I have a 7V solar panel which can power an electric pump to pump water to a height of 30cm when the sun is not behind a cloud. When the sun goes behind a cloud, the power drops too low to power the pump fully. Is there a circuit I can buy which will charge a hefty capacitor and then intermittently discharge once the correct voltage has been reached so that the pump will still pump water intermittently when the sun goes behind a cloud? I have looked at charge pump circuits which seem to do this type of thing, but can I wire my own capacitors to achieve different output voltages and discharge times? I also need to be able to disable the circuit when the panel is in full sun.