If davening alone without a minyan on Rosh Hashana and Yom Kippur does one say all the Piyutim or does it apply only when davening with a minyan?
For someone who davens without a minyan, there is no obligation to say Piyutim, but it is certainly appropriate to do so.
This may not be done during one’s personal Shmoneh Esrei, but may be recited afterwards.
Most Piyutim are said in entirety by both the Chazzan and congregation, and that is how the individual would recite them as well. [Although parts of Piyutim are often marked as “Chazzan” and “Kohol” in the Machzor, this is only in order to highlight which parts the Chazzan says aloud.]
Exceptions: A non-Chazan does not say the paragraph of Misoid that appears at the beginning of Chazaras Hashatz, and in Shacharis he also does not say the paragraph that follows Misoid.
(Copied with permission from Rabbi Lesches of Melbourne, Australia)