Solar enlargers are historcal relics of the victorian era. The photo shop would have a large reflective device on the roof or front window, and a series of mirrors, maybe even front silvered, which were used to channel/pipe sunlight light down to the negative inside the building. Sometimes down into the exposing salon as well
Assistants, by means of ropes and push rods would manipulate the primary mirror to follow the sun thoughout the day.
A very good and accurate answer.
Yes, there was a a "Solar" brand enlarger, but it was not for cyanotype. Rather, it was a relatively low cost diffusion enlarger for 4x5 film and silver gelatin paper.
[FONT=Comic Sans MS]Films NOT Dead - Just getting fixed![/FONT]