And the question is the circuitry for charging the supercap - not the circuitry for powering the logic and transmitter.
Do you think they're not the same? Why?
Yes. One controls the current going into the supercap to charge it. The other controls whether there is current coming out of the supercap to power the logic and transmitter.
For instance: when the solar panel is producing voltage that is high enough to charge the supercap, it is charging the supercap. But the supercap is not powering the logic and transmitter - the solar panel is powering the logic and transmitter.
When it's dark, you want the supercap powering the logic and transmitter - but you don't want the supercap electrically connected to the solar panel.
That all was generally done with "isolation diodes". Of course, today's technology could provide
two smart converters - one for charging the supercap, and the other for selecting the best available power source and powering the logic and transmitter.
Of course, adding a battery (and perhaps a mains adapter) to the situation increases the complexity.
I'm probably not explaining that very well - so perhaps someone else can chime in.