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Gary said:
Yes and no. They cannot store as much energy, but they can
charge and discharge much faster. There are certainly applications
where an ultracapacitor could replace a battery. I have considered
using them for a low drain application where they could be instantly
recharged by plugging (very) briefly into an automotive power supply.
It has been a few years since I used ultracaps, so somebody please
correct me if this is no longer true, but when I used them the
ESR was *very* high and thus the available current was quite low.
The combination of a large capacitance and a high ESR made it so
that I couldn't put a newly-built PWB on a test fixture and test
the board's ability to hold data during a power failure -- the
test was over before the ultracap had time to charge. I had to
add a test to the burn-in fixture. Likewise on the discharge;
short it out for a minute or so and find that it is still charged.
Wikipedia has an interesting energy density chart:
[
http://en.wikipedia.org/wiki/Energy_density ]
A few selected items from the list:
ENERGY DENSITY IN MJ/kg:
-------------------------------------------------------
Spring...........................................0.0003
Capacitor........................................0.002
Supercapacitor...................................0.01
Ultracapacitor...................................0.02
Lead-acid battery................................0.09–0.11
EEStor Ultracapacitor (claimed capacity).........1.0
NiCd Battery.....................................0.14-0.22
NiMH Battery.....................................0.22
Zinc-air Battery.................................0.40-0.72
Lithium ion battery..............................0.54–0.72
Wood.............................................6.0–17.0
Flywheel........................................l0.5
Lignite coal....................................14-19
Cowdung/Cameldung...............................15.5
Methanol........................................19.7
Ethanol.........................................30.0
Anthracite coal.................................32.5
LPG.............................................34.39
Diesel fuel.....................................45.8
Gasoline........................................46.9
Hydrogen.......................................143
Uranium-235 (nuclear fission)...........90,000,000
Hydrogen (nuclear fusion)..............300,000,000
