1983 - Casio CL-301 Solar Calculator
It looks like any other calculator watch of its era except for the small unobtrusive row of dark blue solar cells above the digital display. (Made 1983 through 1984)
This was not the first solar calculator watch. In his book, Watch, Pieter Dorensen cites the LCD solar digital calculator “Micro Computer” or “Chronomat" introduced at the 1977 Basle Fair.
Casio also made a plastic version of the solar calculator watch, the CL-30.