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Capacitors to Replace Batteries?
An anonymous reader writes "MIT's Joel Schindall plans to use old technology in a new way with nanotubes.
'We made the connection that perhaps we could take an old product, a capacitor, and use a new technology, nanotechnology, to make that old product in a new way.'
Capacitors contain energy as an electric field of charged particles created by two metal electrodes, and capacitors charge faster and last longer than normal batteries, but the problem is that storage capacity is proportional to the surface area of the battery's electrodes.
MIT researchers solved this by covering the electrodes with millions of nanotubes.
'It's better for the environment, because it allows the user to not worry about replacing his battery,' he says. 'It can be discharged and charged hundreds of thousands of times, essentially lasting longer than the life of the equipment with which it is associated.'"
Philip Jose Farmer predicted "batacitors" in his novels decades ago. Chalk annother one up for life imitating science fiction.
:-)
Well - its a bit of a no-brainer to any EE kind of guy. No wasteful energy conversion process, etc etc.
Everyone's been waiting for the materials technology to catch up to the rather obvious idea that's all
There are shills on slashdot. Apparently, I'm one of them.
Summary says this technology would allow batteries to charge faster. It's a big understatement since the article says they would only need a few seconds to be fully charged...
First, safety. One of the amazingly cool things about capacitors is that they can deliver all their charge over the course of a few milliseconds. This makes them very useful for things like strobelights and subwoofers. But it can be very, very dangerous: What happens if you drop your in the toilet? Or you drop your iPod and it gets run over by a car? If they have batteries, a short circuit will cause the battery to get warm for a while, or it will release some slightly caustic goo and you have to wash your hands. But if they have capacitors, you get an explosion and a violent electrical arc.
Second, durability. You can beat the hell out of a chemical battery, expose it to shock and vibration to no end and it will continue to operate. These nanotubes, OTOH look awfully easy to break. Breakage could cause two things to happen: loss of capacitance, or worse, an internal short circuit, and see above.
It will be interesting to see how these two problems are addressed, or if these cool toys will be relegated to industrial and other controlled-environment applications.
This is not my sandwich.
I'd gladly pay 4 times (or more) the price of regular batteries to have batteries that recharge in seconds and never need replacing. This will be great in cell phones and laptops, too.
I wonder what one of these big capacitors would do in a crash? At least they're not filled with so many chemicals as normal batteries, but what would happen?
Another important thing about electric (battery) cars is that batteries perform poorly in the cold (due to their chemical electricity-generating process). Considering a good portion of the United States (and the world) is cold for a good portion of the year: this means battery cars are a no-no. A capacitor powered electric car, on the other hand, could operate in the coldest environments (well, except absolute zero) with little performance degredation (the lesser performance would be from moving parts in the car).
A computer once beat me at chess, but it was no match for me at kick boxing.
The thing is, one kg of petrol holds around 45MJ of energy. One kg of NiMH batteries hold around 0.25MJ, a factor of almost 200 less. A lead-acid battery holds half that. A normal capacitor holds 0.002 MJ/kg.
So, even to compare with lead-acid batteries in energy-storage this thing needs to be 50 times better than normal capacitors.
Recharging in seconds is fine, assuming you can build a sensible car that goes oh say 100 miles at the least between recharges, that's perfectly acceptable for most people. Same for cellphones; faster recharging is very nice. But only if you can still go for 2-3 days without recharging, and talk on the phone for atleast an hour or two before its empty.
A car that could only go 20 miles between recharges would not be a hit, not even if the recharge was done in a minute.
I wonder if this could lead to an electric car that is good for the masses where they can cross country and take only 5 to 10 minutes to recharge.
Unlikely at best. The problem is that the rate of energy transfer for chemical storage (that is, fuels, like gasoline) is really, really high. While you could in principle build a station which could recharge your batteries in the same amount of time it takes to gas up your car, it wouldn't be something you'd want to be near.
Why?
When you put gasoline in your car, you are moving power at a rate of about 5 MW. That's the entire output of a small power plant. Liquid fuels, gasoline in particular, are a very dense way to store and transport energy. Electrical wires aren't very good for that in comparison, even with superconductive cables. Think of it this way, even if we could transfer energy from a station to your car with 99.9% efficiency (which is well and far beyond anything we can do in the forseable future), that's 500 W of power that needs to be dissipated at the conversion site between the station and your car. That's going to be too hot to hold like a fueling nozzle for gasoline cars. If we use 48V to move 5MW (48V is gaining traction as a new standard for power transfer), that's 100,000 A of current. Even if we use an insane voltage level like 5 kV, prone to arcing and causing nasty things like fires and death, that's still 1,000 A of current. Not small. If this power is transferred by direct contact, you get immediate electromigration at the contacts, arcing problems when starting and stopping the current (ever wonder why power transmission towers are so tall?). If it's transferred by induction, then the EM fields will be enough to cause cancer (ok, I don't know that one for sure, but it's going to be as if 1000 microwave ovens are all operating right there at your car, something I don't want to be near).
Building an electrical system that can move megawatts of power is not something that will ever happen on the consumer level.
What about improving the efficiency of cars? We can make cars at best an order of magnitude more energy efficient. That isn't going to solve the problems alone.
Now, if, instead of recharging, you swap out batteries (that is, move mass that carries energy instead of moving energy aone), things get far more attractive. Except that people are currently a little leary of exchanging parts of their cars (can you imagine swapping tires every time you went to a filling station?). But that would allow a quick recharging.
The only solution that really makes sense for refueling by recharging is to do it while the vehicle is sitting idle when there is more time available, rather than being driven when there isn't. If you allow 20 hours for a recharge instead of 5 minutes, the power transfer rate drops to 20 kW which isn't so bad. Add in an order of magnitude higher efficiency vehicles and perhaps live with shorter distances between recharges, and you get down to the kilowatt range which is entirely doable (1.5kW can be supplied from a single, standard US household outlet).
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
Yeah, this is a much better idea. That 'average draw', although high, could work out more favorably for the power companies because it would give them a stable power generation requirement, rather than wasting power or shutting off the turbines when there is no demand.
Imagine the size of a megawatt-hour capacitor!
the real at&t mix
There's a good reason that we're not using high-voltage, large capacitors currently to run our electrical devices: price. (In addition to storage space, of course, but let's pretend the carbon nanotube thingy could take care of that). The potential energy stored in a capacitor, U, is defined by
.5 * 1 Farad * (20V)^2
U = 1/2 * C * V^2
Where C is the capacitance, in Farads, and V the Voltage. For comparison's sake, a typical 1.5 Volt AA battery is rated for around 2000 milliamp-hours (why they use this ridiculous measurement, I don't know, but it's all I can find). So a tiny AA battery stores the potential energy
U_battery = 2000E-3 Amps * 1.5V * 3600 seconds/hours
Or, it stores 11,000 Joules. Now, searching for big capacitors on froogle, I came up with a link from Autotoys for a 1 Farad capacitor, on sale for a mere $42 (which is actually really cheap for one of those bad boys, but anyways..). It claims to have a "surge voltage" of 20V. So, assuming it's charged to 20V, the potential engergy in the capacitor is
U_cap =
So this $42, huge capacitor stores 200 Joules, in comparison with our AA battery that stores 11,000 Joules. In addition to the problems of price, miniscule total energy storage, storage space (making impractical for electrical car use.. you'd need a TON to power a car for an hour.. 100 HP = 75kW, for an hour, that's 270 MJ.. that's a lot of capacitors), in order to get the most out of capacitors you have to charge to a very high voltage (since U goes up with V^2), so you need a high voltage DC power supply, and finally, unlinke batteries, capacitors' voltage goes down exponentially with time, so you need clever (i.e. large, complicated) circuitry get out a constant voltage from a capacitor bank.
Basically, capacitors have their place (namely, smoothing voltages, or storing small amounts of power for quick discharge, i.e. camera flash), and batteries have theirs. The article is very light on specifics, but even if, say, the Cost / Farad goes down by an order of magnitude, and they manage to shrink the size as well.. I still don't see much changing. They also don't mention whether these things work at high-voltage. If they can't be charged up to 500+ Volts, they're not going to be able to store much energy. I'm not an expert on capacitor design, but if you look around for high-voltage capcitors (they go up to 10kV+), they pretty much all have tiny capacitances (e.g. 800pF, 10kV). I assume there must be some inherent difficulty in making them with both a large capacitance and high-voltage rating (or perhaps too dangerous.. who knows?). Don't get your hopes up just yet.
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Building an electrical system that can move megawatts of power is not something that will ever happen on the consumer level. No one will ever need more than 64KB...
You realize that you have now committed the classic blunder (second only to getting involved in a land war in Asia). Millions of engineers are now scrambling to prove you wrong, at any cost!
Here is how I would do it: Battery in car is a one meter square, 2 cm thick. Charging station brings over their one meter square battery, places it on top of yours. Power is transfered at 50 volts x 100,000 amps - but that 100,000 amps is flowing through a "wire" half a square meter in area, which is the equivalent of 0.1 amps through a somewhat standard 1mm wire. In other words: the efficiency is basically 100% (it would be hard to estimate before doing it, but very high); the grid can see a long slow charge (as the Charging station can slow charge their transfer battery); the energy transfer is done at 5MW, so it takes only a few seconds to fill your car.
OK, I think you owe me lunch now!
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