Energy of a Capacitor

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E=1/2 CV^2

Take a 3000F capacitor at 2.7V -

E=1/2 3000 *7.3= 11kJ. If released over 1 second - with is 11kW!

If released over 30 seconds for passing a car - gives you 370Watts. That's not bad, at about 550 grams. 10kW would be 27 of these - or 33 lb. About half the weight of a battery. But price is $1000, or 10x higher. It's better for the smaller caps. But still, with lifetime of 1M cycles compared to 1000 cycles - that is way cheaper for lifetime design.