question about capacitors

[Harmonica Lover]

Do capacitors collect energy and store it until an external event
causes them to discharge. Or are their capacitors that will collect
energy and store it until the capacitor hits some peak level and
discharge on it's own.

Specifically. I'm curious if a simple circuit can be designed where
energy is obtained from a solar cell. The capacitor stores the energy
until it reaches the point that it is full, and then discharges the
energy which can run a very small motor like a beeper motor for a small
time like a second or two.

Thank you,
Jim

 

[JeffM]

Do capacitors collect energy and store it
until an external event causes them to discharge.
Harmonica Lover

Yup. An ideal capacitor does just that.

In the real world, there is a shunt path
(the resistivity of the dielectric has some finite value).
..
..

Or are their capacitors that will collect energy
and store it until the capacitor hits some peak level
and discharge on [its] own.

That would typically be a 1-time event

(destructive breakdown of the dielectric
due to an overvoltage condition).

There are somee high-voltage ceramic capacitors
that have a spark gap built into them
http://www.google.com/images?q=capacitor+gap+globalsources
such that the gap's breakdown voltage is reached
before that of the ceramic dielectric.
..
..

Specifically. I'm curious if a simple circuit can be designed
where energy is obtained from a solar cell.
The capacitor stores the energy
until it reaches the point that it is full,
and then discharges the energy
which can run a very small motor like a beeper motor
for a small time like a second or two.

"Everything should be as simple as it is, but not simpler."

--Albert Einstein
You just exceeded the limits of the system.

What you want will requre external circuitry
in the form of a threshold detector (comparator).
This requires "active components".