At one point, Earth nearly choked to death on pollution. However, its inhabitants woke up, and within a generation, everything from trucks to toasters were covered in solar panels. (DIS: "An Obol for Charon")
Schematics of the Mariner 2, Nimbus 1, and Ranger 5 spacecraft depicting the locations of the solar panels was stored in the USS Enterprise's library computer database. This database was accessed by the Talosians in 2254. (TOS: "The Cage")
Retconned material shows solar panels and solar platforms used aboard NASA's Mariner 2, Nimbus 1, and Ranger 5 space probes when they were launched in the mid-20th century. Solar panels were also included in the International Space Station.
Schematics of the Mariner 2 and Ranger 5 spacecraft were from the archives of the National Aeronautics and Space Administration - Jet Propulsion Laboratory.