Hi,

I just had the exact same issue, I fixed it by clicking on the desktop and then back in the game.

Platforn Windows 10, Steam, 0.17.4

I agree items have an internal buffer but belt immunity equipment works immediately after adding the solar panel and not after accumulating the energy reserve. Do not interrupt the action every few seconds to accumulate energy, it does not work only in the middle of the night.

I put in one portable solar (maximum power output: 30kW) panel and belt immunity equipment (energy consumption: 100kW) into modular armor and it worked
Should this work?