitors or supercapacitors as energy storage devices in circuits.

To explore the possibility of using capacitors to store energy in circuits, the researchers investigated the charging/discharging behavior of 126 resistor-capacitor (RC) combinations of 18 resistors, three ceramic capacitors, and four aluminum capacitors. They found that the RC combinations that are the best in terms of quick charging and long-term discharging consist of circuits with a small resistor, a large resistor, and a large capacitor. Some of these circuits could be charged in less than 20 seconds and hold the charge for up to 40 minutes, while having relatively large capacitances of up to 100 milliFarads (mF).

How to quickly store a large amount of electricity and control long-term discharging in an electrical circuit: (a) The capacitor (C) is quickly charged by closing switches S1, S2, S3, and S4. (b) To store the electricity in the capacitor, switches S1, S2, S3, and S4 are then opened. (c) Long-term discharging is carried out by closing S2 and S4, which closes the output circuit, and then using the variable resistor to control the discharging. ©2014 AIP Publishing LLC

"The greatest significance of this work is the discovery of an RC region that offers quick charging and long-term discharging in an electrical circuit," Fukuhara told Phys.org. "We think that this system will become an important method for storing much energy or only small amounts of energy in the near future. For this purpose, the storage must change from an electrochemical to a physical device."

The researchers attribute the quick charging and long-term discharging to the damming effect of the large resistor in the circuit. They explain that the relationship between the resistance and the capacitance of a supercapacitor is similar to that between the plug size and the amount of water in a water tank. The larger the plug (resistor), the more water (capacitance) the tank can hold. Until now, the damming effect of this RC combination on storage in such circuits has been overlooked.

The results also showed that a "dry" or "solid" supercapacitor made of an amorphous TiO2 surface with nanometer-sized cavities provides better performance than typical supercapacitors that use liquid solvents. The researchers' earlier work on these dry TiO2 capacitors showed that they have several advantages for energy storage, such as a large capacitance of 4.8 F, wide operating temperature range from 193 to 453 K, and large voltage variation from 10 to 150 V. In contrast, traditional EDLCs suffer limitations in all of these areas.

"Besides the early original researchers of electric circuits, people have believed that circuits are used only for quick charging and prompt discharging," Fukuhara said. "Consequently, the damming effect of this RC combination on electrical energy storage in such has been overlooked. When we began researching the dry physical capacitance using solid materials only, we began questioning the usual usage of capacitors based on the conventional concept."

In the future, the researchers plan to work on further improving the performance of these dry supercapacitors in order to make improvements to the system overall.

"Our plans are to develop dry, physical electric for use by electric vehicles, AC transmission lines, and charging of large amounts of lightning or large amounts of currents stored in air," Fukuhara said. "However, it will take a long time."

Explore further: Energy storage in miniaturized capacitors may boost green energy technology

More information: Mikio Fukuhara, et al. "Realizing a supercapacitor in an electrical circuit." Applied Physics Letters. DOI: 10.1063/1.4902410

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gkam
1.4 / 5 (9) Dec 02, 2014
It will be interesting to see if this or the German battery technology they use for power quality now will be the better option.

We see advances like this almost every day. We will not need coal and nuclear power in the future.
Gimp
3.8 / 5 (4) Dec 02, 2014
This is bull tookies, a young girl won a Science Fair project years ago suggesting, designing and implementing this exact technology. I wondered why I never saw it proceed, the technology companies ignored it, just like Detroit is ignoring electric cars.
gkam
1.6 / 5 (7) Dec 02, 2014
gkam
1.6 / 5 (7) Dec 02, 2014
" I wondered why I never saw it proceed, the technology companies ignored it, just like Detroit is ignoring electric cars."
-----------------------------------------------

Detroit had the first chance to develop them. We in committees of the Electric Power Research Institute pumped money into the losers for decades to get the technologies we have today, and we used Detroit carmakers to do it for us.

They learned nothing, stuck in their old mentality of knowing more than the rest of us.
Gimp
3.7 / 5 (3) Dec 02, 2014
RichManJoe
5 / 5 (2) Dec 02, 2014
"They found that the RC combinations that are the best in terms of quick charging and long-term discharging consist of circuits with a small resistor, a large resistor, and a large capacitor. "

Had to check the date to see if it was April Fools Day. Either I am stupid and don't understand what they are talking about here, or I learned this when I was 16 studying for my ham radio license. Have they discovered a way to violate exponential charge and discharge times of capacitors through resistors?
gkam
1 / 5 (6) Dec 02, 2014
"Have they discovered a way to violate exponential charge and discharge times of capacitors through resistors?"
---------------------------------------------

It looks to me as if they are taking advantage of it.
flying_aries3
3.8 / 5 (5) Dec 02, 2014
OK kids, science lesson:

Energy stored in a capacitor is 0.5 * C * V * V

For the best case given: 0.5 * 4.8 Farads * 150 Volts * 150 Volts = 54000 Joules.

One Watt is one Joule dissipated in one second.

So if we had a 100 Watt light bulb, we could power it for 540 seconds, i.e. 9 minutes.

If we had a lawn mower with a 1 horsepower (=746 Watt) motor, we could power it for 72 seconds.

If we had a car with a 50 horsepower (=37.3kW) motor, we could power it for 1.5 seconds.

flying_aries3
2.3 / 5 (3) Dec 02, 2014
Continuing:

They don't mention the size of these capacitors. Capacitance is given by the formula C = epsilon * Area / Separation, where epsilon is electrical permittivity, a property of the insulating material between the capacitor plates. For an air gap, epsilon is 8.854pF per meter.

If we could make the air gap be 1 micron = 1E-6 meter wide, then for a 4.8 Farad capacitor, the plate area would need to be 4.8F * 1E-6m / 8.854E-12F/m = 542128 square meters. That's a square 736 meters on a side. A little bit large.
fixitup
4 / 5 (4) Dec 02, 2014
Large "banks" of capacitors have been used in the Electric Utility business, on high voltage systems, for almost 100 years. These large scale capacitors are currently used to correct what is called the deficiencies in a circuit's Power Factor when large motor loads come on line. These capacitors smooth out the distribution of electricity to customers connected to the line. Simply put, and without going into a detail, most here wouldn't understand. Suffice it to say, capacitors today, do not hold their electric charge the way this article says these newly developed capacitors do. A capacitor holds a brief charge while BATTERIES charge and maintain their electricity for longer periods of time. Thus the difference.
BONK__RS
1 / 5 (1) Dec 02, 2014
At first glance it looks trivial, you of course need a low RC to charge fast and a high RC to hold the energy. The variation is in what capacitors can they actually make. It looks like the leakage resistance levels out at 10k for all series resistance below 100R.
So, for a leakage time-constant of about 1 hour (3000s) you can choose any series resistance from 0R1 to 100R, you'd choose the minimum wouldn't you. However its no good if you need to store the energy for more than an hour - or even ten minutes, as you still lose 20% or so, not 63%.
for longer term storage you can go to 1M leakage - about 100 hours RC time but the charging RC goes to 1 hour. this is fine for solar storage.
Isn't it all simple linear programming?
Eikka
5 / 5 (5) Dec 02, 2014
I think there's some crucial information missing from the article, or it is translated incorrectly, because there seems to be nothing other than elementary electronics here and no explaination why it does anything special.

Adding resistors in parallel or series to a capacitor does not increase its capacity to store energy, and the discharging and holding circuit diagrams omit the resistors entirely.

It seems to me that they've simply optimized for a specific RC damping value (not "damming") that results in the fastest charging times with the minimum ohmic loss over the resistors - but that seems like nothing but some sort of undergraduate exercise.

So where's the beef?
BONK__RS
3 / 5 (2) Dec 02, 2014
its the capacitors they can make - they cant make low ESR without higher leakage.
but its still a bit of a schoolboy problem, agreed.
gkam
1 / 5 (6) Dec 02, 2014
"So where's the beef?"
----------------------------------

It's not a steak, it's stir-fry, . . another one of the many techniques to improve the technologies we will be using.
Eikka
5 / 5 (6) Dec 02, 2014
"So where's the beef?"
----------------------------------

It's not a steak, it's stir-fry, . . another one of the many techniques to improve the technologies we will be using.


I read the paper over and over again, and still could not find anything. It's completely trivial.

Their conclusions are completely self-evident: Have a large parallel resistor for low self-discharge, and a small series resistor for fast charge. The "damming effect" they refer to is simply another way to say that large parallel resistances across a capacitor leak less current.

All they seem to have done is pick the most optimum pair of resistors out of a selected bunch for a given size of a capacitor and presented this as a "superior circuit", which is a simple optimization problem anyone can solve if they need such a circuit.
Eikka
5 / 5 (5) Dec 02, 2014
its the capacitors they can make - they cant make low ESR without higher leakage.
but its still a bit of a schoolboy problem, agreed.


It may still be possible that this circuit represents the internal model of a capacitor they wish to build, but that's unlikely with the additional circuit diagrams with the switches that wouldn't be available if they were talking about the ESR and self-leakage of a capacitor - because you can't switch off the internal resistances of the cell.

Basilioexablm CASTLE
2.3 / 5 (3) Dec 02, 2014
Personally I am fascinated with flywheels.
Eikka
5 / 5 (5) Dec 02, 2014
I also find it rather peculiar that they should state:

no research work has been carried out previously on the use of capacitors as electrical energy storage devices in circuits


Consider that in every introductory course to circuit design and especially filters, students are made to model and calculate exactly such RC circuits in terms of their frequency and phase response, and indirectly, their function as energy storage devices. One has only to study the same equations in terms of energy instead of voltage or current or frequency, and the same results pop out.

And Toyota and others have used supercapacitors as energy storage devices in their hybrid car prototypes.

So to say there's no research on the subject is like... when are we now, in the 18th century?
TulsaMikel
1 / 5 (1) Dec 02, 2014
@Basilioexablm CASTLE
Flywheels should already be on bicycles, in cars (braking energy) and storing vast amounts of energy for later use!
Also imagine a flywheel with a varying diameter.
Eikka
5 / 5 (3) Dec 02, 2014
Also imagine a flywheel with a varying diameter.


That should be an engineering challenge. Since angular momentum is conserved, you could arbitrarily change its speed across a narrow range, but what for?

Volvo I think is already prototyping flywheels for cars using a continuously variable transmission to connect them to the rear axle of a car.
EyeNStein
not rated yet Dec 02, 2014
Must be kindergarten physics day. Anyone who tries to store energy in RC circuits clearly hasn't understood I squared R losses.
If they were pumping the C through an inductor (like a switch mode power supply does) or using Hi Q resonance to store energy (e.g. superconducting L and C) they might have the basis of a workable system.
kochevnik
1 / 5 (1) Dec 02, 2014
In school we drank in an off-limits area. Someone dared to charge a 1 farad capacitor, then apply a spanner across the terminals. The spanner vaporized. I bet if you add some low-pass filters and attach this to the mains you can make great fireworks
TopCat22
1 / 5 (1) Dec 02, 2014
charge your car or cell phone in 20 seconds ... lasts for as long as you have the appliance.

Wireless appliances throughout the home that draw power for a few seconds and run for hours on a charge.

These things have been around for over a hundreds years and not one bothered to research???
andyf
1 / 5 (1) Dec 02, 2014
Nothing new here, folks. Please move on, but tick the 1* button before you go. It seems phys.org can't tell the difference between basic electronics and science news without our feedback.
italba
1 / 5 (1) Dec 02, 2014
@flying_aries3: Maybe you don't know that you can buy a 4.8 F or bigger capacitor now for less than $100, and it's just a little bigger than a soda can... http://www.bossau...acitors/
imido
Dec 02, 2014
This comment has been removed by a moderator.
EarthlingX
1 / 5 (2) Dec 02, 2014
I see this article as a pebble thrown into a pond. In science sometimes obvious must be spelled out. It may be they didn't find reference which would cover all requirements for their future work, but that is just as valid speculation as any.

As for ripples, well, there could be some time dilation involved (wormholes ?), as they were already present even before this paper, as stated in commentaries above.

For those interested in application, 500F at 2.5V for about 7€ :
http://www.aliexp...apacitor

flying_aries3
1 / 5 (1) Dec 02, 2014
@italba: What's the rated voltage? Bet it's less than 150 volts...
Mike_Massen
1 / 5 (5) Dec 02, 2014
fixitup offered
..These large scale capacitors are currently used to correct what is called the deficiencies in a circuit's Power Factor when large motor loads come on line. These capacitors smooth out the distribution of electricity to customers connected to the line.
Your 1st sentence re Power Factor correct in general but, Power Factor Correction (PFC) is not just re 'large loads', it's dynamic to ensure voltage & current in phase much as possible PLUS filters used to minimise various harmonics as far as possible eg from older SMPS loads which tend to flatten the voltage waveshape

Your 2nd sentence, sorry not quite correct couldn't be big enough as it seems you imply smoothing out over more than couple cycles. Power utility capacitors are used for PFC & dealing with transients so in that specific case you could call it smoothing but not with much capacity as others observed.

Toying with 3500F supercaps at mo only 2.7v each but, high self discharge.
Mike_Massen
1 / 5 (5) Dec 02, 2014
imido claimed
Capacitors have the problem: they're ineffective storage medium or dangerous one.
Your generalisations are often 'off the money' in Science one needs to be specific or otherwise choice of language can be very misleading - remember others read your comments, you therefore have the responsibility to be factual & please as precise as possible which also means handling a little more complexity - ie. Please don't be simplistic...

3500F 2.7V caps safe.

Super caps, even current tech with comparatively high self discharge rates are very good at soaking up transients & storing them long enough to redistribute most power such as to batteries. Eg. A Vehicle brakes sharply, generator transfers to supercaps, which then manage that discharge safely into batteries. Nice concept but not economically viable for mass production (yet).

Industry sources of transient power which can utilise supercaps more effectively but, these are proprietary.
retrosurf
not rated yet Dec 03, 2014
I think Eikka and RichManJoe are on the right track here.

If you look at the circuit, there is the suggestion of a buck/boost architecture, but no mention of it. The paper is freely available online, and the more you read, the more underwhelming it gets.

italba
3 / 5 (2) Dec 03, 2014
@flying_aries3: Here http://www.ioxus.com/modules/ you can find capacitor modules up to 20.8 F 162 V. Enough?

p.s. The price for a single cell 5000 F 2.7 V is just $175. http://powerelect...pacitors
Eikka
5 / 5 (4) Dec 03, 2014
What's the rated voltage? Bet it's less than 150 volts...


Typical super/ultra capacitors operate at a couple volts per cell.

The problem is that their electrolytes start to break down at higher voltages. Supercapacitors are more a hybrid between true capacitors and batteries in that they have an electrolyte between two electrodes, and easily separated positive and negative ions dissolved within the electrode that are drawn to the electrodes when charged.

But unlike batteries, these ions aren't absorbed into the electrodes, so they remain only loosely attached and that provides for the rapid charge/discharge rate. Since they stick on by electrostatic rather than chemical bonds, the ions' electric field push others away and that provides for a much smaller energy density than batteries - on the order of 30 times less.

Higher energy densities can be achieved by less charge on the electrodes and higher voltages in between, but the electrolytes can't handle it.
Selena
Dec 03, 2014
This comment has been removed by a moderator.
Modernmystic
1 / 5 (1) Dec 03, 2014
Then there is safety to address too....anyone know what happens when a capacitor fails catastrophically? The more energy you're storing the bigger the boom too...

Selena
Dec 03, 2014
This comment has been removed by a moderator.
OneStopCircuit
1 / 5 (2) Dec 03, 2014
Continuing:

They don't mention the size of these capacitors. Capacitance is given by the formula C = epsilon * Area / Separation, where epsilon is electrical permittivity, a property of the insulating material between the capacitor plates. For an air gap, epsilon is 8.854pF per meter.

If we could make the air gap be 1 micron = 1E-6 meter wide, then for a 4.8 Farad capacitor, the plate area would need to be 4.8F * 1E-6m / 8.854E-12F/m = 542128 square meters. That's a square 736 meters on a side. A little bit large.


I agree, not to mention flying_aries3 that a) Current cannot change instantaneously through an inductor and b) the current source is INDEPENDENT, so we would need to re-route the current from the source. It took 2 seconds to simulate this on multisim and get a HUGE error
Mike_Massen
1 / 5 (5) Dec 03, 2014
LOL ! Selena claimed
I know perfectly what I'm saying - the shortcut of large capacitors usually leads to explosion
Don't be alarmist. Manufacturer's have been through risk assessment analysis re differential pressures re containment re change in resistivity WHEN breach of ANY sort. 'Explosion' you claim is more a gaseous effusion & not that violent at all. I know I have been in electronics/electrical for 30+yrs and seen a few failures, they are messy & noisey but not that dangerous. Even greater care is taken these days & much easier re modelling of breach dynamics - u are talking to an Engineer in THE field !

Look Selena/imido, Suggest u adopt your correct sock puppet when replying, otherwise u look like a duplicitous emotionally feeble fetus having both 'arrived' on same day of November 10th, 2014 ;-) LOL ! :-)

Hey re super caps, self discharge not THAT high AND still starts a car too, brilliant:-
https://www.youtu..._kYq3mHM
Mike_Massen
1 / 5 (5) Dec 03, 2014
Selena/imido claimed
..The capacitors differ from batteries in their ability to release all their energy at once.
U wouldnt blurt your CRAP if U KNEW how they r made or the principle on which they operate. A failure of the (mostly aqueous) electrolyte only makes a mess & bad smell, not a goofy excuse it's a bomb - get an (Engineering) education puh-lease - FFS !

Selena/imido claimed
The bigger and more energetically dense the capacitor is, the more http://www.forens...tion.jpg becomes eminent. One doesn't need to be a scientist...
Obviously u have NO technical knowledge !

Why did U specifically OMIT detail report ?

This was NOT a supercap failure, I saw this ages ago, its a UPS smoothing cap failure which ALSO failed thermal shutdown, ie get an education in electronics of power systems, its seems by a bad stroke of LUCK u came across me of all people in the field - LOL !

http://members.ii...s/Power/
imido
Dec 03, 2014
This comment has been removed by a moderator.
Mike_Massen
1 / 5 (6) Dec 03, 2014
imido/Selena
https://www.youtube.com/watch?v=6OaR58pLmlQ... Note the delay, after which the poor capacitor reemerges at scene...;-)
U R lying by being a complete d..k, U purposefully omitted this video subtitle:-
"Exploding a 1 farad autohifi capacitor. I will show you it doesnt like inverse polarity."

LOL ! This incident & with negligible detonation forces was a full "SETUP" by REVERSE polarity, ie only a Dumb Dick would do that in any engineering design & a further Dumb Dick to offer it here - ie U R complete failure !

Is that best U can do Selena/imido ?

An overvoltage breach, in normal specified use does NOT result in a reverse polarity condition, why on earth would U be so obviously stupid that ANY technical person would see you contrived a lie, can't u appreciate the world has (many) smarter people ?

I am absolutely convinced U will lie at the drop of a hat, have NO understanding of the field or any supporting technical aspects.

Try, be smarter :-)
flying_aries3
1 / 5 (1) Dec 04, 2014
@italba: OK, 20.8F charged to 162 volts holds 0.5 * 20.8 * 162 * 162 = 272.9 kiloJoules.

Getting a 1000kg car from 0 to 100km/h (=27.8m/s) would require
0.5 * 1000 * 27.8 * 27.8 = 385.8kJ

OK, so a couple of fully-charged 20.8F in parallel could boost you during acceleration (or capture regenerative braking energy). I'll buy that.

The capacitor you cite is in a UPS, according to the website. It doesn't give the volume in liters. I might guess about 25 liters, a cube about 30cm on a side... OK, I'm sold.

Horus
1 / 5 (1) Dec 04, 2014
What's clearly missing from this report, and most likely protected IP not listed in the paper, is the material properties of the resistors, capacitors and their electric field screening/dampening properties regarding charge.
MR166
5 / 5 (1) Dec 04, 2014
Yet another complete BS article from Physics.org Lets say you want to store 1.3 KWH of energy. That would require a 10,000 farad 100 volt capacitor. I dare you to find one of those. Perhaps you could use a 10,000,000 farad 2.7 V capacitor instead.

Any resistances in series or parallel are just parasitic losses and are a net loss of power.

imido
Dec 04, 2014
This comment has been removed by a moderator.
Mike_Massen
1 / 5 (5) Dec 05, 2014
imido claimed
The current supercapacitors come at price 1 USD per farad
U obviously havent checked for ages, I have 6 off 3500F caps, total was less than $500...

imido making straw
The storage of 1 kWh in this way would cost 100.000 USD (and after one day you would have 0,5 kWh only)
U did CV^2/2 did u for 10MF? - at what voltage ?
Please redo your (cost) calc based on say $100 per 3500F supercap for 2.7V ?

imido didnt make the connection with
But the people want to be fooled and the researchers wants another money for research grants
How is this relevant to your claim ?

imido
This is the main reason, why the really effective research (like the cold fusion) gets delayed for nearly one century
SRI & GEC did research on CF, dropped it but, here is electrically controlled Fusion in a chip U can get from Sandia:-
http://www.gizmag...p/23856/

SRI/GEC did a cost benefit analysis, guess the result, doh !
Mike_Massen
1 / 5 (5) Dec 05, 2014
Horus observed
What's clearly missing from this report, and most likely protected IP not listed in the paper, is the material properties of the resistors, capacitors and their electric field screening/dampening properties regarding charge.
These are trivial matters easily addressed in any production engineering process, Electro Magnetic Compliance (EMC) and associated Radio Frequency Interference (RFI) issues are simple straightforward adjustments to any design. I have been involved in this field and the methods used to address standards re EMC emissions, although requiring some electronics expertise, are not considered proprietary or if they were (claimed as such) its often (only) an ambit claim of product designers. Many materials are available cheaply to address EMC/RFI etc

The other area is of course power supply transients, the infamous 'flicker test' for power line AC perturbation, these are also easily addressed with active components eg Mosfets etc
imido
Dec 05, 2014
This comment has been removed by a moderator.
Mike_Massen
1 / 5 (5) Dec 05, 2014
MR166 claimed
Yet another complete BS article from Physics.org Lets say you want to store 1.3 KWH of energy. That would require a 10,000 farad 100 volt capacitor.
U sure or R U "off the money" again ;-)

From above & CV^2/2 gives 50MJ & dividing for 1Hr gives 13,889W continuous ie U can supply 13.9 KWatts for one hour.

For MR166, Algebra is great u can work backwards from your aim of 1.3KWHr as you now know the equation but, I'm not sure if u can (yet) apply it ;-)

MR166 claimed
I dare you to find one of those.
Have you heard of google, u can find suppliers of components to achieve whatever scale u want but, whoops u need (good) math, tut tut

MR166 claimed
Perhaps you could use a 10,000,000 farad 2.7 V capacitor instead
Um, thats only 2857 x 3500F 2.7 super caps, quite doable, would make a nice (short run) drag car

MR166 claimed
..are a net loss of power.
Maybe not that high but, necessary compromise re EMC/RFI for a commercial product.
Mike_Massen
1 / 5 (5) Dec 05, 2014
imido/Selena appears deluded with this idiocy
SRI/GEC did a cost benefit analysis, guess the result
The people like you should be punished with forceful buying of supercapacitor capable to store their energy consumption for their own money
Wrong !
Huh ? Never forced anyone to buy super caps.
Expended my own capital, never forced anyone to use theirs !

U posted about super caps after u quoted my comment re SRI/GEC re cold fusion

Do u imagine these are related or I drew some relationship, are u completely nuts ?

imido/Selena claimed
Eg "this capacitor" stores 1.2 Watthour for 177.60 USD
Actually rated 2.1WHr but, expensive & low current so why choose that ?

imido/Selena claimed
Could you calculate the cost of storing this energy during winter with these supercapacitors? I guess, you couldn't afford it even in thousand of your future lives
Why do that, when u can have batteries or piped/bottled gas ?

No one is forcing U as U claimed, r u a d..k ?
Eikka
5 / 5 (4) Dec 05, 2014
I know I have been in electronics/electrical for 30+yrs and seen a few failures, they are messy & noisey but not that dangerous.


Capacitors as they are now aren't particularily dangerous because they contain relatively little energy. They're more like firecrackers - a bang and some smoke, maybe someone loses a finger if they're stupid.

And a reverse voltage condition does not produce a very violent reaction because there is barely any energy stored in the capacitor itself. It just starts to gas out and builds pressure until the steel canister breaks.

Once you store energies approaching a kWh in a capacitor cell, they do become quite dangerous, literally explosive with few means to contain a short.

And capacitor cost per kWh IS astoundingly high. The cheapest I can find is $4000/kWh. I don't understand what you're trying to prove here.
Eikka
5 / 5 (4) Dec 05, 2014
Manufacturer's have been through risk assessment analysis re differential pressures re containment re change in resistivity WHEN breach of ANY sort.


Don't assume that because a risk assesment has been made, that the risk itself has been successfully mitigated.

We simply don't use large-enough capacitors yet to be of considerable risk. Consequently, they're of little use for large scale energy storage since you need such an absolutely huge number of them. Soldering literally millions of capacitors together in the style of a Tesla battery is too expensive for any practical application because of the labor, and the materials required for the cells.

MR166
3 / 5 (2) Dec 05, 2014
Yea Mike my calculations were off by a factor of ten. That does not change the fact that the article was pure BS worthy of being published on April Fools Day. RC circuits are as old as electronics and I guarantee that Prof. Mikio Fukuhara found absolutely nothing new or noteworthy working with resistors and 1/1000 farad capacitors.

I hope that this is not one of these peer reviewed papers you are always talking about.
Gino
3 / 5 (2) Dec 05, 2014
One thing I did not find reading thru the comments is that unlike a battery as you draw power from a capacitor the voltage continually drops and chopper type electronics are needed if a constant output voltage is required.
This all adds to the cost and reduces efficiency.
MR166
1 / 5 (1) Dec 05, 2014
Gino you are 100% correct about the voltage decline. I think most automobile and all solar systems have inverters anyway so that is not too much of a problem except for the fact that the inverter will have to operate over a much wider voltage range and that can make it more expensive.
Mike_Massen
1.8 / 5 (5) Dec 06, 2014
Eikka muttered many comments but, didn't address them at anyone in particular, yet asked
And capacitor cost per kWh IS astoundingly high. The cheapest I can find is $4000/kWh. I don't understand what you're trying to prove here.
Who did u direct that comment to, since no one has replied was it me ?

What are you claiming Eikka, supercaps are too expensive ? but, there is a market of sorts for specific applications, so its a matter of supply & demand & u are not in that loop so what r u trying to converge upon ?

Surely u could see I was simply responding to others, thats it, not specifically the article, this is what happens from time to time from so many posters, not unusual...

Eikka elswhere offered
Don't assume that because a risk assesment has been made, that the risk itself has been successfully mitigated.
That was directed at me, so u should know current supercaps have relief values & burst modes which don't result in dangerous explosions...
Mike_Massen
1 / 5 (4) Dec 06, 2014
MR166 claimed
... the inverter will have to operate over a much wider voltage range and that can make it more expensive.
Maybe but, it depends on other possibilities not covered by article or comments here - one particularly simple approach is dynamic connections Eg parallel to serial switching or partially so - such that most power can be drawn without need for comparatively more expensive inverter front ends or (god forbid) tap switching on primaries & secondaries ;-)

The latter of which is still a very useful, practical & traditional approach in use & most cost-effective, smarts available these days with semiconductors & phasing for example makes these seamless & eminently efficient - application engineering allowing of course...

MR166 blurted
I hope that this is not one of these peer reviewed papers you are always talking about.
U SHOULD know by now, it all depends on the topic, the interest of the quoter & especially the value of the data/analysis.
italba
3 / 5 (2) Dec 07, 2014
@flying_aries3: Firstly you said that a 4.8 F capacitor would be "quite big", then you asked for a 150V one, now you want a full replacement for an automotive lithium battery? Isn't ready yet, that's why we still use batteries! Lithium batteries can store at least 10 times the power of a supercapacitor, but they're improving in a faster pace. Today's best choice should be a supercapacitor/battery hybrid, maybe in some years we could consider a full capacitor electric car.
Eikka
5 / 5 (3) Dec 07, 2014
What are you claiming Eikka, supercaps are too expensive ? but, there is a market of sorts for specific applications, so its a matter of supply & demand & u are not in that loop so what r u trying to converge upon ?


Simply to the topic of the article: capacitors as a means for large-scale energy storage.

For that application, they are currently much too expensive, and there seems to be no immediate prospect for them getting significantly cheaper in the future.

That was directed at me, so u should know current supercaps have relief values & burst modes which don't result in dangerous explosions...


Yes, and these mechanisms work as long as the failure is slowly outgassing the electrolyte. However, when you increase the amount of energy held in the cell beyond a couple kJ, an internal short will become energetic enough to instantly vaporize materials. It can't be safely vented anymore, and the casing will just turn into shrapnel.

Eikka
5 / 5 (3) Dec 07, 2014
The main safety issue in batteries vs. capacitors is that batteries are limited in their rate of reaction to release energy, whereas capacitors are only limited by their internal resistance for electric current. When the insulator breaks, all the charge rushes through at once as fast as it possibly can, breaking more and more of the insulator as it does so, leading to an exponentially accelerating release of energy.

That means a battery will catch fire and burn like gunpowder, whereas a capacitor will act more like high explosive. Black powder vs. dynamite.

If released quickly, the energy equivalent of a pint of gasoline is enough to bring a house down - so it's obvious that a very large value, very compact capacitor cell that holds energy in the order of kilowatt-hours would be an extremely hazardous device.

Eikka
5 / 5 (3) Dec 07, 2014
To mitigate the problem of sudden release of energy, the capacitor would need to have a very high internal resistance to limit charge mobility within the electrodes and electrolyte, but that would make a very slow and very inefficient capacitor.

The other alternative is to split it up into a myriad of smaller cells that each contain not enough energy to breach their containment - and that in turn will give you a bank of capacitors that consists of mostly packaging material, which means it will have very low energy density and high cost.

The third alternative is of course a compromize, where you trade between cost, efficiency, and safety. You can have only 2 out of 3 at the same time.

MR166
not rated yet Dec 07, 2014
BTW 1KWH of energy is equal to about 4 sticks of dynamite. Let's hope that there are no internal shorts in these giant caps.
italba
1 / 5 (1) Dec 07, 2014
@MR166: 0.13 liter of gasoline can give the same energy, just add air.
MR166
5 / 5 (1) Dec 07, 2014
"@MR166: 0.13 liter of gasoline can give the same energy, just add air."

And your point is???????????

Let me remind you of the title of the paper "Can capacitors in electrical circuits provide large-scale energy storage?"

Capacitors by their very definition discharge their total energy in a very short period of time.

Large scale energy capacitor storage involves megawatt hours of energy storage IE potentially atom bomb scale worst case failures.
gkam
1.7 / 5 (6) Dec 07, 2014
"Capacitors by their very definition discharge their total energy in a very short period of time."
-----------------------------------------

Time to learn Ohm's Law.

Discharge time is dependent upon applied voltage and the resistance of the circuit.
MR166
not rated yet Dec 07, 2014
OK GKAM that was an erroneous statement. I was talking about a fault situation where there is an external or internal short circuit.
gkam
1 / 5 (5) Dec 07, 2014
Okay. Know of any? Caps with which I have familiarity are usually taken out by spikes pushing a vulnerable spot to discharge. I have seen this become a problem only once - in a C-130 at Edwards AFB, which would surround the flight deck with flames every so often as the electrolyte in the radio power supply capacitor vaporized, shooting up and wrapping the enclosure around the control cables, under the flight deck in the radio rack.

I know now what caused it and what to do, but that was in 1966, and I was green.
italba
1 / 5 (1) Dec 08, 2014
@MR166: 0,13 L of gasoline, plus air, can do a lot of damage too in "worst case failure".
gkam
1 / 5 (5) Dec 08, 2014
Yeah, but that almost never happens, . . unless you get rear-ended.

And that never happens.
Maya no n
1 / 5 (1) Dec 09, 2014
Super-capacitors nibble around the edges of improved energy management. They squeeze that last bit of performance out of inverters for applications, such as solar cell energy transformation to the grid at frequencies of KHz and higher. This is an insignificant improvement in a mode of energy production that is already highly efficient. The challenges for solar have moved beyond cell efficiency and inverter efficiency into the realm of storing this cheap daytime electricity for nighttime demand. Yes, super-capacitors that could store daytime energy for night-time delivery would be extremely valuable, but scaling the parameters of super-capacirtors does not lead to economically viable energy storage from dusk-to-dawn. Boosting capacitance increases energy loss due to self-discharege on this time-scale. Boosting sub-msec energy efficiency, super-capacitors play an insignificant role in comparison to the unsolved challenge of storing daytime energy for nighttime usage.
gkam
1 / 5 (5) Dec 09, 2014
That is why flow batteries and others will probably be used for large power shifts. Ultracaps can assist in Power Quality and reactance control.

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