Automatic capacitor discharge circuit
Since I dont know the details, here can be a possible aproach. The whole idea is to generate a constant width pulse for discharging cap thru mosfet (and cap protecting resistance) once the voltage reaches desired level (about 10v in this case). This pulse is generated with monostable circuit fired by voltage monitor made with zener. The components needs to be designed according timings , i.e. cap size, discharge rate etc.. For higher accuracy use 555 timer as monostable and TL431 as voltage monitor.
In waveforms the green is cap voltage, blue is discharging pulse.


To avoid &quot;shorting&quot; solar cell thru 1 ohm resistance when discharging, the panel can be disconnected for this short of time adding P-chan mosfet right after cell.