Capacitors and supercapacitors explained
A capacitor is an energy storage medium similar to an electrochemical battery. Most
batteries, while able to store a large amount of energy are relatively inefficient in
comparison to other energy solutions such as fossil fuels. It is often said that a 1kg
electrochemical battery is able to produce much less energy than 1 litre of gasoline;
but this kind of comparison is extremely vague, mathematically illogical, and should
be ignored. In fact, some electrochemical batteries can be relatively efficient, but that
doesn’t get around the primary limiting factor in batteries replacing fossil fuels in
commercial and industrial applications (for example, transportation); charge time.
High capacity batteries take a long time to charge. This is why electrically powered
vehicles have not taken-off as well as we expected twenty or thirty years ago. While
you are now able to travel 250 miles or more on one single charge in a car such as
the Tesla Model S, it could take you over 43 hours to charge the vehicle using a
standard 120v wall socket in order to drive back home. This is not acceptable for many
car users. Capacitors, on the other hand, are able to be charged at a much higher
rate, but store (as already mentioned) somewhat less energy.
Supercapacitors, also known as ultracapacitors, are able to hold hundreds of times
the amount of electrical charge as standard capacitors, and are therefore suitable as
a replacement for electrochemical batteries in many industrial and commercial
applications. Supercapacitors also work in very low temperatures; a situation that can
prevent many types of electrochemical batteries from working. For these reasons,
supercapacitors are already being used in emergency radios and flashlights, where
energy can be produced kinetically (by winding a handle, for example) and then stored
in a supercapacitor for the device to use.
A conventional capacitor is made up of two layers of conductive materials (eventually
becoming positively and negatively charged) separated by an insulator. What dictates
the amount of charge a capacitor can hold is the surface area of the conductors, the
distance between the two conductors and also the dielectric constant of the insulator.
Supercapacitors are slightly different in the fact that they do not contain a solid
insulator.
Instead the two conductive plates in a cell are coated with a porous material, most
commonly activated carbon, and the cells are immersed in an electrolyte solution. The
porous material ideally will have an extremely high surface area (1 gram of activated
carbon can have an estimated surface area equal to that of a tennis court), and
because the capacitance of a supercapacitor is dictated by the distance between the
two layers and the surface area of the porous material, very high levels of charge can
be achieved.
While supercapacitors are able to store much more energy than standard capacitors,
they are limited in their ability to withstand high voltage. Electrolytic capacitors are able
to run at hundreds of volts, but supercapacitors are generally limited to around 5 volts.
However, it is possible to engineer a chain of supercapacitors to run at high voltages
as long as the series is properly designed and controlled.
A capacitor is an energy storage medium similar to an electrochemical battery. Most
batteries, while able to store a large amount of energy are relatively inefficient in
comparison to other energy solutions such as fossil fuels. It is often said that a 1kg
electrochemical battery is able to produce much less energy than 1 litre of gasoline;
but this kind of comparison is extremely vague, mathematically illogical, and should
be ignored. In fact, some electrochemical batteries can be relatively efficient, but that
doesn’t get around the primary limiting factor in batteries replacing fossil fuels in
commercial and industrial applications (for example, transportation); charge time.
High capacity batteries take a long time to charge. This is why electrically powered
vehicles have not taken-off as well as we expected twenty or thirty years ago. While
you are now able to travel 250 miles or more on one single charge in a car such as
the Tesla Model S, it could take you over 43 hours to charge the vehicle using a
standard 120v wall socket in order to drive back home. This is not acceptable for many
car users. Capacitors, on the other hand, are able to be charged at a much higher
rate, but store (as already mentioned) somewhat less energy.
Supercapacitors, also known as ultracapacitors, are able to hold hundreds of times
the amount of electrical charge as standard capacitors, and are therefore suitable as
a replacement for electrochemical batteries in many industrial and commercial
applications. Supercapacitors also work in very low temperatures; a situation that can
prevent many types of electrochemical batteries from working. For these reasons,
supercapacitors are already being used in emergency radios and flashlights, where
energy can be produced kinetically (by winding a handle, for example) and then stored
in a supercapacitor for the device to use.
A conventional capacitor is made up of two layers of conductive materials (eventually
becoming positively and negatively charged) separated by an insulator. What dictates
the amount of charge a capacitor can hold is the surface area of the conductors, the
distance between the two conductors and also the dielectric constant of the insulator.
Supercapacitors are slightly different in the fact that they do not contain a solid
insulator.
Instead the two conductive plates in a cell are coated with a porous material, most
commonly activated carbon, and the cells are immersed in an electrolyte solution. The
porous material ideally will have an extremely high surface area (1 gram of activated
carbon can have an estimated surface area equal to that of a tennis court), and
because the capacitance of a supercapacitor is dictated by the distance between the
two layers and the surface area of the porous material, very high levels of charge can
be achieved.
While supercapacitors are able to store much more energy than standard capacitors,
they are limited in their ability to withstand high voltage. Electrolytic capacitors are able
to run at hundreds of volts, but supercapacitors are generally limited to around 5 volts.
However, it is possible to engineer a chain of supercapacitors to run at high voltages
as long as the series is properly designed and controlled.
