So far, these replys are giving you some good tips, allow me to chime in with my thoughts:
Forget the individual charging, you are going in circles there, consider a 12 V lead acid batt often used in burgular alarms and electric scooters. Use Ian.w suggested strings of three.
Now the use of panel (voltage) for sending, maybe you would be better to have just one sensor, perhaps salvaged from one of those little stand-alone units, it's certain those work, in a sunny / open spot. So far, that looks like PANEL - BATTERY - Sensor, but you next will put the switch. Heck, a 2n2222 NPN can switch your entire yard (and shed inside). Just don't charge, only charge that medium sized battery, on your covered porch.
By the way, I've been trying to make up an optical - electronic oscillator, blinky light, by pointing an LED at the little solar cell, in my stand- alone unit. You may have noticed: frequently without hysterises some garden lights may blink, as dusk comes.
You're on the right track, for those replies look good.
More questions / feedback as you go, looking fwd to that. - RJHayward