ZephyrOS: https://github.com/zephyrproject-rtos/zephyr

Would there be value in modeling this system with TLA+?

Why build another open product?

There are a few GitHub topics for solar electricity:

solar: https://github.com/topics/solar

photovoltaic: https://github.com/topics/photovoltaic

pv: https://github.com/topics/pv

battery-management: https://github.com/topics/battery-management

ups-management: https://github.com/topics/ups-management

inverter: https://github.com/topics/inverter

Photovoltaic system: https://en.wikipedia.org/wiki/Photovoltaic_system