Grid-tied solar inverters, as a general rule, do not (
cannot) output any power at all in the absence of grid power.
The act of plugging in a normal grid-tied solar inverter with a regular ass-plug[0] is just exactly as safe as plugging in any other electrical appliance is.
(There are other concerns, but the physical plug is not amongst them.)
0: https://xkcd.com/37/