Solar pumps are popular to make a small fountain in the garden pond.
Unfortunately, during cloudy days there is not enough current to drive the pump motor.
Present project describes how get pump running also in cloudy days or in shaddow.
Energy from a solar panel (10W peak, 21V) charges a car-audio super-capacitor (1F, 20V), that can drive a pump motor for ca 5 seconds at a time. Circuit is based on a voltage comparator and a logic-level MOS-FET transistor (for example, IRFZ40, BUK555-60A ).
The construction is intended for small greenhouse irrigation. It is self regulating - in sunny days pumps more water to your tomatoes. Could be used for aquaponics.
This is an autonomous circuit and, in principle, could be used to make for example a solar RC boat, grass cutter, or wireless telemetry transmitter.
Please read the attached word file.