I have just written an orchestral piece which begins with a cor anglais solo, but it occurred to me that most of the orchestras I've seen have only had one cor anglais anyway, so I am wondering whether the designation of 'solo' for those bars is necessary?

David

I would put in the word "solo" to make it very clear.

It is probably good to let the player know he/she is playing a "solo"

Indeed, a 'solo' marked at mf is going to be different in dynamic than a normal passage at mf.

"Solo" has two functions in orchestral music: for multi-instrument sections, like strings, it means that only one should play, usually the section principal; in other parts it indicates that the passage is more important than the rest of the part. Schoenberg and Berg invented a special notation to replace the second meaning: a capital H with a horizontal bar extending from the top of the righthand vertical, standing for "Hauptstimme" and meaning "principal voice"; they also use an N, similarly extended, standing for "Nebenstimme" and meaning "second voice". You can see these illustrated some way down this page.