Why not use capacitors to store power instead of batteries ?

[FreeBTU]

I hope it's not against the forum rules to reply to the old thread...

Perhaps peak loads are a good use of CAPS.
Many devices have power on peaks that are much higher than the normal load. Such peaks last only a second or less. Not much of an issue with many small appliances but those 1kW devices may cause a serious peak load,
Instead of over sizing a the battery system a CAP may be a good way to handle the peak and keep the voltage stable.
An added benefit is that caps smooth out the voltage during non peak use.

Just a thought.

[Mike90250]

not a crime to use old threads

Caps have internal inductance and resistance, and the cables connecting them would need to be same beefy cables as battery cables. Caps are 50x size of battery for amount of USEABLE power.
example : Only using 12.75 to 12.73V = just a .02v difference. Then the easily useful power has been consumed from the cap and it's all on the battery.
Ripple caps can be found in large inverters, and they do supply this peak demand, via low inductance internal traces in the inverter.

[highvoltpower]

Practically we use capacitors when we require a large amount of charge to be flown within fractions of seconds, battery provides a nearly uniform voltage and effective in long use, but when it comes to discharge a large amount of charge in a fraction of second.

[bcroe]

Besides all the other good reasons listed above, there is the issue of charge/discharge curve. A battery maintains a somewhat constant voltage
over most of its energy storage range. Removing energy from a cap means the voltage will continuously drop, and you won't have have most
of the energy until the voltage is a very small fraction of the starting level. This makes it very difficult to use for bulk energy storage. Bruce Roe

[DanKegel]

Mazda uses them for a regenerative braking system called i-eloop it offers on the Mazda 6 (and it's actually in stock in Los Angeles).

http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=35982&id=35981

shows that it reduces co2 emissions by 14 grams/mile (from 290 to 276) and mpg by 1 (from 31 to 32).
That's a pretty small improvement. I have no idea whether it's worth it, and if I were buying a hybrid, I'd aim higher and go for one where the regenerative braking energy was actually used to accelerate the car and not just reduce alternator drain.
But at least it's an example of supercapacitors actually being used in motor vehicles. Maybe it'll make more sense later.

The voltage droop issue means you might need an inverter of some sort to match the output of the capacitor to the voltage you want, which presumably adds cost.

[DirtyRob]

In short, to answer your original question OP, the reason they arent used is because people like you with good ideas come to places like this so people with no imagination can shoot it down. You can most certainly create a circuit to control discharge rates from the cap. You can absolutely make switching happen in said circuit to allow it to exhibit both the benefit of fast charging and the regulated discharging of it as an extended energy source.

The only con I can agree with by any of the posters on this thread is the cost one, at this point in time. Another thing to consider is this Capacitor/Battery comparison is really just semantics. The second you make a circuit attached to it that regulates it ... it is in effect a battery at that point ... even though you did use a capacitor. Battery=Capacitor=Battery. All youre doing with a cap is essentially separating out the capacitive element already found in all batteries. You can add to any capacitive circuit and make it into a battery. You could use the capacitive nature of an extremely long length of wire to make a battery even. But yes in the end it comes down to cost and practicality.

It sounds like most of these guys think it impossible to use in the form of some kind of home battery bank replacement ... but I can tell you they work just fine in small circuits as battery replacements. As replacements to button cells for clock circuits ... ive even driven solar powered audio amps with a super cap to help maintain gain when the unit is suddenly in a low light area. There are all sorts of possibilities. Dont let the norm discourage you.

[SunEagle]

In short, to answer your original question OP, the reason they arent used is because people like you with good ideas come to places like this so people with no imagination can shoot it down. You can most certainly create a circuit to control discharge rates from the cap. You can absolutely make switching happen in said circuit to allow it to exhibit both the benefit of fast charging and the regulated discharging of it as an extended energy source.

The only con I can agree with by any of the posters on this thread is the cost one, at this point in time. Another thing to consider is this Capacitor/Battery comparison is really just semantics. The second you make a circuit attached to it that regulates it ... it is in effect a battery at that point ... even though you did use a capacitor. Battery=Capacitor=Battery. All youre doing with a cap is essentially separating out the capacitive element already found in all batteries. You can add to any capacitive circuit and make it into a battery. You could use the capacitive nature of an extremely long length of wire to make a battery even. But yes in the end it comes down to cost and practicality.

It sounds like most of these guys think it impossible to use in the form of some kind of home battery bank replacement ... but I can tell you they work just fine in small circuits as battery replacements. As replacements to button cells for clock circuits ... ive even driven solar powered audio amps with a super cap to help maintain gain when the unit is suddenly in a low light area. There are all sorts of possibilities. Dont let the norm discourage you.

True, capacitors are used to maintain voltage in circuits for short duration to act like a battery. I used them in my RC plane so my receiver continues to work even if the battery drops low for a brief period when I ramp up the motor. But they do not have a lot of storage capacity.

One problem is that a capacitor discharges very fast although it can be controlled through circuitry. Another problem is that it takes a lot of space for a capacitor to store a lot of energy compared to a different type of storage medium like a battery.

So when you look at the space needed for storage based on the energy density to support your needs along with the circuitry to control the discharge it starts to become very impractical as a long term energy storage system. Even if cost wasn't a problem.

IMO if I was spending my money on research it would be in battery chemistry that is low cost and high energy density then in a capacitor design.

[solarix]

"because people like you with good ideas come to places like this so people with no imagination can shoot it down." I resent the impugning of our motives in trying to help people on this forum.
I'm sorry if you do not like the answers, but do know that we are (with a few exceptions) sincerely trying to give good advice in order to help others "go solar". There are very, very few things that are "new under the sun" and that we haven't seen before.
Capacitors are good for energy storage applications where you need fast energy transfer and batteries are good for energy storage applications where you need high capacity - preferably with high density. Thus the big cost advantage of using batteries with solar applications....
(By the way - if you want to see a really radical, "new under the sun" storage technology, check out what is called a "liquid metal battery" on youtube.

[DirtyRob]

True, capacitors are used to maintain voltage in circuits for short duration to act like a battery. I used them in my RC plane so my receiver continues to work even if the battery drops low for a brief period when I ramp up the motor. But they do not have a lot of storage capacity.

One problem is that a capacitor discharges very fast although it can be controlled through circuitry. Another problem is that it takes a lot of space for a capacitor to store a lot of energy compared to a different type of storage medium like a battery.

So when you look at the space needed for storage based on the energy density to support your needs along with the circuitry to control the discharge it starts to become very impractical as a long term energy storage system. Even if cost wasn't a problem.

IMO if I was spending my money on research it would be in battery chemistry that is low cost and high energy density then in a capacitor design.

Space maybe ... weight no. There are tradeoffs when you decide not to put a bunch of rare earth metal or heavy liquids in a unit. The main take away should be that by using capacitors+circuitry you are essentially separating out the bare electrical relationships that already go on in a battery and are not a slave to the inherent physical properties of whatever element youre using in that battery.

But i get what youre saying. Its easier to slop it by throwing together chemicals and measuring their output till it works for the application than it is to actually harness and manipulate everything actually going on in that battery. Itll come with time though. I think they (capacitors) work great in plenty of battery-esque applications as is though.

[DirtyRob]

"because people like you with good ideas come to places like this so people with no imagination can shoot it down." I resent the impugning of our motives in trying to help people on this forum.
I'm sorry if you do not like the answers, but do know that we are (with a few exceptions) sincerely trying to give good advice in order to help others "go solar". There are very, very few things that are "new under the sun" and that we haven't seen before.
Capacitors are good for energy storage applications where you need fast energy transfer and batteries are good for energy storage applications where you need high capacity - preferably with high density. Thus the big cost advantage of using batteries with solar applications....
(By the way - if you want to see a really radical, "new under the sun" storage technology, check out what is called a "liquid metal battery" on youtube.

Yeah, i don't know, i guess I was expecting something a little more encouraging coming from a forum backing one of the more progressive technologies out there. It just seemed to glare, stand out, how much alike the responses are and how they align with the same motives outside in the world that have kept this very technology (solar power) such a slow growing thing. I just did not expect to see it here of all places, is all ...

It sounded like this guy was pitching electric to the gasoline guys out there, lol, "electric is just too uncontrollable and doesnt deliver energy the way you want in a car, and not for as long or with enough horsepower, the battery would b e so big and expensive that no one would buy an electric car ... etc"

Just saying though, my first reaction when i read his question was "Ok, how can I make this guys idea work for him ... lemme read on and see what other people have thought of as a solution. Oh everyones solution is only actually a list of why they arent even going to attempt anything ... oh how useful."

I checked out a bit on those liquid batteries by the way and saw MIT and immediately thought "oh shoot next they are going to energize the liquid and flow it into a MEMs device to a well within it to deliver the effects of a battery to some much smaller device embedded in a chip or organism."

[smily03]

Personally, I think that the key is using things for their intended applications -- that's how you get the most efficiency and bang for your buck. It's true that you can try to make things work in unintended applications, and sometimes it even works fairly well. But that doesn't mean that it works the best out of the options. Sometimes the best way of doing stuff is pairing technologies together, with each technology being used for its sweet own spot.

For example, my neighbor can ride their lawn mower uptown to the store. Does it work? Yup. Is it the ideal mode of transportation? Not really. Just like trying to mow my lawn with my car wouldn't work very well. But paired together, I can haul a lawn mower somewhere with my car, and then mow with the mower.

Applying that to the current conversation would mean batteries for power and storage, capacitors for smoothing and working to offset deep brief peaks in loads. It works the same way with big amps in car audio -- use the alternator and battery for the normal loads, and capacitors to handle cases where the amp draws a large load for a big bass kick.

[DirtyRob]

Personally, I think that the key is using things for their intended applications -- that's how you get the most efficiency and bang for your buck. It's true that you can try to make things work in unintended applications, and sometimes it even works fairly well. But that doesn't mean that it works the best out of the options. Sometimes the best way of doing stuff is pairing technologies together, with each technology being used for its sweet own spot.

For example, my neighbor can ride their lawn mower uptown to the store. Does it work? Yup. Is it the ideal mode of transportation? Not really. Just like trying to mow my lawn with my car wouldn't work very well. But paired together, I can haul a lawn mower somewhere with my car, and then mow with the mower.

Applying that to the current conversation would mean batteries for power and storage, capacitors for smoothing and working to offset deep brief peaks in loads. It works the same way with big amps in car audio -- use the alternator and battery for the normal loads, and capacitors to handle cases where the amp draws a large load for a big bass kick.

Capacitors in place of batteries is a need though, we are just fortunate to currently be on a rock rich in heavy metals. The stuff we are making batteries from is rather rare in the grand scope of things.

[J.P.M.]

Yeah, i don't know, i guess I was expecting something a little more encouraging coming from a forum backing one of the more progressive technologies out there. It just seemed to glare, stand out, how much alike the responses are and how they align with the same motives outside in the world that have kept this very technology (solar power) such a slow growing thing. I just did not expect to see it here of all places, is all ...

It sounded like this guy was pitching electric to the gasoline guys out there, lol, "electric is just too uncontrollable and doesnt deliver energy the way you want in a car, and not for as long or with enough horsepower, the battery would b e so big and expensive that no one would buy an electric car ... etc"

Just saying though, my first reaction when i read his question was "Ok, how can I make this guys idea work for him ... lemme read on and see what other people have thought of as a solution. Oh everyones solution is only actually a list of why they arent even going to attempt anything ... oh how useful."

FWIW, one observation I've made about posters around here is that, like many other things and other places/situations, the information from the more experienced is often viewed as a wet blanket on the enthusiastic but situationally ignorant ideas of the inexperienced. Sometimes reality is a tough sell.

I'd like to think I'm one of the biggest fans of alternate/renewable energy around, and I think I may know some stuff, but part of being a fan is to help inform folks that it's not the savior of the world, and also to speak truth (as I may see the truth anyway) to the B.S. that only harms and slows down the sane implementation of R.E. - the source of the harm coming from the general solar /R.E. ignorance of the public which sustains and allows the Con men to thrive.

Welcome to (hopefully, at least to some degree) the forum of few(er) illusions. Encouragement - sure. Unconditional acceptance of doubtful/wrong/dangerous (?) ideas and just plain B.S - probably not from professionals who collectively know better.

[Sunking]

Capacity as batteries is as old as a battery itself. They do not nor are they batteries.

Capacitor only have one battery like characteristic in that they can be charged and discharged extremely fast. That s it. . Their energy density make them completely useless for energy storage. Lead acid batteries energy density is high enough at 50 wh/Kg, a capacitor is piss poor at 10 wh/Kg. Not even remotely close to the 200 wh/Kg needed to be useful in energy storage and EV's.

Lastly how are you going to get the high voltages and large capacitance. Power does not add when you string capacitors in series. It divides You do no thave to be a genius to figure out that completely eliminates them as power storage. Once you know that, then you have to be a Moron to proceed.

[DirtyRob]

Capacity as batteries is as old as a battery itself. They do not nor are they batteries.

Capacitor only have one battery like characteristic in that they can be charged and discharged extremely fast. That s it. . Their energy density make them completely useless for energy storage. Lead acid batteries energy density is high enough at 50 wh/Kg, a capacitor is piss poor at 10 wh/Kg. Not even remotely close to the 200 wh/Kg needed to be useful in energy storage and EV's.

Lastly how are you going to get the high voltages and large capacitance. Power does not add when you string capacitors in series. It divides You do no thave to be a genius to figure out that completely eliminates them as power storage. Once you know that, then you have to be a Moron to proceed.

It doesnt take a moron, but a masters, to think capacitors dont add voltage in series, capacitance in parallel. You can put them in arrays. They just have to be matched. Same as you not mixing battery values and burning the smallest in the chain out. But then again why would you. Capacitors are easy to build. Just make 1 instead of a matched series.

But again, there is a capacitor in every battery. You can draw an equivalent circuit for any battery and it will consist of a capacitor of some type. That's just how batteries work at an atomic level.