Based on these descriptions
http://www.skateisi.com/site/sub.cfm?content=events_national_event_descriptionsI would assume solo is "artistic solo".
And it appears there are no required elements for either Artistic or Spotlight.
I have to say I don't really understand the difference between Artistic and Spotlight. I would say that if you already have your program, if it doesn't fit the "theatrical performance' requirement of Dramatic, it would be better to go with Artistic solo.
Artistic:
"Skaters perform a program to music with emphasis on strong edges, flow, choreography, innovative moves and musical interpretation. There is no score for technical ability in this event. Event level is based on skater’s freestyle test level.
Spotlight:
"This is an entertaining & “fun” routine that emphasizes the skater’s acting ability and not technical skating skills. There is no score for technical merit in this event. The skater must pass a test for Tots, Pre-Alpha to Delta or Freestyle to determine the spotlight event level.
Spotlight events are divided into three categories listed below. Please mark the correct category on your entry form.
a) CHARACTER – a famous or easily identifiable character.
b) DRAMATIC – a theatrical performance that sets a mood and evokes an emotional response.
c) LIGHT ENTERTAINMENT – an entertaining or light-hearted performance.