solar day vs twenty-four hour period

solar day and twenty-four hour period both are nouns.

Word	Noun	Adjective	Verb	Adverb
solar day	Yes	No	No	No
twenty-four hour period	Yes	No	No	No

As nouns, solar day and twenty-four hour period are synonyms defined as:

solar day and twenty-four hour period: time for Earth to make a complete rotation on its axis

Other synonyms of solar day include 24-hour interval, day, mean solar day, twenty-four hours.

solar day (noun)	twenty-four hour period (noun)
time for Earth to make a complete rotation on its axis	time for Earth to make a complete rotation on its axis