Panels unhooked in the sun

Pretty much 100% of the consumer grade panels (mono and poly crystalline) will be fine up plugged (just keep connectors from sun/water/dust if unplugged themselves).

The only panels that I know of (and I am no expert) are some thin film panels (CdTe cadmium-telluride) that are typically used on utility scale solar farms. Those panels have to be connected/loaded or they will quickly degrade.

Just as a note of interest, loaded solar panels run cooler than open circuit panels... The energy that goes to the load keeps panels from becoming hotter. Unconnected panels, still flow current internal to the cell, which generates heat locally.

And remember, that any battery based system draws current when needed (battery charge/loads), and stops drawing current when battery is full and no loads. So running "unloaded" in sun is standard operation for off grid solar power systems.

-Bill