Energy of a Capacitor

E=1/2 CV^2

https://www.khanacademy.org/science/physics/circuits-topic/circuits-with-capacitors/v/energy-capacitor

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.