interesting article ...... particularly the bit about car body panels being developed as super capacitors for energy storage instead of batteries
couldn't make it link sadly
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Norman Skinner
Studied Electrical Engineering (Graduated 1968)
How are capacitors better than batteries?
How are capacitors better than batteries?
Let us answer as though the question was “How are capacitors better than rechargeable batteries”.
At the present time batteries and supercapacitors are inversely equal in their capabilities. The strengths of one technology is the weakness in the other.
Some answers here say that capacitors, super or otherwise cannot be used as a voltage source. This is correct. But like a rechargeable battery, capacitors can be used for energy storage. Many reputable commercial companies are selling the bundled supercapacitor as an energy storage device just like rechargeable batteries. Here are some of them:
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Photo from Maxwell.
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Photo from Eaton.
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Photo from Skelton.
Where the supercapacitor is better than a rechargeable battery is the following.
The supercapacitors have very fast charging times. Typically, 1 to 10 seconds compared to 10 to 60 minutes for a cell phone battery.
The recharge cycles of supercapacitors are typically 1 000 000 cycles whereas rechargeable Lithium-ion batteries max out at 1 000 recharge cycles. That is 1 000 times better.
Life time of supercapacitors is 10 to 15 years where as rechargeable lithium-ion batteries last 5 to 10 years. (never personally had a cell phone of laptop battery last more than 5 years)
In terms of specific power supercapacitors can discharge their stored capacity almost instantaneously and deliver specific power up to 10 000 Watts per kilogram. Lithium-ion batteries are at a maximum 3000 watts per kilogram.
Supercapacitors are also safer than Lithium-ion batteries (current technology, may change with future developments) as they cannot be overcharged and explode. Rechargeable batteries are prone to gassing, heating up (catch on fire) and exploding when overcharged.
Where the supercapacitor is worse than rechargeable battery is the following.
Specific energy for a supercapacitor is an average of 10 milliwatt hours per gram whereas lithium-ion has up to 300 milliwatt hours per gram.
Energy per unit volume is not good in a supercapacitor at about 15 watt hours per litre whereas a lithium-ion battery has 1200 watt hours per litre. A supercapacitor to power your smart phone would have to be 50 mm (about 2 inches) thick.
Cost is a real issue when thinking about supercapacitors. Supercapacitor cost is around $20-00 per watt whereas batteries come in about $1-00 per watt. Research is focussed in bringing down the manufacturing costs.
Another disadvantage of the supercapacitor is the severe voltage decreases as the charge diminishes. Batteries also have a voltage decrease but it is minor by comparison. Here is what happens to the voltage in both devices:
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Charge-discharge voltage curves, by Elcap, via Wikimedia commons.
Here is a comparison chart of the various supercapacitor technologies, normal capacitors and lithium-ion batteries:
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The supercapacitor has been used as a battery for a very long time. Since 1971 we have been using supercapacitors as the power source for maintaining computer memory. If fact the development of the supercapacitor has a long history dating back to the 1950s. In 1957 a patent was registered for an extremely high capacitance device, long before the word supercapacitor was known. Here is a time line of the development of the supercapacitor.
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Just imagine if the graphene supercapacitor becomes a commercially viable technology. It has been proven as a concept and has been patented by the University of Central Florida. We could have a fully electric vehicle with the source of all the power for the vehicle built into the body panels. No large battery compartments. A 500 mile travel distance between recharges. Recharge time of 5 minutes. Oh wow, quicker than a petrol refill.
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Photo from UCF
In conclusion.
The supercapacitor is better in some respects to the conventional rechargeable battery and it also has some serious disadvantages. As the supercapacitor develops it will become even better. The future of energy storage (the largest problem for renewable energy) may well be solved by the renewed development of the supercapacitor. It is already being used in major energy reserves and is being tested by Long Island Rail Road as an alternative to spinning flywheels.
Hope this answers the question.
Regards
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but interesting stuff!
All hinges around storage...
