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